The PHILCO Phorum
Bakelite block question-66MB - Printable Version

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+--- Thread: Bakelite block question-66MB (/showthread.php?tid=5994)


Bakelite block question-66MB - Jim Dutridge - 02-15-2013

According to the 66MB schematic, the block #26 is suppose to be 2 100pfd caps but the part number, 8035-B says they are 110pfd caps. Also, the resistor, #25,is suppose to be a 50K but the resistor in this is a 51K. Also the parts list says a 50K but gives the color code green-brown-orange which clearly says its a 51K. So whats correct?

RE: Bakelite block question-66MB - tab10672 - 02-15-2013

It may be a revised code there so close that it shouldn't matter either way

RE: Bakelite block question-66MB - Ron Ramirez - 02-15-2013

110 pF is generally no longer a standard value. While the original 8035-B would have had 110 pF caps inside, 100 pF mica caps will be fine as replacements.

Resistor (25) can be replaced by 51K, no problem. I have seen this as well as a parts list calling for 100K but the radio has a 99K inside, and vice versa. Philco pulled these sort of stunts in the mid-1930s. Icon_crazy

RE: Bakelite block question-66MB - Jim Dutridge - 02-15-2013

OK, didn't have enough 100 pf to make a complete block so I cobbled together a 47 and 56 to get a 103 pf, actually measured 102, and a 100 to complete the block. I'll put in a 51K to match what was actually in the radio. Now, only things left are find that replacement 6UF can capacitor and get my speaker reconed.

RE: Bakelite block question-66MB - Jim Dutridge - 02-20-2013

Another question, what type of bulb was used in this radio? This has a holder I've never seen in a radio before. Not a bayonet or screw base holder but, for lack of a better word, a clip-in style holder. I was thinking maybe a 44 but its an awful tight fit as far as the height goes.

RE: Bakelite block question-66MB - Chuck Schwark - 02-20-2013

{Ron - 110 pF is generally no longer a standard value...}

FYI, 110pF. is a standard value in dipped silver-mica types.

Mouser has them:

http://www.mouser.com/ProductDetail/Cornell-Dubilier/CD15FD111JO3/?qs=sGAEpiMZZMtLiKaZgV7flZAQh3t86oTB5GmqeSkK7fk%3d

Probably overkill for a post detector tweet filter, but I happened to have some on last block I needed them for.

Chuck

RE: Bakelite block question-66MB - Ron Ramirez - 02-20-2013

Very interesting, and I stand corrected! There was a time when I could not find 110 pF mica caps, and I don't think even Mouser had them at the time. Oh well.

There is a page I was thinking of, where the author, wa2ise (who is a Phorum member) advocates the use of 33 or 47 pF caps in place of the old 100 or 110 pF caps:

Quote:Another thing you should address is the small RF filter caps on the audio output of the detector. Have them too big and you can get tangent distortion because they take too long to discharge to allow a full amplitude 5KHz sine wave thru without getting tangent clip. Change the (usually) 100pf caps to around 33 to 47pF.

http://pw2.netcom.com/~wa2ise/radios/feedback.html

I've replaced 110 pF micas with 33 pF micas in some of my own sets since reading this tip a few years back. They did no harm, although I don't have any fancy test equipment to measure the difference.

Perhaps wa2ise will jump in here with some comments of his own.

RE: Bakelite block question-66MB - Chuck Schwark - 02-21-2013

If you are not hearing any fidelity issues, then it won't be a problem.

Chuck

RE: Bakelite block question-66MB - jph14 - 02-21-2013

Jim,
I believe a 44 bulb is correct. Unfortunately, I took a spill on the ice and can't get to shop due to resulting injury. Hopefully, in the near future, I will check the 66 and get back to you if you still need the data on the bulb. I remember it being a tight fit.
Joe

RE: Bakelite block question-66MB - Jim Dutridge - 02-21-2013

Thanks for that information Joe. Thats what I put in was a 44. Still need my 6UF can cap.