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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Need to fix old valve radio
I have a very old valve radio from a company called Lafayette.
It has 6 valves which are 6v6 gt 6x5 gt 6sq7 gt 6sk7 gt 6sa7 gt This radio was working fine but recently has developed the following problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? Sorry, I accidently posted it to the wrong group. To add to the above, it is a MW/LW/SW type and the problem occurs on all of the bands. Thanks in advance. |
#2
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Need to fix old valve radio
....and lastly, the radio has not been used since the last time I
tested it about 10 years ago. Then it worked fine, no I tested it again and suddenly there is this problem. It is entirely possible that it was knocked (I hope not dropped) while in storage, but there is nothing visibly broken, and all the valves do glow. BTW, I tried removing the valves one by one and seeing if one valve did not "make a difference", but this approach did not work, any valve removed results in no sound at all. |
#3
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Need to fix old valve radio
On 4 Mar, 23:28, wrote:
...and lastly, the radio has not been used since the last time I tested it about 10 years ago. Then it worked fine, no I tested it again and suddenly there is this problem. It is entirely possible that it was knocked (I hope not dropped) while in storage, but there is nothing visibly broken, and all the valves do glow. BTW, I tried removing the valves one by one and seeing if one valve did not "make a difference", but this approach did not work, any valve removed results in no sound at all. Schematic now available, at |
#4
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Need to fix old valve radio
wrote in message
oups.com... On 4 Mar, 23:28, wrote: ...and lastly, the radio has not been used since the last time I tested it about 10 years ago. Then it worked fine, no I tested it again and suddenly there is this problem. It is entirely possible that it was knocked (I hope not dropped) while in storage, but there is nothing visibly broken, and all the valves do glow. BTW, I tried removing the valves one by one and seeing if one valve did not "make a difference", but this approach did not work, any valve removed results in no sound at all. Schematic now available, at I thought I was following this thread but I'm wondering if I lost something along the way.... the pictures/schematics shown in said website, are they for the radio (Lafayette brand?) that this post was originally about? Was this radio made by Air King/sold under Lafayette? Or am I presuming the radio to have been a "Lafayette" due to the name of the poster? By the way, thanks for the info... Though "I" didn't need it, I collect any decent info I find - just in case. |
#5
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Need to fix old valve radio
"Radiosrfun" wrote in message ... wrote in message oups.com... On 4 Mar, 23:28, wrote: ...and lastly, the radio has not been used since the last time I tested it about 10 years ago. Then it worked fine, no I tested it again and suddenly there is this problem. It is entirely possible that it was knocked (I hope not dropped) while in storage, but there is nothing visibly broken, and all the valves do glow. BTW, I tried removing the valves one by one and seeing if one valve did not "make a difference", but this approach did not work, any valve removed results in no sound at all. Schematic now available, at I looked at some of the pictures. My guess is that you basically need to measure every resistor and capacitor in this set. You most likely have several resistors that have gone WAY up in value and several capacitors with excessive leakage resistance. Do not be surprised if you have to replace every one of those wax coated capacitors and many of the resistors as well. A usual suspect for your symptom is the resistor that feeds the plate of the audio amplifier (6SQ7) which should be in the 100K to 470K ohm range. David |
#6
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Need to fix old valve radio
David wrote:
"Radiosrfun" wrote in message ... wrote in message oups.com... On 4 Mar, 23:28, wrote: ...and lastly, the radio has not been used since the last time I tested it about 10 years ago. Then it worked fine, no I tested it again and suddenly there is this problem. It is entirely possible that it was knocked (I hope not dropped) while in storage, but there is nothing visibly broken, and all the valves do glow. BTW, I tried removing the valves one by one and seeing if one valve did not "make a difference", but this approach did not work, any valve removed results in no sound at all. Schematic now available, at I looked at some of the pictures. My guess is that you basically need to measure every resistor and capacitor in this set. You most likely have several resistors that have gone WAY up in value and several capacitors with excessive leakage resistance. Do not be surprised if you have to replace every one of those wax coated capacitors and many of the resistors as well. A usual suspect for your symptom is the resistor that feeds the plate of the audio amplifier (6SQ7) which should be in the 100K to 470K ohm range. Hi... Don't have any idea how valid it was, but back in the days when the dinosaurs were walking around we used to gently squeeze the wax caps with a long nose... if they were soft, they were replaced on general principle. Take care. Ken |
#7
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Need to fix old valve radio
Personally, in this sort of situation I reckon the shotgun approach is the way
to go - just replace all the crappy caps, and all resistors over 50k - saves a lot of time and in many cases fixes the problem in a short time. If the fault is still there there is not a lot more to check David (a different one) David wrote: I looked at some of the pictures. My guess is that you basically need to measure every resistor and capacitor in this set. You most likely have several resistors that have gone WAY up in value and several capacitors with excessive leakage resistance. Do not be surprised if you have to replace every one of those wax coated capacitors and many of the resistors as well. A usual suspect for your symptom is the resistor that feeds the plate of the audio amplifier (6SQ7) which should be in the 100K to 470K ohm range. David |
#8
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Need to fix old valve radio
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#9
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Need to fix old valve radio
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#10
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Need to fix old valve radio
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#11
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Need to fix old valve radio
That is a typical radio here in the USA .
