AC or DC TX - UK Vintage Radio Repair and Restoration Discussion Forum

60 oldjohn · 27th Dec 2022, 8:09 pm

Can a mains Transformer run on DC supply?

John.

GrimJosef · 27th Dec 2022, 8:12 pm

No. The voltages are induced in the secondary windings by a changing magnetic field in the core. By definition DC doesn't change, so it can't induce a changing field.

Cheers,

GJ

Red to black · 27th Dec 2022, 8:12 pm

no! is the simple answer

60 oldjohn · 27th Dec 2022, 8:24 pm

Quote:

Originally Posted by Red to black

no! is the simple answer

Exactly what I thought. Bush AC34 circuit.

John.

paulsherwin · 27th Dec 2022, 8:39 pm

Yes, it's a contradiction in terms. Transformers only work with AC. If you put DC into a transformer primary, you just get an electric heater. Somebody in the Olden Days has made a draughting error.

turretslug · 27th Dec 2022, 9:02 pm

I gather that several Bush models (and ISTR some other makers) used series-string valves in both AC/DC and AC-only sets, presumably to simplify production, with AC-only models feeding the heater string from an appropriate-voltage tapping on the HT secondary. Possibly, the draftsman substituted the transformer symbol for the dropper symbol in the circuit diagram without also altering the wording?

Cathovisor · 27th Dec 2022, 9:07 pm

An unusual howler from the offices of the W&ET there.

60 oldjohn · 27th Dec 2022, 10:16 pm

I suspected a printing error. Then I did wonder if the wiring was intended be connected to the primary side and used as an auto TX on DC, but I don't think this was suggested. I don't know if an auto TX would work on DC.

John.

Sideband · 27th Dec 2022, 10:18 pm

Yes this has been noted before. I noticed it when restoring my own AC34 and suspect Turretslug is correct in his assumption. Bush used several chassis with series string valve heaters but using a transformer. It simply meant they could use exactly the same chassis and just substitute a dropper for the transformer in the case of DC mains. It's a shame that Trader didn't notice the error before going to press.

Cobaltblue · 27th Dec 2022, 10:20 pm

I suspect the circuits for the DAC34 and AC34 were drawn up at the same time.

One of the things that should not have been copied across!

Cheers

Mike T

Dave Moll · 27th Dec 2022, 10:26 pm

Surely the comments above equally apply to an auto-transformer. The best it could achieve is to act as a (not very good) dropper.

Radio Wrangler · 27th Dec 2022, 10:26 pm

Could be quite frisky if anyone tries wiring one that way. Drafting or translation of technical things by non-technical people, who don't understand what they're describing is always risky.

Autotransformers don't do DC either, of course.

David

60 oldjohn · 27th Dec 2022, 10:33 pm

Thank you everyone, point taken. When I first saw the circuit I did not know if it was a mistake or some ingenious circuit, I now know.
This might as well be closed.

John.

paulsherwin · 27th Dec 2022, 10:34 pm

Lots of early 50s Ekco sets also used series string heaters and a mains transformer. It may have simplified the parts inventory, and perhaps U-series valves were priced lower than E-series.

27th Dec 2022, 8:09 pm	#1
60 oldjohn Dekatron Join Date: Dec 2004 Location: East Yorkshire, UK. Posts: 3,988	AC or DC TX Can a mains Transformer run on DC supply? John. __________________ My favourite text message "I'll be there in five minutes, if not read again"

27th Dec 2022, 8:12 pm	#2
GrimJosef Dekatron Join Date: Sep 2007 Location: Oxfordshire, UK. Posts: 4,311	Re: AC or DC TX No. The voltages are induced in the secondary windings by a changing magnetic field in the core. By definition DC doesn't change, so it can't induce a changing field. Cheers, GJ __________________ http://www.ampregen.com

27th Dec 2022, 8:12 pm	#3
Red to black Nonode Join Date: Mar 2010 Location: Sunderland, Tyne and Wear, UK. Posts: 2,476	Re: AC or DC TX no! is the simple answer __________________ I don't suffer from Insanity. I enjoy every minute of it.

27th Dec 2022, 8:39 pm	#5
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,964	Re: AC or DC TX Yes, it's a contradiction in terms. Transformers only work with AC. If you put DC into a transformer primary, you just get an electric heater. Somebody in the Olden Days has made a draughting error.

27th Dec 2022, 9:02 pm	#6
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,398	Re: AC or DC TX I gather that several Bush models (and ISTR some other makers) used series-string valves in both AC/DC and AC-only sets, presumably to simplify production, with AC-only models feeding the heater string from an appropriate-voltage tapping on the HT secondary. Possibly, the draftsman substituted the transformer symbol for the dropper symbol in the circuit diagram without also altering the wording?

27th Dec 2022, 9:07 pm	#7
Cathovisor Banned Join Date: Dec 2022 Location: Peterborough, Cambridgeshire, UK. Posts: 418	Re: AC or DC TX An unusual howler from the offices of the W&ET there.

27th Dec 2022, 10:16 pm	#8
60 oldjohn Dekatron Join Date: Dec 2004 Location: East Yorkshire, UK. Posts: 3,988	Re: AC or DC TX I suspected a printing error. Then I did wonder if the wiring was intended be connected to the primary side and used as an auto TX on DC, but I don't think this was suggested. I don't know if an auto TX would work on DC. John. __________________ My favourite text message "I'll be there in five minutes, if not read again"

27th Dec 2022, 10:18 pm	#9
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,577	Re: AC or DC TX Yes this has been noted before. I noticed it when restoring my own AC34 and suspect Turretslug is correct in his assumption. Bush used several chassis with series string valve heaters but using a transformer. It simply meant they could use exactly the same chassis and just substitute a dropper for the transformer in the case of DC mains. It's a shame that Trader didn't notice the error before going to press. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

27th Dec 2022, 10:20 pm	#10
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,875	Re: AC or DC TX I suspect the circuits for the DAC34 and AC34 were drawn up at the same time. One of the things that should not have been copied across! Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

27th Dec 2022, 10:26 pm	#11
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 6,130	Re: AC or DC TX Surely the comments above equally apply to an auto-transformer. The best it could achieve is to act as a (not very good) dropper. __________________ Mending is better than Ending (cf Brave New World by Aldous Huxley)

27th Dec 2022, 10:26 pm	#12
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,899	Re: AC or DC TX Could be quite frisky if anyone tries wiring one that way. Drafting or translation of technical things by non-technical people, who don't understand what they're describing is always risky. Autotransformers don't do DC either, of course. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

27th Dec 2022, 10:33 pm	#13
60 oldjohn Dekatron Join Date: Dec 2004 Location: East Yorkshire, UK. Posts: 3,988	Re: AC or DC TX Thank you everyone, point taken. When I first saw the circuit I did not know if it was a mistake or some ingenious circuit, I now know. This might as well be closed. John. __________________ My favourite text message "I'll be there in five minutes, if not read again"

27th Dec 2022, 10:34 pm	#14
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,964	Re: AC or DC TX Lots of early 50s Ekco sets also used series string heaters and a mains transformer. It may have simplified the parts inventory, and perhaps U-series valves were priced lower than E-series.