Tubelab SE CCS help needed

[jrenkin]

I am having trouble with my TSE driver circuit and need help.

For the life of me I cannot get a set voltage near 175 volts as recommended in checkout at the plate of the 5842.

I have B+ of 390V present at the drain of the CCS, a constant current of 8.449 mA over R16 and the cathode resistors, regardless of settings, which seems ok.

All components are correct and attached properly.

When I adjust R9 I get a range from 1.5 ohm to 337 ohm as I presume is expected, giving me a max cathode voltage of about 2.87V.

The plate voltage only adjusts between roughly 103 and 109V max. I can get another few volts by adding more cathode resistance, but what is going on?

Are my CCSs both bad?
Is this fine, since my current is ok, at 8ish mA?
Both channels behave the same and I have swapped tubes without making more than a several volt difference.
Currently the grids are floating, I had them grounded through R8, but that didn't seem to help.

I have also disconnected the bias and output circuits completely so I am testing the driver circuit in isolation. It behaves the same, I just wanted to make sure that something else wasn't the problem. B+ was normalized to the load with a variac.

Thanks for any input!

 

[rknize]

The CCS is doing it's job. It's having to lower the plate voltage to keep the current in check. Your 5842s are running really hot for some reason. Make sure that grid is grounded and the grid stopper is in place! The 5842 loves to oscillate. Do you have a scope? Maybe it's just oscillating.

 

[jrenkin]

Thanks!

I suppose I will reinstall the grid stopper and R8 and see. Then I can set up the scope if needed, it is a digital and software needs to be reloaded and all. At least it is working something like it should.
Maybe I just have 4 bad tubes.

 

[jrenkin]

Got it! Oh, it sounds so nice....