There Has to Be a Better Way.

[Winky Dink]

It took the written explanations AND the sketch to get through to me. Thanks, everyone.

[Winky Dink]

When I finished everything under the chassis, I mentioned to my wife that I was ready to reinstall the tuner. She usually doesn't show much interest, but this time she offered to help put the tuner on the chassis:

https://picasaweb.google.com/lh/phot...eat=directlink

Yeah--she's from Boston.

I did finish reassembling the chassis except for the "shadow meter." I tested the filament circuit with a 6-volt battery, putting the tubes in one at a time. Then I brought out the isolation transformer and the variac (Chinese knock-off). I gradually increased the power, but at 90 volts I didn't even get a glimmer from the pilot light. Arg-g-gh! I forgot to turn on the RADIO! I started again, got the tubes all aglow and the transformer outputs were all good, but absolutely no sound. Arg-g-gh! I forgot to plug in the speaker! Again, this time with the radio turned on and the speaker plugged in, I got up to 115 volts, and still got nothing but dead silence. Arg-g-gh! I forgot to put in the 80--the only tube that was missing when I bought the set.

Finally, I got some response. I can tune in a couple of AM stations, but get howling, growling, and squealing when I get close to tuning the other local stations. On the "police band" I get a lot of noise, and on the shortwave I get nothing. That may sound disappointing, but I'm delighted that I could get it to talk at all. I'm going to leave it alone for a couple of days and then try to make it work like a proper radio.

Thanks for the help I've received so far. Here are upper- and under-chassis before/after photos. You can download them, print and frame them. They make perfect Christmas gifts!





Happy holidays to all.

[Reece]

That was using her noodle to get that tunah in place. Nice work, all. Sounds like you've got some bad contacts or the thing out of alighnment. It'll straighten out.

[Kevin Kuehn]

That's quite the transformation you've accomplished there. Would love to see more close up pictures of the detailing.

[Winky Dink]

I'm figuring out a few things myself.

The set came with an 89 replacing a 78 as an IF or RF amp. I replaced it with a good 78, and that eliminated a loud hum.

Most B-C voltages were 30% higher than Philco specs. Rectifier was putting out 410 volts instead of the specified 300v. Switched in different used 80 and the output went down to 330v most tube voltages are reasonable.

Made my first foray into alignment. Spent hours trying to make the signal generator give an audible output before I determined that the connecting cable was defective. I adjusted each capacitor to obtain max noise (AM band only).

So now I have a usable radio with fair-to-poor AM reception and some extraneous noises.

Now I'm stuck on a couple of B-C voltage issues. Here's the latest test results:



I can't figure out why the voltage to the plate on 85 is so low. All components test OK, and I've even tried replacing the resistors 48 and 49 with new ones. Would it be worthwhile (or risky?) trying a lower resistance for the 99K resistor?



Full schematic:

https://picasaweb.google.com/lh/phot...eat=directlink

If you're interested at all, here's a small album detailing replacement of missing condenser cans:

https://picasaweb.google.com/coldrb/...eat=directlink

[old_coot88]

Originally Posted by Winky Dink

?...I can't figure out why the voltage to the plate on 85 is so low. All components test OK, and I've even tried replacing the resistors 48 and 49 with new ones. Would it be worthwhile (or risky?) trying a lower resistance for the 99K resistor?

What is the (plate) voltage with the 85 removed? Does it jump up to the full 267 volts? If it does, i would try this (with the tube re-installed):

Since the 99K is the plate load resistor, shunt the 32K that's in series with it. Try maybe a 22K, a 10K, then a full shunt. That'll raise the voltage without losing signal-voltage swing across the 99K. See if this improves volume any.

...I adjusted each capacitor to obtain max noise (AM band only).

Which capacitors did you adjust? The ones in the IF cans, or the ones in the front end?

full schematic:
https://picasaweb.google.com/lh/phot...eat=directlink

Link won't come up on my rig. But found the Riders on Nostalgiaair
http://www.nostalgiaair.org/PagesByM...2/M0013822.pdf

[Winky Dink]

The full voltage did show up with the 85 removed. I tried the series of shunts, but there was no discernible change in volume. I have pretty good volume already.

The alignment was to two caps each on 1st & 2nd IF transformers, then two caps each on the three RF transformers, then the single "oscillator series."

