2A3 TSE blown Fuse and MOSFET

[btran]

To 2A3 TSE amp. gurus,

I built 2A3 TSE about a year ago, just now it blown fuse and Q1,Q2 MOSFET. I replace them with new type 2SK3563Q and also change 30K ohms resistors for resistor R14, R25.

Now I start to do the check out for it and observe the B+ is 380V, just 5AR4 rectifier tube. In the power supply I have 4.7uF/450V for C4, choke 6H/150 ohms for R4 and 150uF/450V for C5. Is it normal or too high? Because the 2A3plate voltage is 300V max. I don't want to toast the 2A3 tubes.

Regards,

Binh

[rknize]

The voltage will sag under load. Right now you have no load without any other tubes installed.

[btran]

Rknize,
thank you for your assistance. When I do the adjust of the bias pots (R12 or R23), I have wierd reading. According to the check out procedure I should have negative voltage from the grid of output tubes to the ground. From reading I have -70V on R12 but +326V on R23. Could you tell me what I should do next?

[Evenharmonics]

I've had a problem with Sovtek 2A3 in my TSE. Here's a discussion. It has to do with its current draw. What brand is your 2A3?

Originally Posted by btran

Rknize,
thank you for your assistance. When I do the adjust of the bias pots (R12 or R23), I have wierd reading. According to the check out procedure I should have negative voltage from the grid of output tubes to the ground. From reading I have -70V on R12 but +326V on R23. Could you tell me what I should do next?

What are the readings at R7 and R30 (per this instruction)?

[Doc Jr 8156]

I am with Evenharmonics here. I also had a problem using JJ 2A3s. The current draw is much more than the regulator can provide. I converted my TSE to 300B and change the power tranny. Happily ever after. Godspeed.

[rknize]

Originally Posted by btran

Rknize,
thank you for your assistance. When I do the adjust of the bias pots (R12 or R23), I have wierd reading. According to the check out procedure I should have negative voltage from the grid of output tubes to the ground. From reading I have -70V on R12 but +326V on R23. Could you tell me what I should do next?

Does the voltage on the grid change when you adjust R23? If so, I would double-check your work on (and the value of) R25. If all seems well, check the gate voltage on both FETs (either at the coupling cap or at R15/26.