So I am testing some things on a build.
It is real tight quarters, so I am checking things before I get it all wired up, and might have to access something under the board...stuff like that.
Anyway.....
All the tube sockets are in, and the heaters are wired.
The OT is wired up to its primary and secondary.
I have B+ on the plates.
I do not have the B+ wired past the screen supply yet.
The only tube I have installed at the moment is the 6X5 rectifier.
So I want to check the neg bias supply. It is all wired up (I think) except for the last connection to the 220k resistors that meet up with the 1k5 grid stoppers on the power tubes.
I get 400VDC across that first 56k resistor, but it stops right there. Nothing across the diode. No caps charge up.
Shouldn't I see neg voltage all the way until my wires stop being connected to something.?
Thank You
https://tubeamparchive.com/download/file.php?id=26172
Bias Test
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martin manning
- Posts: 14308
- Joined: Sun Jul 06, 2008 12:43 am
- Location: 39°06' N 84°30' W
Re: Bias Test
HH, when you say "across," do you mean from one end to the other or to ground? Also, you say 400V DC. Before the diode you should be measuring AC. If you are not seeing any DC voltage downstream of the diode, then the diode must be open or there is a missing connection.
In the linked circuit you should see about -50V to ground after the diode (with 300VAC supplied). At the top of the tremelo intensity pots you should see from -20 to -45V depending on the bias pot settings.
In the linked circuit you should see about -50V to ground after the diode (with 300VAC supplied). At the top of the tremelo intensity pots you should see from -20 to -45V depending on the bias pot settings.
Re: Bias Test
Hey Martin -
I should be asleep That is part of the problem.
Yes I meant VAC. I also meant 300, not 400.
I am sure you recognize your excellent handy-work.....
I had this working in another chassis, but finally had to abandon that chassis because it was just too small.
Most of the bias circuit stayed intact, with the exception of that first diode and resistor.
I think I have ruined a few diodes. Do not know if I have zapped them with static from my own hands, or something else. But yes, the (new) diode was open. Just did not want to believe it I guess.
I should put you on retainer. Will get a new (functioning) diode in there later today. That should do it I hope.
I always seem to think there is some kind of mysterious, and complex answer..... some times I miss the obvious.
Thank You
I should be asleep That is part of the problem.
Yes I meant VAC. I also meant 300, not 400.
I am sure you recognize your excellent handy-work.....
I had this working in another chassis, but finally had to abandon that chassis because it was just too small.
Most of the bias circuit stayed intact, with the exception of that first diode and resistor.
I think I have ruined a few diodes. Do not know if I have zapped them with static from my own hands, or something else. But yes, the (new) diode was open. Just did not want to believe it I guess.
I should put you on retainer. Will get a new (functioning) diode in there later today. That should do it I hope.
I always seem to think there is some kind of mysterious, and complex answer..... some times I miss the obvious.
Thank You