BAKELITE BLOCK TYPE capacitors - Printable Version
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BAKELITE BLOCK TYPE capacitors - fenbach - 12-31-2019
do these typically [or ever] go bad and/or should they be replaced regardless? i'm working on a Philco 60 that has several. i'm guessing that the small ones [.00011uf and even .015uf] will be fine, but one is a double .05-.05uf, part no. 3615-AJ. the .015uf is an audio coupling cap. the rest are all bypass. they all seem to be in working order now. I've replaced all the other caps, and the radio plays well enough.
https://web.archive.org/web/20110716100022/http://www.philcorepairbench.com/bblokcap.htm
RE: BAKELITE BLOCK TYPE capacitors - Paul Philco322 - 12-31-2019
Good reading, maybe some answers. Paul
https://philcoradio.com/library/index.php/shop-talk/general/bakelite-block-data/
RE: BAKELITE BLOCK TYPE capacitors - radiodale - 12-31-2019
I rebuild every Bakelite block in every Philco I restore (not repair). Then I do not have to worry about about tracking down another failure. It is worth the time invested.
RE: BAKELITE BLOCK TYPE capacitors - Nathan Slingerland - 12-31-2019
Same here. I have yet to find a non-leaky bakelite block capacitor unless it's a true mica cap (only for very small values - and then not 100% of the time).
The great thing about bakelite blocks is they look 100% original when restuffed. Much easier to deal with than restuffing cylindrical paper caps.
If you'll be doing a bunch of them I highly recommend Steve Davis's tools. There are photos in my 38-116 restoration thread:
https://philcoradio.com/phorum/showthread.php?tid=19459&pid=150140#pid150140
He sells them on eBay sometimes.
RE: BAKELITE BLOCK TYPE capacitors - Steve Davis - 12-31-2019
More likely than not they are all leaky. Number 33 is audio coupling, if leaky, can drive the output hard and burn out OP transformer or the field coil as can the tone control caps. Number 20 if shorted, can also burn out the field. Number 49 if shorted can put a dangerous current on the chassis, replace with .01 safety cap. For safety, reliability and performance it is best the just replace them all. While you are at it check all the resisters, some have probably drifted high.
Steve
RE: BAKELITE BLOCK TYPE capacitors - morzh - 01-01-2020
I have never met one with the value not having gone up at least twice due to leakage. No exceptions for me: gut and restuff, or replace.
RE: BAKELITE BLOCK TYPE capacitors - Radioroslyn - 01-01-2020
>i'm guessing that the small ones .00011uf...
I thought so too. On my 116B after abt 6months of operation the volume would go down and back up by it's self. I hadn't replaced them. After replacing those two 110mmf caps all is well. They were foil/paper.
RE: BAKELITE BLOCK TYPE capacitors - Kestas - 01-01-2020
These .00011 mf capacitors also fooled me on the first Philco I restored. I thought they were mica until someone pointed out they were paper capacitors.
RE: BAKELITE BLOCK TYPE capacitors - morzh - 01-02-2020
I also had this question about 110pF ones. I guess, in backelite blocks they did not use micas. At least those in 1937 radios (37-116) were tar potted paper.
RE: BAKELITE BLOCK TYPE capacitors - Nathan Slingerland - 01-02-2020
I have seen them sometimes be mica - sometimes not. To distinguish I check small value bakelite blocks with my capacitance meter. If it won't give a reading or it's off my more than say 10% I replace.
RE: BAKELITE BLOCK TYPE capacitors - fenbach - 01-04-2020
thanks for the help with the bakelite caps in my model 60. which i will replace.
but now I have several follow-up questions to steve davis's post about cap no. 49. he says to replace it with a safety cap. I'm guessing that would mean and X-Y cap?
but even more, I'm curious to know why it's even there?? I've worked on radios that don't have any connection between the power source and the chassis. most recently a Belmont/Airline 585. which, in turn makes me wonder if I couldn't/shouldn't just remove it???
and now I'm remembering that someone suggested putting an X-Y cap across the power line in an AA5 radio to reduce the amount of hum. is one configuration better somehow than the other????
RE: BAKELITE BLOCK TYPE capacitors - Jake Blake - 01-04-2020
" I've worked on radios that don't have any connection, . . . "
You are wise to note that.
There are different schools of thought about all this. For me, the jury is still out on whether these caps are really needed to shunt interference coming in the a.c. line, in this day and age, ( my 39-6 seems to be playing just fine without it). But the far-more important issue for me is, the wisdom, ( or lack thereof), of manufacturers connecting them before the power switch, instead of behind it.
No radio that leaves my workbench has them connected that way.
RE: BAKELITE BLOCK TYPE capacitors - Steve Davis - 01-04-2020
Yes, the line capacitor should be a y2 also, I would reduce the value to .01 to keep the leakage current to little lower value. The purpose of this cap is not so much to filter line noise (it is pretty ineffective at doing that). The main reason for it being there is to provide a ground path for the antenna circuit. Without this cap, the radio will have a much reduced sensitivity unless you provide a ground connection to the chassis. If this were my radio, I would add a second y2 cap to the other side of the line, ahead of the switch, just as Philco did with most of their other models. The reason I would do this is it will limit the voltage on the chassis to 60 or so no matter if the radio is off or on or which way the plug is inserted in the receptacle.
Steve
RE: BAKELITE BLOCK TYPE capacitors - morzh - 01-04-2020
About adding the second cap:
For other reasons - maybe, but for safety...
When you use a voltage 2:1 divider, its impedance as the signal source at the centerpoibt is half of that of the single cap.
So 0.01uF cap lets through 0.45mA max current at 120V.
The two to one divider of two 0.01uF caps will lower the voltage to 60V. But it will still let 0.45mA max current.
PS. Neither one is dangerous.
RE: BAKELITE BLOCK TYPE capacitors - Stall-U-Rated - 01-04-2020
Swiped a pair out of a DVR to use in a radio im restoring. This radio had only one as pictured in the corner. So, i unsoldered the center conductor from it and tucked it to the side and installed these 2 little fellas...
Steve