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Spare valves

Brian S

pfm Member
I am about to take possession of a new amp. It uses 4×6922, 4×KT90 and 2×6H30 valves. The amp. is 'self biasing'. In the case of valve failure, can I replace valve individually? Would pairs be better? Please, not quads. At this stsge, I am only looking to keep the amp. on the road, not yet exploring alternative set ups. Thanks for any advice.

Sorry for posting this on wrong forum, initially.

Brian S
 
Sounds like a Graaf gm50!
I've only ever replaced the 4xKT90's/88's as a Quad matched set. Maybe that's not necessary, but as I'm not an expert with valves, better safe than sorry.
I'm sure some valve guru's will be along with more informed advice soon.
If it is a GM50, you've got a bloomin' lovely amp.Takes a hell of a lot to beat it, I think.
 
I am no valve Guru, however, ...

I would just swap the failed valve out and if you detect a change in the way your amp sounds then have the valves checked/measured out so you can match them where it matters.

I have an EAR 516 power amp and for that I have a complete new set of output valves ready but I don't think I would swap all of them in if I just had one valve die on me. I would just replace with a used one I have. When I got it back from service with approximately matched valves (done by Tim d P) from EAR Yoshino, one of the output valves and two of the input valves had been crushed during shipping. I just swopped them out for some similar ones I had at hand. To me the sound is great, but perhaps I was just lucky?

This reminds me that I will have to have all my input and output valves measured and matched so I know which ones to pair. The EAR 516 has 8 valves in total in its dual mono circuit (4 x PFC802 + 4 x PL508). So I think I will have to match the valves in left and right pairs.
 
It really is a nice amp, I'm sure you'll enjoy it. I sold mine just before Christmas and sometimes wonder why.

It's not hard on valves I only ran mine at a quarter to the hour and found it plenty loud enough. Don't know about only replacing one valve at a time though, I did them all in a onner but you right about the automatic biasing, makes things a doddle.
 
I do not know your amp but suspect that most amps are supplied with just to get you going valves! 'Rolling' valve amps can make an incredible difference to performance. A pair of 6922 Genalex Gold Lion will cost about £60, other makes are available. Your personal circumstances will be your own benchmark but to expend much less might lead to less performance.
 
I do not know your amp but suspect that most amps are supplied with just to get you going valves! 'Rolling' valve amps can make an incredible difference to performance. A pair of 6922 Genalex Gold Lion will cost about £60, other makes are available. Your personal circumstances will be your own benchmark but to expend much less might lead to less performance.

Thanks for this. My valve anxiety stems from my having upgraded the valves in my 300b. I invested in five hundred quids worth of Pasvane. The sound was very impressive but a 300b valve went after 4 weeks and a PS2- CV181-T-M11/2 after 5 month. The CV181 was out of warranty. The Graaf uses twice as many valves - 'personal circumstances'! This was supposed to be a second system - I'm just an irresponsible old bugger.
 
Thanks everyone for input. The answer is: replace with matching pairs. Advice from manual. The amp arrived today, ex demo model. Delivered, and set up for me by 2nd Hand HiFi - excellent service. They are located in Stockton on Tees - new showroom to open soon.

I am astounded. The amp sounds superb. Audionote Js. Bryston BDP1 music player.
Brian S
 


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