[Hammarlund] Replacing caps in HQ-129 and others

[Carl]

----- Original Message ----- 
From: "Charles Ochs" <chuckochs at hotmail.com>
To: <hammarlund at mailman.qth.net>
Sent: Tuesday, December 22, 2009 2:06 PM
Subject: [Hammarlund] Replacing caps in HQ-129 and others


>
> 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:


Having been trained by the US Navy as an ET, worked at National Radio as 
Service Tech and Manager and having continued servicing all brands for 
myself and customers for almost 47 years I consider myself a pro. Been a ham 
since 1955 and Extra Class since Incentive Licensing was in effect..
I also have a few comments.


>
>
> 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.


Not a correct statement. Yes all paper caps should be replaced. That 
includes those in plastic and metal as the internal construction is still 
the same and the way they are sealed has very little bearing on the leakage. 
I have NOS caps here sealed in plastic of all brands, sealed in ceramic, and 
Sprague Vitamin Q's sealed in metal and glass. They ALL leak.

Some ceramic disc BYPASS caps of the 50's have been showing up with 
substantial leakage. Some frequency determining ceramic TUBULAR caps have 
gone way out of tolerance or simply failed. I had a real head scratcher some 
months ago in a HRO-60 and anyone familiar with a Collins PTO knows about 
the ceramic cap issue.




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


Those late 1940's to early 60's BBD's and the Bumblebee just happen to be 
the most widely used as well as problematic, they are both Sprague. Solar, 
Sangamo, Goodall, Aerovox, etc, etc are no better now. Some Sangamos were 
known as Pink Firecrackers within 8-10 years of new.



> 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.


We really wont know for another 30-70 or so years. The sealed capacitor 
block in my AC operated 1927 Radiola 18 still shows virtually no leakage. 
The manufacturing process changed soon after to cut costs and it was a 
continuous downhill slide once the beancounters took over. Its no better 
with todays SS offshore crap.


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



Correct but with a big caveat. Always start with the PS and other 
electrolytics. Do not even turn on the radio first as it doesnt take much to 
fry a transformer. Then replace all paper caps in the audio output stage, 
typically only 1-3 in most sets; this now offers protection to the audio 
output transformer. If the set has a driver transformer replace those in 
association with the driver tube also. Also replace the AC line bypass caps 
so you dont get zapped.

Now you are ready to turn on the radio; there are several ways, pick the one 
you want but this is my procedure. Remove all the tubes and plug the line 
cord (replace if it needs it, a 3 wire is a good idea) into a Variac set at 
0V or dim bulb tester (a 100W lamp in series with one side of the line 
cord). Turn on the power and slowly bring up the Variac to 115V. If no loud 
noises from the transformer (shut off if its humming) measure the B+ AC at 
the rectifier socket; it will be a bit higher than the voltage chart if OK. 
The dim bulb will stay dim if OK and light brightly if there is a short.  I 
wont get into the AC/DC sets here.

Turn off and now plug in the rectifier and audio output tube(s) to provide a 
small load. Bring it up with the Variac or bulb and measure the DC, it will 
also be a little high but not over the electrolytic ratings if you used the 
proper voltage ratings.

Turn off and plug in all the other tubes, hook up a speaker, turn on and set 
the controls for normal use on the lowest band available. You should now 
have at least some hiss out of the speaker. Hook up an antenna, even a 
10-20' hunk of wire should be OK. If you now have typical band noise or even 
BC stations (probably distorted) you now have the beginnings of a good 
radio.

If there are no signals then trouble shoot for a cold tube, open IF can 
coil, etc. I wont get to that level here, follow the schematic and work your 
way out to the antenna. Some minimal test equipment is required; thats a 
whole other subject.

Assuming you have some sort of signal then proceed changing the other papers 
caps THREE AT A TIME starting at the last audio stage you already worked on 
and proceeding toward the antenna, and then turn on the radio. There may be 
no improvement yet but hopefully its not worse; even pros make mistakes.

There is absoluely no benefit to using Orange Drops in any circuit no matter 
what the mythmakers try and force down your throat. Their radial leads are 
also a poor form factor in many sets as well as take up excessive space. 
Modern disc ceramic caps make better bypasses at RF/IF ( A few exceptions in 
early 1930's sets exist but a vey easy fix will solve any oscillation with 
discs and the end result is a much better performer) and are also applicable 
in low level audio and AGC circuits. There are small 400 & 630V axial lead 
tubular film caps (several colors available) that can be used anywhere and 
at high level audio. The smaller caps of either type make for a neater and 
less crowded chassis. Watch for paper caps used across output transformers 
and usually rated at 1KV or more, use the same or a larger voltage rating.



