[Mike_RF]

MrFixr55

Thanks, I will keep you posted. The chassis has a very long way to go.

I am in the process of ordering stock to rebuild it. I have lots of stock for communications receivers, but this thing is a total new story for me. So I need to put some parts in to get it done.

I look forward to first light!

Theres nothing like the feeling of firing up an old radio you just resurrected. However I have a feeling that a session of coil winding might be coming my way. But we shall see.

Cheers!

[MrFixr55]

Mike, that is a beautiful cabinet. If the speaker has a paper or fiber "spider", it will sound better than the metal spidered Model 20 speaker which seriously limited the "excursion" of the cone.

BTW, do NOT run this radio without the speaker connected, the screen grid in the 47 may overcurrent and burn out, shorting the tube.

Terry, the 47 is, in fact, a pentode. The tube has only 5 pins but the suppressor grid is connected to the filament - heater at mid-point. That is why they can get away with 5 pins.

[Mike_RF]

MrFixr55

C26? That shows as a resistor on the PDF posted here? Or did you mean C24 and C30? Can you clairify?

Well, shes a dusty ol girl thats for sure. I understand it has been sitting since the 1950s. (or more) But the nice part about it is that its not molested. 

How much of these resistors will be out of tolerance?  A few? All   This is going to be a real labor of love thats for sure.

I think im going to pull all the tubes and fire up the power transformer and make sure its ok before replacing caps etc.

Cheers!

[Radioroslyn]

Sorry guys I had 24A on my mind. I must be low on my Mercon/Dextron I'm slipping.

[MrFixr55]

@Terry, save some Mercon V for me, I am slipping too.  I also need new ball joints.

@Mike,  , Yeah, it is C24.  that is a multisection cap.  I have not done a 90, but I have done other Philcos of that vintage (20, 80, 89)

The good news-  The radio is unmolested and should be a good performer.

The bad news- The filter caps are likely shorted, the other caps (those bakelite thingies) and resistors are likely out of spec. 
These caps also short.

The really bad news-  The RF and 1st Detector transformers are prone to open coils due to reaction between the cellulose inter-coil insulators and the lacquer on the wires.  This is covered by several articles by Ron Ramirez and others on how to rewind these coils.

Here's what to do to check this out:

1. Remove the tubes after verifying their location. Clean the dust off the chassis.  A leaf blower will work fine.  Windex will clean the tubes, but do so one at a time and re-mark the tube number if erased by the cleaning.
   
2. Locate C52, the Line filter (the power wiring goes to this).  Disconnect the "caps" (Capacitors, otherwise referred to as condensers in early literature) inside the block by passing a drill through the rivet to sever the connections between the caps and the terminals the drill bit should be a size that is as close to the hole in the rivet as possible.  Do this because these caps can short and either make the chassis hot or short the power input.
   
3.  "Ohm" the resistors.  They should be within 20% of the documented value.
   
4. Reinstall all tubes except the Type 80 rectifier.  This will put a filament load on the transformer but not a lode on the Hi voltage "B+ windings.
   
5. Carefully power up the set.  If you can put an ammeter in series, do so.  Verify the "heater" voltage for all tubes except the rectifier is 6V AC. (All tubes except the rectifier are in parallel.)  Check for leakage, or excessive heating of the transformer.  VERY Carefully verify the voltage between the 2 smaller "holes" in the 80 Rectifier socket.  There should be about 600-700 Volts AC between them.  Carefully verify the voltage between the 2 large holes in the 80 Rectifier socket.  There should be 5V AC between those contacts.  Power down the set and remove the tubes.
   
6. Replace ALL caps starting with the filter caps.  There are 2 ways to do this.  The quick way is to just replace them. do not "bridge" them.  For the Bakelite caps, pass a drill bit through the rivets to sever the connections as in Step 2, above.  Solder the replacements to the tabs.  Some of these bakelite blocks contain 2 caps or contain a cap and resistor.  The true Restorer's way is to hollow out the blocks and insert the new caps and resistors if exist in these blocks.  The true Restorer will also "stuff" the filter caps with new ones.  There are articles on how to do this on the Phorum.  Do not forget to replace the 2 "Bypass Cap" blocks and the caps in the tone control.
   
7. Replace any out of spec resistors.
   
8. Add tubes, connect the speaker and an antenna, and take the radio for a test run.  If you have a Variac or a "dim bulb" tester, use them (See articles in the Phorum for details).  Watch the 80 and other tubes for flashing, indicating shorts.  Watch the 47.  If the screen grid or plate start glowing, shut down.
   
9. You should be rewarded with static or stations.
   
10. Finish cleanup and restoration.
    
11. Enjoy your handiwork, and say a prayer for the folks who built, sold, bought and used this radio, as they are all likely deceased.  Think of all of the historical broadcasts that were received by this radio.  Be sure to play it relatively often.
    
12. Keep us all posted on the progress!!
    

 

[Mike_RF]

MrFixr55

Thanks for the list. Im sure the order of operations will come in handy. I kinda saw already that you have to heat those Bakelite boxes and push out the old caps. All of the caps, Bakelite and filters will be restaffed in original housings. Lotsa work ahead for sure.

