Valves and Bias in TW Amps

[Littlewyan]

Hi guys

In Ken's Trainwreck Pages he said that due to something done at the Trainwreck factory you won't have to rebias your Trainwreck for a long time. Why was that? What did he do? I also got the impression from other sources such as the TW website that valves last a long time in TW Amps. Is this true? All I could think of was the extra protection that Ken installed in his amps helped.

[Blackburn]

They're well built and it's my personal opinion that 6CA7s will stay very happy in an Express for a long time due to how they're running. The 6BQ5 TWs on the other hand are definitely running hotter and I would imagine wouldn't last as long, also because there are double the tubes and double the chance of something going wrong with one. The extra protection such as spike suppressor diodes and MOVs do help out, but I'd say the amps wouldn't be 'at risk' without them.

All that being said, TWs were generally installed with the best of the best NOS examples and could be another reason for the longevity that has been mentioned. Just my $.02

Edit: As for the bias, Rockets and LPs are cathode biased and don't need to be 'set', whereas the Express is fixed and can be adjusted. With good old 6CA7s I don't think they'll vary to the point of throwing the bias way off or anything and will probably sound fine just dropped in.

[geetarpicker]

Well, being an owner since '89 Express I think the real truth was the relatively low plate voltage make bias less critical. Ken always told me that anything short of a red plate condition was worth a listen, and you can basically go by ear from there. In my experience there seems to be wider sweet spot bias wise with a lower plate voltage amp. Some higher B+ amps can be tricky to find that point where they loose the crossover distortion, but aren't yet red plating. Back to the TW, I don't think Ken did anything special with his bias setup just that his amps can sound good with quite a range of bias settings.