[Hammarlund] Replacing caps in HQ-129 and others

[Charles Ochs]

Hello all. 

Picked up the conversation about bad caps in an HQ-129, and have some advice-for what it's worth. 

Here is how the pros do it:

 

You should assume that any radio made prior to the early 1960's will have ALL bad capacitors, even if, at first, things appear otherwise. After that, makers turned to ceramic caps to a large extent, and these seldom cause problems and should NOT be randomly replaced (such as those found in HQ-180s). Going back a little further in time we find radios like the Heath Mohawk(1958) that use paper caps that have better plastic, and are probably OK, but at least should be TESTED.

Before this point in time, we have the infamous "Black Beauties of Death" and most of us know what that means!

 

The capacitors being manufactured today FAR surpass their earlier counterparts, and with careful selection, it is often possible to "improve" the operation on boat-anchor radios, particularly in the "stability" and "drift" areas.

 

ALWAYS replace ALL of the old "paper" capacitors, whatever they look like, and whatever condition they APPEAR to be in. 

 

Check ALL of the micas that look like chicklets. 

Own a reliable (digital) capacitor meter, or have some other instrument on your bench that you can trust. Mica capacitors should  ALWAYS be checked for both capacitance AND breakdown voltage. For this, you will need a megger, like a hand-cranked Biddle, or an electronic megohmmeter, such as a General Radio, or a Freed. Often, it will be a better use of your time to just go ahead and replace them. Use NEW silver-micas. 

If you  are into the front end a particularly difficult radio, such as a Halli SX-28, or SX-62, just replace them ALL as quickly as you can, and move on. You will REALLY be wasting your time if you have to go back in there again! 

 

Electrolytics require a somewhat different approach. Small electrolytics should be treated like "papers". Just replace them-period. Can types are very hard to find (and expensive) these days, although AES has many in stock. These should be tested in the radio, and often they will be found to be OK. Re-forming may be necessary, and the ones that are OK will, most likely, continue to be so,  as long as the radio is used periodically. Often a judgement call is required here.

 

Resistors are a somewhat different matter. Own a decent digital multi-meter. Check ALL resistors and replace those that have risen over their specified tollerance ( 5-10-20%). In some cases, such as grid bias resistors in PP audio stages, try for tighter tollerances. It is often more important that they be MATCHED, rather than their exact value be correct. Some radios, such as National HRO-50s and 60s, will require nearly ALL of their resistors replaced. This is not a reflection on the radio, but rather the resistor manufacturer, in most cases.

 

Have the schematic with you on the bench, and, as you move along, check what is on the schematic with what you see in front of you. Be VERY suspicious of any previous repairs / parts changes. You can not know what a previous tech was up to, and these parts may not be correct, or even wired up properly. Again-use your schematic, and the parts list. 

 

Always remove ALL of the old part leads from the tie points. Doing otherwise is simply sloppy work, and will often come back to bite you with intermittant connections, solder bridges etc.

 

One other thing: Do NOT assume that, just because a component is new, that it works as it should. Always test new capacitors and resistors BEFORE installation. The small additional time that this takes will pay for itself in reliability of operation, and confidence in your work.

 

Restoring boat-anchors is a very time consuming operation, and requires skill, patience, and good practices regarding testing, soldering etc. I restore radios for a living, and have been doing it for decades. Long ago I learned that the time invested in this approach pays off very well, and there is nothing like the feeling that you get when you flip the switch, and EVERYTHING works as it should. If this approach is NOT followed, you will pay dearly with time wasted chasing down nasty little problems, such as those mentioned.

Do it right, do it once. Move on and enjoy your radio.

 

Chuck N1LNH

East Bridgewater MA