With a little help... KT88 PP UL Amp - Page 11

Herr Grau · 09:34 PM

Well, the bias voltage, regulated via R21 and R31, produces a current through R32 and R33, which makes them the measuring points for the actual bias current. Since the resistor ist 10 Ohms, I regulated the bias voltage in a way that 650mV are dropped across each of them. I don't care for the actual voltage at the grid, I only measure over the cathode resistor.

Herr Grau · 10th March 2010, 12:29 PM

Important lesson: Don't ever drop a pizza in an amplifier!
I was lucky it was the other one which is still pretty early in it's building phase....

Well, soldering the other resistor to the input I somehow managed to shorten the input. Next days are going to be exams, so I shouldn't even be thinking about amps.. But afterwards I'm gonna fix that and try removing the PSU from the case.
That clearly shows, that I'm out of ideas.

SGregory · 24th March 2010, 05:24 PM

Herr Grau,
Exams finished yet? Curious to see if you had made progress?

Herr Grau · 24th March 2010, 06:23 PM

Exams are over now and I'm at my parents for a few days to get some R&R. When I get back home, I'll try all the things left on my mind, specificaly increasing the distance between the driver board and the chassis and removing the PSU from the case. I'll report back when I did.

gabdx · 14th January 2013, 02:15 AM

What happened?

Herr Grau · 15th January 2013, 03:02 PM

Hi. The amps are done, but I havent had real spare time on my hands for as long as the last posts, thus I havent written about it. Sorry about that. The hum problem was solved by moving the B+ supply away from the Pre-Stage. Now they just sound great. I can only recommend the circuit.

7th March 2010, 09:30 PM	#101
Herr Grau diyAudio Member Join Date: Nov 2008 Location: North-Western Germany	Well, the bias voltage, regulated via R21 and R31, produces a current through R32 and R33, which makes them the measuring points for the actual bias current. Since the resistor ist 10 Ohms, I regulated the bias voltage in a way that 650mV are dropped across each of them. I don't care for the actual voltage at the grid, I only measure over the cathode resistor. Last edited by Herr Grau; 7th March 2010 at 09:34 PM.

24th March 2010, 05:24 PM	#103
SGregory diyAudio Member Join Date: Apr 2003 Location: Southern Tier NY	Herr Grau, Exams finished yet? Curious to see if you had made progress? __________________ Living Life Doing the Waltz in 4/4 meter.

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10th March 2010, 12:29 PM	#102
Herr Grau diyAudio Member Join Date: Nov 2008 Location: North-Western Germany	Important lesson: Don't ever drop a pizza in an amplifier! I was lucky it was the other one which is still pretty early in it's building phase.... Well, soldering the other resistor to the input I somehow managed to shorten the input. Next days are going to be exams, so I shouldn't even be thinking about amps.. But afterwards I'm gonna fix that and try removing the PSU from the case. That clearly shows, that I'm out of ideas.

24th March 2010, 06:23 PM	#104
Herr Grau diyAudio Member Join Date: Nov 2008 Location: North-Western Germany	Exams are over now and I'm at my parents for a few days to get some R&R. When I get back home, I'll try all the things left on my mind, specificaly increasing the distance between the driver board and the chassis and removing the PSU from the case. I'll report back when I did.

14th January 2013, 02:15 AM	#105
gabdx diyAudio Member Join Date: Jan 2008	What happened?

15th January 2013, 03:02 PM	#106
Herr Grau diyAudio Member Join Date: Nov 2008 Location: North-Western Germany	Hi. The amps are done, but I havent had real spare time on my hands for as long as the last posts, thus I havent written about it. Sorry about that. The hum problem was solved by moving the B+ supply away from the Pre-Stage. Now they just sound great. I can only recommend the circuit.