Tubelab SE checkout shows -300V Bias voltage? - Page 3 - diyAudio
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Old 22nd November 2011, 07:26 AM   #21
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Quote:
Originally Posted by jrenkin View Post
Any updates on this? I am too curious.
Nope, I had to park it for a while, because I started to see 'things'... ;-)
Built another SSE, so I have good sound when I get onto trying to figure this out again. Right now I am on Maui for another week to replenish/extend my self-contained underwater breathing apparatus skills and admire the life that could care less about bias, cathodes and grid-stoppers.

Before I stopped working on the TSE, I tried to systematically go through the circuit with the scope to figure out where the signal goes bad, but as soon as I hooked up my scope probe, things turned really nasty. There was really bad static coming through the speakers and the current through the power tubes rose dramatically, so I ended the experiment very quickly.
This happened at various points in the signal path; not sure what I am doing wrong. I thought I knew how to use my scope.

Once I get back from my trip, I am planning to start over by checking all components for proper values again, before doing any more live-circuit testing.
The interesting thing was that everything checked out fine; I was able to properly adjust the plate voltages for the drivers and the bias adjustments were no problem either. B+ was right were it should be.

Anyway, I'll make sure to post my findings once I figure this out.

Aloha!
Stefan
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Old 25th November 2011, 02:50 PM   #22
adwsail is offline adwsail  United States
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Well I'm going to throw my 2 cents in. I've had my TSE for 4 or 5 years now and just rebuilt it for the third time, my bad. This time its going into a nice wood chassis, point to point wired. While not for the faint of heart it really isn't tough to do. Some of you may even have seen my Pass Labs Xen V9 build, Pictures of your diy Pass amplifier.

With only the 5AR4 in circuit my voltages are as follows:

B+ 403
B- 268

Xformer AC 301/302 referenced to gnd
Transformer is a 6K56VG, C5 is 470uF, C6 is 100uF, R6 is a 10w 10K wafer, Q1 is an FQP1N50, C9 is a .22uF Auricap, R34 is a 100ohm Caddock.
300B grid is -143 and -135 adjusted to max negative voltage

With the 5842 and 300B's in place voltages are as follows:

B+ 308
B- 231 at R13/R14 junction
At pin 3 (grid) on 300B -62vdc

R12 is adjusted for 58ma across R18. (0.58vdc drop across R), no signal, 8ohm resistive load on output.

Like several others that negative bias really concerns me but everything else seems ok??? I have not put a signal through it yet nor have I put speakers on it. It would be nice if any of you could confirm or red flag my negative bias voltages.

I don't know if this will help anyone or simply muddy the water further but this forum is great for helping each other!!
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Old 25th November 2011, 03:03 PM   #23
adwsail is offline adwsail  United States
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After my last post I got to looking and remembered I was concerned about my B+ so I put a 36k ohm in for R14. I'm starting to think that was unnecessary and I should go back to the 20k based on my operating B+. Any thoughts??
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Old 26th December 2011, 01:06 AM   #24
adwsail is offline adwsail  United States
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Any comments at all???
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Old 26th December 2011, 04:43 AM   #25
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B- is fine. R14 depends on the B+ as it regulates the dissipation of the mosfet. I think you can stay with a lower value
Just check the temperature of the fet.

D

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Old 26th December 2011, 01:10 PM   #26
adwsail is offline adwsail  United States
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Thanks Nikon, i appreciate the confermation, have a happy New Year one and all.
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