Jtm45 need help on new build

[William Martin]

This is the data sheet for the JJ ec803s that I have in V2
This should be good with the higher preamp voltage, right? From what I can tell 250v is fine

 

[william vogel]

Ok, I was just going by the voltage chart on Metro Amp instructions. So I shouldn’t worry about the high voltages on the preamp tubes? At least until ivan get a hold of the NOS tubes you recommend?
Would the only drawback to the high preamp voltages be a shorter lifespan?
It’s not blowing fuses anymore and I’m not using the standby at all. At the moment I’m running a 5u4 but if you say the voltages are ok I’ll run the GZ34 and take new readings.
I have the other PT on the way but now I’m rethinking it.
Thanks for your input!

The voltages for the preamp should be fine. If you get the tubes I’m recommending, you won’t have problems and they’ll last a long time. I don’t use current production preamp tubes because they fail. When I build amps I measure every resistor, capacitor, everything. The only voltage I measure is the HT at the fuse, the plates and the screens, set bias and start running signal through and watch the output waveform. Unless I see something abnormal and maybe the power output isn’t right (it’s always right), I never measure preamp voltages because it’s unnecessary if everything looks good. My amps are consistent.

 

[William Martin]

The voltages for the preamp should be fine. If you get the tubes I’m recommending, you won’t have problems and they’ll last a long time. I don’t use current production preamp tubes because they fail. When I build amps I measure every resistor, capacitor, everything. The only voltage I measure is the HT at the fuse, the plates and the screens, set bias and start running signal through and watch the output waveform. Unless I see something abnormal and maybe the power output isn’t right (it’s always right), I never measure preamp voltages because it’s unnecessary if everything looks good. My amps are consistent.

Thanks for that!

 

[William Martin]

Here’s the new voltages with a Genalex GZ34 rectifier
If I were to switch the 10k resistor back to the 8.2k should be just right but i think I’ll leave it for now and send the replacement PT back