Newbie BootHill 5E3 build

andrewRneumann

Tele-Afflicted
Joined
Mar 22, 2020
Posts
1,587
Location
Cincinnati, OH, USA
Glad it's working!

I did some more research about that 17V reading on the grid of the cathodyne. It's basically a false reading that crops up due to the impedance of the regular voltmeters most everyone uses. The actual voltage is much higher than that, but there is no way to measure it accurately without a better voltmeter. I ran into the same problem when measuring the grid bias voltage on the long-tail pair phase inverter I'm building right now. I suspect this is a problem on any valve with bootstrapped input impedance (grid leak is connected to some point in the cathode resistance instead of directly to ground). Not having seen this before, it really threw me for a loop!

The solution is to measure the voltage at the tail of the grid leak resistor instead of directly on the grid itself--I believe someone suggested that.

Enjoy that amp!
 

D'tar

Friend of Leo's
Joined
Jan 11, 2013
Posts
3,685
Location
WNY
I like to see the readings on every pin of each tube. Knowing this anomaly, all we really care about is vdc present here. If no vdc we likely have an issue. If it is between 15-50vdc, its probably wired proper and conducting.

Just my .02$
 




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