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KT88, (ect) Single ended amp, SEUL

Hello all. Just finished this amp pretty much to Keggers original Schematic but using 807 output tubes and a 12bh7 preamp tube. Amp sounds excellent but I wonder if I am running the 12BH7 properly. Plate voltage is 124v and Cathode voltage is 3.5v. Seems to me this tube needs a bit more current? The 807's are running UL with 404v on the plate, 403v on the screen and 29v on the cathode giving about 22W dissipation and they seem happy with that.

http://stargeezer.net/807amp1.JPG
http://stargeezer.net/807amp2.JPG
 
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Project looks very nice, :thumbsup:
I like the operating parameters of the 807 as well, yah that looks quite good to me.

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Now as to the 12BH7, honestly I'd say the current on the tube isn't low at all, if my calcs are about right I get just under 9.5ma, that's pretty solid.
In fact it were me I'd drop it down to just under 8ma and closer to 170v at the plate with about 6v bias. (using a second LED/larger voltage drop)

Having said that the 12BH7 is pretty low gain to drive that amp to full power without some pretty good preamp output/gain to go along with it there.
The way the circuit is wired right now, if you haven't I'd suggest dropping an 12AT7 or 5965 in there an see how you like it, it's a "better" gain match.

Your 12BH7 will work, just it'll take a bit more twisting of the preamp volume pot to get full power out of the amp there.
 
Hey, nice amp. Just a comment about your set up. It probably is not a good idea to put your subwoofer on the same stand as your amp and turntable. It could negatively affect the sound from the t'table.
 
Thanks Kegger. I did roll a few tubes in there including a 12at7. To my ears the 12bh7 just sounded better. Maybe because I do not (actually cannot) listen at high volumes. It definitely had more bottom end. My second choice believe it or not was an ecc99. I use them quite a bit in guitar amps and I really liked it in this one. I think I may rewire the heater and roll some 6xxx tubes next.

primosounds said:
Hey, nice amp. Just a comment about your set up. It probably is not a good idea to put your subwoofer on the same stand as your amp and turntable. It could negatively affect the sound from the t'table.
Click to expand...

That sub is actually not hooked up in this setup. Its for the speakers in the right of the picture and is put on the floor when in use. Your right though, that turntable picks up everything on that rack including the humming of the transformers. I thought it was the amp at first but dropping the needle on and off the deadwax you could hear it. I usually put foam under the feet and that cures it. The amp itself is dead quiet.
 
Kegger said:
Project looks very nice, :thumbsup:
I like the operating parameters of the 807 as well, yah that looks quite good to me.

--------------

Now as to the 12BH7, honestly I'd say the current on the tube isn't low at all, if my calcs are about right I get just under 9.5ma, that's pretty solid.
In fact it were me I'd drop it down to just under 8ma and closer to 170v at the plate with about 6v bias. (using a second LED/larger voltage drop)
Click to expand...

After looking at the data sheet your suggestion makes sense. Since the max current is listed at 20mA I drew a load line from 380v to 19mA. Putting the quiescent voltage 2/3 of 380 at 250v gives approx 6.5mA. That's around -12v bias. I'm sure its much more linear to the left of this point.
 
stargeezer said:
That sub is actually not hooked up in this setup. Its for the speakers in the right of the picture and is put on the floor when in use. Your right though, that turntable picks up everything on that rack including the humming of the transformers. I thought it was the amp at first but dropping the needle on and off the deadwax you could hear it. I usually put foam under the feet and that cures it. The amp itself is dead quiet.
Click to expand...
Ok, i was hoping that is what you were doing. But, i have seen guys using their speakers as the t'table base lots so i just thought i would throw that out there just in case. cheers.
 
Damn. Is Kegger dead? Just noticed. My hat off to him. He helped instructed me before on building one of the tube amp.
 
ccheath said:
Damn. Is Kegger dead? Just noticed. My hat off to him. He helped instructed me before on building one of the tube amp.
Click to expand...

R.I.P. Kegger

Our good friend, moderator, great and generous man, Kegger, died in a car crash, this afternoon. His two parents, in the car with him, critically injured. https://www.clickondetroit.com/news/1-killed-2-injured-in-roseville-hit-and-run-crash-with-larceny-suspects-fleeing-fraser-scene The world...
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