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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Mon 26, 2018 6:21 pm 
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A lot of the criticism about replacing caps centers on the fact that people don't understand the entire process, meaning the steps that must occur before the caps get replaced.

This includes a whole battery of tests to confirm that major components like transformers are good and that the set can likely be restored with reasonable cost and effort.

Only then does the actual recap begin.

- Leigh

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Mon 26, 2018 6:28 pm 
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processhead wrote:

For the beginning collector/restorer, I suggest replacing only the capacitors that have the potential to damage a set or present a safety hazard.

Paul old boy, how would a beginner know which caps those are?

Assuming you are referring to just Electrolytic's, I would have to disagree. ALL original caps, beyond mica's, should hit the waste basket, unless they are going to be restuffed.

Leigh wrote:
A lot of the criticism about replacing caps centers on the fact that people don't understand the entire process, meaning the steps that must occur before the caps get replaced.

This includes a whole battery of tests to confirm that major components like transformers are good and that the set can likely be restored with reasonable cost and effort.

Only then does the actual recap begin.

- Leigh

With respect, I think a post like this would scare newbies away. For the garden variety AA5, what's to test before recapping at least the filter caps? There are generally no irreplaceable or expensive parts in these circuits.

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Mon 26, 2018 6:56 pm 
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fifties wrote:
For the garden variety AA5, what's to test before recapping at least the filter caps?

This thread is not limited to repairing AA5 radios.
The thread title is: "Public obsession with replacing capacitors" in any radio.

You're trying to limit the discussion because your general approach is so obviously wrong.

As with any set, you check all coils, transformers, and controls before proceeding.
And check the tuning capacitor to make sure the plates are not shorted or deformed.

- Leigh

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Mon 26, 2018 8:33 pm 
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fifties wrote:
processhead wrote:

For the beginning collector/restorer, I suggest replacing only the capacitors that have the potential to damage a set or present a safety hazard.

Paul old boy, how would a beginner know which caps those are?

Assuming you are referring to just Electrolytic's, I would have to disagree. ALL original caps, beyond mica's, should hit the waste basket, unless they are going to be restuffed.


Perhaps I should have been more clear. I fully agree with replacing all electrolytic and wax paper capacitors.

The point I was trying to make concerned a novice tech replacing all caps at one time before applying power vs. replacing filter caps and grid coupling prior to initial powering up.

A novice who undertakes major rewiring and replacement of all caps can make mistakes that are difficult to back track and correct.

Getting the set up and running, and then replacing 2-3 caps at a time and retesting, provides an opportunity to locate potential wiring errors at each power test interval.

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Mon 26, 2018 8:35 pm 
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Leigh wrote:
fifties wrote:
For the garden variety AA5, what's to test before recapping at least the filter caps?

This thread is not limited to repairing AA5 radios.
The thread title is: "Public obsession with replacing capacitors" in any radio.

You're trying to limit the discussion because your general approach is so obviously wrong.

It's obvious to me that it ain't wrong, 'cause I've been doing it for umpteen years with NP.

And I'm not "limiting the discussion", but simply pointing out that not just the majority of tube radios are AA5's, but also that those are the circuits we recommend to newbies, to begin with. Or would you suggest that their first repair effort be on something more complex?

processhead wrote:


Getting the set up and running, and then replacing 2-3 caps at a time and retesting, provides an opportunity to locate potential wiring errors at each power test interval.

Couldn't a said it better myself. In fact I did. :wink:

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Mon 26, 2018 9:05 pm 
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processhead wrote:
Getting the set up and running, and then replacing 2-3 caps at a time and retesting, provides an opportunity to locate potential wiring errors at each power test interval.

It certainly does.

Just follow the smoke.

You are grossly confusing techniques that work for experienced restorers with recommendations tailored to inexperienced novices. Two very different situations.

- Leigh

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Mon 26, 2018 9:24 pm 
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Over and out.

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Mon 26, 2018 9:33 pm 
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processhead wrote:
Over and out.

I don't blame you. Me as well.

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Mon 26, 2018 9:52 pm 
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processhead wrote:
Over and out.
Me too.

- Leigh

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Tue 27, 2018 2:05 pm 
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Leigh wrote:
processhead wrote:
Over and out.
Me too.

- Leigh

It's either "Over" or "Out". The only one who says, "Over and out" was John Wayne. :wink:

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Tue 27, 2018 2:32 pm 
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Don Cavey wrote:
Leigh wrote:
processhead wrote:
Over and out.
Me too.

- Leigh

It's either "Over" or "Out". The only one who says, "Over and out" was John Wayne. :wink:



Oh way to go Don !! Had to get them started again eh? Now there will be nine pages of "how to properly communicate via two way radio"...... with quoted examples, links to other forums, and probably twenty seven 8x10 colour glossy photos to boot! I'm sure someone, somewhere has a two-way radio protocol manual to scan and post...

Nicely done ... :wink:


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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Tue 27, 2018 3:56 pm 
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First i admit, i didn't read through all 9 pages of this ongoing debate over changing / not changing capacitors, so if this has been mentioned I apologize!

