SB-301 bfo adjustment (now is SB-102 S-meter stability)

[Bernie Murphy]

In the SB102, Heathkit did change the S-meter circuit and substituted a 33K 
1 watt resistor instead of the 22K resistor and some other minor changes in 
circuit. The adjustment pot has a very narrow range and I am sure that 
causes some issues as well.

My old  HW-100 that I built in 1967 does not have any problems with the 
S-meter drifting all over the place.

I have been trying to get the S-meter circuit stable the on a pair of SB102s 
and I have yet to swap out the 33K 1 watt resistor. I replaced the 100K 
resistors and the ceramic .02 ufd bypass cap with a mylar .022 cap in the 
screen circuit.  The S-meter still drifts all over the place as the rig 
warms up.  I just put my temperate probe on the 33K resistor and it reads 
around 42 C so there is heat there for sure.

Anyone tried a 2 watt 33K ohm resistor in the circuit on a SB102 to see if 
that cures the S-meter drift issue?

73, Bernie


----- Original Message ----- 
From: "Schichler, Alfred" <ASchichler at MICROWAVEDATA.COM>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Friday, November 17, 2006 9:05 AM
Subject: Re: [HEATH-TEMPE] SB-301 bfo adjustment


> Thanks for the info. The HW-101 BFO frequencies are the same as the 
> SB-301,
> so the BFO mod should work.
> I plan on trying that as soon as I get some free time. I'll check out the
> S-meter stability mod also. That might be applicable to the SB-301, but 
> I'm
> not sure.
>
> Al, WA2AS
>
> -----Original Message-----
> From: W6CUX [mailto:w6cux at earthlink.net]
> Sent: Thursday, November 16, 2006 1:59 PM
> To: Schichler, Alfred
> Cc: HEATH at LISTSERV.TEMPE.GOV
> Subject: Re: [HEATH-TEMPE] SB-301 bfo adjustment
>
> Al,
> Look on pages 7-8 of this document:
> http://members.tripod.com/NRWILLIAMSON/Hw101.pdf
>
> This data is available other places but the one shown was the first one
> I found. The discussion relates to a HW-101 but applies directly to a
> SB-301 BFO.
>
> 73, Stu W6CUX
>
> Schichler, Alfred wrote:
>
>>I know this has been brought up before, but I can't find the information 
>>on
>>changing the BFO frequency to get the same pitch background noise in USB
> and
>>LSB on my SB-301. I was going to fix it a while back, but never got around
>>to it.
>>I think there is a mod that tells you how to do that, like installing a
>>trimmer cap or something like that. The pitch is higher on LSB than on 
>>USB,
>>so I think the BFO frequency might be too low (too far from the filter's
>>center freq on LSB, and too close on USB).
>>
>>Any mods or other info on this would be appreciated.
>>
>>Thanks,
>>Al, WA2AS
>>
>>
>>
>
>
>
>
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