Super Reverb Amp reissue bias

[Colas LeGrippa]

Hi,

I have a stock super reverb amp reissue amplifier on my bench ( 2000, year of mfg ) and the bias is way too cold. I just plugged in new JJ's 6L6's and the cathodes read 15mV right b4 the 1 ohm resistors on the PCB, when bias pot is fully clockwise ( hottest ). The 430V on the plates, would call for a bias of approx 40mA. Why is the bias circuit so cold ?

Colas

[sluckey]

That is cold. The schematic I have shows -52VDC on the grids and 33mV on the cathodes.

[Colas LeGrippa]

yeah right on -52 and 33

[LooseChange]

430v seems low too. Should be around 460v. Try another set of tubes first.

[Colas LeGrippa]

yes sir too low indeed: GZ34 defective, with bias circuit corrected, new 6L6's showed 340V on the plates.........with new GZ34: 460V. Biased at 40 mA, new amplifier, totally.

colas

[Platefire]

Wow! never had that before. My experiance with tube rectifiers is they are usually working at full potential or not at all. Plate

[LooseChange]

I've had my share of bad Rectifier tubes and mostly GZ34's.

[Colas LeGrippa]

Yeah Platefire, me too, first time I see a «half defective» rectifier tube !

Colas