Is there a preferred flavour of ice cream?
PaulS said:
Ripper - thanks for links and the vote of confidence. In Bancroft there are no guitar techs or amp techs so over the years I have had to become resourceful and teach myself, it has paid off because I saved a few buddies trips to the city and I get to play with a lot of neat gear sometimes. :food-smiley-004:
One more quick question is there a preferred brand of 12AT7 or 12AU7 to use ?
Paul, I've found that 99.9% of tonal differences in the preamp come from the very first tube in the chain, or V1 as it's termed. This is the one farthest from the output tubes. After that not only are my ears not good enough to notice any differences but I've never known anyone else that can either. I'm not saying there's not somebody with mutant bat ears that could do it out there somewhere, just that if I were you I wouldn't worry about it!
Besides, it's mostly personal taste and how can one make an absolute judgement on what someone ELSE would like?
I would caution that if you try a 12AU7 it will fit and appear to work but don't totally write it off if you don't like it. This tube requires different values of parts feeding it than a 12AX7, 12AT7, 12AY7, 5751 or whatever to run properly. So to give it a fair shake you can't just plug it in. You really should at least change the plate resistors in the phase inverter circuit to maybe 22K or so instead of the much higher values you'll likely find.
Come to think of it, Ampeg often used a phase inverter circuit with a gain of unity (no gain at all) anyway. So changing tubes at this position might be a waste of time.
I hear a lot of mojo spread around about different brands of tubes, Paul. I agree there are some differences but they tend to be rather subtle. Since most people don't know enough to make circuit changes they tend to seize on doing easy things, like swapping tubes. It's easier to get all anal about such stuff rather than learn some real theory. These ideas are often championed by guys who may really know better but they're selling something they want you to buy!
The hifi world is just full of stuff like this. I still vividly remember a hifi house in Oakville that in their catague offered "non-oxygenated" speaker wire, at $400 per foot! US dollars! They would sell you a 12AX7 tube for $50 that came with its own "Testing Certificate" suitable for framing. If you actually understood the theory behind tubes you'd quickly see that there was nothing special about the tube. It was merely an ordinary brand that they tested and not surprisingly, found it to have exactly the specs you would have expected anyway!
As Kurt Cobain said, "Just play the damn thing!"
