McMichael Twin Supervox DC Model - UK Vintage Radio Repair and Restoration Discussion Forum

zenitht · 25th Jul 2017, 9:05 pm

Hi
Does anyone have any information they would be willing to share on this rare version 200/250V DC.

Dumb question of the day:- Is there any way to convert it to run on AC. My guess is no due to the completely different circuit, but didn't know if there was a AC/DC Converter that might do the trick instead?

Any help or advice, gratefully received.

Thank you
BR
Graham

TrevorG3VLF · 25th Jul 2017, 9:16 pm

How about a bridge rectifier? If a smoothing capacitor is used the voltage may be high and a dropper resistance may be needed.

250-0-250V transformers are available but I would look for a 200V isolating transformer with a bridge rectifier and smoother so that the chassis can be earthed.

Could you show us the power input circuit diagram? My Trader disc has died.

zenitht · 25th Jul 2017, 9:56 pm

Hi
Thanks Trevor. That's part of the problem, I don't have access to the DC version of the chassis, only the normal AC version, sorry.

AC/HL · 25th Jul 2017, 11:19 pm

It's here: http://www.service-data.com/section....in-supervox-dc
As it's DC mains there's very little in the power supply. The valve heaters and dial light are in series with just a Barretter, and the two speaker energising coils are in series across the mains! Smoothing is a 40H choke input with a single 4UF smoothing cap.

vinrads · 26th Jul 2017, 8:23 am

I made a power supply for a Columbia DC set not a problem used bridge rectifiers I had a tx that gave me above the voltages I needed , and then a regulator, adjustable type so as get the LT spot on , then I think a transistor regulator for the HT .Mick.

zenitht · 26th Jul 2017, 12:56 pm

Hi and thank you very much for the great response. Does anyone know of someone who could supply such a unit AC/DC Convertor suitable for connection from mains to set, please?
Many thanks
Graham

Herald1360 · 26th Jul 2017, 4:28 pm

It's not likely to be a common off the shelf item!

DiY or commission job most likely sources.

26th Jul 2017, 5:26 pm

If it was mine I would go for the isolating transformer approach. Say 225V (the middle of the range) would give 160V RMS, a couple of 40-0-40V transformers, a bridge rectifier and a large (100uF) capacitor would supply its needs.

zenitht · 26th Jul 2017, 6:05 pm

Hi and thanks for all the good advice.
Would anyone be prepared to build one for me. All costs covered naturally.
Thanks

Herald1360 · 26th Jul 2017, 7:45 pm

Hmm, could be interesting.....

Does anyone know what dc supply voltage this was designed for? With a barreter I guess it could be fairly wide range.

What's the resistance of the speaker field coils? They might make quite a difference to the power pack design.

What valves does it use? The circuit in the service data collection is somewhat lacking in helpful information like that.

Ed_Dinning · 26th Jul 2017, 8:02 pm

Hi if you want to keep the set looking original it may be wise to have the power supply as a separate block that will fit in the back of the set if there is space.
It is a fairly simple circuit and the main difficulty will be finding a transformer with the correct voltages. If you have the space you may find it easier to use more than one transformer with the secondary's in series.
Regulators should not be necessary as you have a baretter and the modern mains is probably more stable than some of the old DC supplies.

It should be a nice set when it is running.

Ed

26th Jul 2017, 8:09 pm

Quote:

Would anyone be prepared to build one for me.

I would, drop me a PM.
To keep this in the thread, are there any ratings labels on the set?

TrevorG3VLF · 27th Jul 2017, 2:00 pm

There is a 40H smoothing choke input (#4) so you may be able to dispense with a storage capacitor. The voltage delivered will be 0.9 * input RMS. A 1:1 isolating transformer should be easy to obtain.
The 4uF capacitor can be raised a lot (100uF?) or supplemented.

Herald1360 · 27th Jul 2017, 4:54 pm

Would there be any issues with hum from the heaters if full wave unsmoothed dc is used to feed them?

zenitht · 27th Jul 2017, 6:31 pm

Hi

Details on rear of receiver simply says 200/250 Volts DC. No other ratings.

julie_m · 27th Jul 2017, 9:21 pm

Quote:

Originally Posted by Herald1360

Would there be any issues with hum from the heaters if full wave unsmoothed dc is used to feed them?

Unlikely. There are plenty of radios running series heater chains straight from AC without unlistenable levels of hum.

Also, remember, the output from an old-fashioned DC generator using a traditional commutator and brushes is basically equivalent to the output from an alternator via a bridge rectifier without smoothing. The current that gets induced is still a sine wave; only now, the connections are being swapped over every half-turn, so it will always be flowing in the same direction through the load.

Herald1360 · 27th Jul 2017, 11:30 pm

But the dc generator output would be more like multiphase rectified ac with much less and higher frequency ripple than single phase full wave.

We still don't know what the valve types are- whether they're typical ac series heater chain ones or something else?

AC/HL · 28th Jul 2017, 12:17 am

There were separate ranges of valves for DC, but presumably the heaters were suitably insulated.

zenitht · 1st Aug 2017, 2:21 pm

Thanks

I'll ask again. Would anyone be prepared to build me a PSU. Cost (within reason) is not an issue. I'm not able to do it myself, I do not posses the expertise in electronics.

cheers

vinrads · 1st Aug 2017, 7:55 pm

I didn't respond due to you are in Sussex , and I am in Derbyshire If you could get it to me I would gladly make a power supply for it . Mick.

