[Hallicrafters] SX-101A Converter Subchassis

[Roy Morgan]

0..
On Dec 8, 2008, at 6:48 PM, Mark K3MSB wrote:
> 1)  T2 and T5 contain a pair of 300 pf and 390 pf caps respectively;
> I assume they're 10% 500V Silver Mica caps.

Get new caps at a good price from justradios.com in Canada.

> 2) C206 is a 2.2 pf 10% ceramic.  I don't expect this to be bad;  Is
> this one of those "dog bone" type caps?

It could well be a dog bone, or the ceramic tubular ones that have a  
hole down the middle.  I have found two of these type caps (very low  
value) in Halli radios over the last year or two.  Though I have not  
looked up the function of C206 in the SX-101, I'm guessing that it's a  
coupling cap between two tuned circuits.  If so, one end is at B+ and  
the other end is at a grid (and may have AGC applied to it).  Sooo..if  
this seemingly innocent cap fails, it can take out the B+ dropping/ 
isolating resistor feeding the plate, and possibly apply B+ to the AGC  
line, or the grid of the next tube in line.

I suggest you replace it.

Roy

> ...  I still need to do the filter switch caps and
> the subchassis.

You may mean the bandwidth switch.  On the subchassis: tag all the  
wires you have to remove, make notes about their locations and routes,  
and if you like, solder long wires to their ends that get pulled along  
the original route of the lead as you pull the subchassis out.

Replace all components in the subchassis.  you would not be happy if  
one of the caps in there turns out to be leaky after you get the whole  
thing back in place, or if after a few hours of operation a resistor  
rises in value.

> The radio decides to change frequency every now and then, and I can
> typically "make it better" by changing the mode switch back and forth
> a few times.

This often happens if the tuning cap (or bandspread cap) have dirty  
rotor wipers.  Carefully apply a drop of De Oxit (or whatever they  
have changed the name to now) to each and every wiper contact point.

Roy

Roy Morgan
k1lky at earthlink.net
529 Cobb St.
Groton NY, 13073