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In Reply to: RE: Initial A/B test between PP and SE 6bq5 amps posted by vinnie2 on June 28, 2017 at 04:17:58
Vinnie I know you said you did not want to invest in interstage transformers so I would try a direct coupled schematic even if you do not use it in the long run. Get rid of any grid stop resistors again just for the test no ccs no mu followers etc. Find the most basic schematic and no feedback.
You get the point. Also build a bread board adjustable fixed bias at least for the power tubes. Then you can dial in the current by ear.
There is a problem somewhere if you can not hear a difference between those 3 tubes in the set circuit. There is a clog in the drain. I went away from main stream builds years ago but I realize that interstage transformers cost some dough. Come think of it Andy got pretty good results with the cheap Hammond interstage. Might want to search that out.
Well at least you are trying and listening which is more than most anymore. I also just remembered are you still using the high frequency and/or a switcher filament? If yes go ac on the cheap, even if some hum. You can always add back all the great things that are supposed to be great on paper latter.
You got time so have some fun.
Enjoy the ride
The only possible clog in the drain is through the switch setup I put together, and I can't imagine what that would be. The output of each of two amps go to the switch and then one button determines which amp is feed to the speakers. Both amps stay on the whole time. There are 10 ohm/30 watt resistors across the output terminals of each amp to make sure they remain under a load during switching, but they are identical for each amp. I compare two amps at a time, and change out only one at a time so I have a reference point from the last test. Last but not least I have read in several different places on the internet that say the biggest difference would be between pp & se, not between different tube types.
Have you ever done a similar a/b test with two se amps with different output tubes when both amps were on full time and you could switch between them with a push of one button? So far no one has chimed in that they have tried this and got different results than I did. I wish someone would, because I think it is the only valid way to test them for similar sound.
To be honest I am not a single ended guy.
Heard a big difference between 45 vs 2a3 single ended in someone else's system.
Anytime I change a tube in a phono stage, pre amp, driver or power tube I hear a difference. I hear differences in caps resistors etc. Change the b+ or current thru a tube and it will change the sound. Your tube examples are big time different. So the only thing I can guess is some component is getting in the way.
You might post over on the set forum and bottle head. Maybe Paul will chime in. He knows what he is talking about.
Well keep up the good fight you will get to the bottom of this.
I am surprised Paul hasn't chimed in on some of my posts already. If anyone should be able to give us knowledgeable answers to some of these questions it would be him. Maybe he doesn't want to start a major debate!
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