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 Post subject: Admiral 20A1 recap - Need Advise
PostPosted: Jul Thu 27, 2017 1:38 am 
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Location: parkersburg west virginia
Hi All
I am in the process of recapping / restoring a Admiral 20A1 chassis. i am now going through the process of ordering new capacitors, however, i am having a difficult time trying to find replacement Mica capacitors.
is it possible to just use disk capacitors in place of the Mica's?
Does anyone here know of a source for both Mica & Silver Mica capacitors? any help is appreciated.

B.T.W. i also am in need of a .03 @ 1500 VDC. i can't seem to find one from the resource i have


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jul Thu 27, 2017 4:07 am 
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Others will have an opinion as well, but mica capacitors should not be replaced by disc capacitors.

But more importantly, I would not concentrate on mica capacitors. You might not want to twist them around as it could break the lead to body seal. Mica capacitors are often still good, being much more reliable than most.

Do the paper and electrolytic capacitors first.

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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jul Thu 27, 2017 2:49 pm 
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One thing to be aware of is that in ~the mid 60's the 'standard value' numbers changed instead of 2, 3, 4, 5 (X10 to a negative or positive power) they went 2.2, 3.3, 4.7, 5.6, 6.8, 8.6....There is such a thing as manufacturing tolerance most papers were ~10-20% so capacitance has enough wiggle room that it will work fine if you pick the closest modern standard value.

Voltage: it is the highest voltage a cap can take without failing....It is perfectly fine to select a new cap with a higher voltage rating than original (in fact it will make the set more robust). I tend to buy rated 630V bulk of the paper cap values I most need for tube stuff (and use it to replace any value 600V or less), and special order the occasional 1000, 1600, 2000V cap I find (or if I'm impatient I put two or more caps in series to increase effective voltage rating).

I agree with the others: genuine micas (but not papers in mica's clothing) have a fairly low failure rate and each one should be considered innocent until proven guilty, at least in RF/IF/Sound/Video circuits...However in sweep stages (Horiz and Vert) micas are subjected to much more electrically strenuous conditions and have a moderate to high failure rate. Some automatically replace sweep micas, I tend to have spares on hand and see if they are bad before replacing them.
One additional reason not to change micas that are in the RF/IF system is that changing then may throw the alignment off, and performing an alignment correctly on a TV requires a lot of equipment, skill, time, and patience....Better not to mess up alignment in the first place than break it and fix it.

Just radios in canada has a decent supply of micas IIRC.

IIRC the big suppliers Mouser, Allied, Digikey, etc have them if you figure out the correct settings for the site filters.


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jul Thu 27, 2017 2:58 pm 
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robert1 wrote:
B.T.W. i also am in need of a .03 @ 1500 VDC. i can't seem to find one from the resource i have


Here are some 0.033uF @ 1,600 VDC capacitors from DigiKey and Mouser Electronics.

https://www.digikey.com/products/en/cap ... ageSize=25

http://www.mouser.com/Passive-Component ... znZ1ykkkma


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jul Thu 27, 2017 5:48 pm 
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Guys, I appreciate all the help.
the "Micas" that i am referring to is there are Five 1000pf capacitors that are in the vertical & sync separator circuits that i question. these are large beige colored "postage stamp" capacitors. these are the ones that i was wanting to replace with ceramic disk capacitors.


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jul Thu 27, 2017 6:06 pm 
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1000pF = .001uF u=10^-6 P=10^-12 I'd replace those 'Micas' with the same film caps I use to replace paper caps....It is not uncommon to see 'mica' caps over 1000pF that are really papers in disguise.

Don't replace papers or large micas in TVs with ceramic if you can help it.


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jul Thu 27, 2017 6:25 pm 
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Electronic Memory wrote:
One thing to be aware of is that in ~the mid 60's the 'standard value' numbers changed instead of 2, 3, 4, 5 (X10 to a negative or positive power) they went 2.2, 3.3, 4.7, 5.6, 6.8, 8.6....There is such a thing as manufacturing tolerance most papers were ~10-20% so capacitance has enough wiggle room that it will work fine if you pick the closest modern standard value.


i already knew that & already replaced most of the paper / electrolytic caps with ones that were within 10% - 20% of their ratings.

