Capacitor replacement.

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Nathaniel Steele
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Capacitor replacement.

Post by Nathaniel Steele » Tue Jul 31, 2018 12:30 pm

The rodent has been evicted, but I have some lightning damage to these capacitors on my tower lighting Choke, anyone know where I can purchase replacements? I'm not familiar with this type, given my limited AM experience.

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Thanks!

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RGORJANCE
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Re: Capacitor replacement.

Post by RGORJANCE » Tue Jul 31, 2018 1:19 pm

RF PARTS has those gray mica caps. I think I saw them the other day when I was looking at their web side.

The other possible source is Nebraska Surplus Sales (or maybe listed as Surplus Sales of Nebraska).

Most times. I have seen those caps in a brown color with a combo of solder tabs and holes for slipping bolts thru.

Fossil

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RGORJANCE
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Re: Capacitor replacement.

Post by RGORJANCE » Tue Jul 31, 2018 1:23 pm

Duhh! Getting old.....try Phasetek and Kintronics also since they both maker twr liting chokes. They probably have them inn stock.

I should have thought of those folks first.

Fossil

Nathaniel Steele
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Re: Capacitor replacement.

Post by Nathaniel Steele » Tue Jul 31, 2018 1:46 pm

didn't see that value at RF parts. I always forget about the nebraska surplus place, I'll check.

I think the combiner is a phasetek so I can call them, I figured it might be one of those cheaper if you find your own source kind of parts.

Google gave me mostly ebay links to the (older?) brown style you speak of.

Thanks!

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Re: Capacitor replacement.

Post by RodeoJack » Tue Jul 31, 2018 6:41 pm

Commercial Radio Company used to carry that type, but when I did my recent DX-10 refreq, they told me the type was going out of production... at least that's what I understood them to say. That was over a year ago, so maybe something has emerged as a replacement.

In any case, you can try them. 802 226-7582

Nathaniel Steele
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Re: Capacitor replacement.

Post by Nathaniel Steele » Wed Aug 01, 2018 7:50 am

Phasetek will be getting back to me with a price today.

I'll check out commercial radio company.

Thanks.

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Deep Thought
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Re: Capacitor replacement.

Post by Deep Thought » Wed Aug 01, 2018 10:42 am

The value is not critical. Anything from 0.01 up will work...their job is to equalize the RF potential on the windings on the "hot" end and give an RF path to ground on the "cold" end. The voltage rating is more important, and you might want to up that to 1 KV or higher.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

Nathaniel Steele
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Re: Capacitor replacement.

Post by Nathaniel Steele » Wed Aug 01, 2018 1:08 pm

Thank you Sir!

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Deep Thought
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Re: Capacitor replacement.

Post by Deep Thought » Thu Aug 02, 2018 11:50 am

One other thing...none of those windings is grounded. Is there a separate static drain coil in there? If not, that's why the capacitor popped when lightning got a bit too close.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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Re: Capacitor replacement.

Post by radio_guru » Sat Aug 04, 2018 9:26 am

May be joining in this thread late. Apologies.

I just went through this with Harris coils over the past 18 months. I needed to retrofit three towers with Harris OEM coils which didn't have the bypass caps on them originally as part of a site rehab project. (Why not buy new??...well the array was OEM Harris to start and I had spares which I'll likely never use again elsewhere.) I found a bunch of the correct value 0.02 5KV caps on E-Bay and bought them all. The balance will remain on site as spares.

Now a couple things to impart---These look like CSP/Phasetek chokes. Make sure you procure and use the ***same*** values as was originally installed. On a DA, the value coupled to the tower could sufficiently change the base impedance. Maybe enough to show as a change on the antenna monitor. Remember, the lighting choke and SDC bridge the toroid if you are using TCT's. It's less critical for sample looped towers.

Second, I recall a conversation last year with Tom King on this matter. They have been experiencing challenging times procuring high quality mica capacitors for this mission. Since Sangamo and CDE stopped producing them here in the USA, the quality of the devices have dropped precipitously and frequently will not meet spec. I can't speak for Kurt's experience on this matter. But I trust Tom's assessment.

Third, replace all three on that side at once. There is a high probability that if one failed due to strike, the other two have also likely started to break down due to over-voltage/over-current. To be safe, replace all 6. They're not that much money to buy, but a pretty significant effort to replace if you need to remove the coil. Including off-air time.

Good luck........RG

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Deep Thought
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Re: Capacitor replacement.

Post by Deep Thought » Sat Aug 04, 2018 11:28 am

radio_guru wrote:
Sat Aug 04, 2018 9:26 am
On a DA, the value coupled to the tower could sufficiently change the base impedance.
The difference between 0.01 uF and 0.02 uF is ~j15 ohms or less at AM broadcast frequencies. Using Phasetek's data these are in series with a coil in the +j1200 ohms or higher range so that amounts to 1.25% or less change in the overall shunt reactance for one winding taken separately. Mid-band it is 0.2%. If your tower is unstable enough for this to cause a significant difference in base impedance you've got more of an issue than the lighting choke bypass caps.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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Re: Capacitor replacement.

Post by radio_guru » Mon Aug 06, 2018 6:54 am

I agree that it will in all reality not on most towers. The original post didn't specify if the tower was 90 deg. or something more wild. Like 130 deg.---Which is sensitive to just about anything that might change.

And my suggestion to keep them all the same is more a reflection to avoid creating a transformer arrangement between what will be an ever so slightly out of balance set of coils. Which I have personally seen create some odd issues. Installing the original and same values across all of them cured the matter.

As is the case with every installation, YMMV....

RG

Nathaniel Steele
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Re: Capacitor replacement.

Post by Nathaniel Steele » Tue Aug 07, 2018 3:18 pm

This is a single tower non D, but it is a combiner. tower originally built for 780 had a 1400 added about 18 months ago (a few months before I took over). Height is 82.3 meters, at 1400 it is 138.4 degrees and at 780 it is 77.1 degrees, according to the license anyway. I'm far more experienced with FM than AM, so please do let me know if I'm making a mistake.....

Phasetek quoted me $90 each....that seems a tad high to me but what do I know?

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kkiddkkidd
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Re: Capacitor replacement.

Post by kkiddkkidd » Tue Aug 07, 2018 5:46 pm

Nathaniel Steele wrote:
Tue Aug 07, 2018 3:18 pm

Phasetek quoted me $90 each....that seems a tad high to me but what do I know?
A very few years ago $90/ea would have been scandalous but is cheaper than what I recently paid from another vendor. Limited supply has really jacked up the prices.

Later,
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

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Deep Thought
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Re: Capacitor replacement.

Post by Deep Thought » Tue Aug 07, 2018 10:27 pm

Nathaniel Steele wrote:
Tue Aug 07, 2018 3:18 pm
This is a single tower non D, but it is a combiner.
Not to put too fine a point on it, but the photos show no DC connection from the tower to ground through the lighting choke. If that is indeed the case you need to add a static drain.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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