Crosley model 170

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Re: Crosley model 170

Post by Guest on Sun Aug 18, 2013 9:48 am

Please don't stop, this is good information. I'm sorry I haven't been more involved but I've been consumed with a few issues myself.

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Re: Crosley model 170

Post by Wildcat445 on Sun Aug 18, 2013 11:25 am

Thanks, guys. I was beginning to wonder if this contraption was hooked up to Mars or somewhere like that.

More investigation into what happened to this capacitor. The (incredibly horrible) service notes indicate that voltage readings indicated are for measurement with an "instrument of 1000 ohms-per-volt sensitivity." The input filter capacitor is indicated as a 12 uf @450 electrolytic. It is a single capacitor can mounted on the front of the chassis. The other three electrolytics are in a three-way can mounted on the rear of the chassis. The input filter cap that I replaced was of later manufacture than the radio, dated 8-56, a Mallory, and was 8uf @450 volts. I replaced it with a 10 uf cap, under the chassis, mounted on a terminal strip.

This begs the question of just HOW I was measuring voltage. This radio was built in 1932 give or take a year. I do not own an "instrument" with 1000 ohms-per-volt sensitivity. Even my el-cheapo Lowes special that I gave $14.99 for is 20,000 ohms-per-volt. I have a Triplett and a Simpson VOM, both WW2 vintage and they are 20,000 ohms per volt. Then I have three VTVM,s. So any readings that I take with my "instruments" will be higher than those indicated on the service notes, due to decreased circuit loading (unless I am all wet in my thinking.) Without getting into engineer thinking and complicated mathematical formulas, (which I can't even imagine doing) it is obvious that the voltage values given in the service notes will be lower than what I actually will measure with my more modern "instruments." The value for B+, given in the service notes are 355 volts at the rectifier cathode at 117 volts line voltate. The line voltage as we speak is 117.4 volts. That is the value that I read with my Triplett VOM. But with a VTVM, it reads 390 volts. When I increase the line voltage to 122, the B+ readings increase to 425 with the VOM, and 465 with a VTVM. This is over the rating of the filter cap, which is 450 volts.

Just as a side note, I recently had performed some corrective surgery on my ISO/VARIAC/dim bulb homebrew contraption. The VARIAC had developed a "dead" spot in the rheostat, and the voltage output was unstable at about 117 volts or thereabouts. I cleaned the rheostat and now the Variac will put out about 135 volts maximum. I had been tinkering with line voltage on the night that the cap blew, so it was possible that I had cranked the voltage up even past 122 volts. So it is at least theoretically possible that B+ had exceeded the rating of the capacitor by a considerable amount, at least for a short period. I really thought that I had unplugged the radio when I was tinkering with the Variac, but, with my getting senile and forgetful, anything is possible.

And, how do they rate the voltage on caps? At 1000 ohms-per-volt or at 20,000? Are we measuring apples and oranges here? The cap that failed was an Illinois Capacitor, presumably made in the good ol' US of A. The one I replaced it with was certainly foreign-made. The replacement, thus far, (knock on wood) is working fine.

I do not believe in bucking transformers and such nonsense, and firmly believe that if a radio will not work in a current environment, as it was designed and built, then it will be a shelf queen. This may be a case where a 20 watt resistor of about 100 ohms or so in the primary circuit of the power transformer may be a good idea. Or increase the input filter cap to a 525 volt cap. The service notes give 269 volts as the correct voltage for the plates of the 2A5 output tubes. I need to look it up in the RCA tube manual to see what the max is for these tubes. They are running lots higher than that now, measured with anything that I have.

We state the case that filter caps should be changed, PERIOD, and this is probably good advice. This case demonstrates the fact that even if we do the "right" thing, somtimes other factors come into play to put us right back into the duck soup. This radio works incredibly well, considering what it was like when I started. I am going to make at least a feeble effort to make the chassis look a little better. There are two covers for the top and back of the chassis that will not go back on. This chassis creates lots of heat, and it is a 10 tube cathedral. I want every one of those 10 tubes to be able to be seen. This thing may be high on my list of the best radios that I own. The current leader is my Philco 40-180. This thing may give it a run for its money. The old Crosley has a 9 inch Rola speaker that sounds like a 12 incher. I am not going to worry much about voltage and such now. The transformer seems to be happy, so that is a good thing. I am not going to run it 24-7. The wife has declared it as "hers." So it will likely see limited use.

Regards

WC


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Re: Crosley model 170

Post by Wildcat445 on Sun Aug 18, 2013 6:25 pm

I thought I had it. I thought I had it fixed. I thought I was done with drama. Wrong.

