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| Ron Stone, GW3YDX - EMail ron@gw3ydx.demon.co.uk
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Chaps
At last I have decided to part with the faithful Drake L7.
This station is about to enter the era of ceramic tube technology.
As I can't track down an Alpha 78 the choice is boiling down to
either the Command Technology HF2500 with the Svetlana option,
or the ETO 91 B, also with the 4CX800 tubes.
I like the look of the solid build of the Command Technology amp and
the parts coming from Peter Dahl and other manufacturers of known
quality. The ceramic bandswitch looks particularly meaty, but I
do not like at all the lack of any means of protection of the tube
grids in the event of a severe mistune, or the lack of any SWR
protection circuitry.
The Alpha as you know is built in Bulgaria. There is a nagging
doubt about the parts, but the protection looks pretty good in the
spec sheet. The control grids anyway seem to have some protection,
but I have yet to establish what would happen if you lost your plate
volts while in transmit. Usually fatal for a tetrode unless some kind
of screen shutoff is available for that eventuality. Same comment
about the screen supply applies to the Command Tech amps of course.
I talked to Ray Heaton (ETO) who got a bit vague about the exact
details of the protection. I faxed Patrick Stein (Command Tech)
asking a lot of awkward questions about the protection and have yet
to receive a reply 2 weeks on. Not a good sign.
On this reflector we must have somebody who has these amps and who can
comment. I would be particularly interested in the technical details
of the screen supply arrangements for both amplifiers, and how the
91B has behaved in production models. The Conway Reef one blew up but
that has been attributed to a dodgy mains supply. Cant really draw
any conclusions from that. I understand that the 91B is subject now
to a 2 to 2.5 month delay.
73
Ron
ps - the guy who offered me a Alpha 89. Please contact me again.
Ur price was a bit high - but we could discuss !
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