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Post by swampcooler on Jul 29, 2007 11:55:43 GMT -7
Hi,
I'm trying to get my 50 watt EL34 class AB amp to run cathode biased. Here's what I have done so far:
I have disconnected the grid/pin 5 bias voltage on both tubes and grounded the resistors of both pins 5. What do I do with the now unused bias supply wires?
Pin 1, suppressors, goes to ground.
I have taken both cathodes at pins 8, connected them and then sent them to ground through a 470 ohm 10 watt resistor, with a 47 mfd bypass cap. My current draw is now 35.5 ma with 404 volts on the plates. It should be operating, I think . . . ?
I have no sound at all, not even when I check voltages with my meter around the tube pins - no scratches or any hiss, nothing. When I wire it back to fixed bias, it still works fine.
Any thoughts on this? I would really like to make this work for me and my amp.
Thanks for your replies, Swampcooler
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Post by Telemanic on Jul 30, 2007 10:57:55 GMT -7
Hi swampcooler, i responded on your other thread but since reviewed my VERY limited experience with playin with circuits, in particular cathode biased ones. I see now that referencing the grids to ground thru resistors would or should be normal, but still wondering if any feedback figures in, or if the 45 is ultralinear? Not sure if it would even make a difference tho. Let us know when ya get er syphered out!
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Post by billyguitar on Jul 30, 2007 11:14:51 GMT -7
I was wondering about the ultralinear question myself. I went to the Z web site and no mention is made about it there.
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Post by jimmydeez on Aug 2, 2007 11:54:33 GMT -7
I think a cathode biased KT45 would be great. I thought about making my 6545 cathode biased a little while back.
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Post by Jim @94 Amps on Apr 2, 2008 15:50:20 GMT -7
The 45 is not ultra linear. Are you familiar with tube amp circuits? It sounds like you don't have the grids connected to the phase inverter. I also must state that I do not condone modifying Z amps!
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Post by myles on Apr 14, 2008 17:16:55 GMT -7
I agree on Jimboyokol on modding Z amps and in fact I dislike modding Fender BF or Marshall non-master volume amps as well.
As far as cathode biased EL34 amps .... I never heard one I liked and the ones that are around eat tubes like there is no tomorrow.
A little bit of history .... the first RxES thought was for an EL84 based amp and it did not make the cut.
The fellow that started this post just said "his EL34 based amp" or something to that extent. It may not be a KT45. If it is something like a Crate or Carvin sort of amp then playing around is no big deal to me but modding a KT-45 would be something I would never do. If he wants something different than he should just buy something different rather than ruin a great amp.
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