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Nick Gorham Nick Gorham is offline
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Default 6N1P conflicting heater/cathode voltage specs

Iain Churches wrote:
"Patrick Turner" wrote in message
...


Ian Thompson-Bell wrote:

I have two data sheets for the 6N1P, both Russian with English
translations, which seem to give conflicting values for maximum heater
to cathode voltages.

One specifies Ukh as +100V and -250V. As the k precedes the h I assume
these are cathode voltages relative to the heater, so this spec says the
cathode can be at most 100V positive with respect to the heater.

The other describes these parameters in words. It says: Voltage between
cathode and heater:

- with heater at positive potential 100V
- with heater at negative potential 250V

I take this to mean the heater can be up to 100V above the cathode or
250V below it, which seems to me to be the exact opposite of what the
other spec says.

So, which is right?

Cheers

Ian


Probably all is misleading.

I'd never run a cathode at a dc potential of more than +/- 70V with
respect to the heater.

So if you have a CF where the cathode swings maybe 135Vrms, as might be
the case if driving
an 845 grid in class AB2, then be prepared to have the filament and itsa
voltage supply and transformer winding
also swing as well, which may mean you also need a screened tranny
winding to prevent stray C coupling to the mains.



If you don't have a dedicated winding, you can use a pair of
resistors across one of the B+ first filter caps to total 1M and adjust
their values to give you the elevated voltage you need at the centre
of these two. You then apply this voltage to both sides of the heater
cap via 100 Ohms resistors. The heater supply must, of course,
float. It works well. Details are given in Rozenblit's book. a small
decoupling cap (I use 0.1µF) is required at the junction of the two
resistors, and also on each leg of the heater at the tube socket.



I think Patricks point was if you have a valve where the cathode moves
+- 190v then no fixed reference will work for that heater, and the only
choice is a supply for that valve that only feeds that valve and is
allowed to swing with the cathode. This of course implies that for two
chan, you need two of the supplies.

And then as mentioned, the cathode will have to drag the supply around
with all its associated capacitances.

--
Nick