[BrendaAnnD]

On the 85 plate voltage, if resistors 48 and/or 49 have gone way up in value it can cause this. So can a gassy 85 that is drawing too much current.

[Winky Dink]

Tried a different 85;
Substituted new components for C50, C51, R48, R49;
Disassembled tone control to inspect and test C62;
Inspected all wiring for poor solder joints, shorts, and miswiring;
Replaced the tire on the wheelbarrow;
But 85 plate voltage remains 44V.

Thanks for all the advice on possible causes of the low voltage. With the radio performing well, I'm not going to pursue the issue any further at this time (unless, of course, someone has another idea to try).

The hum is under control! After much experimenting, I found putting both C58 and C59 at 12mfd leaves a barely perceptible hum. Incidentally, when I received this set those condensers had been replaced with a pair of 12mfd cardboard-tube electrolytics.

[Image: https://lh6.googleusercontent.com/-em4HB...520645.jpg]

Also, the power transformer seems OK--doesn't get hot.

So, I only have to add 4mfd to the C58 can. Thanks for helping me keep those in a safe range.

[morzh]

C58 can get the increase. Do not increase C59 (which is 12uF). It will simply raise your voltages.
The C58 will not raise voltage and will attenuate the hum if it is caused by pulsation in the power voltage.

BTW is your field coil 445 Ohm as shown?

[Winky Dink]

Got it. The only thing I need to do before returning it to the cabinet is to do the alignment one more time. C59 remains at 12uF, C58 is increased to 14 or 16uF, and the hum is gone.

Field coil was actually 460 Ohms the last time I checked.

[morzh]

Its ine then.

[Winky Dink]

Well, it's not exactly "in." I had the set performing beautifully. Excellent reception of all local stations and crisp, clear tuning. Almost no noise between stations.

Did I put it into the cabinet then? No-o-o-o, I had to tweak the alignment one more time. I think the dial on my $89 signal generator slipped on the shaft. It's a round shaft with no index for the correct position. Totally screwed up the alignment, and I haven't recovered it yet. I've tried to recalibrate the signal generator with a Bose Wave Radio, but I can't be sure I have the correct position of the dial to set the IF.

So, I'm repeating the IF and AM band alignment procedures again and again, hoping to hit the jackpot and end up where I was two days ago. On the bright side--it doesn't hum!

[Image: https://lh4.googleusercontent.com/-Q807t...erator.jpg]
(I bought this TSG-17 new on eBay. After I discovered and fixed a defective cable, it actually worked pretty well for a few months. The identical model is sold under several other company names for up to $185. I wouldn't recommend it to a friend.)

[morzh]

Wink

Go on eBay and buy a cheap working counter - I got mine for $25 about 1-1/2 years ago.
Make sure they do claim it is working and has been used recently.
If you can ask someone with a good working signal gen - check it. Mine is dead on.

then before doing alignment warm up your gen and then use the counter to set your frequencies.
Using an unknown quality signal only makes things worse.

[Winky Dink]

I will look into that. I looked at eBay yesterday for another generator, but found nothing that gave me confidence in the instrument's functionality or accuracy. Thanks.

[TA Forbes]

Absolutely get a reliable frequency counter.

It really does not matter what your dial on your sig gen indicates, you use an F counter to get the F required and go from there.

A Frequency Counter is an instrument worthy of sending to a cal lab regularly to ensure it is right.

[morzh]

Another gen won't get you much of anything - they all pretty much are not very accurate unless calibrated. And even then. get a counter.

[Winky Dink]

After much hit-or-miss alignment, I hit a combination that got the set back to the condition it was in a couple of days ago when I first managed to eliminate the hum. There was no hum with the set on the bench. Put it back in the cabinet, power on, and I get the same hum again--maybe a little less hum. Tried a few things. Moved the set around the room. Plugged it into the isolation transformer that I had been using. Took off the bottom dust shield which had aluminum strips on it. Went outside and swung a dead chicken over my head three times. But it still hums (the radio, not the chicken).

So, I'll leave it alone while I try to procure a reliable counter. When I'm ready to play the alignment game again, then I'll put it back on the bench to see if it still hums outside of the cabinet.

[morzh]

Is your bench grounded?
Have you tried grounding the chassis?

[Winky Dink]

This thread is starting to sound like the Flight 370 news reports, "FLASH--ALERT--BREAKING NEWS--Nothing has changed!"

Bench is wood. Just now I tried grounding the chassis. In a few days I'll have a signal generator paired with a frequency counter and I'll pull the chassis then and check everything again.

But what I haven't done is to reseat each of the tubes. Several times I've had pins lose contact for no apparent reason.

[Winky Dink]

It's still humming, but...
I followed the advice given here and picked up a frequency counter. I checked the counter by feeding the generator signal on top of several AM stations, then switching the signal to the counter. The counter seemed to be accurate throughout the AM frequencies.

[Image: https://lh3.googleusercontent.com/-B56dt...520506.JPG]

Then I redid the AM alignment on the Philco 645, using the counter to determine the signal generator settings. The result was that the tuning at the high and low ends of the band was sharper then it had been...BUT in the middle of the band I get these horrendous noises. I've run into this before with another AM set, and I'm curious about the cause and the resolution.

This is what it sounds like (link should take you to a 30-second video):

https://picasaweb.google.com/coldrb/Jul1...directlink

I could eliminate the noise by readjusting the compensating condenser for the detector, but the next time I turned the set on, the noise was back.

So, what do you think? Is this a known phenomenon?

[Arran]

That sounds like motorboating, a low frequency oscillation, it's often caused by a defective or open bypass capacitor.
Regards
Arran