[Premium-Rx] TenTec RX-340

[Charles P. Steinmetz]

Heinz wrote:

>I have a problem with my TenTec RX-340 which I got from a 3rd hand owner.
>Immediately after 'power on' it is totaly deaf. Within the next 10
>minutes it slowy gets better, but sensitivity is still about 40dB down
>compared to my Telefunken E1800/3.    *   *   *
>
>I executed the BITE tests with following results:
>BITE 1 FAIL
>BITE 2 FAIL S/A: MIXER1
>BITE 3 RESULT: 000:004
>
>With my limited knowledge it appears that the mixer1 board is
>defective. It seems somebody already changed the 2SC1971 transistor.

First, note that TT calls for BITE tests to be run only after 
disconnecting the antenna and headphones and warming the receiver up 
for more than 1/2 hour.

You could get BITE 3 = 000:004 if the first mixer balance is way off, 
although I would not think that this would make the receiver totally 
deaf.  So, it may be something else entirely.

To balance the first mixer:

1. Set the receiver frequency to 0 Hz

2. Set the receiver mode to CW1

3. Adjust R5 and C11 for the lowest S meter reading.  This must be 
done iteratively until you get the S meter reading to its lowest 
possible value.  (These adjustments are accessible through the holes 
in the first mixer board shield -- the shield nearest the front 
panel.)  Note that the adjustments, particularly C11, are VERY touchy 
-- probably more so than any electronic adjustments you have ever made before.

The 1st IF output on the back panel should have around 30 mV p-p of 
45 MHz with lots of harmonics, given an RF input of S-9 or so, CW, 
center-tuned.  If you have this, the problem is downstream of the 
mixer itself (T2-T4, diodes D1-D4) and could be the post-mixer FET 
amp (Q2-Q7), the roofing filters (FL1, FL2), or the output amp (Q8).


Best regards,

Charles