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Hammarlund Restoration - Capacitor Selection




 
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Author Topic: Hammarlund Restoration - Capacitor Selection  (Read 3813 times)
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aa5wg
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« on: October 16, 2014, 08:36:08 PM »

Hello to all,

I have a physically nice Hammarlund HQ-170A-VHF that needs to have the capacitors and some resistors and switches/variable potentiometers replaced.

I am very picky about this radio and what to use the very best replacement components from the best/reliable suppliers.

What type and make of capacitors, resistors and potentiometers should I use?

Thanks to all in advance.

73,
Chuck

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N8ETQ
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Mort


« Reply #1 on: October 16, 2014, 09:39:15 PM »



    Tom has what you need..

http://hayseedhamfest.com/hq170_a__180_a_recap_kit_260936940.html

    Maybe yours is different but I thought all the small caps
in those were disc's, very reliable.

    These guys will have everything else.

https://tubedepot.com/

GL

/Dan
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WBear2GCR
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« Reply #2 on: October 17, 2014, 12:05:35 AM »

Resistors are a good question. Depends on the power rating. You can still get carbon comps, but for 1w-5w carbon film resistors are imo a good bet.

Although it is not often mentioned, resistors can have a voltage rating. Good idea to look, and also notice how much voltage is likely to appear across it based on where it is in the circuit. For example a cathode resistor will not see much voltage, usually.

I have read but do not know how true it is that they are preferable, but apparently many who restore these radios prefer ceramic caps. You want NPO type unless spec'd other wise, and the higher the voltage rating the better.

Pots are tricky. Some of the older ones had a different range of rotation compared to the typical pot available now. I'd try to not replace any pots unless they are hopelessly bad. The usual solution is one of the Caig products - the black and red can, can't recall the name on the can right now - not the "gold"... ah, DeOxit. That's it. Also pots today have become pricey. Then too it is difficult to know what the taper might be... so that has to be determined.

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_-_- bear WB2GCR                   http://www.bearlabs.com
KC4VWU
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« Reply #3 on: October 17, 2014, 01:16:39 PM »

I agree with Bear, replace only what needs replacement. Check your replacement parts before you put them in circuit; could save a lot of grief later. Potentiometers are certainly replaceable, but I've found that mostly all can be gingerly coaxed back into good repair with a little effort. I'm not advocating the "rejuvenate the electrolytic cap" theory by any means, but some things are worth trying to repair, rather than replace.

IMO, a rx like that, which was manufactured in the more modern era of tube technology, deserves a focus more towards performance rather than the restoration "correctness" of internal passive parts. Sticking with any service bulletins for factory suggested upgrades and avoiding any senseless mods or drilling and blasting, go to Mouser and order up. One word of advice, don't be in no hurry, and check your work often. That one probably has very few, if any, wax paper caps though since Hammarlund was well known to use ceramics for bypass and coupling around that period.

73, Phil   
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aa5wg
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« Reply #4 on: October 19, 2014, 08:18:19 AM »

Bear, Dan, Phil and all,

What about orange drops vs. yellow drops?

Thank you for your earlier comments.

Chuck
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KC4VWU
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« Reply #5 on: October 19, 2014, 03:33:08 PM »

Hi Chuck,
              The way I see it there are a couple:
1. Aesthetics,  the color of the caps and the fact that the orange drops are a bit bulkier than the yellow polypropylene. The leads are oriented differently, in which one may lend itself better to positioning than the other. If you'll do a little digging, I believe someone on this board had posted a good tutorial on how to distinguish the "banded" foil end for replacement caps. Please don't crucify me for this, but I don't. and I haven't ran into any troubles thus far; but it may bite me in the future (knock on wood).
2. Cost, besides buying used black beauties for that "vintage sound", a lot of the music crowd loves orange drops, so quite naturally their popular and pricey. CDE made the exact same caps that were a dark brown, chocolate drops if you will, and I've found them to be a lot more affordable. You can find polypropylene cap assortment kits very reasonably priced.
     In the long run, it sound like you'll be keeping the rx for a long time, so I'd say use good name brand replacements, use plenty of solder wick and be gentle removing the old caps, take your time, and have fun reviving an old friend.

73, Phil
           
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WBear2GCR
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« Reply #6 on: October 19, 2014, 07:37:37 PM »

In the RF areas where there were molded mica, I have been reading that people prefer the better quality ceramic caps.

For larger coupling caps, I doubt that you'd find any difference between mylar and polypropylene caps. Mylar (polyester) caps costing less. Polypropylene giving slightly better specs. Higher voltage rating always being a better choice, no matter what the cap. In tube rigs, temperature rating, if there is one might be a deciding factor on which to pick.

In general I'd pretty much ignore what the guitar amp folks prefer as far as parts preferences. Most of that is based on tradition/superstition. I'm hooked up with over 200 full time techs in that business, and pretty much every one of them to a man would tell you the same thing - assuming they were not posturing for some reason.

Orange drops, yellow, hey I have some in white! Are they any good?  Wink

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aa5wg
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« Reply #7 on: October 19, 2014, 09:55:22 PM »

Phil, Bear and all,

I recently found this radio and plan on keeping it a LONG time.
It was my Novice receiver back in 1974.

I have been a ham for years but this is my first restoration.
It has been to many years to know the pros and cons of
various capacitor types.  This is why I am asking for help.

If there is a different type of capacitor that would do better
electrically and/or mechanically or temperature wise then I
need to learn the differences. 

i.e. If the radio used a disk ceramic is there a better choice than
disk ceramic?  If the radio used a mica capacitor is there a better
choice than mica, etc.

Again, guys I appreciate your teaching me about capacitor selection.

Chuck
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