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24.205.128.2
In Reply to: RE: Runaway 7581A posted by Thermionic27609 on July 03, 2009 at 08:06:07
They sit in a pretty hot enviroment most of the time (during use, of course). Use same wattage rating resistors, nothing fancy, as you want them to act as "fuses" for the power tubes*.* (I know that you prolly already know that, but Fender INSISTS on the disclaimer). :^)
Edits: 07/04/09 07/04/09 07/04/09 07/04/09 07/04/09 07/04/09 07/04/09
T, since you've worked on Fenders, ever see a pink ceramic based STR 415 (6L6GC) or STR 416 (6CA7). I believe both were special issues the 415 for Fender's Evil Twin and the STR 416 for the Mesa Boogie Mark III. I'd love to get a pair or two of each, NOS.
I have to talk to old guitar amp nuts who actually remember these tough, great sounding tubes. I remember someone actually put nearly 700 VDC on those STR 416 and they hardly glowed. Remember the blue and red glass Tesla E34L's?
I've heard of those pink-based tubes, but I've never seen one.
I'm just starting to work on Fender amps. Some of the designs seem pretty hard on the miniature tubes, running them at excessive plate voltages, etc... I guess these were designed back when tubes were cheap.
Yeah, but a lot of amps run plates at high voltage. I remember working on a CJ monoblock that ran a hefty voltage on the 6CG7. Gotta be sure that the cathode resistor/bypass caps are within tolerance, so the current draw is ok. And coupling caps are ok.
BTW... if you drop the plate voltage, sometimes the great headroom of the amp kinda goes away. As well as the crunch in the overdrive. Anyhow, need for quiet gain stage tubes (esp the first stage) is a must. I like BP RCA 7025 or Euro (TFK or Philips made) ECC83 in that position. They give nice overdrive and stay quiet, despite the crazy abuse.
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