25th Jul 2017, 9:05 pm	#1
zenitht Triode Join Date: Feb 2005 Location: Horsham, West Sussex, UK. Posts: 35	McMichael Twin Supervox DC Model Hi Does anyone have any information they would be willing to share on this rare version 200/250V DC. Dumb question of the day:- Is there any way to convert it to run on AC. My guess is no due to the completely different circuit, but didn't know if there was a AC/DC Converter that might do the trick instead? Any help or advice, gratefully received. Thank you BR Graham

25th Jul 2017, 9:16 pm	#2
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	Re: McMichael Twin Supervox DC Model How about a bridge rectifier? If a smoothing capacitor is used the voltage may be high and a dropper resistance may be needed. 250-0-250V transformers are available but I would look for a 200V isolating transformer with a bridge rectifier and smoother so that the chassis can be earthed. Could you show us the power input circuit diagram? My Trader disc has died.

25th Jul 2017, 9:56 pm	#3
zenitht Triode Join Date: Feb 2005 Location: Horsham, West Sussex, UK. Posts: 35	Re: McMichael Twin Supervox DC Model Hi Thanks Trevor. That's part of the problem, I don't have access to the DC version of the chassis, only the normal AC version, sorry.

26th Jul 2017, 8:23 am	#5
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,766	Re: McMichael Twin Supervox DC Model I made a power supply for a Columbia DC set not a problem used bridge rectifiers I had a tx that gave me above the voltages I needed , and then a regulator, adjustable type so as get the LT spot on , then I think a transistor regulator for the HT .Mick. Last edited by vinrads; 26th Jul 2017 at 8:30 am.

26th Jul 2017, 12:56 pm	#6
zenitht Triode Join Date: Feb 2005 Location: Horsham, West Sussex, UK. Posts: 35	Re: McMichael Twin Supervox DC Model Hi and thank you very much for the great response. Does anyone know of someone who could supply such a unit AC/DC Convertor suitable for connection from mains to set, please? Many thanks Graham

25th Jul 2017, 11:19 pm	#4
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: McMichael Twin Supervox DC Model It's here: http://www.service-data.com/section....in-supervox-dc As it's DC mains there's very little in the power supply. The valve heaters and dial light are in series with just a Barretter, and the two speaker energising coils are in series across the mains! Smoothing is a 40H choke input with a single 4UF smoothing cap.

26th Jul 2017, 4:28 pm	#7
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: McMichael Twin Supervox DC Model It's not likely to be a common off the shelf item! DiY or commission job most likely sources. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

26th Jul 2017, 5:26 pm	#8
Guest Guest Posts: n/a	Re: McMichael Twin Supervox DC Model If it was mine I would go for the isolating transformer approach. Say 225V (the middle of the range) would give 160V RMS, a couple of 40-0-40V transformers, a bridge rectifier and a large (100uF) capacitor would supply its needs.

26th Jul 2017, 6:05 pm	#9
zenitht Triode Join Date: Feb 2005 Location: Horsham, West Sussex, UK. Posts: 35	Re: McMichael Twin Supervox DC Model Hi and thanks for all the good advice. Would anyone be prepared to build one for me. All costs covered naturally. Thanks

26th Jul 2017, 7:45 pm	#10
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: McMichael Twin Supervox DC Model Hmm, could be interesting..... Does anyone know what dc supply voltage this was designed for? With a barreter I guess it could be fairly wide range. What's the resistance of the speaker field coils? They might make quite a difference to the power pack design. What valves does it use? The circuit in the service data collection is somewhat lacking in helpful information like that. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

26th Jul 2017, 8:02 pm	#11
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,195	Re: McMichael Twin Supervox DC Model Hi if you want to keep the set looking original it may be wise to have the power supply as a separate block that will fit in the back of the set if there is space. It is a fairly simple circuit and the main difficulty will be finding a transformer with the correct voltages. If you have the space you may find it easier to use more than one transformer with the secondary's in series. Regulators should not be necessary as you have a baretter and the modern mains is probably more stable than some of the old DC supplies. It should be a nice set when it is running. Ed

27th Jul 2017, 2:00 pm	#13
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	Re: McMichael Twin Supervox DC Model There is a 40H smoothing choke input (#4) so you may be able to dispense with a storage capacitor. The voltage delivered will be 0.9 * input RMS. A 1:1 isolating transformer should be easy to obtain. The 4uF capacitor can be raised a lot (100uF?) or supplemented.

27th Jul 2017, 4:54 pm	#14
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: McMichael Twin Supervox DC Model Would there be any issues with hum from the heaters if full wave unsmoothed dc is used to feed them? __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

27th Jul 2017, 6:31 pm	#15
zenitht Triode Join Date: Feb 2005 Location: Horsham, West Sussex, UK. Posts: 35	Re: McMichael Twin Supervox DC Model Hi Details on rear of receiver simply says 200/250 Volts DC. No other ratings.

27th Jul 2017, 11:30 pm	#17
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: McMichael Twin Supervox DC Model But the dc generator output would be more like multiphase rectified ac with much less and higher frequency ripple than single phase full wave. We still don't know what the valve types are- whether they're typical ac series heater chain ones or something else? __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

28th Jul 2017, 12:17 am	#18
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: McMichael Twin Supervox DC Model There were separate ranges of valves for DC, but presumably the heaters were suitably insulated.

1st Aug 2017, 2:21 pm	#19
zenitht Triode Join Date: Feb 2005 Location: Horsham, West Sussex, UK. Posts: 35	Re: McMichael Twin Supervox DC Model Thanks I'll ask again. Would anyone be prepared to build me a PSU. Cost (within reason) is not an issue. I'm not able to do it myself, I do not posses the expertise in electronics. cheers

1st Aug 2017, 7:55 pm	#20
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,766	Re: McMichael Twin Supervox DC Model I didn't respond due to you are in Sussex , and I am in Derbyshire If you could get it to me I would gladly make a power supply for it . Mick.