500B recap attempt reveals problems...

I tend to agree with Tim, I don't think it's your IBAM board.

You would need to lower the value of the four resistors on your board for your 'hot' Tung-Sols, like 8k or 10k. Along with the caps they have taken the place of R129, R135 & C85.

I'd take some close ups of your output tube sockets and its wiring, plus the power cans and its wiring.
 
Definitely a drawing of how you've got everything wired up. IBAM board can easily be checked outside of circuit to make sure it's cool.
 
Bruce, Tim, many thanks for your help.
I think I've found the problem and you were right.

Well, before I installed my first IBAM I thought about different ways to split the 220K resistors. One of my ideas involved using a terminal strip attached to one of the OT screws.
I didn't like how it looked like, the thick OT wires were in the way. So I put it back together like this and tightened it well...

The result was 0 ohms to ground. The orange wire carries the screen voltage for the outputs.

DSCF0701.JPG

I actually laughed when I found this.

Amen.
Pete
 
Yep, it was that wire. Replaced it and everything works like a charm!
I don't think I need to change anything on the IBAM board.

I got -24V on the control grids with the IBAM pots wide open which translates to only 10mA on my Tung Sols. I managed to dial in 36mA (360mv across cathode resistors) on each tube though it took me a while as it only stabilized after about 20 minutes.

That multiplied by 397V (my plate voltage) gives 14.3W dissipation which equals to 75% of the maximum value.

So far it sounds simply A W E S O M E.

Also, my tape head to second phono input conversion works very well. Will describe it later.
 
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Yep, it was that wire. Replaced it and everything works like a charm!
I don't think I need to change anything on the IBAM board.

I got -24V on the control grids with the IBAM pots wide open which translates to only 10mA on my Tung Sols. I managed to dial in 36mA (360mv across cathode resistors) on each tube though it took me a while as it only stabilized after about 20 minutes.

That multiplied by 397V (my plate voltage) gives 14.3W dissipations which equals to 75% of the maximum value.

So far it sounds simply A W E S O M E.

Also, my tape head to second phono input conversion works very well. Will describe it later.

Yeah! Glad it worked out for you. Will love to hear what you think after you tidy it up and have a long term listen.
 
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