[Hallicrafters] Recapping

[GARDGORE at aol.com]

Unless you really know what you are doing I would advise against wholesale 
capacitor replacement. I have personally seen receivers that were recapped that 
never worked quite right afterwards and were put up for sale by frustrated 
inexperienced owners. If correct alignment means sweep generators and 
oscilloscopes to you then you know what I mean. If you don't have the technical 
experience yet you can probably still fix your newly acquired receiver and get it 
working fairly well without making a huge project out of it. Not all capacitors are 
actually critical. You can fix 90% of capacitor problems by paying attention 
to the coupling caps and the plate and screen bypass caps. It is recommended 
to perform a good careful visual inspection on the entire circuit as part of 
your check list procedure first before applying power. Caps that are leaky and 
have high voltage on them will usually show signs in their outward physical 
appearance, i.e., cracked or split tubes, leaking oil or dripping wax, bubbles on 
the outside or overheated or charred resistor nearby. Before starting any 
work on a newly acquired receiver try to get the set at least somewhat working 
(if possible) to establish some sort of a base line. I'm assuming here that the 
filter cap has been addressed first, this is important. Measure tube pin 
voltages and compare to the manual or a chart for your particular unit to assess 
its overall health. Any voltage reading (using the recommended "ohms per volt" 
meter) that is more than 20% off probably indicates a problem on that circuit. 
Pay close attention to the coupling caps. You don't want B+ on the control 
grids, they are supposed to be negative with respect to the cathode. Sometimes a 
red flag to this condition can be observed when you have a tube that quickly 
gets hotter than the others or hotter than it should. I'm not talking about 
rectifiers and output tubes here, they're always hot. I'm talking about say a 
lineup of 6BA6 or 6SK7 IF amplifiers and one runs hotter than it should for some 
reason or runs much hotter than the others of that particular type. It takes 
experience to recognize this sometimes but I always like to check the running 
heat from transformers and some tubes with my hand from time to time to catch a 
failure as early as possible. I have too many receivers to recap them all and 
I like to rotate them around from time to time and enjoy using them all. I 
have adopted the above procedure which is a good compromise to keep them all 
operating, to have time to play with them all and help keep them more original 
which is really important to me personally.

Regards, Greg

PS- The filter caps do not necessarily always need to be replaced. If they 
pass the leakage test under the recommended current in milliamperes at the full 
rated voltage then they are OK for now. Generally speaking for the usual size 
filter caps I look for a leakage under 2 mills for stuff made in the Forties 
through the Sixties. Newer stuff should leak under a milI and sometimes stuff 
made in the Thirties will leak over 5 or 6 and still be good. I know I am 
taking a chance here and I don't recommend this for everyone but my goal is to stay 
with the original when possible to keep the history intact and this is done 
only after careful testing to be sure it is safe to apply power. If you are 
inexperienced and not sure how to test and evaluate filter caps and lack the 
proper testing equipment then yes, they should always be replaced with newly 
manufactured parts to be safe. I am assuming some risk with the way I do it but I 
also keep a close watch on everything when it is running. Kind of like driving 
a 1936 Ford around with the original type brakes when retrofit modern 
hydraulic brakes would be safer. There's a kind of thrill that comes from messing 
around with antiques that the average person just wouldn't do I guess.