[davidff]

My chassis has electrolytics with 200 volts. Is it possible to get away with higher micorfarad values and only 160 volts? I would prefer not to use my 450 volt caps if I can get away with using the 160's. Any advice is appreciated.

[morzh]

1. Always give the link to your radio and the exact cap you refer to.
2. No, in general the rule "uF times Volts is constant" does not exist. Especially with tubes, especially in the rectifier filters you need the uF you have and the volts should be same or higher.

[codefox1]

Never use a lower voltage replacement capacitor. 450 volt electrolytics are fine, for the pennies difference, many of us just keep an assortment of 400 or 450 volt types which fill 99% of replacement needs.

[davidff]

All caps replaced with higher voltages,( only a few wax caps remain) now the radio no longer has any humm as before, and the phono works with a new cartridge, but the radio will not receive any stations, just an open band. I checked the oscillator tube, and it is fine. From what I could see both oscillator coils have continuity ( as long as I tested them correctly), and I am puzzled on why I am not getting signal.

[TV MAN]

Did the radio work before the recap, aside from the hum? Also, those wax caps that werent replaced - guilty. Replace em. Remember, leave the micas alone - that is the Pf/uuF low value caps in the RF and IF sections.

[davidff]

It did not work, just a regular bad electrolytic total non tunable hum. I did not realize initially, before I recapped that the 7B7 was bad also. Now the hum is gone, and the amp. is fine, but no stations. There are about 3 paper caps left, I will replace them.

[morzh]

David

Be methodical about it, don't do the cavalry charge thing.
1. Have you checked ALL your tubes? If not, do not proceed untill you do. Or buy know good tubes if you don't have a tester and replace all those with possible exception of audio output and maybe the rectifier as it seems like you do have voltages and such.
2. Try to pass a buzz through the schematic - touch grid caps of tubes involved and see if there is a reaction - buzz, or whatever - you should hear t in the audio. Be careful, fo not touch wrong stuff and while touching, make sure you yourself are not grounded. Or use a long metal object with an insulating handle if this feels more comfortable - screwdriver, soldering iron etc.
3. Provided your chassis does not smoke while being powered, measure all voltages according to the voltage chart. Compare, note all large discrepancies.

Then come back.

[davidff]

I have another working player and substituted the tubes to confirm they work fine. The other one works perfect as I restored it a few years ago with all new caps, etc. The new unit works on the phono, so I know the amp is fine. The volume control also responds on the radio side, but no stations received. I never did voltages before, but now is a good time to give it a try.

[morzh]

Well, get a DMM. It will measure higher voltages than the old-style voltmeter but understasnding the fact it does not load the circuitry one could extrapolate the new reading and relate it to the old one that is listed in the voltage chart.

In any case if you see 0V where you should see 100V is a red enough flag so you do not have to wonder about 10-30V difference.

Also, you did not metion if you replaced the out-of-spec resistors.

[davidff]

I remember reading that there is a way to put a working radio next to mine and then I can determine if mine is oscillating by picking up the other radios reception? Does any one know how I do that? Apparently that avoids needing to check the oscillator tube voltages.

[Eliot Ness]

Turn on an operating radio tuned to 1455 kc next to your Philco. Tune the Philco up and down around 1000 Kc and if the osc/mixr is working, you should hear a rushing or squealing in the other radio.

The principle behind this is if the IF is 455 kc and you tune to 1000 kc on the dial, the Oscillator will operate at 1455 kc. You should then be able to hear the signal on another radio tuned to 1455 kc.

Edit: If I looked at the right schematic your Philco has an IF of 455, but you might want to double check.

[morzh]

Well,


This is obviously a quick way, but eventually myself I always prefer to look at things with a scope whenever possible.

First, this is very educating. Nothing enhances your understanding of how circuit fiunctions as looking at the waveforms.
Second, the waveshape has in itself all the information you need for diagnostics.
If your oscillation is out of order the scope wil show it. If your audio amp has a crossover or limiting t what not, it will show it. If you have inrush or oscillation on power-up, it will show it.

I would recommend everyone - get a scope. A meter is like a stethoscope, and a scope is a finer tool like an EKG. Sometimes one is enough, sometimes you want to know more.

[Eliot Ness]

....I would recommend everyone - get a scope.....

Well sure, but we both know that ain't gonna happen

Some may never want to progress past the stethoscope stage, and that's OK, as long as they recognize their limitations. But we have to offer simple alternatives (when possible) to those who don't ever plan on using a scope or we risk scaring them away from the hobby.

[morzh]

I agree. Especially if one starts a hobby and not sure whether or not he will proceed with it past that one special radio his grand gramma left him, I say, wait 'till later to start throwing bucks in gearing up. But when 2nd and 3rd radio are on their way and the wife is still not threatening separation, you might meet the incoming hordes loaded for bear.

Still, today eBay is full of old used analog scopes within $200 range which is CHEAP!!! so maybe instead of one radio less one could get a scope. It's an investment.

[Warren]

I did buy a technics scope from ebay. My problem is I need practice with it, but am looking forward to the practical experience.