One of the screen resistors is burned (colors are gone and it's cracked). Should I change both? The other reads at 465k, but it should be 470k.
If you're talking about the 6V6's screen resistor it shout be 470 Ohm, not 470K Ohm. I would replace the both as well as the 6V6 set.
Thank you Mr. Z. Yes, I meant 470 Ohm, not 470k. It burned after I tried another set of 6V6 tubes (JJs) from another amp (Traynor Darkhorse). The tubes I was using with the Z28 (Tung Sol) were not in the amp when it happened. Do I still need to change them or simply recheck the bias?
Well a shorted 6V6 will cause the Screen resistor to pull too much currant, then burn. The tube caused the resistor to fail. So don't use the set there in when the failure happened. Yes you need to check bias EVERY time you swap output tubes in a fixed bias amp. Set the bias to 28 mA per tube.
Post by crimsonqueen on May 10, 2017 11:24:36 GMT -7
I gave up on finding the resistor around town and ordered some from Digikey. They arrived the next day! I took me a while to get to the repair, but I changed them and replaced the power tubes with JJs. I also rebiased the amp. I don't know if the resistor had been faulty for a while, or if I had not biased the amp properly when I got it last year, but it now sounds amazing!
I played an improvised blues gig yesterday and used the new and improved Z28. I was blown away!
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