Date: Fri, 16 Apr 2010 21:09:38 -0500
From: Mike Lucas <W5CHR@Bellsouth.net>
Subject: Re: [Amps] Grounded grid matching circuit
On 4/16/2010 8:44 PM, k7fm wrote:
> Well, you can have a broadband input - well sort of.
>
> Assuming you have excess driver power, you could dissipate the extra
> power in a swamping resistor. Determine how much power is to be
> absorbed by the swamping resistor. Then, since you know the input
> load and load of the amplifier tubes, you will use an unun to match
> impedances and also provide a low impedance load for the final cathode.
>
> Then you will also not have to worry about overdriving the final tube
> and relying on ALC.
>
> 73, Colin K7FM
>
Colin: Drive power is 100 watts to a 4PR1000 with 5000v on the
anode. I (think) it will make near legal limit output
with a 200 ohm resistor and a 4:1 unun. Will such an input screw up
the IMD without a tuned circuit,
or is a QRP signal (<1500W) unlikely to be noticed on 160 or 75M? I
don't mind experimenting, but I HATE
loud, expensive noises!
## The imd is already screwed up on a 4PR-1000 as is ! That tube
requires a LOT of drive as is. I had one back in the 70's. Switched
PI nets for tuned input. Tube Z is 100 ohms.. not 200. With 4400vdc
UNDER load..and 130 w of drive... power out was 1900w on the low
bands. [B+ supply was 4800 no load.. and 4400 loaded. ] ZSAC was
60-70ma.. with a 6.8 vdc zener in the CT. I would dump the zener..
and run it ZER bias. Easier to drive, better imd. With zero bias,
expect 100 ma of ZSAC.
## I had PI tuned inputs for each band..except 10m. On 10M position,
it was in bypass.. and drove the cathode directly. [separate tuned input
switch] When in bypass mode... swr rose to 2:1... and grid and plate
current, and power out dropped like a rock.. even with re-tuning the
tube xcvr's back then. The PI tuned input iS the key to getting a GG
4-1000 to work right. With 2500 vdc under load... and using tuned inputs
the plate current was 400 ma... and po was 600w. With 4400 vdc under
load, plate current was 600 ma.. and po was 1.9 kw. And in both cases
the drive power was 130w on the low bands. Between 1969-1983...
folks would run as high as 9 kv on a 4PR-1000. Old days !
later... Jim VE7RF
Mike W5CHR
Memphis
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|