[Mike_RF]

Greetings to all- This is my first post on this board. 

I have been restoring old "Boat Anchor" communications equipment for some time now. Mostly stuff like Hallicrafters, Hammerlund, Lafayette and Johnsons transmitters.

So recently i came upon a chance to buy a Philco Model 90 that needed a speaker assy. It was in nice shape cabinet wise, but the radio needs the usual extensive amount of attention to make it fly again. 

So not too smart me buys a complete speaker unit off ebay. AND THEN i find out that there are 2 ouput configurations for the model 90 lowboy. 

Two 47s in a push pull arrangement and one 47 in a single ended set up.

As you can already guess the speaker i bought off of flea bay was for two 47s, not one. Shucks. And of course i discovered this all after the fact.  

So now to try to sort this out. I would really like to see this ol girl play again as the cabinet is nice. What a treat that would be. 

Since this is my first shot at anything this old, this speaker system is something foreign to me. I know little about them. 

So I have the original 3 wire black transformer that was on top of the original speaker. Im thinking i can swap it with the 4 wire speaker when it arrives here.

But... I dont know 2 things. a) can i do that swap? and b) how does one test the original one? From the black wire I have 450 ohms on one side, and from the black to the other wire I have like 500K. This seems high to me. Maybe im wrong. 

So im hoping someone in the know here can bump me in the right direction.

Cheers

[morzh]

No worries.

As long as:

1. Your field coil is good (they are all the same in 90 speakers), and
2. Your voice coil is good, then:

Buy the appropriate 125CSE (single ended) Hammond transformer, install it instead of the existiing one and be happy.

And. I am sure you will easily sell the 90 p-p transformer on eBay as long as it is good.

[Mike_RF]

Thanks Kindly for the response.

However the original speaker is totally destroyed.

I am unsure of the terminology, But the black transformer that was attached to the speaker, I believe one side of it is open. One side measures bang on 450 ohms, the other side seems open.

So all i have to deal with is the speaker thats on its way from ebay.

Can this push pull unit be used? The coil is only 100 ohms more from 450 to 550?

Cheers

[Mike_RF]

Ok

I think I stand corrected.

I think the output transformer is ok. On the primary side i have 450 and on the secondary side I have 0.3.

I was expecting that the field coil was installed and working when it was not.

So, that brings two questions.

1) Can I put my old single end transformer on the new speaker? Remove the push pull transformer and install the single ended one? I think the voice and field coils are the same. Hence i think i can swap the transformer and be happy.

2) The main unit needs to be gone thru. No ifs and or buts. Re cap. New resistors. Check tubes etc. But my question is, what causes these field coils to burn out or go open? Would it be bad filter caps? A bad tube? A short to ground? Something caused the field coil to go open on this unit. Need to be on guard and make sure it gets resolved.

Cheers and Thanks Kindly!!

[Radioroslyn]

Hi Mike and welcome.

This might help you see what the differences are between the 2 speakers you are looking at and the one you are getting. The model 70 and it's other alliterations use the same speaker as your single 47 model 90. Also bear in mine that the resistance for the opt that you are quoting is the dc resistance not the ac load that is presented to the tube. 

https://philcoradio.com/library/index.ph...-21-70-90/

GL de N3GTE

[MrFixr55]

Hi Mike,

While I was writing this, RadioRoslyn put up a much better post than I did. I am leaving this but read his post also, as he has a VERY good article attached1
Personally, I am not a fan of the speaker that was originally installed in the model 20 (and likely the 70 and 90 as they are very tinny. I installed a modern speaker in my 20 and am much happier with the tone. Since mine is a Frankenradio to begin with, I was not quite worried abut authenticity.

In your post of approximately 7:20 PM, are you describing the "bad" transformer as being from the original speaker or from the one purchased from e-Bay?  If you are describing the original speaker, there are 3 leads from the speaker.  One lead is from the Output Trans primary to the plate of the 47.  Another wire is shared with the B+ connection of the output transformer primary and the field coil.  The 3rd wire is from the field coil to a voltage divider that supplies B+ to the screen grids of the 24As.  


