Cap Question

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Cap Question

Post by Guest on Thu Dec 27, 2012 6:43 pm

I am getting together the components I'll need to use in my philco 42-355 and wanted to ask advice on a replacement value for an 18uF electrolytic cap. It is shown in the vicinity of the 6X5G tube on Riders' Vol. 14 Pg. 43. It is the cap marked 89. I hope to get things set before I have my foot operated on. I then will have two weeks off from work and may be able to concentrate on getting at least a good start on the radio. Thanks.

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Re: Cap Question

Post by Dr. Radio on Thu Dec 27, 2012 8:57 pm

Yikes, foot surgery. That doesn't sound fun....

18 uF as you know is not a value available today. They do make 15 uF caps, but they are hard to find at higher voltages. 22 uF is an industry standard value, so the 22uF should work fine for you.

Hope that answered the question.
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Re: Cap Question

Post by Guest on Fri Dec 28, 2012 12:05 am

That was my guess, but I wanted to ask in case there were any advantages to another value. Hopefully the surgery will eliminate the problem without creating another.

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Re: Cap Question

Post by GaryRabbitt on Wed Jan 23, 2013 10:28 pm

Use the 22uf, and plan to ditch the 6X5. Seriously.
Last year I had 5 sets that used a 6X5 and each one had a burned transformer from a shorted 6X5.
If the trans has the current available, use the 6AX5. If the trans is already operating on it's capability (ie Zenith) then a diode rectifier may be used. Cheap insurance to save a transformer.

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Re: Cap Question

Post by Guest on Wed Jan 23, 2013 10:56 pm

That must be the other achilles heel in these units apart from the brittle insulation to the transformer. I've made a note of that, thanks.

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Re: Cap Question

Post by Bill Cahill on Wed Jan 23, 2013 11:04 pm

Bad idea on the diodes. They will allow alot more voltage, and, will change all your voltages, and, the surge will blow your electrolytics.
The problem with the original tubes was that they didn't put a spacer between the two plates. On the later ones they put a mica spacer there, then, staggered the plates. Alot less troublesome.
Hey, Gary. Welcome back.
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Re: Cap Question

Post by Ken g on Thu Jan 24, 2013 3:43 am

If you use diodes just check the voltage across the filters during warm up to see that the voltage stays below the rating on the filter .
These 6x5 are interesting . I have only seen one short out . I run them in my radios and no shorts sence .

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Re: Cap Question

Post by Bill Cahill on Thu Jan 24, 2013 9:24 am

Like I said. Staggard plates, no shorts. The early ones had the plates one right over the other.
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Re: Cap Question

Post by Dr. Radio on Thu Jan 24, 2013 10:06 am

I always install a fuse on the incoming power into the transformer. Then I never have to worry about fried transformers.....
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Re: Cap Question

Post by Bill Cahill on Thu Jan 24, 2013 10:09 am

Very good idea..........
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Re: Cap Question

Post by Guest on Thu Jan 24, 2013 10:22 am

Dr. Radio wrote:I always install a fuse on the incoming power into the transformer. Then I never have to worry about fried transformers.....

I like that and will keep it in mind for the next time I have to deal with this.

Thanks! Very Happy

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Re: Cap Question

Post by Guest on Thu Jan 24, 2013 3:04 pm

I installed one on a console I restored for my neighbor. A bulkhead mount fuse holder doesn't look too bad on the chassis. As an added bonus, I just had my foot surgery and have to rest it at a level with my heart, making bench work a poor prospect.

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Re: Cap Question

Post by GaryRabbitt on Thu Jan 24, 2013 9:33 pm

Dr. Radio wrote:I always install a fuse on the incoming power into the transformer. Then I never have to worry about fried transformers.....

You better start worrying Smile . That will do nothing to stop your transformer from being fried at all. The current draw while the trans is burning up might not exceed the amperage of the fuse on the primary. A common thought though, but it won't work.

Well, yes it will blow after the trans has melted the wires together, and presents a short to the primary side. By then your trans is toast anyway.

But a fuse on the center tap of the trans might help, some have used pilot lamps on each side of the HV as a fuse. That will stop the trans from burining up the HV.

Now, we all need to know which 6X5 tubes are the later model. The X arranged plates?

Yes, you do need to monitor the startup voltage if using a diode, and usually a resistor is put in series with the B+ to get the voltage right. It should not blow the electrolytics if the rating is not exceeded. You do need to check the voltages after diode installation. Still I'd rather replace electros, than to change a transformer. On the last Zeniths I used diodes on, I installed a Dale resistor mounted to the large chassis. Startup voltages never got close to the max 450v rating.

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Re: Cap Question

Post by jerryhawthorne on Fri Feb 22, 2013 5:45 pm

Yes Gary, from what I have learned the "X" plate arrangement was much better. I have that arrangement on my Zenith chairside now. When received it the power transformer was toast do to the old style 6X5. This was a replacement for the original! Another new transformer and a new 6X5 with the X plate arrangement and so far so good but don't really run it a lot. It's been 6 years.
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Re: Cap Question

Post by Wildcat445 on Fri Feb 22, 2013 6:29 pm

I agree with Jerry. I have never had a problem with a 6X5, either. I put a fuse in the primary of the power transformer, as well. Never had a problem with that, either. Perhaps ignorance is bliss, but I don't see how a fuse would fail to protect the primary. Maybe if you used too large a fuse?

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