The problem it has is most likely bad paper capacitors and filter capacitors . Replace those and spray the tube pins and volume control with cleaner and it should work fine . That radio is not worth much . Its an ugly style . More of a fun project than anyhing else . |
#12
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Need to fix old valve radio
wrote in message oups.com... I have a very old valve radio from a company called Lafayette. It has 6 valves which are 6v6 gt 6x5 gt 6sq7 gt 6sk7 gt 6sa7 gt This radio was working fine but recently has developed the following problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? The power supply. Check the high voltage. Could be the rectifier valve. |
#13
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Need to fix old valve radio
Charles Schuler wrote:
wrote in message oups.com... I have a very old valve radio from a company called Lafayette. It has 6 valves which are 6v6 gt 6x5 gt 6sq7 gt 6sk7 gt 6sa7 gt This radio was working fine but recently has developed the following problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? The power supply. Check the high voltage. Could be the rectifier valve. Hi... It's been a long long long time, but I don't believe any of those quoted are a rectifier. Perhaps selenium, or silicon. Take care. Ken |
#14
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Need to fix old valve radio
Hi...
It's been a long long long time, but I don't believe any of those quoted are a rectifier. Perhaps selenium, or silicon. Could be selenium ... difficult to tell from what has been posted. |
#15
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Need to fix old valve radio
"Ken Weitzel" wrote in message
news:GjJGh.1217418$1T2.465404@pd7urf2no... Charles Schuler wrote: wrote in message oups.com... I have a very old valve radio from a company called Lafayette. It has 6 valves which are 6v6 gt 6x5 gt 6sq7 gt 6sk7 gt 6sa7 gt This radio was working fine but recently has developed the following problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? The power supply. Check the high voltage. Could be the rectifier valve. Hi... It's been a long long long time, but I don't believe any of those quoted are a rectifier. Perhaps selenium, or silicon. Take care. Ken The 6X5 is the rectifier. After 10 years of shelf time, the most likely thing that you should look at is the electrolytic capacitors in the power supply. They are probably dry by now and need to be replaced. Since tube equipment runs hot, you should replace them with 105C temp range units. Cheers!! -- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Some days you're the dog, some days the hydrant. |
#16
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Need to fix old valve radio
"Ken Weitzel" wrote in message news:GjJGh.1217418$1T2.465404@pd7urf2no... It's been a long long long time, but I don't believe any of those quoted are a rectifier. Perhaps selenium, or silicon. 6X5 is a full wave rectifier. I'd check the main electro (multi part) and the resistors across it. |
#17
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Need to fix old valve radio
Ken Weitzel writes:
Charles Schuler wrote: wrote in message oups.com... I have a very old valve radio from a company called Lafayette. It has 6 valves which are 6v6 gt 6x5 gt 6sq7 gt 6sk7 gt 6sa7 gt This radio was working fine but recently has developed the following problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? The power supply. Check the high voltage. Could be the rectifier valve. Hi... It's been a long long long time, but I don't believe any of those quoted are a rectifier. Perhaps selenium, or silicon. Tubes/valves rarely go bad just sitting. I'd start by checking electrolytic capacitors. --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
#18
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Need to fix old valve radio
On Mon, 05 Mar 2007 00:16:38 GMT, Ken Weitzel
wrote: Charles Schuler wrote: wrote in message oups.com... I have a very old valve radio from a company called Lafayette. It has 6 valves which are 6v6 gt 6x5 gt 6sq7 gt 6sk7 gt 6sa7 gt This radio was working fine but recently has developed the following problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? The power supply. Check the high voltage. Could be the rectifier valve. Hi... It's been a long long long time, but I don't believe any of those quoted are a rectifier. Perhaps selenium, or silicon. Take care. Ken 6X5 is the rectifier... Could be bad, but is there any hum? If yes, check the filters, too. |
#19
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Need to fix old valve radio
On Mar 4, 5:18 pm, wrote:
I have a very old valve radio from a company called Lafayette. It has 6 valves which are 6v6 gt 6x5 gt 6sq7 gt 6sk7 gt 6sa7 gt This radio was working fine but recently has developed the following problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? Sorry, I accidently posted it to the wrong group. To add to the above, it is a MW/LW/SW type and the problem occurs on all of the bands. Thanks in advance. Got a model number? It sounds like a transformer powered all-band 1940's superheterodyne set. Later sets used 12, 35 and 50 Volt versions of those tubes in series diretly across the AC power mains. Then they were replaced by miniature versions of the same type of tubes. The schematics for these sets are all almost identical, the 6say is converter, 6sk7 is IF amp, 6sq7 is detector and 1st audio amp, and 6v6 is audio output, 6x5 is rectifier. Volume control is at input to 1st audio amp. Do you have a scope so you can look at the signal from that point to the speaker? If so, I can walk you thru the testing needed. H. R. (Bob) Hofmann |
#20
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Need to fix old valve radio
On 5 Mar, 02:18, "hr(bob) " wrote:
On Mar 4, 5:18 pm, wrote: I have a very old valve radio from a company called Lafayette. It has 6 valves which are 6v6 gt 6x5 gt 6sq7 gt 6sk7 gt 6sa7 gt This radio was working fine but recently has developed the following problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? Sorry, I accidently posted it to the wrong group. To add to the above, it is a MW/LW/SW type and the problem occurs on all of the bands. Thanks in advance. Got a model number? It sounds like a transformer powered all-band 1940's superheterodyne set. Later sets used 12, 35 and 50 Volt versions of those tubes in series diretly across the AC power mains. Then they were replaced by miniature versions of the same type of tubes. The schematics for these sets are all almost identical, the 6say is converter, 6sk7 is IF amp, 6sq7 is detector and 1st audio amp, and 6v6 is audio output, 6x5 is rectifier. Volume control is at input to 1st audio amp. Do you have a scope so you can look at the signal from that point to the speaker? If so, I can walk you thru the testing needed. H. R. (Bob) Hofmann Bob, thank you. I don't have a scope. I think you are right about the "series" thing. They are protecting the valves these way, if someone takes one out everything stops working. Here is more information: The model number is very faint, but it ends with E629, maybe IE629 There is also a 4 digits serial number, 2xxx Probably not too many of those about today :-) Made in America Rated 110 to 125 Volts 50-60 cycles 40W Yet (strangely) was always operated from 220V. I need to change the power cable, it is probably the original and is crumbling in a very dangerous way, so I might get a glimps to the internal components. It looks like a big job simply to take the unit out from the wooden box without damaging the tuning mechanics. I wonder if it can simply slide out or if it needs to be lifted out (bad). Oh, and another interesting thing, the pickup coil doesn't use ferite core like nowadays, there is a huge drum and on it the coil is wrapped. |
#21
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Need to fix old valve radio
In article . com,
wrote: There is also a 4 digits serial number, 2xxx Probably not too many of those about today :-) Made in America Rated 110 to 125 Volts 50-60 cycles 40W Yet (strangely) was always operated from 220V. I need to change the power cable, it is probably the original and is crumbling in a very dangerous way, so I might get a glimps to the internal components. It looks like a big job simply to take the unit out from the wooden box without damaging the tuning mechanics. I wonder if it can simply slide out or if it needs to be lifted out (bad). Be aware that many radios of this time were 110 volts and used the mains cord as a dropper to obtain that from 240. -- *Very funny Scotty, now beam down my clothes. Dave Plowman London SW To e-mail, change noise into sound. |
#22
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Need to fix old valve radio
On Mar 5, 9:58 am, "Dave Plowman (News)" wrote:
In article . com, wrote: There is also a 4 digits serial number, 2xxx Probably not too many of those about today :-) Made in America Rated 110 to 125 Volts 50-60 cycles 40W Yet (strangely) was always operated from 220V. I need to change the power cable, it is probably the original and is crumbling in a very dangerous way, so I might get a glimps to the internal components. It looks like a big job simply to take the unit out from the wooden box without damaging the tuning mechanics. I wonder if it can simply slide out or if it needs to be lifted out (bad). Be aware that many radios of this time were 110 volts and used the mains cord as a dropper to obtain that from 240. -- *Very funny Scotty, now beam down my clothes. Dave Plowman London SW To e-mail, change noise into sound. |
#23
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Need to fix old valve radio
On Mar 5, 9:58 am, "Dave Plowman (News)" wrote:
