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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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Old Gernanium Transistor Repair
I have an old 8 gernamium transistor, protable AM radio that is noisy
on weak stations when cold. It works reasonably well when set it in the sunshine and warms up. The problem seems to be the RF section since the noise goes away when the volume is turned down. I'm suspecting the germanium transistors may be the problem and wondering which one might be replaced with a silicon variety to cure the temperature problems? I'm not sure what all 8 transistors do. Two are in the output stage, and another is used as a audio driver that drives the audio input transformer.There are four RF coils, the usual oscillator (red) and mixer (yellow) and white (1st IF) and (black (second IF). But that only requires 6 transistors, and there are eight total. The detector is a diode, so they didn't use a transistor for that. I haven't figured out what the other 2 transistors do. I'm thinking of replacing the oscillator transistor with a high gain silicon variety to try and eliminate the temperature problems? Any other ideas? -Bill |
#2
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Old Gernanium Transistor Repair
wrote in message oups.com... I have an old 8 germanium transistor, portable AM radio that is noisy on weak stations when cold. It works reasonably well when set it in the sunshine and warms up. The problem seems to be the RF section since the noise goes away when the volume is turned down. I'm suspecting the germanium transistors may be the problem and wondering which one might be replaced with a silicon variety to cure the temperature problems? It could be a lot of things. You need to find a way to test which. I'm not sure what all 8 transistors do. Two are in the output stage, and another is used as a audio driver that drives the audio input transformer. Usually two for output, two for audio amps = 4. There are four RF coils, the usual oscillator (red) and mixer (yellow) and white (1st IF) and (black (second IF). But that only requires 6 transistors, and there are eight total. Actually 7. Some radios had non working transistors added to bring the count up. The detector is a diode, so they didn't use a transistor for that. I haven't figured out what the other 2 transistors do. I'm thinking of replacing the oscillator transistor with a high gain silicon variety to try and eliminate the temperature problems? You might need to alter the bias on each transistor you replace. |
#3
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Old Gernanium Transistor Repair
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#4
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Old Gernanium Transistor Repair
Jim Land ) writes:
wrote in news:1163387574.804150.266160 @h54g2000cwb.googlegroups.com: I have an old 8 gernamium transistor, protable AM radio that is noisy on weak stations when cold.... Try over on alt.antiques.radio+phono... they'll enjoy hearing about your germanium transistors. I don't know. There has been debate in the past over there about what's relevant to the newsgroup, and some have felt transistors aren't old enough. Michael |
#5
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Old Gernanium Transistor Repair
In article tGS5h.2707$_Z2.2344@edtnps89,
Homer J Simpson wrote: I'm not sure what all 8 transistors do. Two are in the output stage, and another is used as a audio driver that drives the audio input transformer. Usually two for output, two for audio amps = 4. Perfectly easy to manage with three - one driver only. -- *Could it be that "I do " is the longest sentence? * Dave Plowman London SW To e-mail, change noise into sound. |
#6
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Old Gernanium Transistor Repair
Michael Black wrote:
Jim Land ) writes: wrote in news:1163387574.804150.266160 @h54g2000cwb.googlegroups.com: I have an old 8 gernamium transistor, protable AM radio that is noisy on weak stations when cold.... Try over on alt.antiques.radio+phono... they'll enjoy hearing about your germanium transistors. I don't know. There has been debate in the past over there about what's relevant to the newsgroup, and some have felt transistors aren't old enough. Michael Some of them think that A****er Kent radios are too new for that group. Ignore them, there are a number of transistor radio collectors in that group. I have most of the "Sams Transistor Radio Manuals" in my collection: http://home.earthlink.net/~mike.terrell/HWSTm.html The Sams index is available online. -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida |
#7
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Old Gernanium Transistor Repair
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#8
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Old Gernanium Transistor Repair
On Sun, 12 Nov 2006 19:12:54 -0800, wrongaddress wrote:
I have an old 8 gernamium transistor, protable AM radio that is noisy on weak stations when cold. It works reasonably well when set it in the sunshine and warms up. The problem seems to be the RF section since the noise goes away when the volume is turned down. I'm suspecting the germanium transistors may be the problem and wondering which one might be replaced with a silicon variety to cure the temperature problems? I'm not sure what all 8 transistors do. Two are in the output stage, and another is used as a audio driver that drives the audio input transformer.There are four RF coils, the usual oscillator (red) and mixer (yellow) and white (1st IF) and (black (second IF). But that only requires 6 transistors, and there are eight total. The detector is a diode, so they didn't use a transistor for that. I haven't figured out what the other 2 transistors do. I'm thinking of replacing the oscillator transistor with a high gain silicon variety to try and eliminate the temperature problems? Any other ideas? -Bill Since warmer=drier, I might look for paper tubular caps. When moist, they leak badly. |