Electronic Memory wrote:
I agree with the others: genuine micas (but not papers in mica's clothing) have a fairly low failure rate and each one should be considered innocent until proven guilty, at least in RF/IF/Sound/Video circuits...However in sweep stages (Horiz and Vert) micas are subjected to much more electrically strenuous conditions and have a moderate to high failure rate. Some automatically replace sweep micas, I tend to have spares on hand and see if they are bad before replacing them.
One additional reason not to change micas that are in the RF/IF system is that changing then may throw the alignment off, and performing an alignment correctly on a TV requires a lot of equipment, skill, time, and patience....Better not to mess up alignment in the first place than break it and fix it.


i was not planning to replace the ones in the Horizontal oscillator & in the video circuits as i know those are "true" Mica's. Fortunately, all of the capacitors in the IF, RF, & audio stages are the original black colored disk capacitors, & i have never seen one of those go bad.
the "Mica's" that i am referring to are rather large & are rated at 1000pf. @ 350 Volts. i suspect those may be bad since they are being used as ether coupling or feedback according to the Riders Schematic.
also, according to Riders, two of these are in place of what is supposed to be .001 capacitors. these are linking the vertical osc to the sync separator (6AL5)

Electronic Memory wrote:
Just radios in canada has a decent supply of micas IIRC.
IIRC the big suppliers Mouser, Allied, Digikey, etc have them if you figure out the correct settings for the site filters.


Thanks, i will get them from Justradios.
B.T.W. this set is all original & never had been serviced underneath. it even had most of the original tubes still in it.


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jul Thu 27, 2017 8:14 pm 
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Some of those molded caps with square bodies are actually paper inside, especially when you get into larger values like .001. They can look exactly like mica caps, and have exactly the same type of markings. The only way to be sure is to break one open.

It's a Catch-22 situation since if they actually are mica and you disturb the leads to disconnect the cap and do a leakage test, you have probably just ruined it, so might as well just replace. In that circuit position, a modern film type cap should be fine.

The real micas in the horizontal osc and sweep sections have a fairly high failure rate and some people are now automatically replacing them once they see the set work. Don't touch the ones in the IF's or the tuner unless you have proven operational problems which can be traced back to a specific capacitor.

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Experience is what you gain when the results aren't what you were expecting.


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jul Fri 28, 2017 1:07 am 
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Unfortunately there are several different ways the dots can arranged. In one common way for caps with two rows of 3 dots, if the first dot (upper left most dot) is black then the cap is a mica cap. If it is silver or white then it is a paper cap.

If the brand name on the cap is MicaMold then it is almost certainly a paper cap.

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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jul Fri 28, 2017 3:32 am 
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Location: Woodinville, WA USA
Here are two articles that may be useful. The first describes my restoration of an Admiral console with the 20A1 chassis:

https://antiqueradio.org/Admiral24A12Television.htm

The second has advice about choosing replacement capacitors:

https://antiqueradio.org/recap.htm

Good luck with your project,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jul Fri 28, 2017 6:53 pm 
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philsoldradios wrote:
Here are two articles that may be useful. The first describes my restoration of an Admiral console with the 20A1 chassis:

https://antiqueradio.org/Admiral24A12Television.htm

The second has advice about choosing replacement capacitors:

https://antiqueradio.org/recap.htm

Good luck with your project,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html


Thanks, Phil. hopefully, i won't run into problems. i do know that the 10BP4 test perfect with good cutoff. also, this set has not seen much servicing other then one capacitor & some tubes being replaced. i suspect that the crt was just replaced before the set was retired.
i am now in the process of checking for out-of spec resistors while i wait for the capacitor order to come in


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jul Sat 29, 2017 3:21 am 
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Glad that your CRT is good. That is certainly a giant step in the correct direction. Please keep us posted and with pictures if possible.

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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jul Sat 29, 2017 6:26 am 
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Location: parkersburg west virginia
Don Cavey wrote:
Glad that your CRT is good. That is certainly a giant step in the correct direction. Please keep us posted and with pictures if possible.


I will do that. another nice thing is that the chassis is pretty clean & rust free. apparently, it must have been stored in a dry, clean place. i got this set a couple of years at the auction at the E.T.F a couple of years ago. it still has it's original back.


