[Boatanchors] Re SX-130 question

John Kolb jlkolb at jlkolb.cts.com
Wed Feb 1 22:18:27 EST 2012

As usual, I'm shooting from the hip at an rx I know nothing 
about  :)   I could at least looked it
up in the Dachis book and seen the product detector.  Looks like the 
SX-130 was the SX99
with a new dress.

One would think that if turning down the RF gain cleared up the 
distortion, that the problem
is the ratio of the IF and BFO signals.  BFO output could be too low 
or the IF output too high.
Maybe one of the caps in the 10 to 1 cap divider mentioned elsewhere 
bad - even possibly
the rx connected to a super antenna system with lots of gain.

The set can be tested for microphonics by turning up the audio gain 
to cause it,
or use headphones to absolutely prevent it.


At 06:08 AM 2/1/2012, Bill Fuqua wrote:

>   It does have a product detector however, the bias on the tube 
> seems a bit strange.
>Perhaps it is to reduce the gain so that AM and SSB reception audio 
>levels are about the
>same. The screen voltage is about 24 volts and plate about 65V. 
>Perhaps the product
>detector is being driven by the IF signal. 6BE6 pentagrid converter 
>tubes were primarily
>intended for low level mixing, not high level and  have considerable 
>conversion gain.
>Bill wa4lav
>At 03:05 AM 2/1/2012 -0500, John Kolb wrote:
>>This is common to most (all?) receivers which do not have a product
>>detector for SSB but simply
>>add a BFO signal to the IF signal going into the AM detector.  This
>>is true even of the R-390 receiver.
>>For the BFO signal to replace the missing carrier of the SSB signal,
>>it needs to be much stronger than
>>the SSB signal components.  If the SSB signal is strong, the BFO may
>>not be enough stronger to
>>serve as a carrier.  In this case, turning down the RF Gain reduces
>>the SSB signal to a proper level
>>to work with the BFO signal.
>>With the RF gain turned down, the AGC will probably be less
>>effective, so constant adjustments
>>of it may be necessary (riding the gain).
>>At 08:49 PM 1/31/2012, Ron Barlow wrote:
>> >Many thanks to all who replied to my request for info on the SX-130.
>> >The owner (a member of the Hallicrafters mailing list) states that
>> >the RF gain control must be reduced to obtain good copy on SSB. He
>> >states that if the RF gain control is advanced, the audio distortion
>> >becomes severe.
>> >  He asks if this situation, is normal, for this particular receiver.
>> >  He sent along a copy of the owners manual, which states that
>> > "under certain conditions, it may be found advantageous to reduce
>> > the RF GAIN setting for improved reception." Judging from the
>> > owners description, his receiver seems to require a great deal more
>> > attention, to the RF gain control, than the owners manual suggests.
>> >  Unfortunately, I do not have access to the receiver, and I have
>> > never operated an SX-130. Therefore, I am not in a good position to
>> > judge whether his receiver is operating normally. Any and all
>> > advice is greatly appreciated, and I will forward it to the owner
>> > of the receiver.
>> >                                        Many thanks & 73 de Ron  N4GJV
>> >
>>Boatanchors mailing list
>>Boatanchors at puck.nether.net

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