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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
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negative ground ?
No user switchable option. I can see its possible to rewire the vibrator so
you still get right polarity for the anode supplies. Heaters presumably happy enough powered the other way round but how to change the biasing of the valves ? |
#2
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negative ground ?
"N_Cook" wrote in message ... No user switchable option. I can see its possible to rewire the vibrator so you still get right polarity for the anode supplies. Heaters presumably happy enough powered the other way round but how to change the biasing of the valves ? Unless it's a synchronous vibrator, it should run equally well on either polarity. The radio doesn't get anode voltage from the car's DC, it gets it from the radio's DC-DC converter (vibrator, transformer, rectifier, filtering). |
#3
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negative ground ?
Brenda Ann wrote in message
... "N_Cook" wrote in message ... No user switchable option. I can see its possible to rewire the vibrator so you still get right polarity for the anode supplies. Heaters presumably happy enough powered the other way round but how to change the biasing of the valves ? Unless it's a synchronous vibrator, it should run equally well on either polarity. The radio doesn't get anode voltage from the car's DC, it gets it from the radio's DC-DC converter (vibrator, transformer, rectifier, filtering). With positive ground you automaticly get a negative voltage for biasing but what to do in the negative ground case ? In this case its a synchronous mechanism but its easy enough to get inside to rewire it for the opposite polarity, it is the biasing voltage I cannot fathom out. |
#4
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negative ground ?
"N_Cook" wrote in message ... Brenda Ann wrote in message ... "N_Cook" wrote in message ... No user switchable option. I can see its possible to rewire the vibrator so you still get right polarity for the anode supplies. Heaters presumably happy enough powered the other way round but how to change the biasing of the valves ? Unless it's a synchronous vibrator, it should run equally well on either polarity. The radio doesn't get anode voltage from the car's DC, it gets it from the radio's DC-DC converter (vibrator, transformer, rectifier, filtering). With positive ground you automaticly get a negative voltage for biasing but what to do in the negative ground case ? In this case its a synchronous mechanism but its easy enough to get inside to rewire it for the opposite polarity, it is the biasing voltage I cannot fathom out. This must be an unusual radio (by old US car radio standards). No valve car radio I have ever seen has used the car's battery supply for any voltage other than the valve heaters. All DC voltages to run the valves come off the output of the transformer, with bias voltages developed by raising the cathode of the valve above B- (making the grid negative with respect to the cathode, but not with respect to ground). |
#5
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negativeground ?
Brenda Ann wrote:
"N_Cook" wrote in message ... Brenda Ann wrote in message ... "N_Cook" wrote in message ... No user switchable option. I can see its possible to rewire the vibrator so you still get right polarity for the anode supplies. Heaters presumably happy enough powered the other way round but how to change the biasing of the valves ? Unless it's a synchronous vibrator, it should run equally well on either polarity. The radio doesn't get anode voltage from the car's DC, it gets it from the radio's DC-DC converter (vibrator, transformer, rectifier, filtering). With positive ground you automaticly get a negative voltage for biasing but what to do in the negative ground case ? In this case its a synchronous mechanism but its easy enough to get inside to rewire it for the opposite polarity, it is the biasing voltage I cannot fathom out. This must be an unusual radio (by old US car radio standards). No valve car radio I have ever seen has used the car's battery supply for any voltage other than the valve heaters. All DC voltages to run the valves come off the output of the transformer, with bias voltages developed by raising the cathode of the valve above B- (making the grid negative with respect to the cathode, but not with respect to ground). I'd like to see a schematic of that beast. I can see using the neg for bias in a 6V pos gnd system, but it would only be -6V, not much. Easy to get that off the xfmr center tap. Ken |
#6
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negative ground ?
