Steve Thompson wrote:
> I've seen them working fine with several different sockets - I've found
> any socket with a built in screen cap is ok at VHF. The original design
> had huge gain, something that was hidden in class C use. It really shows
> when people started piling on the anode volts and linear bias - I
> suspect many just didn't get the neutralising right. Resistively loading
> the grids so it needs 20-30W drive in AB1 makes life much easier.
The gain on mine was high. Drive was around 1W for 600W out in AB1. But
it never had a problem.
I used to get serious TVI issues, which resulted in a visit from the
post office. They checked the amp and was happy with it. I got
restricted to low power for 28 days, which was particularly annoying as
I had to reschedule an MS sked for a time well outside the peak, which
meant the contact was never made.
> The big thing I saw was the need to get the loading right. The original
> design loaded lightly - probably to get the efficiency up for cw use,
> but with higher voltage and linear bias it just gives more gain and
> potential problems.
I adjusted loading to get the screeen current reccomened on the Eimac
data sheet. Power was 600W, which was as per data sheet.
> Personally, I hate tuned link coupling, but that's another soapbox....
>
> Steve
It worked well for me - sorry I sold it. I sold for it £300, which was
quite a bit of money back then. Thinking about the age, I built this
when I was about 15 or perhaps as old as 16, which means it was built 26
years ago. I suspect I sold it when I was about 22, due to TVI problem.
So £300 was quite a bit of money back 20 or so years ago.
I'm afraid to say I think it was used to jam the South London repeater
(GB3SL ??)- or perhaps that was not such a bad thing!! I don't know if
the repeater is still going, but SL was just about unusable back then.
Anyway, the twin 4CX1000A was never such a success. I believe the
4CX1500B might be more successful, as I gather it is a much better tube.
In what way it is better I do not know.
--
David Kirkby,
G8WRB
Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/
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