#9
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Old Gernanium Transistor Repair
"Dave Plowman (News)" wrote in message ... Usually two for output, two for audio amps = 4. Perfectly easy to manage with three - one driver only. But in those days more transistors = more sales. I used to fix such things. |
#10
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Old Gernanium Transistor Repair
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#11
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Old Gernanium Transistor Repair
"J. Todd" wrote:
On Sun, 12 Nov 2006 19:12:54 -0800, wrongaddress wrote: I have an old 8 gernamium transistor, protable AM radio that is noisy on weak stations when cold. It works reasonably well when set it in the sunshine and warms up. The problem seems to be the RF section since the noise goes away when the volume is turned down. I'm suspecting the germanium transistors may be the problem and wondering which one might be replaced with a silicon variety to cure the temperature problems? I'm not sure what all 8 transistors do. Two are in the output stage, and another is used as a audio driver that drives the audio input transformer.There are four RF coils, the usual oscillator (red) and mixer (yellow) and white (1st IF) and (black (second IF). But that only requires 6 transistors, and there are eight total. The detector is a diode, so they didn't use a transistor for that. I haven't figured out what the other 2 transistors do. I'm thinking of replacing the oscillator transistor with a high gain silicon variety to try and eliminate the temperature problems? Any other ideas? -Bill Since warmer=drier, I might look for paper tubular caps. When moist, they leak badly. Paper capacitors? Transistor radios use electrolytic and mylar film instead of paper, but the electrolytics were poor quality, and they don't age very well. The capacitors in tuned circuits are either mica, ceramic or polystyrene. -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida |
#12
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Old Gernanium Transistor Repair
Michael A. Terrell wrote:
"J. Todd" wrote: Since warmer=drier, I might look for paper tubular caps. When moist, they leak badly. Paper capacitors? Transistor radios use electrolytic and mylar film instead of paper, but the electrolytics were poor quality, and they don't age very well. The capacitors in tuned circuits are either mica, ceramic or polystyrene. Lytic caps are easily tested by piggybacking. Just clip a similar value cap on, no need for any soldering or cutting. But really its farily pointless unless you do some fault finding first. NT |
#13
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Old Gernanium Transistor Repair
Get a can Of "Cold Spray" when it is working good, gently spray each
transistor to find which one is causing the trouble. Then replace it with a new germanium transistor. wrote in message oups.com... I have an old 8 gernamium transistor, protable AM radio that is noisy on weak stations when cold. It works reasonably well when set it in the sunshine and warms up. The problem seems to be the RF section since the noise goes away when the volume is turned down. I'm suspecting the germanium transistors may be the problem and wondering which one might be replaced with a silicon variety to cure the temperature problems? I'm not sure what all 8 transistors do. Two are in the output stage, and another is used as a audio driver that drives the audio input transformer.There are four RF coils, the usual oscillator (red) and mixer (yellow) and white (1st IF) and (black (second IF). But that only requires 6 transistors, and there are eight total. The detector is a diode, so they didn't use a transistor for that. I haven't figured out what the other 2 transistors do. I'm thinking of replacing the oscillator transistor with a high gain silicon variety to try and eliminate the temperature problems? Any other ideas? -Bill |
#14
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Old Gernanium Transistor Repair
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#16
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Old Gernanium Transistor Repair
Ancient_Hacker wrote:
wrote: I have an old 8 gernamium transistor, protable AM radio that is noisy on weak stations when cold. By "noisy" do you mean there is lots of background hiss, or do you mean the sound is rough and distorted? Yes, lots of background hiss and roar at low temperature. At 80 degrees F, it's not too bad, but at 55 degrees it whistles and squeals and the weak stations are lost. It works reasonably well when set it in the sunshine and warms up. I'm suspecting the germanium transistors may be the problem and wondering which one might be replaced with a silicon variety to cure the temperature problems? No. The radio was designed to work with germanium transistors. Every stage you change over to silicon will need to be rebiased, retuned, and reneutralized. Not an easy job. I'm not sure the design is the best. They used a couple resistors to set the bias on the output stage, and when the battery voltage falls a volt or so, the output has some crossover distortion. I fixed that problem with a couple diodes in place of a resistor so the bias current stays above zero as the battery voltage falls. I can now drop the supply voltage a couple volts with no crossover distortion. I'd start with replacing the electrolytics. Quite likely they're at about 20% of their original selves. Weak electrolytics can make the radio motorboat, or sound tinny and noisy. Yes, that could be a problem, but the AGC seems to work well, so that capacitor must be ok. -Bill |