First, this is mostly for 1970s and later radios. One issue that seems overlooked when discussing this is how accessible everything is. If it's on a PC board, how much twisting and turning does it take to get to the back side to unsolder a cap? One of the problems i have encountered is the repeated twisting of leads eventually causes one to break. The question becomes when will it snap? Is it still solid or will it break on the next bend? Unless it is stranded wire with numerous strands already sticking out there is really no way to know. This issue must be weighed against the probability of a cap being bad as well. In other words which is more likely to cause the next failure and how serious will it be, the failed cap or the broken lead?

Granted the AA5 radio is probably not a real concern; they survive the changing process very well. But some more complex chassis with limited access become a concern. If the board has plug-in connections and can be completely removed for work, then the flexing of leads is not a concern. But many are not; some have leads soldered on all edges of the board mounted to a chassis. (The engineer that designed that probably never had to work on it!)

Obviously if you have bad caps you have to bite the bullet and make the changes. That would also include power supply electrolytics due to age. But the question becomes should you subject the poorly accessible board to all the extra stress just to change a cap that is good simply because it might fail at some future time? (Forget about the cost, we all know caps are cheap!) It's the collateral damage we do when working on it that is the issue.

For older radios with handwired chassis the above is a concern but not to the extent of later PC Boards. We also must consider the probability of failure as age increases. An electrotylic from the 1940s and 50s as well as many from the 60s is bad. Period. it needs changed. Paper coupling caps are bad and need changed. Bumble bees are bad and need changed. But when to change them?

I have no problem powering up a radio UNDER CONTROLLED CONDITIONS prior to changing any caps. That means after checking for obvious shorts or bad wiring, monitoring power supply voltages and current while bringing up the radio on a variac with current limiting. I sometimes even bypass the radio's internal supply and use my bench supply for B+ so I can keep close watch on what is happening. Experience teaches what is acceptable and what is not. Example, excessive output tube plate current is grounds to immediately change the coupling cap before going on. Hum on the other hand probably means your filter cap is open. You can disregard that for now and continue testing for more serious issues. This allows you to isolate potential problems with other components that if failed may make the entire project a moot point. Why waste time changing stuff only to find later some unobtainium further into the project?

Once you get a handle on the project, (You might even have the radio working somewhat) then is the time to go back and change out caps, out of spec resistors, weak tubes, etc. After that is when I bring things up to spec., make adjustments, etc.


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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Tue 27, 2018 4:19 pm 
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CaveRat wrote:
Once you get a handle on the project, (You might even have the radio working somewhat) then is the time to go back and change out caps, out of spec resistors, weak tubes, etc. After that is when I bring things up to spec., make adjustments, etc.


Oh boy, ya' wanna' be careful there or you'll get a rep for being a moderate, thoughtful, careful tech with a penchant for troubleshooting and logical diagnosis procedures....

Then nobody will like you! :)


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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Tue 27, 2018 4:26 pm 
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If you combine all the threads on this topic, it is a really well-plowed field...

I, for one, will start advising newbies how to find their own best strategy---knowing that everyone will be different.

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Tue 27, 2018 4:36 pm 
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CaveRat wrote:
First, this is mostly for 1970s and later radios.

This is perhaps a major reason for disagreement.

Sets later than 1970 are certainly not ANTIQUE RADIOS, as is the name of the site.

My comments are strictly about servicing antique radios, those being made before WWII.
I also include military gear of WWII vintage in that group.

- Leigh

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Tue 27, 2018 8:31 pm 
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Leigh wrote:
...My comments are strictly about servicing antique radios, those being made before WWII.
I also include military gear of WWII vintage in that group.

...

Do you have a designation for post-war tube radios? Or do you just consider them post-war tube radios? :?

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Tue 27, 2018 10:49 pm 
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Sol wrote:
Do you have a designation for post-war tube radios?
Or do you just consider them post-war tube radios? :?
I just consider them to be "modern".

Any set that was sold new after I started repairing radios (c. 1955) is certainly modern IMO.

- Leigh

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Tue 27, 2018 10:51 pm 
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Leigh wrote:
Sol wrote:
Do you have a designation for post-war tube radios? Or do you just consider them post-war tube radios? :?
I just consider them to be "modern".

Any set that was sold new after I started repairing radios (c. 1955) is certainly modern IMO.

- Leigh

That may be (in your view), but any radio from 1956 would need the same recap treatment as a pre-war set, so the SOP remains equal.

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Tue 27, 2018 10:56 pm 
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fifties wrote:
... any radio from 1956 would need the same recap treatment as a pre-war set, so the SOP remains equal.

That's certainly true.
I generally don't work on post-WWII sets, which is why I use that as a cutoff date.

My comment was posted in response to mention of sets made in the 1970s or later.
Those are new enough that wholesale capacitor replacement MIGHT not be warranted.

It depends greatly on the quality of the caps used in the product.

I have many HP et al units of that vintage that still work perfectly without restoration.
Of course, those are top-quality laboratory gear where parts cost was no concern.

- Leigh

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Wed 28, 2018 12:09 am 
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I'll grant you that 70's (transistorized) gear is modern-er. 'Modern' gear, actually, I would qualify as microprocessor controlled, if not built primarily around one or a few chips. After all, that's pretty much what distinguishes "modern" gear... Yes?

While I admire your honesty in dating what is 'antique' and what is 'modern' as compared to your own esteemed self, at the same time I wonder at your modesty - other personal qualities, knowledge, and capabilities not withstanding.

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