[Heathkit] Re: SB-303 fix up.

[kiyoinc at attglobal.net]

Thanks Glen,

What paint formula or mix do you recommend for SB cabinets? 

Now that I have the SB-303 home, I see that it's in fine shape but was 
owned by a smoker at one time.  The cabinet smells and there is a grey 
film on it.   I desmoked one before by washing the cabinet and wiping 
down the insides with a damp cloth.

This was someone's pride at one time and I will restore it to the best 
of my ability.    It's dates to the 1970's, which makes it about 30 
years old.

Couple odd things about this radio, there's a spinner knob attached to 
the main tuning knob.  It's actually a nice job but I think I have a 
spare Heath main tuning knob.   I got the manual with it.  The manual is 
well worn, no surprise, but it is unmarked.  It looks like the builder 
chose to build without putting check marks in his book.

A fellow sent an off-list email.  Here are my answers to him.

I like playing with Heathkits.  My first transmitter was a DX-60 in 
1963.   I'm not an "expert".  I work on my SB-303's as I have time.  The 
radio was $389 as a box of parts when a dollar was worth something.    
I'm amazed that people let these go for a couple hundred dollars. 

I have one SB-303 that came with 2 SSB filters.  The 2nd filter was 
simply cascaded with the first.  There are no other components, just a 
couple jumper wires.  It works very well.   Signals jump out as you tune 
across the band.   If you tune across a strong carrier, the pitch 
changes and it suddenly drops out.    12 poles of crystal filter sounds 
very good.

In my experience, the electrolytics in the power supply should be 
replaced.  I've seen some dripping white powder.  

Some SB-303's have corrosion on the capacitor shaft contact fingers in 
the LMO.   This sounds like warbling or distortion when you tune across 
a signal.   The voltage of the RF signal varies below spec and the 
waveform jitters on a scope.  I had one that dropped out of oscillation. 

I also had an SB-101, tube LMO, that had a bad capacitor.  This was a 
dog-bone capacitor, where the loop of wire at the end of the ceramic 
tube was not soldered.   The symptom was a very unstable LMO.

The LMO contacts are a bear to get to as you have to disassemble the 
front of the radio to remove the LMO, unsolder it, open the LMO and then 
clean the spring to shaft contacts.  Even with the LMO open, it's not 
easy.    I've used clean cardstock.  I also spray DeOxIt in there.   

I run the LMO on the bench with jumpers to the radio for power.  

Then to put the LMO back in, you have to realign the tuning mechanism as 
part of the reassembly. This takes a hour or more.

The crystal calibrator is dead half the time.  I haven't dug into this 
but I'm guessing the problem is a resistor that's drifted out of spec. 

de ah6gi/4