Quote:
Originally Posted by greg_simons
My own humble contribution would be not to change the polystyrene capacitors around the front end unless they're faulty, Leak chose those types carefully for their low dielectric absorption and stability, substituting different types will badly alter the negative feedback phase response.
|
That's sensible advice in any case.
For the record Greg, my 1962 vintage stereo20 used Silver mica caps in the feedback network and there they still sit to this day. It's just the original Paper in oil TCC or similar coupling caps that are "replace on sight" jobs. One thing is for sure, these amps are a pleasure to work on because of the neat component layout on the tag board and taking one's time to replace resistors and capacitors one at a time is a fairly simple task. I'd also replace the electrolytic cathode bypass caps if original as they are cheap as chips (don't go mad on special grade caps, any good workmanlike electrolytic with a sufficient (25V or over) working voltage will work admirably. I chose higher working voltage ones simply to keep the sizes looking similar to originals. I think it's been mentioned previously, using 2W metal film resistors keeps the look underneath more proportionate if that sort of thing is important to you.
Good luck and I hope the amps give you the listening pleasure that mine have over the years. With good modern parts mine has stayed reliable for the last 15 years.
Lastly, and I think most here would agree, don't get hung up on expensive replacement valves. If the EF86 (TL12+) and ECC83/81(TL12+) valves are still ok and a listen and check of the voltages will give you a good idea, then leave them in as they last very well. I'd think about replacing the EL84 output valves again I'd check the cathode voltages and if inside the design voltages they should be ok, but stick to the reasonable cost end of the market, you don't really need matched pairs as the cathode bias design pretty much compensates for differences in the valves. Again this is from my own personal experience as much as anything else.
That Book of Steven Spicers is an excellent reference tome and full of good info, including the differences between the output transformers.
A.