[Fwd: [Hallicrafters] sx 100]

[Gerry Steffens]

I agree with Mark's comments almost 100%.

However, one caution:  If indicated (and many times it is) it is best to
use the equivalent input impedance meter to check voltages as was
originally used.  Frequently older equipment voltage specifications will
include the input Z of the equipment used to gather the information.  I
have many pieces of service data gathered with as little as 1000 ohms
per volt equipment.  On sensitive circuits, using higher Z equipment can
yield considerably higher voltages than specified.  This can yield much
time consumed chasing high voltages when the only real problem is the
added loading of the original test equipment causing the specifications
to be lower.

Many times VTVMs were not used on original equipment specs.  I have
gathered a set of test meters at various sensitivities for use in
servicing (1000, 5000, 10000, 20000 and extremely high Z ohms per volt)
to avoid false high or sometimes in rare occasions low voltages.

Gerry


Collecting & Restoring E.H. Scott, 
McMurdo Silver, Hallicrafters, Zenith 
Transoceanic and any other interesting, 
radios since 1959
Gerald Steffens P.E.
Oronoco, MN


-----Original Message-----
From: hallicrafters-admin at mailman.qth.net
[mailto:hallicrafters-admin at mailman.qth.net] On Behalf Of Mark V.
Johnson
Sent: Saturday, December 27, 2003 11:15 AM
To: hallicrafters at mailman.qth.net
Subject: [Fwd: [Hallicrafters] sx 100]

With regards to Jerry's msg re: SX-100 and being new to restoration. 
Thought I'd offer my thoughts.  

We all have developed techniques for bringing old sets back to life. I'd

suggest that a shot gun approach to replacing all caps may not be the 
best as a start point. Frankly, I'm  against replacing parts unless 
necessary. I've just  spent  the last few weeks working on 3 pieces of 
old gear where the caps where  all replaced and  in all three cases the 
old caps where just clipped out and new ones tacked soldered in place. 
Some where the wrong values, some had the polarity incorrect and some 
where installed in the wrong points  and  provided me with the chance to

do further bug shooting.
Here is what works for me: 1) Vacuum the piece out and clean as much as 
possible. 2) Carefully re-tighten ALL screws and nuts. Its amazing what 
this will fix. 3) Check tubes with a good quality tube tester and if a 
tube shows weak, compare it  (in the tester) against a known New Old 
Stock tube. If there's a big difference, replace the weak tube. 4) Apply

power as per your prefered method (Variac, full on at once, whatever). 
Take note of what works and what does not. 4) With the aid of the 
manual, (Don't be cheap, get the entire manual either original or copy. 
Its worth it. You have to be a real pro to work just from the schematic.

Schematics don't help with alignment, theory of op's, circuit 
descriptions,  and operation) check all voltages using a hi input VTVM. 
Any voltages out of  spec by at max 20%, chase down why. In all 
likelihood, a resistor has changed value. 6) Once all voltages are good,

start bug shooting your problems. 7) Perform the alignment using a VTVM 
and signal generator.

 By the way, I've replaced more out of spec resistors than I have 
capacitors over the time I've been working on old gear.

Just thought I'd offer my thoughts.

Thanks to the List members.

Mark V. Johnson VE3DJU/VE3DDI

-------- Original Message --------








hi everyone. i have a sx 100 , that needs recapping. i have had this
radio for about 10 years. 
i got it from my uncle ,now sk.  it works very little. low audio, etc. i
want to start
with replacing the caps.




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