alevinthal

Hi Myles, Thanks again for your time. What is your opinion about this idea: since the RT30 sounds good when first turned on, but really sweet after running for an hour or so, might I put it on the bench, measure it at turn-on, run it into a load for an hour, measure it again, and then (maybe) figured out how to swap components to get it to run at those measured currents/voltages normally, and *then* try to keep it cool so it stays there? Is this likely to work? If it does make sense, I could try it myself, but all I have is an EE degree, a basic iron/meter/scope, and limited knowledge of tubes and high voltage design. I am interested in trying, but I'm concerned about killing my best-sounding amp. Maybe Mr Torres can do this, but I don't know if he is willing to do this sort of 'experimental' work (or if I could afford it). Either way, I'll be trying a fan next time out. just wondering, -Adam- P.S. The amp is supposed to be running at 350V B+ but I measured 380V, and I have felt the mains transformer get (too) hot, but it's intermittent. I suspect there might be a short in the primary windings of a turn or two. What would you suspect? I mean to replace it, but haven't gotten around to it. P.P.S What do you think about implementing auto-bias in guitar amps with solid-state regulators? Here's a link to a paper on the subject: http://www.glass-ware.com/tubecircuits/Tube_Auto_Biasing.html

Adam, If you have three tube amps that act the same way in your place, the first thing I would do is check your AC or borrow a variac and try one of the amps on there for a bit. Myles Hi Myles, I guess I misspoke, the MKII is reasonably stable. The Studio 22 definitely drifts. The RT30 is my biggest concern though, since I prefer it to the Mesa's. The mains are probably not the issue since I play out a lot and it happens everywhere. How stable should I expect the tone of a tube amp to be? What might I consider doing to make it more stable? How stable are the tranconductance curves of power tubes, in general? Are they sensitive to changes in temperature, or plate voltage? Might amps running class A be less stable than amps running class AB, since everything gets hotter? This amp runs four el84's at 380V with minimal regulation. A single emitter resistor biases all four tubes. -Adam- P.S. Dan Torres said he wasn't too surprised at this behaviour, and that some/most tube amps will drift, but I hate to have to just accept this. I was going to try a fan at the next show (thursday).

Hi Myles, I have a Randall RT-30, an amp that I love, with a wonderful and unique sound, but it needs an hour to warm up, sounds great for about an hour, and then 'loses the magic' over the next hour. What makes an amp do this, and what can I do to get it to 'warm-up' faster, and then stay in that great tonal zone? I have 2 old boogies (studio 22 and MKII) that act the same way. I have the schematics (as .pdf files) if you are interested in seeing them. -Adam-