[R-390] IF module ---

[rbethman]

Pete,

You have an "early" model IF Deck.  That is essentially the rub - or fly 
in the ointment!

Later models have the filter trimmers accessible by having holes in the 
IF Filter can.

Suggest that you either obtain another cover, and punch the holes for 
access, OR simply punch the holes in the cover you have.

Make adjustments with the cover in place through the holes.

This was also done in depot and repair shops for these radios.

Bob - N0DGN

On 12/7/2011 6:52 AM, Pete Williams wrote:
>
> G'day list..... thanks to the respondents on the 1st Osc problem... fixed
> that with replacement of  capacitor C327 across T 207.
> Now....new problem... alining the IF module per book and no connection to
> the RF module , I find that with the cover off the filters  and no tube
> covers on adjacent tubes , the IF module bursts into oscillation when
> adjusting the 4 kHz trimmer--- but only the 4 kHz trimmer at top. All other
> filter adjustments / trimmers OK. , put the filter cover on and a couple of
> tube shields makes things normal--- but it shouldn't happen.
> Reducing the IF GAIN pot tends to minimize the problem and amplitude of the
> oscillation as shown on the diode load voltage
> Maybe there is a contributing factor in the fact that the AGC voltage is
> less with the 150uV input than what one might expect- hence excessive gain.
> Comments and advice on further directions  appreciated.
> A proper dog this one !
>   Cheers
> Pete VK3IZ
>
>
>