Combined output-and-power-rectifier valves. - UK Vintage Radio Repair and Restoration Discussion Forum

G6Tanuki · 19th Nov 2021, 7:02 pm

These seem to have been a US-specific thing - the earliest I can come across is the 12A7 which gave an amazing 550 Milliwatts of audio output; later came the 25A7, 32L7, 70A7, 70L7, 117M7, 117N7, 117P7 - some of which could give a couple of Watts of output.

They were used in a number of US 'midget' radios - but never seemed to catch on in the UK. Given that they could have significantly reduced the cost of a minimalist AD/DC radio - something which would have helped sales in the depression-era of rhe 1930s - I'm surprised they were not more popular in the UK.

Instead, Europe seemed happier to follow the path of a combined detector-and-high-slope-output-valve [EBL31] but keeping a separate rectifier valve for its poverty-spec radios.

Somewhere I've got a US circuit for a ham-band crystal-controlled transmitter using one of these combined rectifier-and-output valves in a 'transformerless' QRP CW transmitter giving up to 5 Watts of output.

kalee20 · 19th Nov 2021, 8:12 pm

It certainly seems a sensible pairing, the power rectifier as bottlemates with the high-level signal valve. So there'd be little in the way of hum coupled across, and the low-level diodes sharing another bottle where heat generation is much less, is a good idea.

However, with the trend towards miniaturisation, it might have been difficult to squeeze the rectifier and even a small output pentode in a B9A envelope, so the ULY80 never hit the production lines...

Sideband · 19th Nov 2021, 8:21 pm

Don't think it would have been practical with B9A valves. Imagine something like a UL84 crammed in with a UY85 on a B9A base. It would have got very hot.

Octal might have been better...a 35L6 and a 35Z4 perhaps....

Herald1360 · 19th Nov 2021, 8:32 pm

The 117XX valves were really only useful for single valve record players and the odd battery/mains set where more audio power was available when mains operated.

paulsherwin · 19th Nov 2021, 9:31 pm

I agree, I think the intended market was record players. There's quite a well known pantry transmitter design using a 117L7, though it's not much use in 220/240V countries.

turretslug · 19th Nov 2021, 10:13 pm

I'm sure that they'd have done it if they reckoned they'd get away with it.

Quote:

Originally Posted by kalee20

So there'd be little in the way of hum coupled across,

I wonder just how far this could be pushed though, with mains on one base pin and a high impedance signal grid connection on another, even if placed diametrically opposite. A pinchless octal (or similar broad base with good pin spacing) would probably be the best bet! Especially with 200+ VAC supplies, the US market was famous for getting away with a lot and thrifting to the bone.

kalee20 · 19th Nov 2021, 10:47 pm

Good point! The ULY80 will either have a top-cap grid, or a top-cap rectifier anode. (Thoughts on relative merits welcomed!)

turretslug · 20th Nov 2021, 2:17 pm

Given that, pretty much by definition, this putative valve would be for low-cost mass-market radios, the length of screened wire for a top-cap grid and its extra preparation would be a debit point. A rectifier anode connection would only need to be plain wire and the rectifier is likely to be near the dropper anyway, so could be just a short above-chassis link. Detail stuff, but the sort of thing a production engineer would be taking into account.

G6Tanuki · 21st Nov 2021, 5:31 pm

Interesting comments.... the market-segment I was imagining for such a valve was the 'small bedside/kitchen radio' or record-player - where lots of audio really isn't needed [a typical modern solid-state radio aimed at this niche has at most 1 Watt of audio power and I remember some record-players got along quite happily using a pair of OC81 transistors as the output-stage....].

So you could get away with the audio stage being something like the EL91 or the power-side of the ECL80 [or the ECL82 if you must go QRO!] and the HT rectifier would only need to produce something like 50ma for the entire radio.

40mA at 200V for the audio valve, at 50%%-efficiency Class-A that's eight watts of input - should be good for 3 Watts of audio out. Leaving 10mA for the RF/IF stages.

Bearing in mind that this putative valve would be part of a series-heater string, I'd also design for the heater to be a high-voltage one; 100mA heater-chain - Watts used to heat the cathode are not Watts profligately wasted in a dropper resistor.

ms660 · 21st Nov 2021, 5:48 pm

Quite a few mains/battery receivers across the pond used a valve from the 117xx series, here's some Detrola schematics that show the 117M7:

http://www.nostalgiaair.org/PagesByM...1/M0004011.pdf

Lawrence.

Robert Gribnau · 29th Nov 2021, 7:06 am

There are also combinations of beam power tubes and damper diodes, like the 38HE7: https://frank.pocnet.net/sheets/123/3/38HE7.pdf

The damper diode can (ofcourse) be used as a 'normal' half-wave rectifier.

dougietamson · 29th Nov 2021, 12:02 pm

I'm slowly going through a large box of valves kindly given to me.

There is a 3A8GT valve, octal with top cap.

Glass octal type used as combined detector, af amplifier, and rf amplifier. The 3A8GT is used for battery-operated receivers with either 1.4 (parallel) or 2.8 (series) volt dc filament supplies.

Free to anyone who wants it.

Doug.