#17
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Old Gernanium Transistor Repair
wrote:
Ancient_Hacker wrote: wrote: I have an old 8 gernamium transistor, protable AM radio that is noisy on weak stations when cold. By "noisy" do you mean there is lots of background hiss, or do you mean the sound is rough and distorted? Yes, lots of background hiss and roar at low temperature. At 80 degrees F, it's not too bad, but at 55 degrees it whistles and squeals and the weak stations are lost. It works reasonably well when set it in the sunshine and warms up. I'm suspecting the germanium transistors may be the problem and wondering which one might be replaced with a silicon variety to cure the temperature problems? No. The radio was designed to work with germanium transistors. Every stage you change over to silicon will need to be rebiased, retuned, and reneutralized. Not an easy job. I'm not sure the design is the best. They used a couple resistors to set the bias on the output stage, and when the battery voltage falls a volt or so, the output has some crossover distortion. I fixed that problem with a couple diodes in place of a resistor so the bias current stays above zero as the battery voltage falls. I can now drop the supply voltage a couple volts with no crossover distortion. I'd start with replacing the electrolytics. Quite likely they're at about 20% of their original selves. Weak electrolytics can make the radio motorboat, or sound tinny and noisy. Yes, that could be a problem, but the AGC seems to work well, so that capacitor must be ok. Hi Bill... I haven't read the whole thread, so if I'm repeating anyone else please accept my apologies. Why not consider operating it in a warmish room, and spraying local components one at a time (with a few minutes break in between) with "freeze in a can" (whatever they call it in your part of the world) until you find the component that causes it to act up. And just for the heck of it, my bet's on a resistor. Take care. Ken |
#18
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Old Gernanium Transistor Repair
wrote:
wrote: I have an old 8 gernamium transistor, protable AM radio that is noisy on weak stations when cold. It works reasonably well when set it in the sunshine and warms up. The problem seems to be the RF section since the noise goes away when the volume is turned down. I'm suspecting the germanium transistors may be the problem and wondering which one might be replaced with a silicon variety to cure the temperature problems? I'm not sure what all 8 transistors do. Two are in the output stage, and another is used as a audio driver that drives the audio input transformer.There are four RF coils, the usual oscillator (red) and mixer (yellow) and white (1st IF) and (black (second IF). But that only requires 6 transistors, and there are eight total. The detector is a diode, so they didn't use a transistor for that. I haven't figured out what the other 2 transistors do. I'm thinking of replacing the oscillator transistor with a high gain silicon variety to try and eliminate the temperature problems? Any other ideas? -Bill Replacing parts at random on electronics makes not one bit of sense. There are hundreds of components and hundreds of connections, any one of which may be to do with it. There are about about 50 components. This is little portable radio about the size of 2 packs of cigarettes (5.25 by 3 by 1.25). I like it because it's easy to carry around and sounds better than the smaller versions. Trying to repair a radio by replacing geraniums with silicon makes even less sense. Germanium trs are still sold new as well as used. If you dont know what youre doing, leave it alone. Well, if I leave it alone, I can only use it on hot days. I'm trying to figure out a way I can use it on hot and COLD days? Maybe you have a suggestion to overcome the temperature problems? -Bill |
#19
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Old Gernanium Transistor Repair
quietguy wrote:
How many gangs on the tuning cap? Many of the 8 transistor radios had an RF stage - if there are 3 gangs on the tuning cap that is a giveaway David It's just a little pocket size radio (5 X 3 X 1.5) with 2 sections for the tuning cap.It has the usual four RF coils and input and output audio transformers. But that only requires 6 transistors, and there are 8 used. I suppose I can trace out the connections to try and figure out what the extra 2 transistors do. wrote: I have an old 8 gernamium transistor, protable AM radio that is noisy on weak stations when cold. It works reasonably well when set it in the sunshine and warms up. The problem seems to be the RF section since the noise goes away when the volume is turned down. I'm suspecting the germanium transistors may be the problem and wondering which one might be replaced with a silicon variety to cure the temperature problems? I'm not sure what all 8 transistors do. Two are in the output stage, and another is used as a audio driver that drives the audio input transformer.There are four RF coils, the usual oscillator (red) and mixer (yellow) and white (1st IF) and (black (second IF). But that only requires 6 transistors, and there are eight total. The detector is a diode, so they didn't use a transistor for that. I haven't figured out what the other 2 transistors do. I'm thinking of replacing the oscillator transistor with a high gain silicon variety to try and eliminate the temperature problems? Any other ideas? -Bill |
