[Drake] Re: TR7 Pa Problem

[HENRY PFIZENMAYER]

>    1. TR7 PA problem (ik2bcp - Guido Tedeschi)
>
>
> ----------------------------------------------------------------------
>
> Hello All,
>     the TR7 of a friend has the following problem: low power output from 7
> to 30MHz but it is ok from 1.8 to 5MHz
> The receiver is ok, with the same correct sensitivity an all the bands.
> The maximum power output is 150W on 1.8, 3.5 and 5MHz, 70W on 7MHz, 30W on
> 10MHz, 20W on 14MHz, 10W on 18, 21 and 24MHz and 30W on 28MHz
> I measured the RF on driver output and it is ok for all the bands, I think
> that the problem is on some faulty component in the PA that limits the
gain
> in the 7-28MHz band...
> Has anyone had this problem and solved it?
> Thanks and 73
> Ciao!
> Guido, ik2bcp / ab9dg
>
Guido -- Is this the power you measure with the alc controlling the max
output power ?

If so-  it sounds like the directional coupler may be haywire - if the
terminating resistor  R2003 68 ohms across the T2001 toroid sensing the line
current was open , it would have increasing senstivity as you went up in
freq and would shut the pa down quicker.

If its not into ALC - then I would suspect something in the low pass filter
module next. I have heard of problems with the grounds and would check those
(the braided wires from module to case. )  If you did not mind unsoldering
the output from the pa to the filter , you could run the PA directly into a
load , bypassing the filters altogether and satisfy yourself that the PA is
putting out power across the freq range.

Since you apparently have the capability to measure rf voltage , you could
check the voiltage swings at either output collectors and make sure both
sides of the pa are working equally or at least make sure the rf at either
base is equal,. Its not likely , but possible that one of the output
transistors is sick even with the 150 watts out at low frequency.

Anyhow there are some thoughts to think about --

Rgds- Hank K7HP