Ultra R656 rectifiers. - UK Vintage Radio Repair and Restoration Discussion Forum

Robert Darwent · 13th Jan 2008, 1:21 pm

Could members offer their advice on the following please. Referring to the circuit on Trader Sheet 963, the set uses two metal rectifiers in series (type SenTerCel RM2). I intend to leave these in place disconnected for cosmetic reasons and wire modern diodes out of sight underneath. Should I replace with a series resistor and just one new diode or two diodes in series as per the original arrangement. I suspect only one modern diode is necessary but would like opinions please? Many thanks!

Steve_P · 13th Jan 2008, 2:02 pm

Well, 200 Ohms should do. The HT can vary a bit with no problems. Just look up the maximum for the O/P valves and don't go over it.

For AC mains, just check on valve heater voltages too. Choose the exact resistor depending on the values here.

Cheers,

Steve P

Robert Darwent · 13th Jan 2008, 4:48 pm

Quote:

Originally Posted by Steve_P

Well, 200 Ohms should do. The HT can vary a bit with no problems. Just look up the maximum for the O/P valves and don't go over it.

Quote:

Originally Posted by rrdmpb

Should I replace with a series resistor and just one new diode or two diodes in series as per the original arrangement.

Hello Steve

Thanks for that information, appreciated. But what about the number of replacement diodes? One or two in series? Thanks!

ppppenguin · 13th Jan 2008, 4:54 pm

Quote:

Originally Posted by rrdmpb

But what about the number of replacement diodes? One or two in series?

Only pessimists would say 2 in series but at the cost of 1N4007 etc you can afford to be a pessimist

We had a long discussion about diode failure (mainly in the context of diode droppers) a while back in the forum. A reverse polarity diode across the HT rail along with suitable fusing will provide very positive protection against diode failure. I'd probably still just fit 1 diode.

Robert Darwent · 13th Jan 2008, 5:01 pm

Quote:

Originally Posted by ppppenguin

Only pessimists would say 2 in series but at the cost of 1N4007 etc you can afford to be a pessimist

... ...I'd probably still just fit 1 diode.

Hello Jeffrey

My first thoughts were that only one diode would do the job, but as you say using 2 x 1N4007 in series wouldn't break the bank, so I will probably put two in there as in the original circuit. Thank you!

13th Jan 2008, 1:21 pm	#1
Robert Darwent Heptode Join Date: Aug 2006 Location: Sheffield, South Yorkshire, UK Posts: 990	Ultra R656 rectifiers. Could members offer their advice on the following please. Referring to the circuit on Trader Sheet 963, the set uses two metal rectifiers in series (type SenTerCel RM2). I intend to leave these in place disconnected for cosmetic reasons and wire modern diodes out of sight underneath. Should I replace with a series resistor and just one new diode or two diodes in series as per the original arrangement. I suspect only one modern diode is necessary but would like opinions please? Many thanks! __________________ Robert G0UHF www.wavesintheair.co.uk

13th Jan 2008, 2:02 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Ultra R656 restoration Well, 200 Ohms should do. The HT can vary a bit with no problems. Just look up the maximum for the O/P valves and don't go over it. For AC mains, just check on valve heater voltages too. Choose the exact resistor depending on the values here. Cheers, Steve P __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?