Eros voltage reading problem

[Paul Joppa]

158v at the 6922 (or equiv) plate is a bit low, but the critical voltage is the grid to cathode voltage. That should be nominally the same 1.55v; if it falls below 1.3 volts or so then the triode grid may be sucking enough current to kill the bass.

Among the half dozen or so tubes that I measured some years ago, the 6DJ8 varieties were more prone to this than the 6922 types. I think it has to do with the metallurgy of the grid and cathode parts. Anyhow, that's why I built the circuit around the 6922.

[Atom Shop]

158v at the 6922 (or equiv) plate is a bit low......

Any thoughts, Paul, as to what might be the reason?

Atom

[Grainger49]

I think he is saying it is tube dependent.  Try a Soviet Military Surplus 6N23P (6Н23П, USSR Surplus, the -EV sounds better to me).  They are inexpensive versus the high price spread and sound much better than the run of the mill 6922.

[Paul Joppa]

158v at the 6922 (or equiv) plate is a bit low......

Any thoughts, Paul, as to what might be the reason?

Atom

If everything else is good, then a tube with more transconductance than average will require less plate to cathode voltage to obtain the same current.

Seduction operates the tube at the same operating point, nominally 3.8mA and 70v plate to cathode at 1.55v bias. Some tubes would exhibit low plate voltages, 55 or 60 v instead of the design value of 70v; this was with LED bias on the tube so you KNOW the bias is 1.55v. Eventually as the tube ages it will lose some transconductance and the plate voltage will rise.

That caveat above, "if everything else is good," means that the bias voltage as I described earlier must be adequate to prevent grid current.

[Atom Shop]

Thanks for everything, Paul. The Eros is on my bench getting a good inverse RIAA work-out. The 'scope display confirms what I'm hearing (and vice-versa). True Hi-Fi!!!

Atom