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Posted by hurdy_gurdyman [ 4.229.195.209 ] on September 06, 2005 at 23:01:41:

In Reply to: Re: Fisher 500C-how hot is too hot? posted by hurdy_gurdyman on September 06, 2005 at 22:03:42:

I wrote the wrong cathode and grid voltages above. My tired eyes was reading the scale wrong. It should have read:

Plate= 450 V
Screen= 350 V
Grid= -24 V
Cathode= 3 V

I'm not using my old faithful Eico VTVM I've used for many years because the 1 meg precision resistor in the probe has finally drifted to much. I'm using an old archer with different values for each scale. I have it straightened out now.

I also experimented with a resistor in the AC line. All I had on hand was a pair of 50 ohm, 10 watt, so I wired them together for 25 ohms. Here's what I got.

Plate= 420 V
Screen = 330 V
Grid = -22 V
Cathode = 2.6 V

Looks like I'm just not going to get enough negative bias.

I'm almost ready to rewire this back to origional and just buy a set of 7591's. Darn. I prefer EL34's, and dang if this thing doesn't sound sweet.

Dave




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