#20
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Old Gernanium Transistor Repair
wrote in message oups.com... Well, if I leave it alone, I can only use it on hot days. I'm trying to figure out a way I can use it on hot and COLD days? Maybe you have a suggestion to overcome the temperature problems? The real way to fix it is with a signal tracer and signal generator. Isolate to a section and fault find there. |
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Old Gernanium Transistor Repair
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#22
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#23
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#24
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Old Gernanium Transistor Repair
wrote:
wrote: I have an old 8 gernamium transistor, protable AM radio that is noisy on weak stations when cold. It works reasonably well when set it in the sunshine and warms up. The problem seems to be the RF section since the noise goes away when the volume is turned down. I'm suspecting the germanium transistors may be the problem and wondering which one might be replaced with a silicon variety to cure the temperature problems? I'm not sure what all 8 transistors do. Two are in the output stage, and another is used as a audio driver that drives the audio input transformer.There are four RF coils, the usual oscillator (red) and mixer (yellow) and white (1st IF) and (black (second IF). But that only requires 6 transistors, and there are eight total. The detector is a diode, so they didn't use a transistor for that. I haven't figured out what the other 2 transistors do. I'm thinking of replacing the oscillator transistor with a high gain silicon variety to try and eliminate the temperature problems? Any other ideas? -Bill Sounds like a perfect job for a can of freeze spray. Warm it up until the problem goes away, then give suspect components a quick shot of cold. |
#25
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Old Gernanium Transistor Repair
Michael A. Terrell wrote:
wrote: quietguy wrote: How many gangs on the tuning cap? Many of the 8 transistor radios had an RF stage - if there are 3 gangs on the tuning cap that is a giveaway David It's just a little pocket size radio (5 X 3 X 1.5) with 2 sections for the tuning cap.It has the usual four RF coils and input and output audio transformers. But that only requires 6 transistors, and there are 8 used. I suppose I can trace out the connections to try and figure out what the extra 2 transistors do. Does your radio have a brand name and model number? Yes, it's a "Keytone" or "Kaytone" deluxe model, 8 transistor, made in Japan. Chrome faceplate, white plastic body, red plastic back. I searched Google but didn't find much. -Bill -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida |
#26
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Old Gernanium Transistor Repair
James Sweet wrote:
wrote: wrote: I have an old 8 gernamium transistor, protable AM radio that is noisy on weak stations when cold. It works reasonably well when set it in the sunshine and warms up. The problem seems to be the RF section since the noise goes away when the volume is turned down. I'm suspecting the germanium transistors may be the problem and wondering which one might be replaced with a silicon variety to cure the temperature problems? I'm not sure what all 8 transistors do. Two are in the output stage, and another is used as a audio driver that drives the audio input transformer.There are four RF coils, the usual oscillator (red) and mixer (yellow) and white (1st IF) and (black (second IF). But that only requires 6 transistors, and there are eight total. The detector is a diode, so they didn't use a transistor for that. I haven't figured out what the other 2 transistors do. I'm thinking of replacing the oscillator transistor with a high gain silicon variety to try and eliminate the temperature problems? Any other ideas? -Bill Sounds like a perfect job for a can of freeze spray. Warm it up until the problem goes away, then give suspect components a quick shot of cold. Yes, good idea, but the can of freeze spray costs $10, and the radio only cost two dollars. So I put the radio in the freezer for 30 minutes and took it out and it didn't work at all. Then I applied a hot sodering iron to the body of the oscillator transistor and it very quickly started working again. Seems the oscillator doesn't run at low temperature. Would you guess the solution is a silicon transistor? or just adjust the bias on the existing germanium transistor? -Bill |
#27
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Old Gernanium Transistor Repair
wrote in message oups.com... Yes, it's a "Keytone" or "Kaytone" deluxe model, 8 transistor, made in Japan. Chrome faceplate, white plastic body, red plastic back. I searched Google but didn't find much. Might be a collectible. If so, don't screw with it. Sell it to a fool^H^H^H^Hcollector and use the money to buy a good set. |
