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GM7HUD > UHF 05.10.07 00:42l 32 Lines 1329 Bytes #999 (0) @ WW
BID : C04813GM7HUD
Read: GUEST
Subj: Re: MM 432/100 Amplifier Bias?
Path: DB0FHN<DB0MRW<OK0PKL<OK0PCC<OM0PBC<OK0PPL<DB0RES<ON0AR<GB7YKS<GB7SYP<
GB7ESX
Sent: 071004/1603z 78850@GB7ESX.#31.GBR.EU $:C04813GM7HUD [Witham, Esx]NNA V3.1
G6KUI wrote:-
> My MML 432/50 which uses a single CM50 is set at 1 amp quiescent current
> with zero drive ( as per the specification sheet ).
>
> I hope the above info helps.
That's fantastic info Pete, many thanks.
Since 1st experimenting with the amp I've made some progress. It looks like
my FT817 doesn't like the input presented to it. It will give just under 5W
into a dummy load but only about 2W into amp. A little bit of TLC means
that I can now get nearly 18W out when driven by 2W. That sort of fits with
the specs, 10W for 100W out, 2W in for 20W (18 in my case). I exercised the
PTT circuit many, many times manually and the RF switching started working
after that. I think the relay contacts may have been dirty or not closing
correctly.
All I really need now is a primer mover with a bit more "steam pressure" to
see how much output it will give. A friend has a spectrum analyser so I can
tune it for max smoke/min nasties on that.
John G8MNY sent me a note saying that these early UHF PA devices had
considerable hFE but precious little hfe and were often heavily biased to
get hfe's of around 3 or 4. Your data fits in well with his and whilst my
bias may have been got at and may need tweaking, it's in the right area for
me to continue with this amp.
Once more, thanks for the info.
73 de Andy GM7HUD
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