Brenda Ann wrote in message ... "N_Cook" wrote in message ... Brenda Ann wrote in message ... "N_Cook" wrote in message ... No user switchable option. I can see its possible to rewire the vibrator so you still get right polarity for the anode supplies. Heaters presumably happy enough powered the other way round but how to change the biasing of the valves ? Unless it's a synchronous vibrator, it should run equally well on either polarity. The radio doesn't get anode voltage from the car's DC, it gets it from the radio's DC-DC converter (vibrator, transformer, rectifier, filtering). With positive ground you automaticly get a negative voltage for biasing but what to do in the negative ground case ? In this case its a synchronous mechanism but its easy enough to get inside to rewire it for the opposite polarity, it is the biasing voltage I cannot fathom out. This must be an unusual radio (by old US car radio standards). No valve car radio I have ever seen has used the car's battery supply for any voltage other than the valve heaters. All DC voltages to run the valves come off the output of the transformer, with bias voltages developed by raising the cathode of the valve above B- (making the grid negative with respect to the cathode, but not with respect to ground). This one also, on checking. I had not realised that the 12V to the radio is just for the heaters and the dial lamp and the on/off switch. Just leaves whether there is an added RFI noise problem from the "inverter". -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#7
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negative ground ?
In article ,
N_Cook wrote: No user switchable option. I can see its possible to rewire the vibrator so you still get right polarity for the anode supplies. Heaters presumably happy enough powered the other way round but how to change the biasing of the valves ? No need if it's a mechanical vibrator. That produces AC... -- *Procrastination is the art of keeping up with yesterday. Dave Plowman London SW To e-mail, change noise into sound. |
#8
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negative ground ?
Dave Plowman (News) wrote in message
... In article , N_Cook wrote: No user switchable option. I can see its possible to rewire the vibrator so you still get right polarity for the anode supplies. Heaters presumably happy enough powered the other way round but how to change the biasing of the valves ? No need if it's a mechanical vibrator. That produces AC... -- *Procrastination is the art of keeping up with yesterday. Dave Plowman London SW To e-mail, change noise into sound. not this one - synchronous - see recent thread on Ekco CR280. I had to rebuild the contacts to get it working. Needs smoothing yes, because its chopped but not ac. Does not require a rectifier thermionic, Se or Si. But feed it the wrong way and you get negative HT -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#9
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negative ground ?
In article ,
"N_Cook" wrote: Brenda Ann wrote in message ... "N_Cook" wrote in message ... Brenda Ann wrote in message ... "N_Cook" wrote in message ... No user switchable option. I can see its possible to rewire the vibrator so you still get right polarity for the anode supplies. Heaters presumably happy enough powered the other way round but how to change the biasing of the valves ? Unless it's a synchronous vibrator, it should run equally well on either polarity. The radio doesn't get anode voltage from the car's DC, it gets it from the radio's DC-DC converter (vibrator, transformer, rectifier, filtering). With positive ground you automaticly get a negative voltage for biasing but what to do in the negative ground case ? In this case its a synchronous mechanism but its easy enough to get inside to rewire it for the opposite polarity, it is the biasing voltage I cannot fathom out. This must be an unusual radio (by old US car radio standards). No valve car radio I have ever seen has used the car's battery supply for any voltage other than the valve heaters. All DC voltages to run the valves come off the output of the transformer, with bias voltages developed by raising the cathode of the valve above B- (making the grid negative with respect to the cathode, but not with respect to ground). This one also, on checking. I had not realised that the 12V to the radio is just for the heaters and the dial lamp and the on/off switch. Just leaves whether there is an added RFI noise problem from the "inverter". Why would the RFI issues change? If it is a synchronous vibrator, isn't it simply a matter of reversing two transformer connections to convert from positive ground to negative ground, how does this change affect RFI? Regards, John Byrns -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ |
#10
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negativeground ?
N_Cook wrote:
Dave Plowman (News) wrote in message ... In article , N_Cook wrote: No user switchable option. I can see its possible to rewire the vibrator so you still get right polarity for the anode supplies. Heaters presumably happy enough powered the other way round but how to change the biasing of the valves ? No need if it's a mechanical vibrator. That produces AC... -- *Procrastination is the art of keeping up with yesterday. Dave Plowman London SW To e-mail, change noise into sound. not this one - synchronous - see recent thread on Ekco CR280. I had to rebuild the contacts to get it working. Needs smoothing yes, because its chopped but not ac. Does not require a rectifier thermionic, Se or Si. But feed it the wrong way and you get negative HT -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ If you're getting negative B voltage, reverse the two secondary leads going to the vibrator. Ken |
#11
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negativeground ?
