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• *insert roach clip reference here*

  Posted by: DGary on August 4, 2006 at 2:49 PM

• I would be surprised if the circuit doesn't have something like a one meg resistor across the capacitor.

  If the resistor isn't there, add it. One meg should be high enough that it won't affect the circuit operation but, it will automatically discharge the capacitor when the power is off.

  Posted by: Fredex on August 4, 2006 at 3:11 PM

• Photo by Noortje!

  I don't think the resistor is there. It's exactly this circuit: champ 5F1.

  So I should add a 1M .5W resistor across the (rightmost) 16 uF capacitor? Or would I need more wattage? The 10K resistor is 2 Watt.

  The sound is good by the way, just some hum at higher volumes.

  Posted by: remmelt on August 5, 2006 at 5:56 AM

• Looking at the circuit, you actually have three capacitors in parallel that you are discharging with your cable.

  The odd thing about this circuit is that it has just one 6V6 tetrode amplifier tube. Usually (i.e. in every other one I remember) there are two tubes in a push-pull arrangement. To me, that's the classic tube amplifier.

  When there are two tubes there is not that collection of capacitors and resistors you see along the bottom of the circuit. It looks like someone set out to design the most inexpensive amplifier possible, which is not a bad thing since few of us can afford the most expensive top line stuff. I think that has something to do with life being non-fair. You will have an OK amp with somewhat limited power.

  A half watt resistor is fine (remembering that this is free advice and worth every penny!) since at 300 volts it is dissipating a tenth of a watt. That comes from Ohm's Law.

  Of course, once you get this circuit done and you aren't sticking your fingers in there anymore AND you have a case around it all that keeps the unsuspecting from sticking THEIR fingers in there then the discharging resistor won't be needed.

  This has been fun. It's been a while since I've done anything with high voltage tube circuits and that's basically because they scare the hell out of me.

  Posted by: Fredex on August 5, 2006 at 3:27 PM

• Ah, the one tube makes this a class A amp. It doesn't push-pull, all the power comes from this tube. It doesn't need a phase splitting tube nor tube pairs, which makes it easy and cheap. Downside: it runs HOT and isn't very efficient.
  For guitar, this amp makes a sound that some love. Another famous example of a class A guitar amp is the Vox AC30 (Beatles, anyone?)

  The three large caps that are being discharged with the cable are there to eliminate ripple in the power supply. The ripple comes from the AC-DC conversion (in the recitifier tube, another not so efficient part).

  This amp is only 5 Watt, but man is it loud. This is NOT a bedroom practice amp!

  Posted by: remmelt on August 6, 2006 at 9:27 AM

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