Combined Output/Rectifier Valve - UK Vintage Radio Repair and Restoration Discussion Forum

John12868 · 20th Oct 2008, 1:48 pm

Hi Guys,

Is there a UK combined Output/Rectifier valve commonly available?

The reason I ask is that there's a low output AM transmitter on an American website built around an 117L7 valve. It's used as a means to transmit "modern" audio to vintage radio's on the AM bands.

Regards

John

paulsherwin · 20th Oct 2008, 2:01 pm

Quote:

Originally Posted by John12868

Is there a UK combined Output/Rectifier valve commonly available?

I don't know of one. The 117L7 is a bit of an oddball, designed for US record players. It has a 117V heater and combines a 117V half wave rectifier and an output valve in one envelope. It isn't much use in 220-240V countries.

Paul

John12868 · 20th Oct 2008, 2:18 pm

So, I would need to use a seoerate rectifier and output valve, unless I could use a tramsformer to provide the required 117V. The valve seems cheap enough to buy, but the transformer might not be so cheap or readlily available.

julie_m · 20th Oct 2008, 2:19 pm

I think that in the UK, we tended to use early semiconductor rectifiers as opposed to diode valves with mains-fed heaters. Expecting the heater-cathode insulation to withstand the full peak-to-peak mains voltage (cathode is held at +340V by reservoir cap, heater reaches -340V during trough of mains cycle) would be pushing it a bit!

British record players tended to use a UY85 for the rectifier and a UL84 for the amplifier (or a UCL82 if fitted with separate treble and bass controls) with HT straight from the mains and heater voltage from a tapping on the motor (which therefore had to run continuously). Later ones used an EL84 (or ECL82) and a semiconductor rectifier, with the heater (and sometimes the HT) fed from a transformer.

paulsherwin · 20th Oct 2008, 2:30 pm

Quote:

Originally Posted by John12868

So, I would need to use a seperate rectifier and output valve, unless I could use a tramsformer to provide the required 117V. The valve seems cheap enough to buy, but the transformer might not be so cheap or readlily available.

The Lil'7 design which I think you refer to will work with a wide range of output valves, and you can just use a 1N4007 to rectify the HT. You should be using a transformer anyway for safety reasons.

You could use the pentode section of an ECL80, which only needs 300mA at 6.3V. The voltages could be obtained by using a 6V transformer, then a 12V transformer 'backwards' to provide about 120V AC for the HT.

You should of course take care to ensure any design isn't radiating a significant signal beyond your property. The forum rules prohibit the discussion of higher powered MW transmitters.

Paul

Sean Williams · 20th Oct 2008, 3:29 pm

Or just use the 117L7 and a suitable dropping resistor.....

or get a transformer from maplin for about 17 quid...

John12868 · 20th Oct 2008, 3:31 pm

Sounds like the best policy. I've confused myself about thetransformers and now I've got a headache :0(

yesnaby · 20th Oct 2008, 7:04 pm

Hello,

The 12A7 output/rectifier valve can rectify up to 125 V and has a 12.6 V heater. Not sure if this is of any use to you.

Michael

20th Oct 2008, 1:48 pm	#1
John12868 Retired Dormant Member Join Date: Nov 2006 Location: Crayford, London, UK. Posts: 181	Combined Output/Rectifier Valve Hi Guys, Is there a UK combined Output/Rectifier valve commonly available? The reason I ask is that there's a low output AM transmitter on an American website built around an 117L7 valve. It's used as a means to transmit "modern" audio to vintage radio's on the AM bands. Regards John

20th Oct 2008, 2:18 pm	#3
John12868 Retired Dormant Member Join Date: Nov 2006 Location: Crayford, London, UK. Posts: 181	Re: Combined Output/Rectifier Valve So, I would need to use a seoerate rectifier and output valve, unless I could use a tramsformer to provide the required 117V. The valve seems cheap enough to buy, but the transformer might not be so cheap or readlily available.

20th Oct 2008, 2:19 pm	#4
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Combined Output/Rectifier Valve I think that in the UK, we tended to use early semiconductor rectifiers as opposed to diode valves with mains-fed heaters. Expecting the heater-cathode insulation to withstand the full peak-to-peak mains voltage (cathode is held at +340V by reservoir cap, heater reaches -340V during trough of mains cycle) would be pushing it a bit! British record players tended to use a UY85 for the rectifier and a UL84 for the amplifier (or a UCL82 if fitted with separate treble and bass controls) with HT straight from the mains and heater voltage from a tapping on the motor (which therefore had to run continuously). Later ones used an EL84 (or ECL82) and a semiconductor rectifier, with the heater (and sometimes the HT) fed from a transformer. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

20th Oct 2008, 3:29 pm	#6
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,518	Re: Combined Output/Rectifier Valve Or just use the 117L7 and a suitable dropping resistor..... or get a transformer from maplin for about 17 quid... __________________ Engineers make things work and have spare bits when finished

20th Oct 2008, 3:31 pm	#7
John12868 Retired Dormant Member Join Date: Nov 2006 Location: Crayford, London, UK. Posts: 181	Re: Combined Output/Rectifier Valve Sounds like the best policy. I've confused myself about thetransformers and now I've got a headache :0(

20th Oct 2008, 7:04 pm	#8
yesnaby Octode Join Date: Jul 2005 Location: Newport, Gwent, UK. Posts: 1,623	Re: Combined Output/Rectifier Valve Hello, The 12A7 output/rectifier valve can rectify up to 125 V and has a 12.6 V heater. Not sure if this is of any use to you. Michael