#28
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Old Gernanium Transistor Repair
Homer J Simpson wrote:
wrote in message oups.com... Yes, it's a "Keytone" or "Kaytone" deluxe model, 8 transistor, made in Japan. Chrome faceplate, white plastic body, red plastic back. I searched Google but didn't find much. Might be a collectible. If so, don't screw with it. Sell it to a fool^H^H^H^Hcollector and use the money to buy a good set. Yes, I'm thinking about selling it, but I want it to work well, as good as new or better. The radio I'd really like to have is the CCRadio Plus from ccrane company, for $134 at: http://www.ccrane.com/radios/am-fm-r...lus/index.aspx It's supposed to be optimized for 'talk radio' and voice frequencies, but it's a little large to carry around. Runs on four 'D' cells for 250 hours and has a leather case and a bunch of options, solar charger, Antenna amplifier, ect. It's supposed to be one of the best AM radios. I see it on ebay all the time, so I might make a bid and get it for $100 or less. -Bill |
#29
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Old Gernanium Transistor Repair
wrote in message ups.com... Yes, I'm thinking about selling it, but I want it to work well, as good as new or better. The radio I'd really like to have is the CCRadio Plus from ccrane company, for $134 at: http://www.ccrane.com/radios/am-fm-r...lus/index.aspx It's supposed to be optimized for 'talk radio' and voice frequencies, but it's a little large to carry around. Runs on four 'D' cells for 250 hours and has a leather case and a bunch of options, solar charger, Antenna amplifier, ect. It's supposed to be one of the best AM radios. I see it on ebay all the time, so I might make a bid and get it for $100 or less. I somewhat covet a Grundig all wave hand cranked, but I expect it's made in China too. |
#30
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Old Gernanium Transistor Repair
wrote in news:1163559828.809638.315730
@e3g2000cwe.googlegroups.com: The radio I'd really like to have is the CCRadio Plus from ccrane company, for $134 at: http://www.ccrane.com/radios/am-fm-r...lus/index.aspx It's supposed to be optimized for 'talk radio' and voice frequencies... I wonder how that is different from "lacks good bass and treble"? |
#31
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Old Gernanium Transistor Repair
Jim Land wrote:
wrote in news:1163559828.809638.315730 @e3g2000cwe.googlegroups.com: The radio I'd really like to have is the CCRadio Plus from ccrane company, for $134 at: http://www.ccrane.com/radios/am-fm-r...lus/index.aspx It's supposed to be optimized for 'talk radio' and voice frequencies... I wonder how that is different from "lacks good bass and treble"? Some of those CC Crane radios have a high failure rate on the LCD displays. Ask about the model you are looking at on: news:rec.radio.shortwave but be ready for the flaming idiots who like to hijack almost every thread. -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida |
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#33
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#34
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wrote:
wrote: only cost two dollars. So I put the radio in the freezer for 30 minutes and took it out and it didn't work at all. Then I applied a hot sodering iron to the body of the oscillator transistor and it very quickly started working again. Seems the oscillator doesn't run at low temperature. Would you guess the solution is a silicon transistor? or just adjust the bias on the existing germanium transistor? -Bill neither, increase the stage gain. That probably means higher collector R or similar. You may then need to adj the bias a little. Or with an old radio like that it might just be biased way wrong, where gain is down. Meter it and see where Vce sits when not oscillating. NT PS keep slobbering irons off geraniums, they max out at 90C, and slobber doesnt even melt till over 200. Just soldering Ge trs into pcbs is prone to killing them, this is why they typically had long sleeved leads. NT Some of the early, cheap transistor radios used really poor quality transistors. they had so much leakage that they were self biasing. Even if you replace them with a good germanium transistor, they may need the bias adjusted. -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida |
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Old Gernanium Transistor Repair
wrote in message ups.com... Would you guess the solution is a silicon transistor? or just adjust the bias on the existing germanium transistor? I did have one set only (ever) that had weak transistors. It was a minimum count model (5 or 6) and I replaced all of them to get it to work again. |
#36
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Old Gernanium Transistor Repair
Michael A. Terrell spake thus:
Michael Black wrote: Jim Land ) writes: wrote in news:1163387574.804150.266160 : I have an old 8 gernamium transistor, protable AM radio that is noisy on weak stations when cold.... Try over on alt.antiques.radio+phono... they'll enjoy hearing about your germanium transistors. I don't know. There has been debate in the past over there about what's relevant to the newsgroup, and some have felt transistors aren't old enough. Some of them think that A****er Kent radios are too new for that group. Ignore them, there are a number of transistor radio collectors in that group. I have most of the "Sams Transistor Radio Manuals" in my collection: http://home.earthlink.net/~mike.terrell/HWSTm.html The Sams index is available online. Which implies that, at least sometime in the past, there were those who repaired those radios. Did they? I remember when those things appeared on the market, and I always thought of them as disposable items. Did people actually take them in to be fixed? -- Just as McDonald's is where you go when you're hungry but don't really care about the quality of your food, Wikipedia is where you go when you're curious but don't really care about the quality of your knowledge. - Matthew White's WikiWatch (http://users.erols.com/mwhite28/wikiwoo.htm) |
