[Hallicrafters] Restoration hints for the SX-24 and SX-25

[WA1KBQ at aol.com]

Good tips here! I sure noticed a reduction in power transformer heat here  
when I started running all my vintage stuff on 110VAC. The other thing that  
really helped is when I bought a Hakko 808 desoldering gun. Makes it a  quick 
easy job to suck the solder out of a joint first to untie legs  attached to a lug 
to get an old capacitor or resistor off without burning  everything up in the 
process. You cannot restore these things and hope to make  money afterwards. 
It is a labor of love; you do it for the sense of  accomplishment and to have 
a properly working piece of equipment for yourself  afterwards. The SX-24 was 
a good next step up from the S-20R but they are far  too common and not 
necessarily in high demand to sell for a lot of money.  Restoring to sell for profit 
is an oxymoron. It's no different in the  antique car hobby where a restored 
car typically sells for about half what the  restoration costs were (except 
for perhaps certain Corvette models in some  cases). 
 
Greg

In a message dated 1/8/2008 9:36:18 A.M. Atlantic Standard Time,  
km1h at jeremy.mv.com writes:
Very good info Mike.

I recently had to walk  a relative novice thru a SX-25 rebuild and it got a 
bit interesting at times  when he got frustrated.

When I was a tech in the National Radio Service  Dept we used to make many of 
our own tools to get into tight places. For the  SX-25 above I heated and 
bent long nose pliers (just like the old days) and  mailed to him. Wire picks 
bent at various angles can be made from steel rod;  coat hangers can be used 
in a pinch but they are brittle and its easy to  break the point. 
Screwdrivers can be compound bent to reach impossible  places to break a 
screw loose.

Hallicrafters transformers are always  at the edge of failure it seems and it 
is due to their design. If you run  one on a Variac you'll see that the 
output voltage becomes non linear right  around 123-125V and the core is into 
full saturation at 130V. Even partial  saturation results in excessive 
temperature.

Ive not seen the need to  send good transformers out, however all Hallis and 
some other brands are run  at 110V with either a Variac controlled bench 
strip or a 12.6V bucking  transformer.

National claimed in the 30's that the HRO could be run at  135-185 VDC with 
full performance if speaker audio wasnt needed. Recent  S+N/N testing has 
confirmed that dropping the AC down to 110V results in a  reduction in 
backround hiss with a resultant better S+N/N. These tests were  on a SX-28, 
SX-9, HQ-129X, and NC-240D. I havent had time to see if it is  the same with 
miniature tubes.

Carl
KM1H
National Radio  1963-69







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