> Check ALL of the micas that look like chicklets.


Micamold was the largest maker of paper caps in what look like mica cases 
(often referred to as lozenge shaped) but there are others. Any value of 
.005uF and higher has a good chance to be paper; always refer to the 
schematic and parts list. If values dont agree it may be a production change 
or an earlier repair. When in doubt ask questions.


>
> 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.


Wholesale shotgunning of all the micas is a poor idea and not one used by 
the pros. We call that a hack job especially since several manufacturers 
used custom values and this can turn into a major alignment problem. While 
micas are showing failures as they age it is almost always with ones that 
have a 100V or more DC voltage on them.

While a digital capacitor meter can help at times it is an expense to be 
considered if you are only planning on working on one radio, it will not 
find a leaky mica.  A megger is a wasted expense for a radio, Ive never used 
one except on a feedline.

A vintage capacitor TESTER such as a Solar, Sprague and others is fine for 
evaluating micas at their marked operating voltage. Sort of  pricey for a 
good one with a meter and I use a 1941 Solar that had to be recapped first. 
Ive never used one of the cheap ones that use an eye tube like Heathkit so 
cant comment on their usefulness.


>
> 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!



AMEN, and toss in the SX-42. The SX-28 is one radio where it may pay to 
replace some micas; it is the only radio that Ive found problems in the 
front end but its also only about 3-4 micas out of a few dozen radios. The 
trimmer caps are more of a problem by far. Its a judgement call and Ive 
minimized it to just the micas that have shown a history here. I also have a 
1 year warranty on my work.


>
>
>
> 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.


As mentioned earlier in this thread www.hayseedhamfest.com has replacement 
can caps for many radios. Otherwise use new tubular caps either under the 
chassis or restuff the old can; stay FAR away from no name caps found at 
hamfests and antique radio meets; pure Chinese crap. Always buy from a well 
known distributor such as Mouser and stop trying to save pennies. Reforming 
used and most vintage NOS electrolytics and expecting them to last is 
another myth. The internal damage is already done, and eventual failure when 
you least expect it is a given comparable to death and taxes. Spend the 
money.


>
>
> 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.


Yep, that era Nationals including the NC series used resistors that are 
really a problem now. Ive had several screen droppers measuring in the 
megohms. National in those years was run by beancounters of the worse kind. 
Some Hallicrafters are not much better; Ive spent days in SX-42's and 62's 
with caps & resistors. Use at least a 1/2W film for replacement even if the 
parts list says 1/4W. The new ones are much smaller and they dont handle 
overloads as well as the carbon composition. Use a 3W MOX in place of a 2W 
carbon.  Note that many resistors can not be checked in circuit as multiple 
paths exist; one lead has to be lifted.




> 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.


Which may not agree with the radio, Halli in particular is great for this. 
Many of the others serialized or referenced a production run on their 
manuals and it pays to have the manual that matches the radio. Other times 
its a shrug and proceed and take notes.

Some schematics are horrible, even the originals. I take those to Staples 
and have them digitized and blown up and then they are very satisfactory. 
Price is very cheap, about $3 for a complete SX-62 manual for instance.



> 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.


Yes and no. Some socket pins and switch contacts break very easy and then 
you may be in deep doo doo. I use a solder sucker and a pointed solderaid to 
carefully open a hole big enough to pass the new lead in sets that I know 
are problematic. Sometimes you can just push the new lead thru a heated 
terminal. Pigtails and hook wraps look so schlokky (is that a new word?) 
typical of the old radio/TV repair shop hack that was repairing Army motor 
pool trucks 2 weeks earlier.



>
>
>
> 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.
>


Absolutely! Ive found mislabled components 50 years ago as well as recently. 
Even in sets that were supposedly working well from new. Replace the 
component and then redefine "as new" when it really comes to life with a 47K 
screen dropper instead of the orignal 470K well marked as 47K. The manuals 
voltage and resistance charts are your best friend.



>
>
> 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.


Here I agree 100%

Carl
KM1H
National Radio 1963-69
Servicing all brands today.




> Chuck N1LNH
>
> East Bridgewater MA
>
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