2A3 TSE blown Fuse and MOSFET - diyAudio
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Old 14th November 2010, 02:47 PM   #1
btran is offline btran  United States
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Default 2A3 TSE blown Fuse and MOSFET

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
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Old 14th November 2010, 04:15 PM   #2
rknize is offline rknize  United States
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The voltage will sag under load. Right now you have no load without any other tubes installed.
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Old 14th November 2010, 05:10 PM   #3
btran is offline btran  United States
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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?
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Old 14th November 2010, 06:36 PM   #4
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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?

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Originally Posted by btran View Post
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)?
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Old 14th November 2010, 06:45 PM   #5
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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.
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Old 14th November 2010, 06:54 PM   #6
rknize is offline rknize  United States
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Quote:
Originally Posted by btran View Post
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.
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