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  1. Wakarusa

    Dead Power Transformer...cap jobs are for wimps!

    The Good News is that your limiter works just fine :)
  2. Wakarusa

    Dead Power Transformer...cap jobs are for wimps!

    There's a very simple DIY circuit you can construct to test for shorted transformer windings. Consists of a filament transformer, lightbulb socket, lightbulb and, if you're really getting fancy, a couple of switches. Connect 120VAC mains through the lightbulb to the filament transformer...
  3. Wakarusa

    Question: KT66 tubes at low plate voltage

    Pfft. If you like the sports car at 35mph, what's it to him? Snobs take all the fun out of it.
  4. Wakarusa

    Question: KT66 tubes at low plate voltage

    It seems like you already know what the tubes sound like in your amp and that you like them. The question, then, is whether getting that sound is worth the money and it is a question only you and your wallet can answer. As I read it, the question you're asking is "should I not use these because...
  5. Wakarusa

    To much Hum

    If the house started with a fuse box then the electrical outlets may not be grounded -- even if they look like they ought to be. Do you get the hum & radio stations without an instrument plugged in?
  6. Wakarusa

    DC in NFB

    That's the other gotcha with all of this of course :) Whether the phase shift from what you've done is enough to yield positive feedback at certain frequencies.
  7. Wakarusa

    Phase inverter Q for anyone willing to educate me

    The "tail" resistor in the LTP PI design is supposed to act like a current source. Problem is most manufacturers use too small a value to achieve this kind of behavior with the side effect of imbalance and the "plate resistor" debate you mention. A small point for sure, but the idea is that the...
  8. Wakarusa

    Stuff you slap on tubes pins????

    Hope not. Wouldn't think a silicone based compound would perform well due to heat. The Caig pro-gold stuff is what I recommend and use.
  9. Wakarusa

    DC in NFB

    That 0.34mA of current across the OT secondary (let's assume large at 2 ohms) develops less than a millivolt across the OT. Your meter may or may not be sensitive enough to detect it. But it's no worry in any event. DC in the output transformer acts to saturate the transformer core. Without...
  10. Wakarusa

    Can someone educate me on transconductance?

    Miller capacitance is actually one of the interelectrode capacitances (plate to grid in this case) multiplied by one plus the stage gain.
  11. Wakarusa

    What changes do I need to do to switch from 6v6s to 6l6s in a 5e3 Deluxe Clone

    Along the lines of wanting a PT that will deliver 200mA - you need to change the rectifier from a 5Y3 to something with a higher current capacity and less internal resistance (5U4, 5R4, 5AR4). Under the load of 2x6L6 the 5Y3 drags B+ down to the point where you get a fuzz machine. Depending on...
  12. Wakarusa

    Do silver Fender blackface grills turn brown?

    Brandy-new the grill cloth would have been a combo of tan, black, and silver threads. For some of the, umm.., "browner" aged grilles the solution goes like this: new grille + 40 years of cigarette smoke + the occasional bar gig = aged tan
  13. Wakarusa

    Retubing my Fender Reverb tank: What should I expect?

    The original tubes would have likely been RCA. Too, unless you've seen a marked decline in performance, the 12AT7 and 12AX7/7025 could well outlast you. Meanwhile... for my $0.02 the 12AX7/7025 is the important tube in this unit. The input signal is split into wet/dry paths and meet up again in...
  14. Wakarusa

    Reverb eq mod in Super Reverb channel 1

    Assuming no other mischief from your tech, V5 drives the oscillator for the tremolo effect. In or out won't make a lick of difference if the effect is turned off. Heat issues? The amp was designed to have all 6 of those preamp tubes in there. Not to mention that the total heat from the preamp...
  15. Wakarusa

    Will this work for wiring a stereo cab?

    The three jack solution I offered isolates the grounds on the speakers when they are run individually. So yes, there is indeed a way :) However, in looking over the diagram again, I think that I have the terminals all backwards :( I.e. everything on the left of the jacks should actually be on...
  16. Wakarusa

    Will this work for wiring a stereo cab?

    Truth be told, I actually tend to use a couple of jumper sets I made up. Both are single input to twin outputs, maybe 6" long. Plug the outputs into a stereo cab and one jumper gives you parallel, the other gives you series. Easy as can be, no switches, no foolishness :) Edit: Each jumper set...
  17. Wakarusa

    Will this work for wiring a stereo cab?

    The three jack setup let you choose between speakers when you have a cab loaded with two different speakers. Not sure how you'd accomplish this in a two jack setup without also including a switch or having to use a dummy plug in one of the jacks.
  18. Wakarusa

    Will this work for wiring a stereo cab?

    Well... you could try this... I show it using standard mono Cliff jacks (which actually have normally closed contacts as opposed to the normally open shown), but switchcraft style stereo switching jacks would work just as well. Plug into either of the first two and you get a single speaker...
  19. Wakarusa

    Dumb speaker question

    I think the real answer is probably less intuitive than you'd hope. When you short the outputs of something -- a battery, a black box, an amplifier, then you're working against the "internal resistance" of whatever's outputs you've shorted. Whether the "thing" survives is now an application of...
  20. Wakarusa

    Did I offend some one here or what?

    There's also the occasional possibility that the question is either unanswerable (one of the many "what's the best..." threads) or, Lord forbid, something we just don't happen to know (like where to find a schematic for a silver panel Gibson GA-20 RVT. No... the one with 3x12AU7, not the one...
  21. Wakarusa

    Tidy & Neat Wiring - Tips?

    Let me start by saying that if you like the way the amp sounds and behaves, then there's absolutely nothing wrong here. Just discussing layout and lead dress here and what kinda results it can lead to. Running the grid and anode leads in parallel can cause a bit of NFB on the stage since their...
  22. Wakarusa

    Tidy & Neat Wiring - Tips?

    Not to pick nits, but I wouldn't run the plate and grid leads right next to each other on that first gain stage :).
  23. Wakarusa

    Tidy & Neat Wiring - Tips?

    I dust this pic off every now and again and post it to a new thread :) Built on a rainy afternoon, looks like a rat's nest, but follows good routing and layout -- also performs flawlessly and is hum-free.
  24. Wakarusa

    Tidy & Neat Wiring - Tips?

    Probably one of the best places to start is with the generous writings of Randall Aiken. Go to his website ( and follow the "tech info" link. He doesn't break down an amplifier quite the way you want, but he does show the fundamentals the different circuits you'll typically see...
  25. Wakarusa

    So I just designed a valve amp...

    While we're goin' nuts with the man's design... :) Rather than series interstage attenuation my preference would be to split the cathode resistors and bypass (or partially bypass) just one side of the split. You get cathode bypassing for frequency shaping and local cathode fed NFB for frequency...