19th Nov 2021, 7:02 pm	#1
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Combined output-and-power-rectifier valves. These seem to have been a US-specific thing - the earliest I can come across is the 12A7 which gave an amazing 550 Milliwatts of audio output; later came the 25A7, 32L7, 70A7, 70L7, 117M7, 117N7, 117P7 - some of which could give a couple of Watts of output. They were used in a number of US 'midget' radios - but never seemed to catch on in the UK. Given that they could have significantly reduced the cost of a minimalist AD/DC radio - something which would have helped sales in the depression-era of rhe 1930s - I'm surprised they were not more popular in the UK. Instead, Europe seemed happier to follow the path of a combined detector-and-high-slope-output-valve [EBL31] but keeping a separate rectifier valve for its poverty-spec radios. Somewhere I've got a US circuit for a ham-band crystal-controlled transmitter using one of these combined rectifier-and-output valves in a 'transformerless' QRP CW transmitter giving up to 5 Watts of output. __________________ I'm the Operator of my Pocket Calculator. -Kraftwerk. Last edited by G6Tanuki; 19th Nov 2021 at 7:09 pm.

19th Nov 2021, 8:12 pm	#2
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,082	Re: Combined output-and-power-rectifier valves. It certainly seems a sensible pairing, the power rectifier as bottlemates with the high-level signal valve. So there'd be little in the way of hum coupled across, and the low-level diodes sharing another bottle where heat generation is much less, is a good idea. However, with the trend towards miniaturisation, it might have been difficult to squeeze the rectifier and even a small output pentode in a B9A envelope, so the ULY80 never hit the production lines...

19th Nov 2021, 8:21 pm	#3
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,572	Re: Combined output-and-power-rectifier valves. Don't think it would have been practical with B9A valves. Imagine something like a UL84 crammed in with a UY85 on a B9A base. It would have got very hot. Octal might have been better...a 35L6 and a 35Z4 perhaps.... __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

19th Nov 2021, 8:32 pm	#4
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Combined output-and-power-rectifier valves. The 117XX valves were really only useful for single valve record players and the odd battery/mains set where more audio power was available when mains operated. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

19th Nov 2021, 9:31 pm	#5
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,947	Re: Combined output-and-power-rectifier valves. I agree, I think the intended market was record players. There's quite a well known pantry transmitter design using a 117L7, though it's not much use in 220/240V countries.

19th Nov 2021, 10:47 pm	#7
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,082	Re: Combined output-and-power-rectifier valves. Good point! The ULY80 will either have a top-cap grid, or a top-cap rectifier anode. (Thoughts on relative merits welcomed!)

20th Nov 2021, 2:17 pm	#8
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,396	Re: Combined output-and-power-rectifier valves. Given that, pretty much by definition, this putative valve would be for low-cost mass-market radios, the length of screened wire for a top-cap grid and its extra preparation would be a debit point. A rectifier anode connection would only need to be plain wire and the rectifier is likely to be near the dropper anyway, so could be just a short above-chassis link. Detail stuff, but the sort of thing a production engineer would be taking into account.

21st Nov 2021, 5:31 pm	#9
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: Combined output-and-power-rectifier valves. Interesting comments.... the market-segment I was imagining for such a valve was the 'small bedside/kitchen radio' or record-player - where lots of audio really isn't needed [a typical modern solid-state radio aimed at this niche has at most 1 Watt of audio power and I remember some record-players got along quite happily using a pair of OC81 transistors as the output-stage....]. So you could get away with the audio stage being something like the EL91 or the power-side of the ECL80 [or the ECL82 if you must go QRO!] and the HT rectifier would only need to produce something like 50ma for the entire radio. 40mA at 200V for the audio valve, at 50%%-efficiency Class-A that's eight watts of input - should be good for 3 Watts of audio out. Leaving 10mA for the RF/IF stages. Bearing in mind that this putative valve would be part of a series-heater string, I'd also design for the heater to be a high-voltage one; 100mA heater-chain - Watts used to heat the cathode are not Watts profligately wasted in a dropper resistor. __________________ I'm the Operator of my Pocket Calculator. -Kraftwerk.

21st Nov 2021, 5:48 pm	#10
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Combined output-and-power-rectifier valves. Quite a few mains/battery receivers across the pond used a valve from the 117xx series, here's some Detrola schematics that show the 117M7: http://www.nostalgiaair.org/PagesByM...1/M0004011.pdf Lawrence. Last edited by ms660; 21st Nov 2021 at 6:00 pm. Reason: word change

29th Nov 2021, 7:06 am	#11
Robert Gribnau Heptode Join Date: May 2017 Location: Konongo, Ghana Posts: 514	Re: Combined output-and-power-rectifier valves. There are also combinations of beam power tubes and damper diodes, like the 38HE7: https://frank.pocnet.net/sheets/123/3/38HE7.pdf The damper diode can (ofcourse) be used as a 'normal' half-wave rectifier. __________________ Robert

29th Nov 2021, 12:02 pm	#12
dougietamson Hexode Join Date: Mar 2019 Location: Edinburgh, Scotland, UK. Posts: 347	Re: Combined output-and-power-rectifier valves. I'm slowly going through a large box of valves kindly given to me. There is a 3A8GT valve, octal with top cap. Glass octal type used as combined detector, af amplifier, and rf amplifier. The 3A8GT is used for battery-operated receivers with either 1.4 (parallel) or 2.8 (series) volt dc filament supplies. Free to anyone who wants it. Doug.