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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 23rd February 2020, 04:34 PM   #1
pbkrag is offline pbkrag  United States
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Default R25 smokes in tse 300b

My TSE sat Idle for some years because I was having issues with it and and only now getting back to get it running again.

this TSE is setup for 300b tubes.

I powered up with just a rectifier.

b+ 440
b- -175

After some a few min. R25 smokes. I replaced R25 and R14.

Figured I should start out with the proper checkout steps.

Filament voltages were 4.95 each
again b+ 440, b- -175
Grid of right output tube is -58
Grid of left output tube is +350 and slowly climbing

With rectifier in after a few min. r25 starts to smoke again.

I measured across r25 and getting over 600 volts.

So, where do I go from here?
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Old 23rd February 2020, 06:42 PM   #2
Tubelab_com is offline Tubelab_com  United States
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The mosfet connected to R25 (Q2) is shorted. Replace it.
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Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
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Old 23rd February 2020, 10:34 PM   #3
pbkrag is offline pbkrag  United States
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Replaced q2. And no more smoke. Thank you.
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