I have attached the diagrams for the 90 and 90A to this post for your convenience (these are from Nostalgia Air, there may be better ones in the Philco Library.

Philco 90, 70.pdf Size: 849.3 KB  Downloads: 173

Trace these wires out.  It seems that either the output transformer or the field is open.  If the output transformer is open, then you have to find a replacement.  Use the transformer that Morzh recommended.  If the field is open and the transformer is good on the original speaker, and if the field is good on the new speaker, then install the original transformer on the new speaker.

Note the very low voice coil impedence on these speakers on the chart that RadioRoslyn supplied vs the 3, 4 0r 8 Ohm impedence of more modern speakers. this must be taken into consideration if a non-philco replacement transformer needs to be found.

[Mike_RF]

Hi - Thanks for the response.

The speaker frame, voice coil and field coils are exactly the same between the single ended and the push pull. 

The only thing that is different is the output transformer. The push pull has an impedance of 550 ohms while the single end is 450.

So, since the speaker, voice coil and field coils are identical, I am proposing that I simply remove the push pull transformer and install the single ended transformer.

Im just checking it out with the folks in the know before i proceed. 

Cheers

[Mike_RF]

MrFixr55

The original speaker, voice coil and field coil have been completely destroyed.

The only thing I did save off it was the output transformer. I mistakenly though it was open, but further tests show it actually to be still good. So my plan would be to move that single ended original transformer over to the new speaker assy. Remove the push pull transformer and install the singles ended one i have.

Just to be clear, the part number for the speaker, voice coil and field coil are the same. The only part number between the two that is different is that of the output transformer I am proposing to swap.

I hope that helps

Cheers!

[morzh]

>>> So, since the speaker, voice coil and field coils are identical, I am proposing that I simply remove the push pull transformer and install the single ended transformer.

Isn't is what I said.....

And yes, if your origianl transformer is good, you could use that one too.

[Mike_RF]

Morsh

I thought you said to buy and install a Hammond product? And sell the P-P unit.

I have decided to just change the transformer on the P-P unit over to the Single ended unit and use that.


Cheers

[Radioroslyn]

Mike,

Reread my post. Open the link and look at the chart of the different K style speakers. You will see that it lists the load impedance not the dc resistance. For the se 47 it's abt 5.7K

To answer you 2nd question. It wouldn't be bad filter caps as the fc is it the circuit after the HV dc has pass thru the caps. The HV is split the HV coming thru the fc feed the rf amp, mix/osc, and IF amp. The other circuits are fed from #57. A leaky bypass cap could do it. The coil is rated @40ma. Or perhaps rot/bad connection.

[DaleHCook]

Two 47s in a push pull arrangement and one 47 in a single ended set up.

There are three versions of the 90/90A. The first used push-pull 45s, the second used a single-ended 47, and the third used push-pull 47s.

[Radioroslyn]

Mike,

I might be looking at this from the wrong angle. What cabinet contain this 90? a table top (B) or the a floor model ( X,H,or L). I'm thinking you have the B but seems like you've got the console set. Console has a larger speaker (10 1/2"). The chassis are the same.

Obtw The 47 tube is a tetrode (has 2 grids rather than 1).
Sorry was had 24A on my mind....

Yes John there is a easier one to follow in the library.

https://philcoradio.com/library/download...n%2085.pdf

[Mike_RF]

Terry

its a 90 lowboy unit. Yes you are correct it has the 10.5 inch unit.

Cheers!

[MrFixr55]

Mike, yeah, swap the transformer. The Push Pull Job is worth some money, definitely don't trash it!

+1 on Terry's (RadioRoslyn's) comments. Since the field coil is rated for 40 mA, it can drop 125V without burning out. That coil goes from B+ through at least 60K of resistance before getting to B- Do ensure that you replace C24 (Multi-section bypass cap). If it shorts, it can cause the field to overcurrent.

Good luck and keep us posted!