In article . com, wrote: There is also a 4 digits serial number, 2xxx Probably not too many of those about today :-) Made in America Rated 110 to 125 Volts 50-60 cycles 40W Yet (strangely) was always operated from 220V. I need to change the power cable, it is probably the original and is crumbling in a very dangerous way, so I might get a glimps to the internal components. It looks like a big job simply to take the unit out from the wooden box without damaging the tuning mechanics. I wonder if it can simply slide out or if it needs to be lifted out (bad). Be aware that many radios of this time were 110 volts and used the mains cord as a dropper to obtain that from 240. -- *Very funny Scotty, now beam down my clothes. Dave Plowman London SW To e-mail, change noise into sound. Dave is 1000% corret. The line cord that is crumbling is probably in that condition because it has gotten so hot so many times over the years. The cord has to dissipate at least 20 watts or maybe even twice that amount to drop the voltage down to 120 v when used on a 230V circuit.. The first thing to do is to measure the mains voltage - 230V approximately, and then measure the voltage at the set end of that crumbling line cord when the set is turned on and see if it measures about 115 Volts. If so, then the line cord must not be replaced with a regular line cord or everything in the radio will be fried beyond repair. The only way to salvage the radio will be to insert a fixed resistor mounted somewhere inside the radio that will drop the voltage the same as the original line cord is now doing. If it is possible, I would suggest measuring the resistance of the two conductors of the line cord, add the resistance of the two conductors together, and use a resistor of that ohms value as the replacement for the old line cord resistance. The wattage of the resistor will be 120V x 120V divided by the resistance, or 14,400 divided by the resistance of the line cord. It will be a sizeable resistor! Once we get the power input to the radio fixed, we can then start going through the audio stages to see what is wrong. A scope would be nice, but I think we can measure voltages at a number of places and get things fixed. H. R.(Bob) Hofmann |
#24
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Need to fix old valve radio
On 5 Mar, 15:10, wrote:
On 5 Mar, 02:18, "hr(bob) " wrote: On Mar 4, 5:18 pm, wrote: I have a very old valve radio from a company called Lafayette. It has 6 valves which are 6v6 gt 6x5 gt 6sq7 gt 6sk7 gt 6sa7 gt This radio was working fine but recently has developed the following problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? Sorry, I accidently posted it to the wrong group. To add to the above, it is a MW/LW/SW type and the problem occurs on all of the bands. Thanks in advance. Got a model number? It sounds like a transformer powered all-band 1940's superheterodyne set. Later sets used 12, 35 and 50 Volt versions of those tubes in series diretly across the AC power mains. Then they were replaced by miniature versions of the same type of tubes. The schematics for these sets are all almost identical, the 6say is converter, 6sk7 is IF amp, 6sq7 is detector and 1st audio amp, and 6v6 is audio output, 6x5 is rectifier. Volume control is at input to 1st audio amp. Do you have a scope so you can look at the signal from that point to the speaker? If so, I can walk you thru the testing needed. H. R. (Bob) Hofmann Bob, thank you. I don't have a scope. I think you are right about the "series" thing. They are protecting the valves these way, if someone takes one out everything stops working. Here is more information: The model number is very faint, but it ends with E629, maybe IE629 There is also a 4 digits serial number, 2xxx Probably not too many of those about today :-) Made in America Rated 110 to 125 Volts 50-60 cycles 40W Yet (strangely) was always operated from 220V. I need to change the power cable, it is probably the original and is crumbling in a very dangerous way, so I might get a glimps to the internal components. It looks like a big job simply to take the unit out from the wooden box without damaging the tuning mechanics. I wonder if it can simply slide out or if it needs to be lifted out (bad). Oh, and another interesting thing, the pickup coil doesn't use ferite core like nowadays, there is a huge drum and on it the coil is wrapped. I have just finished replacing the power cable. The unit came out as a whole, which was easy. I then was able to see all the components inside. It is very messy as in those days they were no printed circuit boards, but the general impression I got was that damaged was caused to the internal part/s due to storage in the attick, and last summer here in England the summer was the hottest on record, so you can imagine... Everything looks shining, a sort of wet-look, this must mean bad news. On the positive side, I did manage to fix one of the two front panel illumination bulbs - it seemed to be just a contact issue, and after whasing the bulb in some water, it was working again. Now remains only the audio problem. I have taken some pictures, I will post them soon. If someone wants this radio, make me an offer. I can ship worldwide, and I accept paypal. Thanks. |
#25
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Need to fix old valve radio
On Mar 5, 11:19 am, wrote:
