Mohawk troubles

[MATTHEW ERICKSON]

Thomas Bonomo wrote:
>
> I have just finished cosmetically restoring an RX-1 Mohawk receiver and
> have moved on to electrical restoration.  After replacing weak tubes, I
> gave it an alignment and it seems to be working, but this receiver
> doesn't sound very good.  I find that I usually have to run the IF Gain
> all the way down, and often must cut back on the RF Gain as well.
>
> I have measured S9 using a signal generator (100 microvolts) and this
> too confirms that the IF Gain must be set to minimum or 100 microvolts
> pins the S meter.  This receiver has an awful lot of gain!
>
> I also find the AVC to be less effective that most receivers, even
> though it seems to be generating adequate AVC voltage.  Am I chasing
> receiver problems, or is this just the way the Mohawk was designed?  Are
> there any factory changes that improve the performance of this receiver?
>
> Thanks for your help!  Tom Bonomo  K6AD

Hi, Tom!

I had same symptoms on a different receiver. Found out one IF tube had
leakage
and the control grid was pulled-up actually positive. But, because of
the
large decoupling resistor (100K or more), the positive was not seen back
toward the AGC source./ Nor did it show on any of the other tubes. That
one tube was indeed amplifying like a banshee and RF and IF gains had to
be turned down. Distortion can occur if the tube is severly driven into
clipping.

Also, one of those decoupling capacitors---AGC-at-the-grid to ground can
be badly leaky or even shorted. This prevents that grid from going
negative to lessen the gain---but, rather, hold the grid pretty much
at ground.

Hope this gives some ideas.


Regards,


Allen, KJ6XH
http://www.speedlink.com/mattall