[Bob Andersen]

I've finally gotten around to the 38-7CS I picked up a few years ago. You can read about the cabinet restoration over here: http://www.philcoradio.com/phorum/showth...p?tid=3653

This radio had been modified with a record player, headphone jack and some switches. Just as I restored the cabinet to stock, I'm doing the same on the chassis.

[Image: https://farm3.staticflickr.com/2631/4134...87d5_z.jpg]

First thing I did was remove the modifications then did a quick recap.
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That got it playing fairly well However, it wasn't all that loud and the volume control was flaky. Also, the muting switch on the concentric mechanism isn't working.
[Image: https://farm3.staticflickr.com/2925/1457...433a_c.jpg]

[Bob Andersen]

Next, I dove into doing a more thorough job. I removing the whole tuning mechanism so I could get at those manged tube base shields and clean the chassis.

[Image: https://farm3.staticflickr.com/2937/1439...64f5_c.jpg]

I'm replacing them with some salvaged shields held on with cap head screws and nylon locking nuts. I used a pop rivet and knocked out the center pin for the 6K5G base where a grid cap wire feeds through.
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Next came the the tuning capacitor.
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I also dug up a suitable filter capacitor to replace the missing one and restuffed it.
[Image: https://farm6.staticflickr.com/5594/1469...36d5_c.jpg]

[Bob Andersen]

Finally, I had some fun breaking down and cleaning the cone-centric mechanism.

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I was finally able to piece together one well functioning unit using parts from a couple other spares.
[Image: https://farm6.staticflickr.com/5489/1468...d551_c.jpg]

[Bob Andersen]

After putting it all back together, I ran through the alignment procedure and the coils seemed to peak well.

However, the volume is still pretty weak on the broadcast band and fades away even more after a few minutes to where I can barely hear it. Sometimes I can get a big volume boost if I stick my finger on the 6A8 cap, but other times it has no effect at all.

The antenna and IF transformers check out OK and all the DC voltages are dead on. There were only two mica caps which I replaced and it made no difference.

Any thoughts ?

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[Arran]

Maybe resolder some of the grid caps, and replace the remaining grid cap leads?
Regards
Arran

[Bob Andersen]

I have replaced the grid leads and swapped out the tubes - no change. There are a coupe originals resistors left that I'll try replacing next.

If all else fails, I do have an entire spare 38-7 chassis from the tabletop model I can swap parts with.

[codefox1]

Bones would be envious, wonderful work.

[Chuck Schwark]

Is the mute switch working correctly in the dial mech?
Could not tell if you got into the contacts from your pics.
Great work, by the way.

Grounds audio signal during tuning cone to cone.
Connects to the jct. of VOL pot wiper and cap 28.

Chuck

[morzh]

Bob

Have you checked your tubes yet?
See if the fluctuations coincide with AVC voltage (if this radio has AVC), this might give you some scent to follow.

[Bob Andersen]

Chuck - Yes, the muting switch does work correctly, but I disconnected it anyway to eliminate it as a source of trouble.

Yes, I have checked and swapped the tubes, but no change. It does use AVC so maybe I should monitor the AVC voltage as it warms up ?

[morzh]

AVC can be an indicator, yes. If you see it fluctuating with the fading, it is a clue.

[Arran]

What about the plate resistor on the first audio tube? Check the plate voltage there, see if it low or becomes lower the longer the set is left on.
Regards
Arran

[Bob Andersen]

It's fine and does not vary. Now keep in mind that even when the radio is first turned on the volume is quite low and then drops even further. I replaced the candohm resistor and there's no improvement at all. I also swapped out the 6K5 with a 6Q7 after making sure nothing was connected to the diode pins - no change.

[gregb]

I am sure you checked but what's the B+ look like? Have you tried a new output tube, could be gassy

Gregb

[Bob Andersen]

All the voltage are correct and the tubes are good.