A little help on a SLO Clone

[ryanf]

I know most of you aren't into high gain amps, but I hope you guys can help me out as it is only a power issue. The SLO Schematic can be found here (click on SLO Docs: http://homepage.mac.com/WebObjects/File ... US&lang=en),

My B+ is great, but I am worried about the biasing section. I took it off the high voltage line with a 220k resistor.

Voltages:
HV Lines:367V ac
After 220k resistor: 220V ac
After Diode: -60V dc
At bias point "F": about -30 to -50 V dc.

It seems like there is too much voltage going to the diode, seeing as it is supposed to come from a 50 VAC tap. Should I try a bigger resistor?

Thanks in advance,
-Ryan

[brown]

You're getting a Half-wave rectified -60V dc from the HT right?

You can add a little more resistance to the 220k in series to bring the Voltage down to -50V dc.

Also consider that it's going to hit another 15k in series in it's path and the trim pot and the top of a couple of caps. Then the grid leak and then the grid stops on the pwr tubes.

You'll want your bias pot to swing the voltage around -40V dc - assuming your calculations are correct. Is that what you want on the tubes' grids? Are you able to measure it at the tubes? If it's already doing that then there's probably no need to add resistance. You may consider decreasing resistance.

Brown.

[ryanf]

Yes, half wave 60V Dc. For some reason it seemed a little high. Thanks alot!

[drz400]

Yes, half wave 60V Dc. For some reason it seemed a little high. Thanks alot!

You have the whole circuit hooked up? trim pot etc

[ryanf]

Yes, half wave 60V Dc. For some reason it seemed a little high. Thanks alot!

You have the whole circuit hooked up? trim pot etc

Yes I do. No output yet but I've been tracking the signal right up to the last preamp tube with an oscilliscope.