I checked the link to the schematic, and it seems OK. I'll put it here, anyway for easier reference even though the readability is marginal.



I'm puzzled with the grid voltages--more often than not I get appropriate values, but negative instead of positive or vice versa, and it seems to work fine. On the 42s here, however, the value seems to be way off. But it still works.

[dtvmcdonald]

check parts 43, 64, 66 and 67. They involve the grid bias
on the 85. Its conducting too much.

[Winky Dink]

Thanks. I'll look at those tonight.
By the way, I went back and checked the voltage when shunting the 32K resistor to the 85 plate, and there was increase in voltage.

[Winky Dink]

dtvmcdonald may be exactly right. Philco's yearly list of changes include a capacitor from part 64 (BC Resistor) to the junction of 66 and 67. I was ready to do that a month ago, but I put it off because I DON'T KNOW WHICH IS THE C- END OF THE BC RESISTOR. So can someone please tell me which of the three terminals on the BC Resistor is the "C- end."

[Winky Dink]

Well, I put in the additional capacitor and rechecked all of the above-mentioned parts. Every part tests OK. Rechecked all the voltages and they were the same. I have a few other things to look at, but any advice will be appreciated.

[Winky Dink]

I didn't resolve the voltage issues, so I spent several days trying to align this set. For the first 20 attempts, I kept forgetting some step in the process. When I finally got it right, I had fairly good reception above 90 kHz, but much noise and very weak signals below 90. The last step in the alignment is adjusting the oscillator condenser for the lower frequencies, but every time I adjustment it, the output (audible) did not change. I would screw it down to a hard stop, back it out a half dozen turns, and there was no variation in the (barely audible) output.

I finally pulled out that condenser for a close look, but I found nothing amiss. When I was bolting it back in place I noticed a little rust on the adjusting screw, so I put a drop of 3-in-One on it.

When I had the condenser bolted in and rewired, I turned it on and tried the oscillator adjustment one more time. To my amazement, all the lower frequency stations came in strong, clear, and with no noise between stations. That tiny bit of rust had stopped the screw before it got to the right capacitance.

Now I'm sure the set can be aligned, but now the high end of the dial is problematic. I get pretty good reception, but excessive noise between stations. The tracking is perfect. The lower-end stations are very strong, but when you get down to 600 kHz the stations comes in over a range of 40 kilocycles. There should be a way of balancing this, but all I've tried so far hasn't worked. Is it likely that the IF frequency is the problem? Or should I back away from the peak oscillator low-frequency adjustment?

I expect that my cheapo signal generator isn't very accurate. In fact, it's not really an actual signal generator. It's a signal GEMERATOR!



I would greatly appreciate advice on which alignment parameters to address.

[Winky Dink]

Never mind. I started reading some of the old radio repair stuff. When I began reading about antennas, I realized that all the noise is extraneous signal picked up by the antenna. I had it hooked up to 40 feet of inside wire. With just 8 inches of antenna lead, the noise was negligible. With no lead, it's even better.

[Winky Dink]

I had the Philco 645 chassis complete and performing very well. For advice on some electronic details I went to Philco Phorum and got exactly what I needed to know about a mysterious stray wire and the shadowmeter.

Then, two nights ago the radio suddenly, for no apparent reason, went silent. All that I could hear was a couple of stations on top of each other if I hooked up the long antenna and turned the volume to the max.

I checked socket voltages and found a discrepancy in the 6A7--Zero volts at the oscillator grid and 90 volts at the oscillator plate. When the set was working, it had -22 volts and 138 volts. All the other voltages are the same as when the set was working, including the power transformer. All transformer coils show appropriate resistance and continuity. I've checked the continuity of practically every circuit. Also retested and swapped some tubes.

Does the sudden failure and loss of the oscillator voltages point to something I should look into? Any likely, or even possible, causes?

I did query the pholks at the Philco Phorum but haven't seen a reply yet. Maybe I phrustrated them with my questions.

If anyone can help, here's a link to a legible schematic.

https://picasaweb.google.com/lh/phot...eat=directlink

Merci Beaucoup,
Winky

[Reece]

Did you try another 6A7? It gets B+ via the primary of IF transformer: what's voltage on each side of that primary? Also gets B+ through the shadow meter, it appears. Does the meter have the proper continuity?