#37
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Old Gernanium Transistor Repair
David Nebenzahl ) writes:
Michael A. Terrell spake thus: Michael Black wrote: Jim Land ) writes: wrote in news:1163387574.804150.266160 : I have an old 8 gernamium transistor, protable AM radio that is noisy on weak stations when cold.... Try over on alt.antiques.radio+phono... they'll enjoy hearing about your germanium transistors. I don't know. There has been debate in the past over there about what's relevant to the newsgroup, and some have felt transistors aren't old enough. Some of them think that A****er Kent radios are too new for that group. Ignore them, there are a number of transistor radio collectors in that group. I have most of the "Sams Transistor Radio Manuals" in my collection: http://home.earthlink.net/~mike.terrell/HWSTm.html The Sams index is available online. Which implies that, at least sometime in the past, there were those who repaired those radios. Did they? I remember when those things appeared on the market, and I always thought of them as disposable items. Did people actually take them in to be fixed? Who knows. But early transistor radios, that would have used germanium because there was no choice, were not cheap radios. They cost significant amounts at the time. Even later, one could still get decent transistor portables that would have cost a fair amount at the time. I once found a Sony portable from the early sixties, and it has metal casing and is quite heavy, complete with the large speaker. People would have been having those repaired, there's no way they'd toss them if they stopped working. The cheap transistor portables came later. Likely they were less likely to be repaired, but circuit wise they weren't that different from the expensive portables. Michael |
#38
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Old Gernanium Transistor Repair
wrote:
wrote: only cost two dollars. So I put the radio in the freezer for 30 minutes and took it out and it didn't work at all. Then I applied a hot sodering iron to the body of the oscillator transistor and it very quickly started working again. Seems the oscillator doesn't run at low temperature. Would you guess the solution is a silicon transistor? or just adjust the bias on the existing germanium transistor? -Bill neither, increase the stage gain. That probably means higher collector R or similar. You may then need to adj the bias a little. Or with an old radio like that it might just be biased way wrong, where gain is down. Meter it and see where Vce sits when not oscillating. The collector appears to drive the oscillator coil and mixer coil in series (no collector R other than maybe decoupling). There is a emitter resistor of 2K with a drop of 0.35 volts. I figure the oscillator stage is running at 0.35/2000 = 175 miroamps. I added a 3K resistor in parallel with the 2K so the current is increased to 0.35/1200 = 292 microamps. This brings up the gain about 3dB, but the radio still fails at low temperature in the refrigerator. At low temperature there is only noise and no signal. I tried this with a more modern radio using silicon transistors and it works well an 40 degrees or so. So, I'm almost convinced the problem is the germanium transistors. Will continue to investigate. -Bill |
#39
Posted to sci.electronics.repair
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Old Gernanium Transistor Repair
"David Nebenzahl" wrote in message .com... Which implies that, at least sometime in the past, there were those who repaired those radios. Did they? I remember when those things appeared on the market, and I always thought of them as disposable items. Did people actually take them in to be fixed? The first Sony shirt pocket (just) sized one cost me more than a week's wages - at wholesale! I repaired them for a few years until I moved on to other things. |
#40
Posted to sci.electronics.repair
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Old Gernanium Transistor Repair
"Michael Black" wrote in message ... Who knows. But early transistor radios, that would have used germanium because there was no choice, were not cheap radios. They cost significant amounts at the time. Even later, one could still get decent transistor portables that would have cost a fair amount at the time. I once found a Sony portable from the early sixties, and it has metal casing and is quite heavy, complete with the large speaker. People would have been having those repaired, there's no way they'd toss them if they stopped working. The cheap transistor portables came later. Likely they were less likely to be repaired, but circuit wise they weren't that different from the expensive portables. We had a popular Philips model that had a transistor audio output stage (OC71s and OC72s) but still had tubes for the convertor and IF. Later they came out with the OC44 and OC45 and went fully solid state. |