On 5 Mar, 15:10, wrote: On 5 Mar, 02:18, "hr(bob) " wrote: On Mar 4, 5:18 pm, wrote: I have a very old valve radio from a company called Lafayette. It has 6 valves which are 6v6 gt 6x5 gt 6sq7 gt 6sk7 gt 6sa7 gt This radio was working fine but recently has developed the following problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? Sorry, I accidently posted it to the wrong group. To add to the above, it is a MW/LW/SW type and the problem occurs on all of the bands. Thanks in advance. Got a model number? It sounds like a transformer powered all-band 1940's superheterodyne set. Later sets used 12, 35 and 50 Volt versions of those tubes in series diretly across the AC power mains. Then they were replaced by miniature versions of the same type of tubes. The schematics for these sets are all almost identical, the 6say is converter, 6sk7 is IF amp, 6sq7 is detector and 1st audio amp, and 6v6 is audio output, 6x5 is rectifier. Volume control is at input to 1st audio amp. Do you have a scope so you can look at the signal from that point to the speaker? If so, I can walk you thru the testing needed. H. R. (Bob) Hofmann Bob, thank you. I don't have a scope. I think you are right about the "series" thing. They are protecting the valves these way, if someone takes one out everything stops working. Here is more information: The model number is very faint, but it ends with E629, maybe IE629 There is also a 4 digits serial number, 2xxx Probably not too many of those about today :-) Made in America Rated 110 to 125 Volts 50-60 cycles 40W Yet (strangely) was always operated from 220V. I need to change the power cable, it is probably the original and is crumbling in a very dangerous way, so I might get a glimps to the internal components. It looks like a big job simply to take the unit out from the wooden box without damaging the tuning mechanics. I wonder if it can simply slide out or if it needs to be lifted out (bad). Oh, and another interesting thing, the pickup coil doesn't use ferite core like nowadays, there is a huge drum and on it the coil is wrapped. I have just finished replacing the power cable. The unit came out as a whole, which was easy. I then was able to see all the components inside. It is very messy as in those days they were no printed circuit boards, but the general impression I got was that damaged was caused to the internal part/s due to storage in the attick, and last summer here in England the summer was the hottest on record, so you can imagine... Everything looks shining, a sort of wet-look, this must mean bad news. On the positive side, I did manage to fix one of the two front panel illumination bulbs - it seemed to be just a contact issue, and after whasing the bulb in some water, it was working again. Now remains only the audio problem. I have taken some pictures, I will post them soon. If someone wants this radio, make me an offer. I can ship worldwide, and I accept paypal. Thanks.- Hide quoted text - - Show quoted text - When you plugged the radio in after replacing the pilot light for the front panel, were the lamps the same brightness as before the line cord was replaced. If so, then the line cord must not have been used to drop the line voltage from 230V to 115V. The set must be using a power transformer designed for an input of 230V and not the 115V shown on the back panel that you mentioned. I will see what info I can find. Do you have a high-empedance voltmeter available to check the votages on the tubes? Is the bottom of the radio accesible? Do you know how to count tube pins from the keyway? Bob Hofmann |
#26
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Need to fix old valve radio
On 5 Mar, 19:14, "hr(bob) " wrote:
On Mar 5, 11:19 am, wrote: On 5 Mar, 15:10, wrote: On 5 Mar, 02:18, "hr(bob) " wrote: On Mar 4, 5:18 pm, wrote: I have a very old valve radio from a company called Lafayette. It has 6 valves which are 6v6 gt 6x5 gt 6sq7 gt 6sk7 gt 6sa7 gt This radio was working fine but recently has developed the following problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? Sorry, I accidently posted it to the wrong group. To add to the above, it is a MW/LW/SW type and the problem occurs on all of the bands. Thanks in advance. Got a model number? It sounds like a transformer powered all-band 1940's superheterodyne set. Later sets used 12, 35 and 50 Volt versions of those tubes in series diretly across the AC power mains. Then they were replaced by miniature versions of the same type of tubes. The schematics for these sets are all almost identical, the 6say is converter, 6sk7 is IF amp, 6sq7 is detector and 1st audio amp, and 6v6 is audio output, 6x5 is rectifier. Volume control is at input to 1st audio amp. Do you have a scope so you can look at the signal from that point to the speaker? If so, I can walk you thru the testing needed. H. R. (Bob) Hofmann Bob, thank you. I don't have a scope. I think you are right about the "series" thing. They are protecting the valves these way, if someone takes one out everything stops working. Here is more information: The model number is very faint, but