[Chris h]

This Philco just came to me this morning.
I don't post very often, mostly lurking in the background reading all the posts and trying to learn as much as I can.  This is a mid production model 90, I am guessing, as it has the single 47 pentode output. I am not planning on working on this until this winter, sometime. (Have several others in the queue ahead of it.)
What should I be looking out for on this model? Is this one of the models that tend to have open RF or IF transformers?  It does have AF output, picking up strong stations when touching the grid of one of the 24s. (Not sure which one. The PO had been using it this way, against my advise not to use it until it had been properly gone thru.)  The speaker cone looks very brittle and bleached. Like it had been exposed to sun light. The cabinet finish has had something done to it, but it doesn't look too bad.

In the mean time, I will start gathering up capacitors and etc. to dig into it later. Thanks for any insights, advise, or help.

Chris,
N9WHH

[markmokris]

I just restored a model 90 cathedral.  After restoring a number of others - 19, 89, 80, 84, 60, - the model 90 was not nearly as bad as I thought.  I have dealt with the open coils, but I did not have an open coil at all with the model 90 I restored.

I think the biggest issue I had was the friction drive on the tuning capacitor.  The little pinch roller wears and tends to slip as you turn the knob.  But there is info on that problem out there and on this site I think.  I fiddled with it and got it to work pretty well, but not perfect.

Mark K8KZ

[morzh]

I was lucky, no open coils etc. Pretty much was recapping and some resistors change.
Mine is 2x45 output.

[Chris h]

Thank you, both. I did a model 95 a year or so ago, and the biggest issue there was the restring of the tuning condenser. Even the restuff of the filter block wasn't as bad as I thought it was going to be. I had no issues with any of the RF transformers. I am expecting this one to be pretty much straight forward, run of the mill, caps and resistors. But there is always the possibility of a "gotcha" out there someplace. Sounds like it will be a nice cold weather project.

Chris,
N9WHH

[Radioroslyn]

Hi Chris,
Yes older big chassis sets w/ the worm gear in the front and back are a pain to restring. Common issues to pre '36 or so Philcos are open primaries on the rf coils, oscillator coil feedback winding open, fairly rare to find a bad if transformer, open audio driver and sometimes output transformers, spkr field coil open.

Sounds like you've dodged the bullet on most of these but would check the ant coil primary, this might be the cause of the good reception where touching the 24 cap.

GLOM de N3GTE

[Chris h]

Thanks Terry. I thought that I had read about the possibility of open coils somewhere on here. I'll be on the lookout for them when going thru this one. I do have one model 95 that has a missing intestage audio transformer. It has been a long time since I worked on it, but as I recall some previous repairman had removed the iron from the transformer housing and somehow reconnected the leads. I still have to go thru that one and replace the transformer. Thanks for the help.

73
Chris, N9WHH

[Chris h]

Well, now that I have some vacation time to burn, I have returned to my Philco 90 Lowboy. I think I have all the caps & resistors I need for the job, so I started on the power supply first. There have been numerous repairs made to this over the years. Every Bakelite block has been replaced with a wax/paper cap. The blocks are still there and it appears that the insides have been removed or cut out of circuit. They must have gotten awfully hot because most of them are just dripping with wax/tar. A real mess.

I decided to try something; and pulled the first block (across the power cord), removed it from the chassis completely, removed the paper caps tacked onto the terminals, and cleaned the terminals. Scraped out the remaining wax/tar with a screw driver. It was still a mess, all covered with wax/tar. I dropped it into the ultrasonic cleaner with hot water and a good "slug" of Simple Green. Turned on the heat and ran it thru 2 cycles of the cleaner. Pulled it out and it was almost like new. I completed the cleaning of the terminals with the soldering iron, which brought out a little more wax/tar around the rivets. So I dropped it back into the cleaner and ran it thru another 8 min. cycle. This time it came out absolutely clean.

The tone control was next to go into the cleaner, after removing the potted caps. Again, it came out clean, looking like new and ready for rebuilding. I don't know if anyone else has tried this, but it sure worked for me.

I have re stuffed many of the Bakelite blocks, but this radio is the worst I have ever seen. I have not had the need to clean them up before. Just cut the leads, apply a little heat and pop out the old potted cap. Easy! But this does pretty good. Looks much better.

[Chris h]

I have been working on the 90 this week, recapping and replacing out of tolerance resistors. This thing has really been hacked, badly!  I have gotten thru the power supply and AF section and speaker. I powered up this evening and after finding a bad detector, got it playing. I am feeling pretty good about that, considering the rewire from all the hacked up previous "repairs" was quite extensive. It will tune in one strong local station right where it should be on the dial. I checked the IF frequency lwith my scope and it appears to be right on 260 kHz. This is the single tube 47 output, and according to Ron's info in the tech section, it should be tuned to 175 kHz. My question is: can it even be tuned to 260 kHz and operate? I am assuming one of the previous repairmen aligned it to 260 in error? I am just wanting to confirm the correct IF before attempting a change. There wouldn't be an odd ball run that is supposed to be tuned to 260, perhaps?

I won't be doing an alignment until i complete the recap on the RF section. Still need to clean up the tuning condenser too. It needs new rubber bushings which won't allow me to tune the full range of the radio.

Thanks for any insites as to what is going on.

[morzh]

Push pull 47 output 90 has 260kHz IF....

[Ron Ramirez]

Chris said it was a single 47 version, which has an IF of 175 kc as does the 2-45 version.

It is true that the 2-47 version has an IF of 260 kc.

[morzh]

Ron

Yes, I know. This is what's puzzling. But then the 260kHz is not some arbitrary number. It is a valid IF frequency from the 90 family or from 70.
So short of someone replacing IF filters and rebuilding the oscillator (why?) if it is factory, could it be they reused some excess parts and made a batch of non-standard SE-47 90 radios?

[Chris h]

I thank both of you for the replies. I am having trouble with this thing being tuned so far out of spec. I would not have thought that it could be adjusted so far out.  Since it appears that all adjustments appear to be compression caps, I suppose that they may be screwed down pretty tight, if I am thinkin' right.  

It does tune pretty good across the band scale, but most of the stations are pretty weak.  I figured it was mostly due to the bad caps in the RF section.  Perhaps not.

I will dig into it sometime in the next week or so and see what happens.

[morzh]

Chris

No trimmer cap can adjust frequency so it doubles.

[Ron Ramirez]

The dual 47 90 chassis does not have a separate oscillator tube. It uses the same circuit as the 89 and 19, with a tetrode (a 24 in this case) acting as mixer and oscillator.

Philco would not have installed the newer autodyne circuit in the older single 47 90 chassis, else they would have a leftover 27 tube socket with no need for a tube in that position. It was a new (late 1931) development, and it went into Philco's newest version of the 90.

I think the confusion comes from the documentation which was inconsistent over the years, with some sources claiming the single 47 model 90 used a 260 kc IF when in fact it was 175 kc. 260 is not double of 175 - 175 x 2 = 350. It is quite possible that some people have attempted to align their single 47 90s at 260 kc, with poor results, due to the misleading documentation.

Off subject a bit, I always wondered why Philco continued to use the less than ideal autodyne circuit in the 89 with the difficulties they had with it even back then, after the development of the 6A7 pentagrid converter tube. I've converted a 71 and an 89 to use 6A7 tubes, and they work very well.

[Chris h]

Well, I am making progress. I am waiting on new rubber mounts for the tuning condenser. All caps and OT resistors have been replaced. Hopefully the new mounts will arrive today and I can get it mounted. Then I will move on to see what I can do with the IF frequency.