[Boatanchors] SX-130 problem

[Bill Fuqua]

   I believe the AM detector remains in the circuit to produce the AVC voltage.
I wonder if somehow it is loading down the IF signal on peaks and producing 
distortion.
Perhaps a leaky RF by pass capacitor associated with the 6AL5.
Bill wa4lav

    Much more expensive radios used IF generated AGC but not often seen in
lesser expensive ones.

Wow, just hit me. Not likely but has happened in other radios.
   See if there is a difference between using headphones and
speaker. It could be microphonics ,  the local oscillator is a bit sensitive
to vibration and speaker vibrating the LO could make for strange distortion.
Or even loading on the power supply could lead to slight FMing of the
LO.

73
Bill wa4lav


At 01:05 PM 2/1/2012 -0500, Jack Taylor wrote:
>Ron, did he say how he "checked the IF transformers for leakage?
>
>Jack, N7OO
>
>----- Original Message -----
>From: "Ron Barlow" <imalowfer at yahoo.com>
>To: <Boatanchors at puck.nether.net>
>Sent: Wednesday, February 01, 2012 10:24 AM
>Subject: [Boatanchors] SX-130 problem
>
>
>Many thanks for all of the replies, re the SX-130 question!
>I must apologize for not mentioning that this receiver does have a product
>detector (a 6BE6 pentagrid converter, as Bill mentioned). However, it uses
>carrier derived AVC, instead of audio derived AGC. I don't recall ever using
>a receiver with that combination (product detector and carrier derived AVC),
>so I don't have any experience with the results.
>I assumed that the AVC bypass caps, and audio coupling caps were paper
>dielectric type, and I suggested that he replace them. He advised that they
>were disc ceramic types. He has also checked the IF transformers for leakage
>(which would upset the AVC), and he has replaced the resistors in the plate
>and screen circuits, of the product detector. The electrode voltages, on the
>6BE6 are very close to those indicated on the schematic, except for the
>plate voltage (93 v actual vs 62 v, on the schematic).
>The schematic diagram indicates that Hallicrafters used a capacitive voltage
>divider, to reduce the IF signal voltage by a factor of ~ 10, before
>applying it to the 6BE6 signal grid.
>Again, any comments would be greatly appreciated.
>73 de Ron N4GJV
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