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In Reply to: Re: Single 45 Amp question and pics posted by dtut on March 1, 2007 at 12:11:58:
Sorry about having to repost - I'm having "one of those mornings." Going by the photo, there are two drivers. Is that accurate? How did you hook them up?
Follow Ups:
I'm using 1/2 of each driver tube. I used opposite pins on left and right channel so I can swap left with right after a couple of years.
I have 2 options for the 2.5v supply.
First option: A 5vct 3A which only allows me to use 45 tube.
Second option : 2- 2.5v 3a each but no center tap. This allows me to try 2A3 tubes. The problem here is that I don't know how to reference to ground without the center tap. Can anyone help with this ?
At Joseph Esmilla's excellent site - je labs - he shows a 75 ohm 2 watt pot across the filaments of his Simple 45/2A3. The ground is from the wiper. I believe you can do the same with a pair of low value, high watt resistors, again with the cathode resistor and cap taken from the junction between the resistors to ground. Maybe someone else can confirm this - or not. The RCA Tube Application section of their tube characteristics books show the same thing, but without values.
Thanks, you steered me in the right direction. I actually used a couple 100 ohm half watt resistors with a 1.5K 10watt paralleled with 100uf 100v cap to ground. This worked like a charm. I found this method searching google.
After a couple of mods this amp sounds so good now (with 45s )it brought tears to my eyes. It now has so much volume with my horns that I have no interest in using the 2A3. This is good because I stuck a 2A3 in it and the plate voltages dropped much lower ,too low. It still sounded good though, It probably would get very hot. Thanks again for your help.
Les Hudson
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