The Fine Things are Always Hand Made
Bass Choke Renewal
It is winter and so I am getting serious about getting the Philharmonic working. The bass choke can was giving off a nasty smell when I fed power to the radio so I decided to begin there. The photo shows what it looks like inside this piece. It was easy to remove. Two of the capacitors were 400 volts and two were 600 volt. The replacements are all 600 volt capacitors.
My next step will be to replace all capacitors and suspect resistors. Then I will add power again and maybe get a signal!
Comment
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Comment by Bill Liers on January 2, 2015 at 9:13pm
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Found that the .022s I used gave a notch at 64-5 Hz. Paralleled a .01 and a .015 to get it right.
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I just rebuilt the same box and wondered about the tolerances as well. The technical doc for the Phil mentions how to sweep the bass response and look for peaks and dips. I'll report on my findings.
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Comment by Norman S Braithwaite on December 16, 2014 at 11:25am
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I have been using pairs of .05 mfd capacitors in series or .027 mfd capacitors that test low in place of the .025 mfd capacitors. Not knowing how sensitive the circuit is to component values or the difference in values (.02 for two and special .025 used for the other two) I am trying to maintain both (value and difference in value). Yesterday I replaced the same four capacitors in the custom Philharmonic from Marc Arnel. I used a pair of capacitors marked 0.022 and testing 0.0213 in place of the originals marked .02 and I used a pair of capacitors marked 0.027 and testing 0.0264 in place of the originals marked 0.025. Close enough!
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Comment by David C. Poland on December 15, 2014 at 11:18pm
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Norm,
my stock of .02 caps are rated .0233. That close enough? Or do you seek out combinations to maintain original values in this tone unit?
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The Scott Sixteen has a similar unit with 4 caps inside. I dismounted it and used a cutting wheel in my Dremel Tool to cut open the back on 3 sides, to open a big flap like a doorway. Installed new caps with new pigtails matching the color of the original wires. With a Sharpie, I noted the wire colors and values on the exposed side of the unit, and my rebuild date for future owner reference. Bent the "door" closed and reinstalled the unit so the opening is hidden against the side of the chassis. I will use this method this winter on my Philharmonic (I did not know the unit was full of caps the last time i worked on my Philharmonic).
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The vertical mounted capacitors were originally special order 0.025-mfd, 400-volt capacitors. EH Scott Radio Laboratories must have believed it was necessary to have the higher value.
Norman
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Comment by Ken Carr on December 15, 2014 at 10:41am
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Thanks for the comment and encouragement, David. I hope to do an inventory today and put through another order for capacitors. I'm still working out details of the circuit where someone else poked around. I am making progress. That box looks like fun - it's a huge heat sink for my soldering iron. I will tackle it,though. I may be retired but I am never without something to do!
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Yep- those are one set of hidden caps shown on the circuit diagram. Another is the 7 caps inside the metal soldered rectangular box mounted inside left side below the volume expander tubes. Take your time and do it right.
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