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Sickening smell of smoke! Amp was performing great today - first time with a KT88 and replaced 1K 5watt on second bias resistor. About the third time I turned it on, my "short" power light on the line voltage came on briefly, followed by a little smoke and no sound. Traced the problem to R17... a 1K 2 watt resistor near the power tube - it was toast. Hi voltage power section is working fine to that point - but with the resistor out, there's no power to the preamp side. Think the KT88 was too much? I've ordered a 3 watt 1K as a replacement for R17. Any other suggestions/precautions?

Increased screen draw with the KT88 would blow that resistor.

Try another 2W resistor and a different tube before moving on to a higher power resistor.

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http://pdfelectronics.com

I stayed away from the KT88 and settled on running a 6L6GC for my bigger tube needs. I have read of at least one other builder with a perfectly fine Tramp then swapping in a KT88 and something goes pop, either the tube itself or (in your case possibly) a resistor, whichever gives up first. That's just my observation but I wonder whether the KT88 runs things very close to a tipping point where you can be lucky and have no problems at all, ....or not so lucky.

Exhibit A:
viewtopic.php?f=16&t=3384&start=60#p27066

Disclaimer: That's just a purely subjective observation made by me and probably a wrong one.

Thanks guys - hopefully the output trans is OK. Had tried a nice reissue Tung-Sol 6L6GC before going to the KT88 - and it sounded great... almost as much clean headroom as the KT. I'll probably go back to the 6L6

All is well with my intrepid TRAMP, after replacing the blown resistor and firing up a 6L6. I'll be fine-tuning the bias soon... and from what I'm reading.... a current of about 45-50 ma looks good for a 6L6... while the KT88 likes a higher reading, like 60+ ma. Any suggestions for a target range on bias?

My measurements for a 6L6GC are recorded in this thread (linked), hopefully that will give you an idea of ballpark numbers.

viewtopic.php?f=16&p=25603#p25603

If built to spec you should be pretty much good to go with a 6L6, being a Cathode biased amp it should come in at just under 30 Watts dissipation with the VRM at Max.

I have a KT88 in a Tramp and have not had a problem, tho I think the 6L6 is the "bees knees " in this amp!

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Stephen
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