6146

[Gerald Moritz]

Murray (multi-volti at SOFTHOUSE.COM) wrote:

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Hello:

I think at the <1 kv voltages on 6146x's, it's a gas problem, or
whatever other low (relative) voltage problems prevail in tubes.

In moderately hv tubes (say 3-5 kV), like 4-400, 3-500, etc, I've been
told by a now deceased tube engineer that the tube glass often
fluoresces blue at higher voltages...so I guess it depends where you see
it. I have seen 4-400's and a 3-400 runnig about 4000 VDC have blue
glowing glass, but it was nowhere near the grid. filament etc. It was up
near the anode rod and cooler.

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I want to build an amplifier with the russian version of the 3CX1500A7
(GU43b).
But before that I want to get some experience in building such an pa.
So I decided to built a 'little amplifier' with abt. 100 W out.
This little thing should have all the features of his big brother, like:

soft-start for Heater and Plate-voltage
warm-up and cool-down-Timer
regulated dc for heater
protection ciruits for overload, any voltage failures, refl. SWR and so
on...
(a similar PA can be seen at: "A Luxury Linear" by Mark Mandelkern, KN5S,
QEX 05-1996, p.3, ff)

For my little Amp. I want to use either 6146 or PL-500 (HV-Tubes out of an
Color-TV-Set).
I have looked at all my HEATH-Equipment (HW-100 and HP23B, SB400) were the
6146 does a good job.
But there are +800 V at the plate and +750V when key down.


Sure, I could use the HP-23 for powering my PA, but if there is any failure
 I will need a new
transformer (from P. Dahl ?).

So I have only one transformer (2 x 500V) which would be for my amp (my Old
 Sparky, hihi).
But 500V is too low for me.


Datasheet for the 6146 says that 750 V is the upper limit for this tube.
But now I only have
the possibility to give abt. 1000V to the plate.

According to the Email of Murray I think many people transmit with
increased plate-voltage.
Is it save enough for the tube ? Perhaps the tube is very sensitive against
 wrong tuning
and a bad SWR.

It is not the right place for an homebrewed PA, but it is right for a
discussion on the 6146.

Any comments ?
Thank you de Gerald, OE1GOD, Vienna, Austria - Europe

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