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

=====================================
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.

"terry" wrote in message
oups.com...
On Aug 5, 8:15 am, Highland Ham
wrote:
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.


A ground secondary would mean a half-wave rectifier, which would
place a heavy DC bias on the core and might lead to core saturation long
before the full capacity of the transformer is reached..
Hammond derates their transformers by .28 for halfwave rectification
with capacitor input filtering. I think the current is also limited
by a magnetic shunt on the core (removeable, I think..)

If these new inverter supplies use a higher frequency and smaller
toroidal type core, that might open the possibility for easier
mods for ham use. I'd think it would have been featured in one
of the more technical ham magazines by now, though..

Pete

"Uncle Peter" wrote in message
...

"terry" wrote in message
oups.com...
On Aug 5, 8:15 am, Highland Ham
wrote:
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.


A ground secondary would mean a half-wave rectifier, which would
place a heavy DC bias on the core and might lead to core saturation long
before the full capacity of the transformer is reached..
Hammond derates their transformers by .28 for halfwave rectification
with capacitor input filtering. I think the current is also limited
by a magnetic shunt on the core (removeable, I think..)

If these new inverter supplies use a higher frequency and smaller
toroidal type core, that might open the possibility for easier
mods for ham use. I'd think it would have been featured in one
of the more technical ham magazines by now, though..

Pete


"AS IS" the inverter supplies are not suitable for ham use unless you want
to do some EME work on 2.4Ghz. Probably why you havent seen anything about
them. I was just hoping to learn enough about them to make some power
supplies are are usable must like several people have modified the 60 cycle
transformers for various uses.



Jimmie

"Jimmie D" wrote in message
...
If these new inverter supplies use a higher frequency and smaller
toroidal type core, that might open the possibility for easier
mods for ham use. I'd think it would have been featured in one
of the more technical ham magazines by now, though..

Pete


"AS IS" the inverter supplies are not suitable for ham use unless you want
to do some EME work on 2.4Ghz. Probably why you havent seen anything about
them. snip Jimmie

Why is that? Did you find some specifics on the design that would preclude
something like adding filtering to the output to provide a filtered DC
voltage?

Pete