[nuke]

I thought I read somewhere on this site that there was a way to use a Philco 20 speaker and rewire it to be used as a Philco 90 speaker for a single 47. I believe I have done that before with a Philco 20 speaker that worked well but forgot how to do it. I actually have an audio transformer for a Model H speaker I can use too.

[morzh]

You simply not use the centertap.

http://philcorepairbench.com/audioinp.htm

2766 is the 20 transformer (and almost the same as model H one).
As you can see they denoted it with two asterisks which means the CT is not used.

[nuke]

The audio transformer on the Model H speker is a 2848-D. This is for 45 push-pull. It is not clear what taps to use. There are 4 taps plus a pair of wires that go to the voice coil. Obviously I only need one pair of taps but which combination?

[morzh]

Then you have a different H speaker fro mine. I have two, both used a center-tapped transformer, with only one tap in the primary.
I will look later today to see which PN transforfmer I have.

[Ron Ramirez]

The article you are looking for is here:

http://www.philcoradio.com/tech/speaker.htm

[nuke]

Sorry - I think it is the model G speaker. I have the model 90 speaker but want to use the model G 2848 audio trans on it. The 90's is bad.

[morzh]

(I do not know where to find data on 2848 xfmr).


Well, just find the ends of your primary.

A Pushpull for 2x45 impedance is about the same as 1x47.
If it was a pushpull transformer, the ends of it were probably connected to the anodes, use those.

Here what you could do to make sure:


1. Unsolder the voice coil.
2. Using a Variac and a Voltmeter, supply a goodly amount of AC voltage to the full primary (to P-P ends). Say, 60V. Measure the output by the Voltmeter out of the secondary. It should be close to 0.6V.
3. If not, find a tap and an end of the primary that will give you 97:1 ratio, that is 60V fed to primary gives you about 0.6V output. These are your contacts to use.



-----------



Another alternative: at some point you will need a Push-Pull xfmr, so save this one and get an SE transformer with 97:1 ratio. (well, it is 100:1 in Philco 20).

[nuke]

Tried the Philco 77 tranny and that gave me 1.5 volt output. I have another tranny that gives me .8 volt output. It doesn't really fit though.

[morzh]

Philco 77 should be using same or similar xfmr as 90 ith 2x45 which is similar to 20 which can be used for it.

You could also try Ct to end and end to end to see which one works better.

[nuke]

I don't see any center tap. I see 4 tabs and also 2 leads that connect to the voice coil. I get 250 ohms continuity between first set of tabs and no continuity between the other set of tabs. I presume this set is the field coil connection. I do get continuity between each tab of the first set of tabs with only one of the other set. This continuity reads 7 meg resistance.

[morzh]

http://www.nostalgiaair.org/PagesByModel...013838.pdf

http://philcoradio.com/tech/images/77.jpg

These sch are of 77 and show centertapped xfmr.

[nuke]

OK - I figured it out, I took apart my other G speaker and saw the connections. There is one tap that is just a tie point for the coil and the speaker cable. The other tap with the coil connection is the center tap.

Incidentally the 2848 audio transformer is identified in the Most Used Radio Diagrams for the Philco 96.

[nuke]

Just an update. Finished the speaker and tested on a Philco 70 and the speaker worked fine.

[Arran]

The Philco 96 uses Push pull #45s, the model 20s use push pull #71As. What is most important is the ratio between the primary and the secondary, this is why most of those universal replacement type output transformers have only three wires on the primary side, but six taps on the secondary side. I am kind of puzzled by the chart showing the ratio for a transformer for push pull 71A's, 45's, or 50's, it has a note stating that the center tap is not used, you cannot have a push pull pull audio circuit with those tubes without using a center tapped primary on the output transformer.
Regards
Arran

[nuke]

I think they mean the center tap is not used when not in a push pull application - a single tube output.