Valve line up - UK Vintage Radio Repair and Restoration Discussion Forum

radiopotty · 24th Feb 2019, 6:32 pm

Hi Folks
I am putting the finishing touches to a Breadboard Radio.The radio is a 4 valve set design I found whilst browsing a 1923 Modern Wireless magazine. It is a simple design employing twin variable tuning coils and two inter valve transformer sections. No information is given in regard of choice of valves but I assume they would have been straight triodes. I have boxes of 2 and 4 volt LF and HF valves. I would appreciate your advice in choosing your own preferences to help me get the best arrangements.

Many thanks. Frank

Herald1360 · 25th Feb 2019, 12:13 am

1923 would have been bright emitters, you'd be better off with slightly later dull emitter types both from availability and longevity points of view. 2V types would only require one PbSO4 cell to power the filaments. You don't say what the functional lineup is- is it DET, 3LF; RF, DET, 2LF or some other combination? The Mullard PM series is worth considering.

PJL · 25th Feb 2019, 2:57 pm

Best to post a circuit diagram. I agree, 2V filament Mullard PM series are the best option - there are plenty about and I have yet to find a faulty one.

Mike. Watterson · 25th Feb 2019, 2:59 pm

You can use series pairs of NiMH paralleled with diodes to drop the voltage. A Lead Acid is about 2.2V fully charged. A pair of NiMH is 3V (just taken off charge) very rapidly droping to a nominal 2.4V. The end point is 2.0 ideally (1.8V on Lead Acid).
The voltage of Lead Acid rises much more on charge. The valves were designed assuming the cell was always charged separately, because otherwise why have one at all? Replacement HT AND LT PSUs assumed no batteries installed.
I have a jar with diodes to split and combine as well as a fuse where filler would have been. It has a number of C size NiMH in series & parallel for my 1929 four valve suitcase TRF.
From 1926 many earlier breadboards would have had the bright emitters replaced with Dull emitters as they failed. About x10 longer life (or more) and much longer LT run time.

radiopotty · 26th Feb 2019, 9:01 pm

Thanks all.If I knew how to post a schematic I would. I do have a 9 year old grandson.I’ll ask him.
Many thanks. Frank

Mike. Watterson · 27th Feb 2019, 11:14 am

Actually I'd use 1p24b Russian rod pentodes, triodised. Fitted in suitable holders. Or the 1j29b. You can put the pair of filaments in series and under-run at 2V of lead acid, or simply run direct off the 2 x NiMH. A series resistor on filament to set the gain.
Unlike the PM series dull emitters, there are literally millions in NOS date coded from 1977 to approximately 1990.

I'm actually restoring a couple of 1920s sets using these in replica holders with glass bulbs off small halogen lamps. A large car headlamp base looks good, metal collar and the three blades can be removed. Then four pins can easily be fitted.

24th Feb 2019, 6:32 pm	#1
radiopotty Retired Dormant Member Join Date: Jun 2008 Location: Doncaster, South Yorkshire, UK. Posts: 20	Valve line up Hi Folks I am putting the finishing touches to a Breadboard Radio.The radio is a 4 valve set design I found whilst browsing a 1923 Modern Wireless magazine. It is a simple design employing twin variable tuning coils and two inter valve transformer sections. No information is given in regard of choice of valves but I assume they would have been straight triodes. I have boxes of 2 and 4 volt LF and HF valves. I would appreciate your advice in choosing your own preferences to help me get the best arrangements. Many thanks. Frank

25th Feb 2019, 12:13 am	#2
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Valve line up 1923 would have been bright emitters, you'd be better off with slightly later dull emitter types both from availability and longevity points of view. 2V types would only require one PbSO4 cell to power the filaments. You don't say what the functional lineup is- is it DET, 3LF; RF, DET, 2LF or some other combination? The Mullard PM series is worth considering. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

25th Feb 2019, 2:57 pm	#3
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Valve line up Best to post a circuit diagram. I agree, 2V filament Mullard PM series are the best option - there are plenty about and I have yet to find a faulty one.

25th Feb 2019, 2:59 pm	#4
Mike. Watterson Heptode Join Date: Dec 2014 Location: Limerick, Ireland. Posts: 901	Re: Valve line up You can use series pairs of NiMH paralleled with diodes to drop the voltage. A Lead Acid is about 2.2V fully charged. A pair of NiMH is 3V (just taken off charge) very rapidly droping to a nominal 2.4V. The end point is 2.0 ideally (1.8V on Lead Acid). The voltage of Lead Acid rises much more on charge. The valves were designed assuming the cell was always charged separately, because otherwise why have one at all? Replacement HT AND LT PSUs assumed no batteries installed. I have a jar with diodes to split and combine as well as a fuse where filler would have been. It has a number of C size NiMH in series & parallel for my 1929 four valve suitcase TRF. From 1926 many earlier breadboards would have had the bright emitters replaced with Dull emitters as they failed. About x10 longer life (or more) and much longer LT run time.

26th Feb 2019, 9:01 pm	#5
radiopotty Retired Dormant Member Join Date: Jun 2008 Location: Doncaster, South Yorkshire, UK. Posts: 20	Re: Valve line up Thanks all.If I knew how to post a schematic I would. I do have a 9 year old grandson.I’ll ask him. Many thanks. Frank

27th Feb 2019, 11:14 am	#6
Mike. Watterson Heptode Join Date: Dec 2014 Location: Limerick, Ireland. Posts: 901	Re: Valve line up Actually I'd use 1p24b Russian rod pentodes, triodised. Fitted in suitable holders. Or the 1j29b. You can put the pair of filaments in series and under-run at 2V of lead acid, or simply run direct off the 2 x NiMH. A series resistor on filament to set the gain. Unlike the PM series dull emitters, there are literally millions in NOS date coded from 1977 to approximately 1990. I'm actually restoring a couple of 1920s sets using these in replica holders with glass bulbs off small halogen lamps. A large car headlamp base looks good, metal collar and the three blades can be removed. Then four pins can easily be fitted.