Heath SB-102 balanced modulator question

Heath SB-102 balanced modulator question

Post by bruc » Tue, 23 Jan 2001 06:23:49

The SB-102 uses 4 1N191 Germanium diodes in a ring type balanced
modulator. Do these diodes need to be matched?

The symptoms:  I am seeing 2 problems that may be related. One is that
the carrier null trimmer capacitor has no effect; the carrier null pot
does null the carrier when turned way to one side. The other symptom is
that LSB is about 45 watts out while USB is about 100. There are only a
handful of parts in the balanced modulator. Replacing all of them, with
the exception of the trimmer, may be the way to go. Any suggestions?

Thanks,
Bruce N9BH

 
 
 

Heath SB-102 balanced modulator question

Post by Bob Weis » Wed, 24 Jan 2001 10:17:02


Yes, they should really be replaced with a matched quad. Unfortunately,
matched quads may be hard to come by unless you have a large stock you can
choose from.

I replaced the ones in my SB-102 (had similar problems) with 2 matched
pairs from the same production lot.  Sold as NTE type 110MP,  these are Ge
matched pairs intended for use in TV horizontal AFC circuits, and the 2
pairs all tested the same for forward voltage drop. Rig worked FB after
replacement.

Good luck and 73,
Bob Weiss N2IXK


> The SB-102 uses 4 1N191 Germanium diodes in a ring type balanced
> modulator. Do these diodes need to be matched?

> The symptoms:  I am seeing 2 problems that may be related. One is that
> the carrier null trimmer capacitor has no effect; the carrier null pot
> does null the carrier when turned way to one side. The other symptom is
> that LSB is about 45 watts out while USB is about 100. There are only a
> handful of parts in the balanced modulator. Replacing all of them, with
> the exception of the trimmer, may be the way to go. Any suggestions?

> Thanks,
> Bruce N9BH

 
 
 

Heath SB-102 balanced modulator question

Post by Joe » Wed, 24 Jan 2001 11:16:50

The carrier null pot's are usually all shot in all them sets.
Regarding the diodes you can buy 3 dozen 191's cheap at Radio Shack and
match em up on a DVM.
Them set a very picky about V5 and in V7 .....Westinghouse 6CL6's do not
work well

>Yes, they should really be replaced with a matched quad. Unfortunately,
>matched quads may be hard to come by unless you have a large stock you can
>choose from.

>I replaced the ones in my SB-102 (had similar problems) with 2 matched
>pairs from the same production lot.  Sold as NTE type 110MP,  these are Ge
>matched pairs intended for use in TV horizontal AFC circuits, and the 2
>pairs all tested the same for forward voltage drop. Rig worked FB after
>replacement.

>Good luck and 73,
>Bob Weiss N2IXK


>> The SB-102 uses 4 1N191 Germanium diodes in a ring type balanced
>> modulator. Do these diodes need to be matched?

>> The symptoms:  I am seeing 2 problems that may be related. One is that
>> the carrier null trimmer capacitor has no effect; the carrier null pot
>> does null the carrier when turned way to one side. The other symptom is
>> that LSB is about 45 watts out while USB is about 100. There are only a
>> handful of parts in the balanced modulator. Replacing all of them, with
>> the exception of the trimmer, may be the way to go. Any suggestions?

>> Thanks,
>> Bruce N9BH