Amplion Convette M2V - UK Vintage Radio Repair and Restoration Discussion Forum

EF80TVVALVE · 21st Oct 2020, 7:43 pm

Hi all,

I have one of these in original condition, I'm going to restore but also modify it for a radio that requires 4 HT supplies, the highest being 150 volts, so I'll get rid of the QPP supply and use this as the 4th HT supply socket.

Before I begin can anybody recommend a suitable load resistance so I can replicate output voltages on the unit without needing to connect it to the set?

Herald1360 · 21st Oct 2020, 10:24 pm

Difficult without knowing what load currents are taken at the various HT voltages.....

Herald1360 · 22nd Oct 2020, 12:52 am

https://www.vintage-radio.net/forum/...ad.php?t=14340

Has helpful circuit for the unit. Raw HT DC could be as high as about 190V but will be quite load dependent. Replacing the half wave rectifier with a small silicon bridge will give less ripple but probably even higher raw HT.

EF80TVVALVE · 22nd Oct 2020, 10:06 am

Thanks for the link, researching a bit last night it seems a typical current draw is around 12mA although I'm not sure with a set that requires 4 HT supplies, that figure could possibly be for 50s attaché portables which I'd imagine would draw much less

I've replaced the HT rectifier with an 1N4007 and the unloaded (smoothed) voltage is 185v.

Herald1360 · 22nd Oct 2020, 10:52 am

12mA does sound typical for a '50s attache case set and at just one HT- 90V.

If you know the valves in your set and which ones are on each HT voltage a reasonable stab could be made at load resistor values to enable you to "tune" the Amplion circuit to suit.

In any case, as long as you don't exceed the maximum Va ratings for the valves, you could just use the set as the load, it's unlikely you'll do any damage

EF80TVVALVE · 22nd Oct 2020, 12:44 pm

I'm sure the valves are PM22, PM12 and PM1HF. Just guessing but HT4 is 150v which I presume is the Anode of PM22 and HT3 is 120v which I would think is the screen grid of the PM22. The other voltages are HT2 60-80v and HT1 60-80v, I imagine these are supplying the PM12 and PM1HF.

Probably worth me checking this properly but from the valves fitted and the voltages given I'd presume this is so.

I've been thinking it may just be best to run it up on a variac and make sure it doesn't overload the set, but practically it's probably easier to have some suitable loads on it to mimic working conditions whilst I modify it.

21st Oct 2020, 7:43 pm	#1
EF80TVVALVE Octode Join Date: Feb 2010 Location: Leicester, UK. Posts: 1,433	Amplion Convette M2V Hi all, I have one of these in original condition, I'm going to restore but also modify it for a radio that requires 4 HT supplies, the highest being 150 volts, so I'll get rid of the QPP supply and use this as the 4th HT supply socket. Before I begin can anybody recommend a suitable load resistance so I can replicate output voltages on the unit without needing to connect it to the set?

21st Oct 2020, 10:24 pm	#2
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Amplion Convette M2V Difficult without knowing what load currents are taken at the various HT voltages..... __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

22nd Oct 2020, 12:52 am	#3
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Amplion Convette M2V https://www.vintage-radio.net/forum/...ad.php?t=14340 Has helpful circuit for the unit. Raw HT DC could be as high as about 190V but will be quite load dependent. Replacing the half wave rectifier with a small silicon bridge will give less ripple but probably even higher raw HT. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

22nd Oct 2020, 10:06 am	#4
EF80TVVALVE Octode Join Date: Feb 2010 Location: Leicester, UK. Posts: 1,433	Re: Amplion Convette M2V Thanks for the link, researching a bit last night it seems a typical current draw is around 12mA although I'm not sure with a set that requires 4 HT supplies, that figure could possibly be for 50s attaché portables which I'd imagine would draw much less I've replaced the HT rectifier with an 1N4007 and the unloaded (smoothed) voltage is 185v.

22nd Oct 2020, 10:52 am	#5
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Amplion Convette M2V 12mA does sound typical for a '50s attache case set and at just one HT- 90V. If you know the valves in your set and which ones are on each HT voltage a reasonable stab could be made at load resistor values to enable you to "tune" the Amplion circuit to suit. In any case, as long as you don't exceed the maximum Va ratings for the valves, you could just use the set as the load, it's unlikely you'll do any damage __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

22nd Oct 2020, 12:44 pm	#6
EF80TVVALVE Octode Join Date: Feb 2010 Location: Leicester, UK. Posts: 1,433	Re: Amplion Convette M2V I'm sure the valves are PM22, PM12 and PM1HF. Just guessing but HT4 is 150v which I presume is the Anode of PM22 and HT3 is 120v which I would think is the screen grid of the PM22. The other voltages are HT2 60-80v and HT1 60-80v, I imagine these are supplying the PM12 and PM1HF. Probably worth me checking this properly but from the valves fitted and the voltages given I'd presume this is so. I've been thinking it may just be best to run it up on a variac and make sure it doesn't overload the set, but practically it's probably easier to have some suitable loads on it to mimic working conditions whilst I modify it.