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Hi All,
I would like to recap my Model 87 soon. I have a small stockpile of high quality German MKP Audiophiler 400WVDC film capacitors in the higher values that might be usable for the larger filter caps (the 1, 2, and .5uF ones), but also a good supply of the usual 630V yellow caps of indeterminate origin from "Just Radios".
None of the schematics I have seen give voltage ratings for the filter caps. This radio is extremely special to me, so I would prefer to go with quality if possible. This is not to say that the typical yellow ones are bad, but the German caps seem to be manufactured to a much higher standard, and always measure spot-on for capacitance (the larger-value yellow ones all measure a trifle low). Based on the Rider's schematic I've seen with voltage readings, 400V caps won't provide all that much overhead...
Would the 400V caps be suitable for the application? Would it be better to go with the yellow 630s for the sake of higher overhead/increased reliability? Am I just being really picky? Thanks in advance!
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(03-28-2012, 04:59 AM)GuyIncognito Wrote: Hi All,
I would like to recap my Model 87 soon. I have a small stockpile of high quality German MKP Audiophiler 400WVDC film capacitors in the higher values that might be usable for the larger filter caps (the 1, 2, and .5uF ones), but also a good supply of the usual 630V yellow caps of indeterminate origin from "Just Radios".
None of the schematics I have seen give voltage ratings for the filter caps. This radio is extremely special to me, so I would prefer to go with quality if possible. This is not to say that the typical yellow ones are bad, but the German caps seem to be manufactured to a much higher standard, and always measure spot-on for capacitance (the larger-value yellow ones all measure a trifle low). Based on the Rider's schematic I've seen with voltage readings, 400V caps won't provide all that much overhead...
Would the 400V caps be suitable for the application? Would it be better to go with the yellow 630s for the sake of higher overhead/increased reliability? Am I just being really picky? Thanks in advance!
Hi and Welcome to the Phourm,
I'd go with the 630v jobs as I used some 2uf/450v and now it's eating 80 tubes. It did run for about six months at four hours a day. It will save you the trouble of pulling that can apart again.
GL
Terry
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Thanks Terry,
I think I knew that was the right answer all along...just wanted to use those shiny red German caps so badly!
It seems to me that using a type Y 0.015uF @ 250v safety cap would be a sensible precaution for replacing the unit that goes from the power line to the "LOC" terminal (i.e. the one that bridges pins 8 & 9 of the condenser block). The "LOC" terminal can be bridged to the "ANT" terminal with a jumper wire, apparently to use the house wiring/transformer as an antenna. Is this correct, or would a safety cap be overkill?
What rating fuse should be used for a Model 87?
Thanks again!
(This post was last modified: 03-28-2012, 07:46 PM by
GuyIncognito.)
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Don't know much about those Y caps but it sounds reasonable. If you figure 1 amp per 100watts you would be right about 1 amp for your fuse. Be sure to check the plate windings on the RF coils two of mine where open. Not critical about 50t of 32-38g wire. Also the bypass caps (3) with the series resistors. All of mine where very leaky.
My 87 brings back some good memories or me. Back in the mid '60s I was 9 or 10 years old my mom and I bought it at an estate sale. Unfortunately that one is gone,I don't remember where it went but about a year ago I found another 87.
Terry
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You could used the German ones as filter capacitors if you connected them in series, like two 400V 2 uf units in place of a 1 uf unit. Really, paper capacitor values in an old radio are not that critical, especially in a power supply, most others were used for coupling or bypassing, if they are 10% low it won't matter, sometimes 50% low won't matter either. Any place where they needed a precision capacitor they were usually of a small value so the manufacturers typically used mica. Most of the time the micas are still good but do fail on rare occasions, I would leave those alone unless everything else has been ruled out.
Regards
Arran
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Thanks Arran and Terry! Helpful advice--much obliged!
....purely as an academic question, are the voltage specs of the capacitor block listed anywhere? I've looked at five different sources, and they don't seem to be listed anyplace.
Of course, three of the five sources appear to have had the capacity values added in later...
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I guess if I had the time to measure the HV winding of the power transformer I could give you a good answer to your question but haven't so far. I can tell you that on these older set( from the late 1920's and early 30's) they use a low value caps in the filters because that's all that was available at the time. The power transformer is going to be rated at a voltage that is higher that what you would find on newer sets. This is why I would recommend a higher voltage rating for the input cap for this power supply.
Terry
