Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mike Aimer on June 16, 2021, 12:55:07 pm
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Total newb here. Working on a Lectrolab R200B whose schematic calls for a electrolytic can capacitor of 40/40/20/20uF at 150VDC. The closest thing I could find to that was this...
https://www.amplifiedparts.com/products/capacitor-ce-mfg-525v-40402020-f
If you have to stray from the recommended capacitance or voltage, what are the legal limits? What would be detrimental or dangerous?
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A higher voltage rating is no problem at all.
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A tag strip and four separate modern electrolytic caps mounted on the underside of the chassis would be a lot cheaper than that silly $40 can cap. Leave the old one in place for looks.
Or, if you're a complete idiot,
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Thanks for the advice!
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47uF and 22uF are typical modern equivalent cap values. Any discrepancy compared to the schematic values would be significantly less than the tolerance to that nominal value.
Any voltage rating of 150V or more would be fine, eg 250V is a common rating.
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Thanks for your input!
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> Working on a Lectrolab R200B
Be careful with that thing!! It is a AC/DC hot-chassis rig, except the B+ side (not the heaters!) is behind a transformer.
https://lectrolab.wordpress.com/lectrolab-models/r200/
https://lectrolab.files.wordpress.com/2010/06/lectrolabr2003.jpg
That's the R200. The R200B *may* have the heaters on the safer side of a larger power transformer. There's a picture of the schematic sticker of a R200B on that site, and it too has heaters on the unsafe side of the transformer.
This business of leaving the heaters connected to the wall and the B+ isolated seems to have been a momentary fad. Heater insulation breakdown is rare but not all that rare. True, we smoked non-filter Camels while snorting leaded gasoline, assuming we survived WWII/Korea/Vietnam..... but safety expectations did change.
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If you are restoring the amp and want it to look nice for resale then the cap can is the way to go. If you are not concerned with aesthetics then the alternatives have been mentioned. The above photos of
individual radial-axial capacitors for inside a cap can (or to mount them similarly) is a method of restoration so the capacitors look like the original can, but the CE cap can capacitors inside are nothing like that at all.