it ends with E629, maybe IE629 There is also a 4 digits serial number, 2xxx Probably not too many of those about today :-) Made in America Rated 110 to 125 Volts 50-60 cycles 40W Yet (strangely) was always operated from 220V. I need to change the power cable, it is probably the original and is crumbling in a very dangerous way, so I might get a glimps to the internal components. It looks like a big job simply to take the unit out from the wooden box without damaging the tuning mechanics. I wonder if it can simply slide out or if it needs to be lifted out (bad). Oh, and another interesting thing, the pickup coil doesn't use ferite core like nowadays, there is a huge drum and on it the coil is wrapped. I have just finished replacing the power cable. The unit came out as a whole, which was easy. I then was able to see all the components inside. It is very messy as in those days they were no printed circuit boards, but the general impression I got was that damaged was caused to the internal part/s due to storage in the attick, and last summer here in England the summer was the hottest on record, so you can imagine... Everything looks shining, a sort of wet-look, this must mean bad news. On the positive side, I did manage to fix one of the two front panel illumination bulbs - it seemed to be just a contact issue, and after whasing the bulb in some water, it was working again. Now remains only the audio problem. I have taken some pictures, I will post them soon. If someone wants this radio, make me an offer. I can ship worldwide, and I accept paypal. Thanks.- Hide quoted text - - Show quoted text - When you plugged the radio in after replacing the pilot light for the front panel, were the lamps the same brightness as before the line cord was replaced. If so, then the line cord must not have been used to drop the line voltage from 230V to 115V. The set must be using a power transformer designed for an input of 230V and not the 115V shown on the back panel that you mentioned. I will see what info I can find. Do you have a high-empedance voltmeter available to check the votages on the tubes? Is the bottom of the radio accesible? Do you know how to count tube pins from the keyway? Bob Hofmann Hello Bob, (and others) I am not sure about the brightness, since I received you message after I had done the work, I didn't pay much attention to this. I do have a digital DMM. Here are some pictures that I took while repairing the power cord: |
#27
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Need to fix old valve radio
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#28
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Need to fix old valve radio
On 5 Mar, 18:04, Kurt wrote:
wrote: I have a very old valve radio from a company called Lafayette. It has 6 valves which are 6v6 gt 6x5 gt 6sq7 gt 6sk7 gt 6sa7 gt This radio was working fine but recently has developed the following problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? How's the speaker? Could be blown. Distortion could be caused by bias failure. Leaky capacitors (probably called condensors when the radio was built) are a big problem with tube (valve) musical instrument amplifiers. There are several possibilities, but the first 2 that cross my mind a speaker voice coil jammed against pole magnet, due to corrosion or debris bad connection, might be due to corrosion of a friction contact. The other thing is that most of those caps look like waxed or oiled paper types, which have a bad reliability record IME. There are other things that can cause the distortion too, such as a break in the output transformer, or a bias failure. If you dont have a scope, there is a simpler way to check for signal distortion at points along the signal path. Get yourself a very low power audio amplifier, under 1 watt, hook it to a speaker and use this to probe various audio signal points. To protect the amp you'll need to put some components on the input: X--||----/\/\----+----+--- amp signal input | | __ -- \/ /\ | -- radio chassis | | -----------------+----+---- amp ground Now, as long as output power is low, your ears will survive ok. I'd start by checking voltages around the place, such as on the supply lines, or capacitor + tags. You can check the speaker by hooking up an external one in parallel. Dont disconnect the original for the test, if a system like this has no load even for a fraction of a second it can do itself considerable damage. Lytics can fail, but IME are quite far down on the list of most likely failures. NT |
#29
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Need to fix old valve radio
On 6 Mar, 18:55, wrote:
