Vintage Asylum

John - please read below, this might be useful to you

72.54.202.114

In Reply to: RE: Dynaco MKIII w/ SDS board blowing fuses posted by TryPutting it back to Stock with SDS on April 23, 2008 at 06:14:57

John,

I did, still blowing. I think I just run into a type of case where 95% of 85C Pannys in production would last longer at 60C, but I got some from the 5% that would fail, and they failed. Again, I'm using the amps for 4-6 hrs. on average daily, possibly more.

No biggie.

BUT: DON'T use 2W cathode resistors in a fixed bias arrangement. I posted on this issue a couple of weeks ago - if one/both tubes shorts out, the reason those resistors are specified at 0.5W is that they should FAIL FIST in such instances before a tranny or something more valuable fails. Tube shorts out => resistor opens => channel turns off, no harm done.

You then replace the bad tube and the fried resistor and everybody's happy.

I cannot emphasize this enough. I had this happening when my EH KT88 reached end of life, and I have no damage other than one opened resistor. I keep a stock of CMF55 Dale's @ 10 Ohm for all of my needs.

The other safety net in such cases is the fuse, but path to fuse is longer and other parts are in the way and you don't want to lose more than minimum to contain damage.

I hope this helps.
Greets,
Radu.

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