I can briefly translate that article, if you interested in that schematic.
that article covers several key points:
1. "old" GU81M tube is not outdated and still good for linear amplifiers
2. tube, designed for military use, can handle more watts and amps
than mentioned in its specs
3. tube with 3kV plate, 800V grid produces 1500W out and still
dissipates only 450W - well within specs.
4. one or even several GU81M's working @ 10m using pi network to
neurtralize tube capacitance
On Sun, Jan 11, 2009 at 1:05 PM, Thomas Hoeppe <email@example.com> wrote:
> Thanks for all infos! The EX8A design is going an interesting way. If I
> understand it right the main trick is using L matching for the higher bands
> (C plate is already "in the tubes"), and the tuned coil instead of the
> missing C plate. But I don't see the need of the effort with all the taps in
> the HV-side. Is it only to prevent resonances in the anode choke, or are
> there any effects on the high band behaviour I do not understand?
> Thank you for all comments!
> Tom, DJ5RE
> ----- Original Message ----- From: "Alex Malyava" <firstname.lastname@example.org>
> To: "DAVE WHITE" <email@example.com>
> Cc: <firstname.lastname@example.org>; "Thomas Hoeppe" <email@example.com>
> Sent: Sunday, January 11, 2009 6:51 PM
> Subject: Re: [Amps] GU81-M on highbands
>> there is an EX8A schematic - pair of GU81M with double pi-networks -
>> one of them instead of plate choke.
>> that amp works up to 10m no problem and gives 3kW out.
>> On Sun, Jan 11, 2009 at 7:03 AM, DAVE WHITE <firstname.lastname@example.org>
>>> Hi Tom - Somewhere I have a circuit from a Hungarian amateur that uses a
>>> single GU81M on 80-15m. I'll try to find it (a major operation in my
>>> library, and not one guaranteed of success!!) and scan it for you if you
>>> need it.
>>> Dave G0OIL
>>> --- On Sun, 11/1/09, Thomas Hoeppe <email@example.com> wrote:
>>> From: Thomas Hoeppe <firstname.lastname@example.org>
>>> Subject: [Amps] GU81-M on highbands
>>> To: email@example.com
>>> Date: Sunday, 11 January, 2009, 6:15 AM
>>> Has anybody used a single or a pair of GU81-M on highbands? Of course I
>>> see the
>>> problems with the high output capacitance, but there can be solutions
>>> L-tuning or a small L before between tube an plate-capacitor.
>>> Has anybody done that in practice?
>>> Tom, DJ5RE
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