Kolster Audio Output

[RDusel]

Fellow VK-ers,
I'm restoring a 1931 Kolster K60 radio and I'm almost finished. Case came out nice with the original finished cleaned and recoated, all caps and resistors changed (first time I have seen a radio with all dogbone resistors off value), tubes tested and set re-aligned.
The problem I have is that the radio has a slight bit of distortion that did not go away with the re-alignment. Selectivity, Sensitivity are both good but the radio when tuned to the best always sounds like it is just off station a hair.
All coils check with the correct readings but the speaker sounds a bit off, weak on bass (it's an 8" field coil unit, 3ohms) yet the bass returns if you slightly touch the back of the cone.
So I found an NOS Jensen 8" speaker that has the same coil ohms (3) and the same field coil ohms and fits the mounts perfectly.
My question has to do with the output transformer. The factory transformer is rated for a 650ohm primary and a .3 ohm secondary SE.
After reading up on audio output transformers I find that the #47 output tube in this set "likes" a 7K ohm impedance primary. So I bought an output transformer designed with a 7K primary impedance and a 4 ohm secondary impedance.
My question is which transformer to use? Stick with the stock unit that the set was designed for or use the newer unit that matches the specs I found for a #47 tube. I'm thinking the newer transformer may offer better sound from the closer impedance match.
Any and all opinions and advice would be great. If you have any questions let me know.
Circuit diagram attached for your convenience. Thank you all for your help!
Rob

[Einar72]

I think the stock unit could fail at some point in the future. Go ahead and use the modern parts, but hide 'em as best you can if you plan to show it off as original.

[teevee]

Ok, the values shown on the schematic are the DC resistance of the transformer windings, not the impedance..(the 7k and 4 ohms) You can get close to the Z of a speaker with a resistance measurement.
Knowing the load impedance that the output tube wants to see, you can determine the turns ratio needed. So, in this case you need a "Z" (Impedance) ratio of 1750:1, or a "turns ratio" of about 42 to 1. (sqrt of Z).
How does this help? Taking an unknown output transformer, and injecting 1VAC on the secondary, read the AC across the primary. Something close to 42VAC and you're there.
It doesn't have to be super precise. What I use for getting the 1VAC is a small 6v transformer run on a variac.

[Reece]

All other things being equal, the transformer with the most "iron" should have better bass. Weigh them.

[RDusel]

after much consideration I ended up transferring the original transformer to the new Jensen speaker. Sound is much clearer during a test sitting on my workbench.
Still lacking on bass but I haven't mounted it in the case yet, I am sure that will help.
The original transformer was heavier.
Thanks for all the advice and help!
Rob

[Reece]

The cabinet will make a lot of difference in the bass. The "raw" speaker will sound shrill as the bass wave from the back cancels the one from the front.