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What's eating my 5U4s for lunch?

Eng.Mike said:
If you replace your 5U4 with a pair of silicon diodes, your rectified voltage will become significantly higher.
The 5U4 has a voltage drop of about 44 volts and the silicon diodes drop what? 0.6 volts? So with silicon, your plate voltage for all the other tubes goes up and that changes the opperating point for all of the tubes which is a bad thing. You need to compensate for the voltage increase or you may start loosing your other tubes from over-dissipation. The circuit will likely not work as designed tubes running at a different opperating point.

About Chineese rectifiers:
I've only used the Chineese 5AU4 since old stock can't be found at a reasonable price. The ones I've used worked great, lasted longer than the Russian ones and looked like they had copper plates. The wierd thing is that the printing on the glass reads "Election tube" instead of electron tube.
Click to expand...

Yep, it tried to run higher but the voltage reg on the oscillator stage is doing a good job of keeping everything at about 105v.
Even if it did run high, every tube is cathode biased, and so should be self-regulating unless it went way, way up.
I designed this modulator to have voltage amplification only, and it was intended to drive 4 parallel 807s in class AB1 (no grid current), to give about
135watts out. Each of the 807s was to have a 27v 5watt zener in the cathode. I would rather have a little less efficiency, and none of the touchy
problems with grid drive providing bias. I have the parts for the output stage, but never built it. (Too dangerous for someone with my past).
I've never fixed the 6-foot tall 500 watt "Universal Radio" 1950's xmittr either. Maybe it's time to find a good home for this boat-anchor.

Even graphic desingers make mistakes.. The customer I'm at today put a job on the press where the words "Rail City" were somehow entered as
"Rail Clty". I caught the mistake and saved them a LOT of paper waste.
 
Even graphic desingers make mistakes.. The customer I'm at today put a job on the press where the words "Rail City" were somehow entered as
"Rail Clty". I caught the mistake and saved them a LOT of paper waste.

Sounds like you might be working in the dark!
 
I'm the guy from the press manufacturer, I was at a new installation, it was of of the first live jobs they were running on press.
 
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