changing valves?
Time for some new valves in my 900, this brings 2 questions:
1. Can anyone recommend a good quad of 5881s and preamp valves? Im guessing its 12ax7's in the preamp but they come in many different flavours and I'm not overly clued up on valves!
2. How hard are they to change? I know physically changing the valves isn't hard, but will they need biasing or anything? Basically, can I do it myself or should I take it to a tech?
Cheers guys
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Preamp valves are plug and play, power amp valves need biasing. If in doubt, tech for power amp valves. They tend to have their own favourite power valves, if you don't know, best go with them.
Been doing my research, tungsol sound a good call for the power section... So many flavors of ecc83 to choose from, I'm confused!
I'll change the preamp ones myself I think, but I don't know if I dare try the power amp given itll need biasing and all that...
For cheapness and reliability: JJ for power amp.
For cheapness and good tone: Tung-Sol for preamp, but *not* in cathode-follower positions - which V1 in a JCM900 Dual Reverb, V2 in a High-Gain MV and V3 in a SLX are. Tung-Sols and other Russian-made ECC83/12AX7s have a high failure rate in these positions. Use a standard Chinese or JJ in these.
You can spend more on modern valves but I honestly don't think its really worth it - none of them really sound that much different and reliability is a bit variable with most of them. Or you can spend a *lot* more on NOS, which do (in my opinion) genuinely sound better and are often much more reliable, but you really need to know what you're buying.
The JCM900s are not especially valve-sensitive anyway - the Dual Reverb in particular not, because it's really a hybrid amp... which is why V1 is a cathode follower, it's really V2 (in standard Marshall circuit terms), and has a solid-state front-end where V1 would be.
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right, think I'm going to let martinmjw do his worst on this one! going to kit it out for el34s and put some JJs in the power section
Most likely go with jjs in pre too... People say they can be a little dull but its a bright amp and i like plenty of mids so that might not be a.bad thing!
Anyone else got/had/worked on one - what worked??
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