Philco 90 restoration - Printable Version
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+--- Thread: Philco 90 restoration (/showthread.php?tid=22832)
RE: Philco 90 restoration - Simon Wa3uay - 09-20-2021
Hello, Bob; I (we) recently acquired a model 90, looks to be the same 1-47 output with 4 gang tuning condenser as Ron noted (no switch on the back). I hope soon to have the time to work on it, so this is great, I will keep an eye on your progress!
-Simon
RE: Philco 90 restoration - Bob Andersen - 09-20-2021
I'm looking at a 1935 Philco speaker guide that shows the H-3 PN 02951 as the original and H-18 as the recommended replacement.
Both seems to be hard to find items.
RE: Philco 90 restoration - Bob Andersen - 09-20-2021
I picked up a set of Philco tools from Steve Davis and have been practicing his technique on the butchered chassis. That is leaving the bakelite block wiring in place, clipping the internal leads with a small drill bit and poking out the old cap through the eyelets. Works amazingly well. Much better than my old technique of removing the block and chipping it out from the backside. These practically just fell out.
[Image: https://live.staticflickr.com/65535/51498185984_e26bdc3ef0_c.jpg]
Here's another I did that had already been removed from the radio.
A quick twist of the drill bit in an eyelet cuts the thins wires.
A little heat to get things loosened up. I really do mean a little. Only around 130F. I could comfortable hold the block while working on it.
Then a little poke and it slid right out
[Image: https://live.staticflickr.com/65535/51498405365_ffdfe4eb7b_c.jpg]
RE: Philco 90 restoration - Bob Andersen - 09-21-2021
I just realized there is a great writeup on this technique hosted on this very phorum !
https://philcoradio.com/library/index.php/shop-talk/techniques/bakelite-capacitor-rebuild-without-desoldering/
RE: Philco 90 restoration - Bob Andersen - 09-23-2021
I replace the AC line caps with some 0.01uF and WOW! What a difference! Booming volume and many more stations coming in
RE: Philco 90 restoration - morzh - 09-23-2021
Bob
That tells me you were running it with those not replaced?
Honestly, I never do this. First, line caps are critical and if they fail it won't be pretty; second troubleshooting-wise, when all caps have been replaced, it removes many, many question that do not even have to be asked. There could be plenty of other problems....
RE: Philco 90 restoration - Bob Andersen - 09-23-2021
Oh no, I never leave them in. First thing I did was disconnect them. My mistake was running the radio without replacing them or using a proper ground. I was assuming they were there to filter noise off the AC line. Forgot about the RF return path.
RE: Philco 90 restoration - morzh - 09-23-2021
Ah! Happens
To the best of us.
RE: Philco 90 restoration - Steve Davis - 09-24-2021
Mike, he removed the line cap block just to safely do a quick power up with the intention of reinstalling with new caps later on in the restoration. See post #9
Steve
RE: Philco 90 restoration - madsowry - 09-26-2021
Bob I don't know if you noticed on ARF but Joezenithman has a Philco pancake speaker from a 70 or 90 for sale.
Just thought I'd let you know.
Dick
RE: Philco 90 restoration - Bob Andersen - 09-27-2021
Thanks. I found the listing. Too bad it's missing the output transformer. Looks to be in good shape othewise.
RE: Philco 90 restoration - Bob Andersen - 09-27-2021
Well it seems a quality 500K audio taper pot with solid metal shaft is a tricky thing to find. Apparently it's a common part in electric guitars and amps. NOS ones are almost non-existent and modern production looks cheap with short knurled shafts. I'll did through my used parts.
Meanwhile, I'm working on a curious issue. The volume cannot be turned all the way down. Even with the grid of the 27 DET AMP tube grounded there is significant volume. Grounding the grid of the 27 1st AF tube completely kills the sound.
I'm thinking there is some crosstalk between leaky caps. Perhaps inside of the #30 capacitor box ?
I'll start by replacing the #23 coupling cap then move on to box #30.
RE: Philco 90 restoration - mikethedruid - 09-27-2021
Bob, you mean you haven't rebuilt all the bakelite condenser blocks? That should be done to ALL of them to prevent any of these kind of problems. Just because the old paper condenser is in a tar filled bakelite block does not guarantee its immortality. This may or may not solve your immediate problem, but at least it lets you rule out a lot of possible problems. It also acts to prevent future problems as these ancient parts inevitably fail. The only exception I make is the hermetically sealed cans found in Scott receivers which show no signs of leakage. They are pretty much immortal as long as they remain sealed.
RE: Philco 90 restoration - Bob Andersen - 09-27-2021
Only two so far - the AC line bypass and the AVC cap. I'm well aware they all need to be replaced. I'm recording an in depth restoration video series while I work on this. The idea is to do some troubleshooting and replace them one at a time to see the effect.
A bigger concern to me right now are undoing some old repairs where some caps were tacked in parallel and a terminal that was cutoff one block. Also the parts placement diagram doesn't quite match what I'm seeing.
RE: Philco 90 restoration - Bob Andersen - 10-01-2021
Replacing what I believe is the AVC cap for the 24A IF tube and the caps in the #30 box seem to have jus about taken care of the volume issue. The radio is now almost silent with the volume turn all the way down. AVC action is working better too. All the strong, local stations are about the same volume as I tune around the dial.
One metal box and two bakelite blocks remain to be rebuilt. Then a few of resistors need to be replaced and it's alignment time.
I am also pursuing the speaker Dick mentioned above. The cone looks very good but it is missing the output transformer.
I'll get a Hammond 125 SE series transformer if I need to.
Am I correct in thinking that a 5 watt output transformer would be sufficient for a single 47 ?
125BSE $54.79 at Mouser Electronics. Ouch!