On 5 Mar, 18:04, Kurt wrote: wrote: I have a very old valve radio from a company called Lafayette. It has 6 valves which are 6v6 gt 6x5 gt 6sq7 gt 6sk7 gt 6sa7 gt This radio was working fine but recently has developed the following problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? How's the speaker? Could be blown. Distortion could be caused by bias failure. Leaky capacitors (probably called condensors when the radio was built) are a big problem with tube (valve) musical instrument amplifiers. There are several possibilities, but the first 2 that cross my mind a speaker voice coil jammed against pole magnet, due to corrosion or debris bad connection, might be due to corrosion of a friction contact. The other thing is that most of those caps look like waxed or oiled paper types, which have a bad reliability record IME. There are other things that can cause the distortion too, such as a break in the output transformer, or a bias failure. If you dont have a scope, there is a simpler way to check for signal distortion at points along the signal path. Get yourself a very low power audio amplifier, under 1 watt, hook it to a speaker and use this to probe various audio signal points. To protect the amp you'll need to put some components on the input: X--||----/\/\----+----+--- amp signal input | | __ -- \/ /\ | -- radio chassis | | -----------------+----+---- amp ground Now, as long as output power is low, your ears will survive ok. I'd start by checking voltages around the place, such as on the supply lines, or capacitor + tags. You can check the speaker by hooking up an external one in parallel. Dont disconnect the original for the test, if a system like this has no load even for a fraction of a second it can do itself considerable damage. Lytics can fail, but IME are quite far down on the list of most likely failures. NT I don't have such an amplifier. I have a DMM. Regarding the speaker, if it is jammed then I wouldn't here anything, or would I? My inclination is leaking condenser/s, all the components inside look very shining (a wet look) so I think a lot of condenser liquid has vaporised inside. I hope it is not a health hazard (did they use pcb's in such typical radios), but this would explain a reduction in DC level and increase in DC ripple. If anyone knows exactly what the DC level should be and what the AC ripple level should be, I think this will be extremely useful. Also, there is this mysterious problem of the schematic mains voltages, which reads 110-125V whereas this radio was always used with 230V |
#30
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Need to fix old valve radio
On Mar 6, 2:39 pm, wrote:
On 6 Mar, 18:55, wrote: On 5 Mar, 18:04, Kurt wrote: wrote: I have a very old valve radio from a company called Lafayette. It has 6 valves which are 6v6 gt 6x5 gt 6sq7 gt 6sk7 gt 6sa7 gt This radio was working fine but recently has developed the following problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? How's the speaker? Could be blown. Distortion could be caused by bias failure. Leaky capacitors (probably called condensors when the radio was built) are a big problem with tube (valve) musical instrument amplifiers. There are several possibilities, but the first 2 that cross my mind a speaker voice coil jammed against pole magnet, due to corrosion or debris bad connection, might be due to corrosion of a friction contact. The other thing is that most of those caps look like waxed or oiled paper types, which have a bad reliability record IME. There are other things that can cause the distortion too, such as a break in the output transformer, or a bias failure. If you dont have a scope, there is a simpler way to check for signal distortion at points along the signal path. Get yourself a very low power audio amplifier, under 1 watt, hook it to a speaker and use this to probe various audio signal points. To protect the amp you'll need to put some components on the input: X--||----/\/\----+----+--- amp signal input | | __ -- \/ /\ | -- radio chassis | | -----------------+----+---- amp ground Now, as long as output power is low, your ears will survive ok. I'd start by checking voltages around the place, such as on the supply lines, or capacitor + tags. You can check the speaker by hooking up an external one in parallel. Dont disconnect the original for the test, if a system like this has no load even for a fraction of a second it can do itself considerable damage. Lytics can fail, but IME are quite far down on the list of most likely failures. NT I don't have such an amplifier. I have a DMM. Regarding the speaker, if it is jammed then I wouldn't here anything, or would I? My inclination is leaking condenser/s, all the components inside look very shining (a wet look) so I think a lot of condenser liquid has vaporised inside. I hope it is not a health hazard (did they use pcb's in such typical radios), but this would explain a reduction in DC level and increase in DC ripple. If anyone knows exactly what the DC level should be and what the AC ripple level should be, I think this will be extremely useful. Also, there is this mysterious problem of the schematic mains voltages, which reads 110-125V whereas this radio was always used with 230V- Hide quoted text - - Show quoted text - I wouldn't worry about the 115 -230 issue as if it wasn't ok, you would have fried all the tubes and pilot lamps by now. What is the DC voltage on the C14-a, b, c capacitors? Measure from the capacitor terminal to chassis ground. Bob Hofmann |
