ECC88, warm up time

[Allen Wright]

Re #2, dunno, I would never just have heaters "floating". And in a SRPP or a cscode, one needs to set a fixed heater elevation voltage to ensure the tubes are always slightly reversed biased, cathode to heater. Floating may not allow this.

That's my experience.

Regards, Allen

 

[richwalters]

there is sort of diode transfer function (for AC) between heater and cathode .

when you elevate heater above (or bellow ) cathode (which is usually at near gnd potential) you're approaching horizontal part of mentioned diode transfer characteristic .

.

Some years ago this threw me out on a fault find in an amp with a 7199, the pentode voltages were well adrift: the circuit diagram showed heater +50V above ground, ideal for the split load; but apparently not for the pentode section. Ironically, in a mistake I discovered making the heater to cathode at -50V cured all problems. So what does one do ?

richy

 

[Nikon1975]

Is DC lifting possible only with AC ? How is possible if I have regulated DC for the heaters?

BR,

Davide

 

[Allen Wright]

Exactly the same, but your whole regulated heater circuit must be able to be lifted above gnd. So the traffo winding, diodes, regulator etc etc cannot connect to gnd anywhere.

Regards, Allen

PS I have been a NIKON man since the late 60's, and my 60's Nikkormat stilll gets used, along with my D300.