[Central-Electronics] 100V AF phase shifter

[Jim candela]

Bob,

  I looked up the service manual for the 100V on Bama (thanks George), and
in there are a number of reasons the SB rejection may go bad. I am pasting
what CE says on the subject below:


>From 100V service manual on Bama:

SIDEBAND SUPPRESSION
Poor sideband suppression is generally caused by "open" 6 mfd. 50V
electrolytic capacitors in the plug-in MOD CAPS assembly.
If the modulator capacitors appear to be good, remove the PS-2 and take off
the cover. Using a long nose pliers, gently pull on the leads from the mica
capacitors that go to the board. During the original soldering process, the
hot wax from the capacitor case will run down the wire leads to the board,
and result in a poor connection.
This treatment should also be applied to the leads that go into the 9 prong
plug to see that the connections are properly soldered,
Early lOOV's used 3900 ohm, 1 watt, 5% resistors in the plate circuit of
V10, the 12BH7, R146 and R149. These are generally located underneath the
12BH7 socket, with one end tied to the center shield. If the case is
discolored on the resistors, check their value and replace with 2 watt, 5%,
if necessary.



  I wonder about that PS-2 as well, and after looking it over, I notice that
this is much more complex than the 20A version. That said, the function is
the same. I'd be tempted to inject a 1 khz sine wave tone, and with a decent
dual trace scope with matched and compensated 10X probes, look at the phase
A and phase B outputs on a scope in X:Y mode. Ideally you will see a nice
circle, and if not attempt adjustment of the AF balance and AF ratio pots
until you do. With my 20A perspective this gets you close, and the final
tweaks are done when minimizing RF output carrier ripple. You can also do
this in conventional scope mode looking for 90 degree phase shift. This is
delicate to intrepret and easier with scopes with adjustable cursers on the
CRT display. Using a clean external sourced sine wave from 200hz to 5 khz is
also useful to fully evaluate the audio phase shifter. Do you know what the
audio range is where the 100V phase shifter maintains 90 degrees phase shift
accuracy?

On the 20a I have also used the dual trace scope to look at the 9.000mc RF
phase shifter where I can get pretty close asumming the probes have very low
capacity loading (sometimes I solder two 5pf caps into circuit with the
other lead as a connection point for scope probe).


Jim
WD5JKO

-----Original Message-----
From: central-electronics-bounces at mailman.qth.net
[mailto:central-electronics-bounces at mailman.qth.net]On Behalf Of Bob
Sullivan
Sent: Sunday, December 03, 2006 8:13 AM
To: Dennis Petrich; 'K6JEK'; central-electronics at mailman.qth.net
Subject: RE: [Central-Electronics] 100V AF phase shifter


I wish it were true but those little LCR meters - which are wonderful for
many applications - are not very accurate. For example the little Tenma (a
bit more than $100) has measurement accuracy of around +/- .75 to 1%!

73, Bob
WØYVA
Personal site: http://www.isquare.com/personal_pages/ras-hardware.htm


At 07:13 AM 12/3/2006, Dennis Petrich wrote:
>You should be able to use one of those hand held LC meters available these
>days for <$100 bucks....
>
>-----Original Message-----
>From: K6JEK [mailto:k6jek at comcast.net]
>Sent: Friday, December 01, 2006 11:42 PM
>To: central-electronics at mailman.qth.net
>Cc: Bob Sullivan
>Subject: Re: [Central-Electronics] 100V AF phase shifter
>
>
>Bob,
>
>I  took the liberty of posting your response to the reflector since
>others seem to be interested.   That's about what I expected --
>calibrated lab grade equipment.   I'm heartened to hear that the PS-2
>isn't likely the problem.
>
>I'm actually in procrastination mode.   I seem to have lousy opposite
>side band suppression.   I'm thinking about the problem rather than
>doing anything about it -- avoiding hoisting the 100V from the
>operating position to the work bench.   Hoisting is next.
>
>Thanks,
>
>Jon, K6JEK
>
>On Dec 1, 2006, at 6:44 PM, Bob Sullivan wrote:
>
> > Jon,
> >
> > I do a lot of 100V/200V restoration work and infrequently the PS-2
> > requires attention. Most hams don't have the equipment to measure to
> > that accuracy which requires a high-end LCR meter or bridge that has
> > been calibrated. An example would be the GenRad Model 1692. The
> > (fairly) good news is that older versions that sold for 10K and up are
> > now available for a fraction of that cost.
> >
> > When was the last time you sent a piece of test equipment to a
> > calibration lab? Hi.
> >
> > 73, Bob
> > WØYVA
> > Personal site: http://www.isquare.com/personal_pages/ras-hardware.htm
> >
> >
> >
> > At 09:05 PM 12/1/2006, you wrote:
> >> How do you work on the audio phase shift module?   It's full of
> >> resistors and capacitors "bridged to within .1%"   How do you measure
> >> capacitors and resistors that accurately?
> >>
> >> Jon, K6JEK`
> >>
> >> _______________________________________________
> >> Central-Electronics mailing list
> >> Central-Electronics at mailman.qth.net
> >> http://mailman.qth.net/mailman/listinfo/central-electronics
> >>
> >
>
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