Mr. Cook,
This was mentioned in the previous thread on synchronous vibrators. To enable running on reverse supply polarity, just reverse the two HV (HT) secondary leads that would normally go to the anodes of a tube rectifier. Bill(oc) |
#12
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negative ground ?
aaah, this doesn't make sense - on every vibrator radio I ever used (only a
few dozen), you could swap ground polarity and do nothing and it works. Now, if you put in an SS vibrator, then it's a different story. Why are you thinking yours is different? "N_Cook" wrote in message ... No user switchable option. I can see its possible to rewire the vibrator so you still get right polarity for the anode supplies. Heaters presumably happy enough powered the other way round but how to change the biasing of the valves ? ** Posted from http://www.teranews.com ** |
#13
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negative ground ?
Check the vibrator socket. Some, but by no means all, synchronous vibrator
sockets were symmetrical so that the vibrator could be plugged in two ways, one for positive ground and the other for negative ground. If it isn't that kind, then you will have to reverse the wiring as others have mentioned. The reversible vibrators I have seen have + and - symbols on top to show which way to install them. -- Jim Mueller To get my real email address, replace wrongname with eportiz. Then replace nospam with sacbeemail. "N_Cook" wrote in message ... No user switchable option. I can see its possible to rewire the vibrator so you still get right polarity for the anode supplies. Heaters presumably happy enough powered the other way round but how to change the biasing of the valves ? |
#14
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negative ground ?
In article ,
N_Cook wrote: No need if it's a mechanical vibrator. That produces AC... not this one - synchronous - see recent thread on Ekco CR280. Can't seem to find that. I had to rebuild the contacts to get it working. Needs smoothing yes, because its chopped but not ac. Does not require a rectifier thermionic, Se or Si. But feed it the wrong way and you get negative HT Right. Heard of them but never seen one. Is this a UK market radio? It would be strange to produce a positive earth only radio given that even in the UK not all makes went to positive earth. -- *It's o.k. to laugh during sexŒ.Œ.just don't point! Dave Plowman London SW To e-mail, change noise into sound. |
#15
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negative ground ?
Jim Mueller wrote in message
... Check the vibrator socket. Some, but by no means all, synchronous vibrator sockets were symmetrical so that the vibrator could be plugged in two ways, one for positive ground and the other for negative ground. If it isn't that kind, then you will have to reverse the wiring as others have mentioned. The reversible vibrators I have seen have + and - symbols on top to show which way to install them. -- Jim Mueller To get my real email address, replace wrongname with eportiz. Then replace nospam with sacbeemail. "N_Cook" wrote in message ... No user switchable option. I can see its possible to rewire the vibrator so you still get right polarity for the anode supplies. Heaters presumably happy enough powered the other way round but how to change the biasing of the valves ? This one has 2 polarising pins so one way round only. Changing round the 2, 12V supply leads is easier, the can is earthed but not connected internally to the vibrator coil or contacts. a circuit for a synchronous one ( no rectifier required) I've put on http://www.diversed.fsnet.co.uk/vib2.gif -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#16
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negativeground ?
On Jul 24, 12:31*am, "N_Cook" wrote:
This one has 2 polarising pins so one way round only. Changing round the 2, 12V supply leads is easier, the can is earthed but not connected internally to the vibrator coil or contacts. a circuit for a synchronous one ( no rectifier required) I've put onhttp://www.diversed.fsnet.co.uk/vib2.gif OK, the schematic shows the hookup differs a bit from the old Delco synchronous-vibrator system I was referring to back in post # 11. But exactly the same principle applies: To enable running on reverse supply polarity, simply reverse (swap) the two transformer secondary leads, i.e., the ones which have the 1500V buffer cap across them. Been there, done that. It works. Bill(oc) |
#17
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Converting a positive ground valve/tube car radio to negativeground ?
http://www.diversed.fsnet.co.uk/vib2.gif
There appears to be an error in this schematic. Someone else may confirm. The armature should be connected to common negative. Instead, the line from the armature is shown 'jumping over' the common negative line. As shown, this is an open circuit with no DC return path. Make the correction by tying the armature to common neg., and operation of the circuit becomes self-explanatory. |
#18
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negative ground ?