#31
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Need to fix old valve radio
On 6 Mar, 20:39, wrote:
On 6 Mar, 18:55, wrote: On 5 Mar, 18:04, Kurt wrote: wrote: I have a very old valve radio from a company called Lafayette. It has 6 valves which are problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? There are several possibilities, but the first 2 that cross my mind a speaker voice coil jammed against pole magnet, due to corrosion or debris bad connection, might be due to corrosion of a friction contact. The other thing is that most of those caps look like waxed or oiled paper types, which have a bad reliability record IME. There are other things that can cause the distortion too, such as a break in the output transformer, or a bias failure. If you dont have a scope, there is a simpler way to check for signal distortion at points along the signal path. Get yourself a very low power audio amplifier, under 1 watt, hook it to a speaker and use this to probe various audio signal points. To protect the amp you'll need to put some components on the input: X--||----/\/\----+----+--- amp signal input | | __ -- \/ /\ | -- radio chassis | | -----------------+----+---- amp ground Now, as long as output power is low, your ears will survive ok. I'd start by checking voltages around the place, such as on the supply lines, or capacitor + tags. You can check the speaker by hooking up an external one in parallel. Dont disconnect the original for the test, if a system like this has no load even for a fraction of a second it can do itself considerable damage. Lytics can fail, but IME are quite far down on the list of most likely failures. NT I don't have such an amplifier. They are so common I bet you have. An old pair of pc speakers, old walkman, pocket radio, unused cdrom, anything with low volume audio output. If not, try the $ store for something with one in, or any junked audio kit. Or make one, its fairly simple. I have a DMM. Regarding the speaker, if it is jammed then I wouldn't here anything, or would I? When they jam, they jam at one point. The voice coil & cone is not perfectly rigid, so a very tiny amount of movement is still possible. My inclination is leaking condenser/s, all the components inside look very shining (a wet look) so I think a lot of condenser liquid has vaporised inside. I hope it is not a health hazard (did they use pcb's in such typical radios), If this is so you may have an issue, as PCBs were the chemical of choice. A good clean out may be called for. You cant steam clean wax coated caps of course. but this would explain a reduction in DC level and increase in DC ripple. If anyone knows exactly what the DC level should be and what the AC ripple level should be, I think this will be extremely useful. Unlikely, but if you give us the voltages we can tell you if theyre reasonable or out of whack. You can also look up valve data for electrode voltages, but bear in mind valves werent always used in the way the mfr published. Also, there is this mysterious problem of the schematic mains voltages, which reads 110-125V whereas this radio was always used with 230V if it worked on 240 then there's no further issue. Thats assuming the mains lead you removed wasnt a resistance dropper. As always with these things, theres little point guessing, you need to test it out bit by bit. Vale rads are easier to do checks on because the valves all become o/c when no heater power is applied, so most components can be reliably checked in circuit. An analogue meter for this kind of work has the advantage that variations and poor connections are clearly visible, which is not so with a dmm. A DMM should do it though, in most cases. NT |
#32
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Need to fix old valve radio
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#33
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Need to fix old valve radio
On Mar 4, 5:18 pm, wrote:
I have a very old valve radio from a company called Lafayette. It has 6 valves which are 6v6 gt 6x5 gt 6sq7 gt 6sk7 gt 6sa7 gt This radio was working fine but recently has developed the following problem, when the volume is increased the sound is distorted completely, it can only be heared ok when the volume is very low, and putting the ear onto the speaker. Any ideas? The problem is likely to be a bad resistor or capacitor, somewhere in the last two audio stages (6SQ7 and 6V6). The plate of the 6SQ7 should be somewhere around 50 volts. The cathode to grid voltage of the 6V6 should be around 20 volts (negative side on the grid!). Anything wildly different than that may be a problem. I would replace all the wax capacitors in that area just on general principles. They're probably at least a bit leaky and will not be getting any better over time. Also check the resistors, they tend to go up in value. And oh, it could be the speaker rubbing-- try moving the speaker cone by hand to see if it rubs or is stuck. |
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