I have also noted the main ganged tuning cap is loose. Looks like some kinda gromets are toast too.

However I have a few questions.

1) The coils that go open. I assume its just the outer coil that goes? Have you got a link to rewinding info?

2) Do the transformers go? Someone said the Philco transformers are pretty tough and rarely go. Its that the case?

3) You say replace all caps. does that include the 110pF ones? Are they mica? In communications received they seldom go.

4) how fussy is this unit for tolerances? If I replace a 51K resistor with a 50K or 110pF with 100, is it going to cause issues or is it pretty broadly tolerant?

Cheers

[morzh]

1. As far as I remember, there is no inner/outer coil. They are top and bottom. My experience, the smaller coil, I think, the lower, usually goes.
2. No, Philco transformers, especially interstagfe and output, go quite often.
3. No. Unless they are paper caps, 110pF stay. Do not touch mica caps.
4. Not fussy. 20% is ok.

[MrFixr55]

+1 on Morzh's comments.

Below is a link to an article regarding rewinding coils. 

https://philcoradio.com/library/index.ph...lco-coils/

The only one listed for the Model 90 is the RF Primary.  Maybe that means that the other coils are relatively solid. Ohm the coils.  If they check out, you are good.  I had issues with coils in the 20, 80 and 89.  The 20 was easy because it is TRF and the primary windings (the ones that usually go bad) are not critical.  The 80 was not terrible.  The 89 was a nightmare.

I have used a combination of flat and conical faucet washers to replace the rotted rubber grommets that mount the tuning capacitor.  The Experts on the Phorum may be able to tell you if correct reproductions are made.  I may be wrong, but I believe that the only fixed mica caps in this radio are to filter RF from the detector output and AF Amp input.

[Mike_RF]

First off, a great big thanks to all those who have pitched in and helped. Im not a stranger to electronics really. I started off many years ago working for Motorola and GE on the commercial communications side. Repairs, installs duplexing and multi-coupling were specialties of mine. Any ways, mostly transistorized stuff along with a few commercial broadcast FM stations Running stuff like 3CX15000A7s. 

Until now i have mostly been restoring communications tube gear from the 1950s and up. So this Lowboy model 90 is my first step into the realm of the 1920-30s' Hence i have lots of questions. I like doing restores right the first time. 

And yet another question.

C24 is comprised of a .1  .13  &  .25 - How do you know which is which on the schematic? Its currently under a steel cover, will is become apparent once the cover is off which is what value?

When you say ohm the coils are we just looking for continuity or are we shooting for a specific ohmic value?

I havent started work on this thing yet. I have orders caps and resistors. So while I wait for those to arrived I will read and research to be best prepared to make a decent job of it.

Cheers

[GarySP]

Looking forward to your restoration. Take care and BE HEALTHY! Gary

[MrFixr55]

Hi Mike, 

If you open the can, there are likely no indications of value.  Hopefully the schematic is marked.  Since these are "bypass" capacitors, the values may not be important may be able to just pick the highest value in the can and use for all.  Personally, I think that this stuff is simpler than transmitters and UHF stuff.  

Re the coils, I would be starting out just verifying continuity as a "Go - No Go" t, test.  Later on, if there are issues, then concern yourself with whether the resistance is correct.  I would do the first few steps of the "procedure" that I posted prior to stuffing the caps, to discover other "deal breakers" before getting too deep into it.

BTW, I did leave out 2 things:

• Add an in line fuse holder with a 1 Amp fast fuse.
  
• To protect the power transformer from shorts if the filament in the 80 breaks, I place 3A 100PIV rectifier diodes in series between the HV secondary and the 80 plate connection.  Anode to transformer, cathode to 80 plate.  This will protect the transformer in case of a short.
  

[RodB]

Hey Fixr, do you mean 3A 1000 PIV for that diode?

[Radioroslyn]

1N5408?

[Ron Ramirez]

C24 is comprised of a .1  .13  &  .25 - How do you know which is which on the schematic? Its currently under a steel cover, will is become apparent once the cover is off which is what value?

S T O P

Before proceeding, please read the information in the following links:

https://philcoradio.com/library/index.ph...info-1-47/

https://philcoradio.com/library/index.ph...-model-90/

The first gives correct information on the two metal cans which contain three capacitors apiece. (Oh, and it's part 24 and part 30, not C24 and C30.)

The second gives the proper IF frequencies for the three different versions of model 90.

I should add that the capacitors inside cans 24 and 30 are accessed by unfolding four metal tabs on the end where the wires exit the can, then pulling the fiber cover away, and then pulling out the wax-encased guts.

This post from my blog should assist you with those cans:
https://ronsradios.com/2023/05/02/philco...on-part-2/

[Mike_RF]

Ron

Some great information here! Thank you. Many parts will sure help me along the way.

Couple Questions.

-Were you happy with the cap specs you chose for the tone switch? Or where those of known values?

-insofar as the speaker, is the polarity of the voice coil and field coil critical? Do they need to be in a specific phase? I have to swap a single ended transformer over to a speaker that has a double ended transformer and the polarities are not clearly depicted. 

Cheers