In article ,
"William Noble" wrote: aaah, this doesn't make sense - on every vibrator radio I ever used (only a few dozen), you could swap ground polarity and do nothing and it works. Now, if you put in an SS vibrator, then it's a different story. Why are you thinking yours is different? Probably because it uses a synchronous vibrator to eliminate the need for a rectifier tube. Regards, John Byrns -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ |
#19
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negativeground ?
On Jul 24, 7:43*am, oldcoot wrote:
*http://www.diversed.fsnet.co.uk/vib2.gif There appears to be an error in this schematic. Someone else may confirm. The armature should be connected to common negative. Instead, the line from the armature is shown 'jumping over' the common negative line. As shown, this is an open circuit with no DC return path. Make the correction by tying the armature to common neg., and operation of the circuit becomes self-explanatory. Um, it IS connected to common negative were the line comes down from the armature terminal. From that point a line then goes to the bottom end of the .1u input filter cap. Neil S. |
#20
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negativeground ?
On Jul 24, 8:46*am, nesesu wrote:
On Jul 24, 7:43*am, oldcoot wrote: *http://www.diversed.fsnet.co.uk/vib2.gif There appears to be an error in this schematic. Someone else may confirm. The armature should be connected to common negative. Instead, the line from the armature is shown 'jumping over' the common negative line. As shown, this is an open circuit with no DC return path. Make the correction by tying the armature to common neg., and operation of the circuit becomes self-explanatory. Um, it IS connected to common negative were the line comes down from the armature terminal. From that point a line then goes to the bottom end of the .1u input filter cap. Neil S. Maybe the image I'm looking at is different than yours (if that's possible), but mine clearly shows the line from the armature 'jumping over' the negative DC bus, and ending at the bottom of the .1uf cap (the bottom of this cap should also be tied to common neg., but isn't). On my print, the 'jump over' symbol is clearly an error. John B., Halp! :-) Bill(oc) |
#22
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negative ground ?
Jim Mueller wrote in message
acomip... Look to the left near the hash choke; it's connected to common there. It's a strange way to draw it but it is correct. -- Jim Mueller To get my real email address, replace wrongname with eportiz. Then replace nospam with sacbeemail. "oldcoot" wrote in message ... On Jul 24, 8:46 am, nesesu wrote: On Jul 24, 7:43 am, oldcoot wrote: http://www.diversed.fsnet.co.uk/vib2.gif There appears to be an error in this schematic. Someone else may confirm. The armature should be connected to common negative. Instead, the line from the armature is shown 'jumping over' the common negative line. As shown, this is an open circuit with no DC return path. Make the correction by tying the armature to common neg., and operation of the circuit becomes self-explanatory. Um, it IS connected to common negative were the line comes down from the armature terminal. From that point a line then goes to the bottom end of the .1u input filter cap. Neil S. Maybe the image I'm looking at is different than yours (if that's possible), but mine clearly shows the line from the armature 'jumping over' the negative DC bus, and ending at the bottom of the .1uf cap (the bottom of this cap should also be tied to common neg., but isn't). On my print, the 'jump over' symbol is clearly an error. John B., Halp! :-) Bill(oc) Probably a bit difficult getting back to the author, G A Quarrington , printed 58 years ago -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#23
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Converting a positive ground valve/tube car radio to negativeground ?
oldcoot wrote:
http://www.diversed.fsnet.co.uk/vib2.gif There appears to be an error in this schematic. Someone else may confirm. The armature should be connected to common negative. Instead, the line from the armature is shown 'jumping over' the common negative line. As shown, this is an open circuit with no DC return path. Make the correction by tying the armature to common neg., and operation of the circuit becomes self-explanatory. On diags that show the jump for no connection, lines crossing means there is a connection. I like the connection represented by a dot, but on some hard to read prints, this dot can disappear, leaving you wondering, which is it. Ken |
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