I have an original ST-35 from the 1960s and a Dynakit version I built in 2012. All was going well. The old one is in storage and the Dynakit is the daily use. Upon power up the Dynakit one went quiet. I could see one tube was out. I decided to check out the reason (besides 13 year old tubes). Upon opening it up I see a burnt resistor. I was an early adopter of the EFB modification. I made my own board for it, but I no longer have those plans. The 100 Ohm resistor used across the tube pins 8 and 9 was fried for the dead tube. By the way, I have the 2012 version of the Audio Regenesis PC-13 boards in the amp. This is basically my issue - I can't find the original plans covering the EFB mod, the resistor was fried. I don't remember how to check this thing out or how to set the EFB bias pot.
I bought some new 100 Ohm 0.5W 1% resistors to replace the four used in the original EFB mod at each tube. I turned it back on and the tube is still toast (dimly lit and no heat generation). No sound comes out of either side. I also have a matched set of replacement tubes, but I do not want to put them in if I have another issue. Everything else looks fine visually.
A couple of observations:
I see on the one schematic I found of the old EFB mod that there is a 5 Ohm resistor between pins 3 of the tubes on each side. I see TP on either side of those resistors. I suspect that the bias is to be measured there and then adjusted. I do not have 5 Ohm resistors there, just a wire connecting the two pin 3s. Were the 5 Ohm resistors a temporary install to set bias or were they to remain?
Where else should I troubleshoot? Any help is greatly appreciated - I miss the sound. I am using the 1960s one now, but am a little concerned by its age and lack of use.
I bought some new 100 Ohm 0.5W 1% resistors to replace the four used in the original EFB mod at each tube. I turned it back on and the tube is still toast (dimly lit and no heat generation). No sound comes out of either side. I also have a matched set of replacement tubes, but I do not want to put them in if I have another issue. Everything else looks fine visually.
A couple of observations:
I see on the one schematic I found of the old EFB mod that there is a 5 Ohm resistor between pins 3 of the tubes on each side. I see TP on either side of those resistors. I suspect that the bias is to be measured there and then adjusted. I do not have 5 Ohm resistors there, just a wire connecting the two pin 3s. Were the 5 Ohm resistors a temporary install to set bias or were they to remain?
Where else should I troubleshoot? Any help is greatly appreciated - I miss the sound. I am using the 1960s one now, but am a little concerned by its age and lack of use.
