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In Reply to: RE: Have I got this right? posted by vinnie2 on September 01, 2015 at 04:15:49
If they are operated at similar voltages and currents, it would be a valuable test.
I will speculate that the added 26, operating at the lowest signal level, will be the cleanest and purest sound. Or, if both first stages are in fact inaudibly different after the later stage distortion, there might be no discernible difference.
Let the games begin!
Follow Ups:
I went ahead and added a third 26 with the same set up as the other two. The currents and voltages should be similar. I also adjusted the cathode resistor of the 45 and the B+ to get as close to the first set of operating points that Palustris suggested for the 45 (220vdc and 36 mA). I measured 220 volts plate to cathode, and 35 mA with a 1130 ohm resistor that I measured 39.5 vdc across, so my operatring points are pretty close.
I am quite pleased with the sound, it certainly is every bit as good as the 26/26/45 playing with the 76 preamp. I actually think the detail is a little better as I am using the same mono source through one channel as I used before and hearing a few small things I didn't notice last time.
So I guess it is onward and upward. The next step will be to build the 26 preamp first, and then to breadboard the deuce 26 amp in stereo and work on getting it fine tuned. If I still like it then I will probably build it or them. Might be best to go with monoblock amps considering all the iron involved, or a psu unit and a front end unit at least, like I did with the 91A clone. Looks like a couple of good projects for this winter.
One thing I am curious about is Tre's comment about the polarity being reversed because of the third tube. How is it any different this way than if the 26 preamp was stand alone and playing into the deuce 26 amp? Or is it the fact it is another 26 that causes the problem? Should the problem be there with the 76 preamp too? I have not noticed any disceranble diference with either. Both sound good, but the deuce 26 with the 26 pre sounds better. I think I may be hooked on all dht triodes for the forseable future.
It's easy.
Each stage inverts phase.
If you have an even number of total stages then the output signal will be "in absolute polarity", if you have an odd number of total stages then the output will be inverted. So flip your speaker wires.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Is that just the number of stages in the amp, or does it include the stages in the preamp as well? If it does we are back to four. The 26amp I was testing had 3 26's and a 45, but the 3rd 26 is actually the tube from the single 26 preamp I was working on earlier. Each of the 26 stages is identical for the amp and preamp.
Edits: 09/02/15
"Is that just the number of stages in the amp, or does it include the stages in the preamp as well?"
Total stages. A one stage preamp inverts and three stage amp inverts. The two in combination do not invert.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Ok, the one stage preamp inverts odd, then the first stage of the amp makes that even, 2nd stage odd and 3rd stage even again, yes?
.
Have Fun and Enjoy the Music
"Still Working the Problem"
nt
"there might be no discernible difference. "
Except the absolute polarity will be flipped with three stages vs. two.
some say that's not discernible so there ya go!
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Easy to correct for - if you know about it :^) Thanks for the post!
I will give it a try in the next couple of days.
Thanks!
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