WAD KiT 88 to WD KT88?

[Fred Shaw]

Hi, it’s been a long time since I posted here, but I check in most days to see what is happening. My KiT 88 is humming like crazy - 65 mV on one channel and 33mV on the other, in addition some of the test readings are way out. For example V8 k should be 1.5V it reads 2.27, V5 a1 should read 225V but reads 176V etc. As the amp is approaching 20 years old, I was wondering whether it would be possible to assemble the innards of a WD KT88 in the WAD enclosure, but using the WAD transformers and, where compatible, using the existing black gates and pio caps in the new build? Has anyone attempted this or is it totally out of the question? The alternative is to get the amp looked at by someone who knows what they are doing, rather than me who can only follow build instructions!!
All suggestions gratefully received.

Fred.

[John Caswell]

Hi Fred,
Yes of course it "can" be done but frankly not economical to do so, as there are many differences between the two.
I do not think that there is anything seriously wrong with your amp that a competent person could not fix.
Initially have a chat to Matthew of World Designs in Totnes as he may know of a good local technician, failing that send it to me and I will fix it for you.

John

[Richard]

Hi Fred, good to hear from you.

Have you tried new/good valve replacements? Humming and the voltages being off can be due to valves drawing the wrong current due to age. That would be an easy first check and if you go on to rebuild it you'll be needing the new valves anyway. Leaking PIO coupling caps may also be a problem, then failing electrolytics.

Rebuild it, yes, a good idea given the age. New electrolytic and coupling capacitors (WD SAX poly props are very good sounding and won't leak physically or electrically) and check/replace resistors, particularly anode and cathode, as needed. It means removal of the pcb so do the lot in one go.

Using the case to build the WD88 into would be difficult to say the least. I've owned, built and rebuilt, both of these amps and wouldn't consider trying. Even if the parts would physically fit the Kit88 OPTXs are not UL tapped and the HT is too high. WD88 follows the Mullard 5-20 circuit quite closely whereas Kit88 is a lively pentode amp. Re-building it (or having a word with John) would be the way I'd go

[bob orbell]

Hi Fred, good advice from John and Richard, but if this was mine I would junk the PIO capacitors for WD SAX of even simple cheap orange drops, had a members KAT 6550 some time back for attention and ALL the PIO capacitors were leaking, they were Jupiter bees wax, replaced with Orange drops and problem solved. Bob

[Phil Y]

Hello Fred,

Its all been said really but I will also pipe up and say get rid of the PIO caps.
They are simply not reliable. I tried them myself many years ago and had a couple fail and have also had to replace them in amps I have fixed for other people. With reliable plastic film caps available these days, in such wide range of prices and flavours, there is simply no excuse to use them.

I have a Kat88 that I have overhauled myself over the last couple of years and it sounds great. Just get yours serviced and all will be well again for the next 20 years. ☺

Phil.

P.S. I recently replaced the main PSU caps in mine with Mundorf M-lytic HVs to good effect sound wise.

[Fred Shaw]

Wow, thank you all for your constructive replies. It seems the consensus is to rebuild the amp - using new caps and valves. Time is short at the moment but I can see a rebuild in the near future.
Thanks again for taking the time to respond.

Fred.

[Fred Shaw]

Hi John, you have a PM.