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Douglas, Damir, I did some more work on the 300bPP amps [message #9412]

Sat, 17 December 2005 13:32

Tre'
Messages: 34
Registered: May 2009

Baron

Have a look.

Tre'

300bPP

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Re: Douglas, Damir, I did some more work on the 300bPP amps [message #9413 is a reply to message #9412]

Sat, 17 December 2005 14:16

Damir
Messages: 1005
Registered: May 2009

Illuminati (2nd Degree)

Thanks, looks good, but isn`t that the same picture?!

We want a photo from the inside, and some more details...

Huh, I just received grid chokes and now have an interesting problem... Two OPTs, two grid-chokes, six PS chokes, 11 big caps (and some little ones), etc. - all inside 2HE rack... plus PT and tubes on the top...huh

P.S. - Doug received his grid-chokes too, and have a big measurements plan, see "Group Build"...

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Re: Douglas, Damir, I did some more work on the 300bPP amps [message #9414 is a reply to message #9413]

Sat, 17 December 2005 15:20

Tre'
Messages: 34
Registered: May 2009

Baron

Hey,I just worked my butt off sanding that oak

The other pic was just plain aluminum chassis. I will try to do a schematic and post it soon

Tre'

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300bPP amps [message #9415 is a reply to message #9414]

Sat, 17 December 2005 17:30

PakProtector
Messages: 935
Registered: May 2009

Illuminati (2nd Degree)

That looks really good. I have the original Red Oak bottom on my DH amp. Took a long time with a block and 400-grit, then about a week soaking in linseed oil. Darkened just a little bit, and remained smooth. I think I did an intermediate pass with 600-grit after a few days of oil application. Still on the hunt for Southern Live-Oak.

I visited a woodcraft store, and saw some neat stuff. Yellowheart. Mustard yellow and fine grain. I wish I still lived next door to the DIY wood crafter in PA.

I'm looking forward to seeing the schematic Tre'.
cheers,
Douglas

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Re: 300bPP amps [message #9416 is a reply to message #9415]

Sat, 17 December 2005 19:48

Tre'
Messages: 34
Registered: May 2009

Baron

I just sanded and waxed the red oak. I used Trewax.

Schematic for my four chassis 300b power amplifier. Front end power supply not shown.

Tre'

300b

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Re: 300bPP amps [message #9417 is a reply to message #9416]

Sun, 18 December 2005 10:31

Damir
Messages: 1005
Registered: May 2009

Illuminati (2nd Degree)

Nice and simple, my only comment is rel. low B+=350V for the driver that operates at 250V.
You use unbypassed common Rk - did you try to bypass it?
Did you measure the amp?

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Re: 300bPP amps [message #9418 is a reply to message #9417]

Sun, 18 December 2005 12:51

Tre'
Messages: 34
Registered: May 2009

Baron

Damir, I have not measured the amp yet. I will bypass the cathode resistor at some point, tho Allen Wright does the "forced Class A" thing with his CCS in the cathode circuit. Lynn Olsen cautions against it.

With 72 volts bias on the output tubes I should need 144 volts peak to peak for full Class A output. Do you think that is a problem for my driver? If I were to lower the driver cathode resistor value that would lower the plate voltage and raise the max p to p output of the stage, right?

Thanks for the help...Tre'

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Re: 300bPP amps [message #9419 is a reply to message #9418]

Sun, 18 December 2005 14:45

Damir
Messages: 1005
Registered: May 2009

Illuminati (2nd Degree)

You have about Uak=250V - good, and just 100V across the CCS anode load. Voltage "swing" is 72Vp "through" the tube, and 72Vp "through" the anode load - you are very close to the 100V "edge", not counting necessary CCS voltage drop. If you can, rise the B+ for the driver to about 400V. And yes, lower Rk - lower Uak with constant Ia, 820 Ohms would result in Uk=-8,2V, Uak=220V.

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Re: 300bPP amps [message #9420 is a reply to message #9419]

Sun, 18 December 2005 15:32

Tre'
Messages: 34
Registered: May 2009

Baron

OK, I was able to raise the B+ for the driver tubes to 386VDC. Having not taken any measurements before hand, I can only tell you how it sounds. It sounds like there is maybe more headroom. I will bypasss the output cathode resistors when I get some appropriate caps.

Thanks....Tre'

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