[Collins] RE: R388 SSB CONVERSION OR MODS

[Laird Tom N]

>From the WC9M archives:

Hope this helps a little.

Tom Laird WC9M
Moline, IL.

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I got the product detector mod done in accordance with the 68 CQ
article. It works. However, there are a couple of issues.

1.The volume of the radio drops when you switch over to the bfo,
  approximately 50%. I assume this may be due to the voltage divider to
  ground 1.2K in conjunction with the 5 pf cap. The volume with the bfo =
on
  is entirely inadequate. I assume if we did a direct feed with the 5 pf
  cap and deleted the resistor this might improve. Am I on the right =
track?

2.Volume with the AVC off is better than with it on.=20

3.When the af gain is advanced much past 8, the rig goes into a low
  freq audio oscillation.

Otherwise the mod performs as advertised. I am new to tube rigs and =
point
to point wiring. These 40 year old eyes had trouble with that soldering.
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You have detectors with different gains. Sure the audio level will
change. You aren't using the diode detectors with BFO anymore, you are
using the product detector. You raise the product detector's gain by
raising the plate load resistance. You don't want the product detector
coupled tightly to the oscillator, it can inject enough signal to
modulate the oscillator. The oscillator input grid on the product
detector needs enough RF voltage to swing it good (as specified in the
tube data sheet) but no more. Gain of a mixer (which is what the product
detector is) does vary with injection voltage, up until a point.

Volume with AGC off is always greater than with AGC on. AGC can only
reduce the receiver gain. Distortion in the last IF stages should also
be lower with the AGC on. Have you aligned the detector IF transformer
to account for the new circuitry? New circuitry will change the gain of
that last IF stage.

Going into low frequency audio oscillation (motor boating) is a sign of
a need for new electrolytic filter and bypass capacitors. Jerry K0CQ