My neighbor came over today and wanted to know what I was working on. I showed him the Crosley radio. "Does it work?" he asked. "Why, of course," says I. I plugged it in and turned the power switch. I waited. And waited. And waited some more. I could hear static in the speaker. It would not talk a word. Total silence. "Sure it does", replied the neighbor. "Good job." And he walked off.

Now what?

This chassis has a metal bottom cover. It has 1/4 inch holes in it for ventilation. There is a 6"x8" hole in the bottom of the cabinet to mate with the cover. This metal cover had been removed in order for me to work on the chassis. After I had pronounced the radio healed, I put the bottom cover back on. I did not try the radio until the neighbor came over. I took the cover back off to see what was going on and the radio immediately came to life. I put the cover back on and the radio continued playing. Until I tightened the screws. When the last one got about half way tight, the radio quit again. I pulled the cover back off and got to looking really closely. There is a terminal strip with one wire on it riveted to the chassis. The wire on the terminal strip goes to the antenna terminal. This terminal strip was bent enough to allow the wire to come into contact with the metal cover, short out the antenna, thus killing the radio. A simple tweak of that terminal, and we were back in business. With the cover on and bolted down. I am almost afraid to put the chassis back into the cabinet. Hard telling what will bite me next. I really would like to change the wires going to the speaker and field coil, but this thing is possessed. I may leave well enough alone.

Regards

WC

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Re: Crosley model 170

Post by Bill Cahill on Sun Aug 18, 2013 7:07 pm

Did you hook up an antenna wire???
A modern meter is fine, but, voltages are not going to be exactly the same..
Filters are rated at the maximum sustained voltage they can handle at the factory.
If you are using old new old stock filters, I'd highly reccommend against it.
They deteriate, and, will eventually short. The acid inside eats the insulation, especially when dried out from non use..

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Re: Crosley model 170

Post by Wildcat445 on Sun Aug 18, 2013 8:19 pm

The cap that failed was purchased about a year ago. It sure made a lot of smoke when it went. No flames or anything. At this moment in time, everything seems okay. I don't have the radio back into the cabinet yet.

Regards

WC

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Re: Crosley model 170

Post by Guest on Tue Aug 20, 2013 10:41 am

Wildcat, thanks for a great thread, there is some excellent information here that I will save for future reference.

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Re: Crosley model 170

Post by Bill Cahill on Tue Aug 20, 2013 11:06 am

Indeed, many thanks.

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Re: Crosley model 170

Post by Wildcat445 on Wed Aug 28, 2013 9:24 pm

I found a 16uf@1000 volt cap in my stash that I had gotten when I was going thru my oscilloscope. I may install this in place of the input filter cap. I have a probe that I can hook onto the pins of a rectifier to measure B+ and have a hands-free connection. The meter I use to monitor B+ is my RCA Voltohmist VTVM. When this radio is first turned on, before the tubes start conducting, and at 120 volts input, B+ can reach about 475 volts surge. This may be great enough voltage to seriously strain a 450 volt cap. The service literature calls for a 450 volt input filter cap, but this may be considering measurements with a 1000-ohms-per-volt meter. The other filter caps are rated at 250 and 350 volts, and those I replaced with the 450 volt caps. There should not be a concern with those. The B+ on the 2A5 output tubes runs about 322 volts at 117 volts line. The RCA tube manual states max plate voltage to be 315 on those tubes. The tube manual I have was published in 1940, so were they measuring with 1000 ohms per volt meters then? Assuming so, that would make the max plate voltage on the 2A5's measured with a VTVM somewhere around 350 volts or so. B+ has seemed to run high in this radio. So maybe a 1000 volt cap would give a margin of safety with a surge above 450 volts.

I have done all I can do with the cabinet. I can report that it is just okay. Not horrible, not great. It looks better than it did. The toners and stain did not do what I would have liked, due to the deplorable condition of the front veneer on the cabinet. I had to improvise. I am going to shoot three coats of semi-gloss poly on it, wet sand it, put on a final flow coat and call it done. I have brushed three coats of satin poly on the inside of the cabinet, in order to seal the wood and prevent further drawing of moisture. I cleaned up the chassis and buffed the tube shields to get the grunge off them. I repainted the power transformer gray like it was. It is better. It is a Crosley. Crosley chassis appear to be well-built, the the cabinets are horribly made and there is usually little effort made to make the chassis look good. I had to glue and clamp every joint in the cabinet and had to make a couple braces that should have been there when it was built. If they had just melded a Crosley chassis with a Philco cabinet........

Regards

WC

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Re: Crosley model 170

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