On Aug 5, 8:15 am, Highland Ham
wrote:
Had a look at the old quad GG 807 type linear.
COR! that's a real old bit of ham radio.
My own experience with 1625/807's is that with more than 1KV on the
plate they didn't survive long. Any mismatch or off-tuning and flashover
happened pretty fast. Back in the 1960's I had quite a bin full of duds
that went just that way.
Recently I had a fault in my modified kenwood 820s which destroyed 2x
6146B's in a similar way. That's with only 850v plate voltage too.
However it is true that linear amps tend to work better in a high
voltage/low current mode, provided the finals can take it.
My old home brew 100watt linear used a TT21 (KT88 with a top cap plate)
and that worked fine with 1050 volts. Nice and linear and 66% efficient
on 14 Mhz (measured).
I once built an 811A GG linear but never needed the extra power so it
nevergot on the air.
Regards Cliff Wright ZL1BDA

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Re the anode voltage used for PA valves ; the older (1968-1973
generation) Yaesu transceivers (FT 40x & 50x)using TV Line Sweep valves
(tubes) had 2 HV voltage transformer taps resulting in either 650 or
850V-DC .
I always used 650V since 850V caused the valves to be too hot ,due to
the limited (1 small fan ) cooling .
Although I have seen designs including 4 line sweep valves in
parallel, running on 1000 or even 1250 V ,but only with enhanced cooling.

When licenced in 1985 my first transceiver was a FT400 , an excellent
learning piece of kit, involving some 'fried' PA valves.

Frank GM0CSZ / KN6WH- Hide quoted text -

- Show quoted text -

Interesting about 'Inverter' power supplies in domestic microwave
ovens.
Here in this part of Canada have never knowingly seen one that was not
115 volt AC input.
I guess one could call them 'Switching power supplies'?
Our appliances have therefore been pretty heavy and usually with the
transformer mounted inside towards one end.
Several owned and subsequently a number scrapped have all had 60 cycle
transformers.
Have read that the transformers go into saturation each half cycle?
It appears that one end of the HV secondary of the transformers is
often grounded to the frame of the transformer.
However often thought that the substantial 60 Hz. transformers would
be the basis for good (non portable) PA power supplies.