[cknob]

Hi everyone,

About 10 years ago, I bought my brother a completely restored Philco 37-650 Tombstone radio as a housewarming gift for his new, retro style home.  The radio had been restored by Lew Magrish and was for sale on the Radio Attic website for around $750.  The restoration included new electrolytic capacitors, re-stuffed Bakelite blocks, resistor replacement, addition of a 1/4" input jack, a successful fix of the shadow meter and a cabinet refresh.  The radio weighed a ton and worked fantastic on all 4 bands, AM broadcast and 3 bands of shortwave.  About a year ago, my brother told me the radio had stopped working.  It had developed a common problem with all 37-650s in that it played fine for a few minutes and then went silent.  I took it to a local vintage radio restorer who got it working again.  After a month, it developed another curious problem, again, sound cutout that could be solved by any number of interventions.  If you turned the radio on and off rapidly 2-3 times or switch bands in the same manner, it would crackle back to life.  Shorting the tuning capacitor with a screwdriver would do the same.  Each time I did this, the radio would play but playing time before cutout would get shorter and shorter.  Finally, nothing would work and get it going again.  Having gotten, with lots of help from this forum, a Philco 90 Lowboy restored to a reasonable playing condition, I decided to take a crack at the 37-650.  I cleaned all of the tube socket pin holes with electronic cleaner and a stiff, narrow nylon brush (great tool by the way).  I cleaned and replaced suspect wiring throughout the radio and on all the tube cap leads.  I sprayed cleaner in the on/off/tone and separate volume controllers vigorously working them back and forth.  I reassembled the chassis, turned the radio on and it seems to work fairly well now.  I left it on for several hours and switched between AM and shortwave bands without any significant issues.  There are some curious idiosyncrasies though.  As you get near a station, there is a high pitched squeal/whistle requiring exact tuning on a station to null it out.  The radio also gets to a decent level of volume about halfway through the volume control rotation but then gets no louder.  I did an AM alignment getting a very strong, loud signal at 470 kc, much louder and cleaner than the broadcast level.

I'm thinking of going into the chassis to troubleshoot and fix what I can to increase performance and reliability.  The first thing I noticed was Lew had re-stuffed the AC line capacitor block with standard, tubular axial lead caps.  Shouldn't these be AC X-Y safety caps? Does anyone have ideas as to where I should focus to address the whistling issue? 

Thanks in advance everyone.

Chris

[Phlogiston]

They should be. In a Bakelite block there is no reason not to use safety caps. In some radios restuffing an original tubular might prevent installing the safety caps which are mostly a disk. In this case try to use the highest AC voltage cap that will fit. Also adhere to the new standard for these - which I think is no larger than .01. I have seen some large values used - if you like a tingle when you touch your set.

P.S. Check for a bad or intermittent volume control. DO NOT clean it with D5 Deoxit. It will be destroyed. If you have to, use F5.

[morzh]

I hope you did not spray the same cleaner on switches and volume pot.

The volume pot cleaner has no effect on contacts, and contact cleaners destroy the pots.


Check alignment. What you describe with squealing during tuning looks like there might be issues.

And, depending on how much the radio was used, there are tubes that weaken over time.

[Mondial]

Chris, it appears that the squeal could be caused by an oscillation in either the RF or IF amp stages. Does the squeal occur as you tune through a signal on all bands or only on broadcast? Uniformly on a band or only in certain parts of the dial?

If it is selective on only some bands or ranges of tuning, then it is most likely caused by the RF stage. If it happens on all bands and uniformly across the dial then its probably in the IF. Some cheap shortwave receivers actually made the IF amp oscillate on purpose to provide a beat oscillator function for CW reception.

Typically an oscillation like this is caused by a bad ground or open screen grid, cathode or B+ supply bypass cap. You can try jumping a known good .05 uf cap across each bypass and see if it cures the squeal.

[cknob]

Mondial, the squeal seems to have been some kind of atmospheric anomaly and disappeared the following day. It does appear though, I did use the wrong cleaner on the volume pot and it is performing badly, much worse than it was before the cleaning. Lots of crackle and distortion when I touch it. I guess rookie lesson learned. Now it looks like I'm going to have to source a new volume control. Back to the WTB forum I guess!

[TV MAN]

This is the 1st I have heard of D5 destroying controls. What's up with this?

[cknob]

I used a product called BW-100 ECC that I got from Amazon...ECC means electronic contact cleaner. It said it would be safe to use on all types of pots. All I know is the volume control is much worse than it was...plays when turned all the way down, pops and crackles through the speaker when I touch it, lots of distortion, loud buzzing and general mayhem when I move it etc. Sounds like it's gone.

[Ron Ramirez]

It's true, DeoxIT D5 is not good for potentiometers. DeoxIT FaderLube (F5) is what you want to use on potentiometers - and then, only if needed.

[Arran]

You may want to verify that the Bakelite block condensers were in fact restuffed, Lew Magrish is well known for getting his repair guys to do the bare minimum to get a set playing for resale, then charging prices like they actually were fully restored. It is possible that the reason the set cuts out has to do with the grid cap leads, those like to break internally, especially near the clip. The solder joints on one or more grid caps could also be failing, fresh solder may fix them.