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Aug Tue 01, 2017 8:03 pm 
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Location: parkersburg west virginia
Well, I got most of the capacitors needed to do this restore job. i got a couple of pictures as well.

I've been taking my time & doing it step by step just to avoid mistakes. since most of the capacitors were on tie points or strips, i have been desoldering & unwrapping all of the components that were attached to the tie points, that way, i could check resistors that have drifted out of spec. so far, i found five resistors that drifted way high, so i replaced them. i have still got quite a ways to go.

I will be posting more about the restoration as i progress.


Attachments:
Admiral 20A1-2.jpg
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Admiral 20A1-2.jpg
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Admiral 20A1-3.jpg
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Admiral 20A1-4.jpg
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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Aug Tue 08, 2017 8:57 pm 
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Location: parkersburg west virginia
I finally got all of the capacitors changed & replaced a bunch resistors that have drifted out of tolorence. i redone the power supply a few months ago.
i powered it up last night & believe it or not, i got a picture. the horizontal & vertical adjustments were off, but after adjusting them, i had a picture.....that is for about 5 minutes. then the fuse for the HV supply blew.
after shutting it off, i traced out the the cause, it turned out to be the horizontal width coil. the primary winding developed a short to the secondary.
Now, I'm at a stand still until i could find a coil.


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Feb Fri 23, 2018 4:53 am 
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After months of waiting, i still cannot find the width coil for this set. from what i could ascertain, Only the 19A1 & 20A1 chassis used this coil / transformer combination. what makes this coil unusual is that it has a low impedance secondary winding that feeds sync pulses to the 6AL5 horizontal disc tube.

i was wondering if i could use a standard width coil in it's place & look for another source for the horizontal sync pulse to feed into the horizontal disc.


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Feb Fri 23, 2018 8:08 am 
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I wonder if it's possible to repair the old coil?

Not necessarily easy, but I have been saved a couple of times when a friend was able to resuscitate an "unobtanium" coil.

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Feb Fri 23, 2018 8:21 am 
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Location: Elkhorn,Wisconsin,United States
Hi Robert,
Why don't you try and repair the secondary winding. It should only be a few feet of 36 gauge magnet wire. You could remove the defective winding if it is not buried under the 80 ohm primary winding. If it is you may be able to just un-solder the 0.5 ohm secondary coil and cut those tiny wires off.You could then even try to wind a new secondary over the primary if you need to. If you are able to unwind the secondary, then take note of its connections and direction the coil wire is wound. That way you can copy what you removed.
I'm assuming that the primary winding is still intact.
Ed


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Feb Fri 23, 2018 8:26 am 
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Location: Elkhorn,Wisconsin,United States
philsoldradios wrote:
I wonder if it's possible to repair the old coil?

Not necessarily easy, but I have been saved a couple of times when a friend was able to resuscitate an "unobtanium" coil.

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html


Seems we had the same idea Phil, it just takes me too long to type.
I'm currently trying to rewind a Motorola vertical deflection coil, one of kind, for a TS-16a/30a chassis.
Ed


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Feb Fri 23, 2018 7:01 pm 
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Location: parkersburg west virginia
Ed Kozak wrote:
Hi Robert,
Why don't you try and repair the secondary winding. It should only be a few feet of 36 gauge magnet wire. You could remove the defective winding if it is not buried under the 80 ohm primary winding. If it is you may be able to just un-solder the 0.5 ohm secondary coil and cut those tiny wires off.You could then even try to wind a new secondary over the primary if you need to. If you are able to unwind the secondary, then take note of its connections and direction the coil wire is wound. That way you can copy what you removed.
I'm assuming that the primary winding is still intact.
Ed


I thought of that but unfortunately, it is buried under the primary winding :-(.
I would also venture to guess that the Primary winding also may have a few shorted turns close to where the primary-secondary winding's are close to each other. someone in the distant past had worked on this set & had the coil miswired as well as the sections reversed.

regarding trying to manually rewind this coil by hand. i will have great difficulty because of my fat fingers don't work as well as they used to & my vision is not very good anymore. these coils require precision winding to some degree, which is something i am no longer able to do.

this is why i asked if i could replace the coil with a standard width coil & try to find another source for the horizontal sync pulse. i notice that the later Admiral chassis designs use a different method of sourcing the sync pulse


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