Hi all
I bought some Quad IIs, with Quad 22 preamp and Quad FM tuner some years ago. They used to be maintained by a gentleman named Arthur Churms(?) in Cape Town. The preamp gave some "interesting" issues, all types of science fiction pops and whizzes coming from the speakers after playing for some time, and was replaced. The Quad IIs have been faultless, until now.
They originally had EL34s in when purchased, and I found 5 GEC KT66s for such a ridiculous price I won't even mention it here. 4 of the 5 worked perfectly for years (I removed the resistor added to the valve sockets). Suddenly, one of my beloved KT66s in the one amp started shooting what looks like lightning inside, accompanied by a hum from the speaker. I was devastated.
I purchased some Gold Lion KT66s, which sounded just as good to my uncouth ears, but scarcely 2 months later, one of these valves in the SAME amp starting glowing red hot, with a hum from the speaker. I swapped valves between the two amps, and all was fine, I thought. Then another valve started to go red hot in that amp. I thought it was faulty, and sent it back to be replaced (forgetting about the first faulty one). Now of course the other KT66 that originally went red hot in the one amp, goes red hot all the time. The very same day I ship the one KT66 back for replacement :facepalm:
So my amp is eating valves.
It still has the original TCC caps in, and some of the resistors have been replaced. The output transformer also seems original. It's twin has had the TCC caps replaced, and the OTP rebuilt locally. I have replaced the coupling caps on both amps with K40Y units, and also resistor R12.
Who can help me get both the amps sounding great again? I have looked on the internet quite a lot, but everyone seems to just say "replace the coupling caps", which has been done already.
A bit about me: I know about car electronics out of necessity (could not find a proper auto electrician to fix some faults I had, so I learnt how to do it myself), and have a Fluke 88 multimeter. But I know precious little about "conventional" circuitry, let alone valve circuitry! So any suggestions must please be very clear and written as if for toddlers, e.g. "measure voltage in AC between R5 and R7".
Thank you in advance for any advice you might have.
EDIT to add that the EF86s in both amps are looking a little burnt at the top, don't know if that could be a cause for concern?
I bought some Quad IIs, with Quad 22 preamp and Quad FM tuner some years ago. They used to be maintained by a gentleman named Arthur Churms(?) in Cape Town. The preamp gave some "interesting" issues, all types of science fiction pops and whizzes coming from the speakers after playing for some time, and was replaced. The Quad IIs have been faultless, until now.
They originally had EL34s in when purchased, and I found 5 GEC KT66s for such a ridiculous price I won't even mention it here. 4 of the 5 worked perfectly for years (I removed the resistor added to the valve sockets). Suddenly, one of my beloved KT66s in the one amp started shooting what looks like lightning inside, accompanied by a hum from the speaker. I was devastated.
I purchased some Gold Lion KT66s, which sounded just as good to my uncouth ears, but scarcely 2 months later, one of these valves in the SAME amp starting glowing red hot, with a hum from the speaker. I swapped valves between the two amps, and all was fine, I thought. Then another valve started to go red hot in that amp. I thought it was faulty, and sent it back to be replaced (forgetting about the first faulty one). Now of course the other KT66 that originally went red hot in the one amp, goes red hot all the time. The very same day I ship the one KT66 back for replacement :facepalm:
So my amp is eating valves.
It still has the original TCC caps in, and some of the resistors have been replaced. The output transformer also seems original. It's twin has had the TCC caps replaced, and the OTP rebuilt locally. I have replaced the coupling caps on both amps with K40Y units, and also resistor R12.
Who can help me get both the amps sounding great again? I have looked on the internet quite a lot, but everyone seems to just say "replace the coupling caps", which has been done already.
A bit about me: I know about car electronics out of necessity (could not find a proper auto electrician to fix some faults I had, so I learnt how to do it myself), and have a Fluke 88 multimeter. But I know precious little about "conventional" circuitry, let alone valve circuitry! So any suggestions must please be very clear and written as if for toddlers, e.g. "measure voltage in AC between R5 and R7".
Thank you in advance for any advice you might have.
EDIT to add that the EF86s in both amps are looking a little burnt at the top, don't know if that could be a cause for concern?
