EL84 se output transformer

[35L6]

My 1948 Radiola tabletop conversion had an OT like that . I always thought it was a choke winding and wondered if it reduced hum . I blew it up measuring output plate voltage when I forgot to reconect the dummy load . The new OT had more hum ( no winding ) and I wondered if it had better bass response or lacked the hum cancelling . If it can't act as a choke then it must be for hum and perhaps DC .

[mozz]

These may have a air gap on the bottom, will look again to be sure. But, if no air gap, i would need to hook them up as in the schematic? Pin 1 & 4 as my original idea won't work and leave pin 5 hanging?

[35L6]

Air gap ? There was a red wire where the tape is cut that went to the plate . The schematic said 220 Ohm for the plate winding and 12 Ohm for the screen winding . Don't know the turns or wire gauge . If that is an air gap the winding is probably for hum suppression .

[35L6]

If they still work I would hook them up as drawn .

[Helmholtz]

Air gap ? There was a red wire where the tape is cut that went to the plate . The schematic said 220 Ohm for the plate winding and 12 Ohm for the screen winding . Don't know the turns or wire gauge . If that is an air gap the winding is probably for hum suppression .

That's not the Grundig OT from post #13.

[Helmholtz]

These may have a air gap on the bottom, will look again to be sure. But, if no air gap, i would need to hook them up as in the schematic? Pin 1 & 4 as my original idea won't work and leave pin 5 hanging?

If I'm right about the DC flux compensation, this would require a specific ratio of DC currents in the OT primary parts
I think it would be best to use ECL82 tubes with these OTs.
Don't forget these are 2.5W rated OTs and trying to increase power might cause OT saturation (bad sound).
Too high current might even burn the primary wire.

[35L6]

That OT is from the Radiola . I was trying figure out the function of that tap . It's been a mystery for years . Can you see the joint between laminates ? It looks like the varnish runs between them . Is that an air gap or would the air gap be much wider . I don't know what an air gap looks like .

[Helmholtz]

That OT is from the Radiola . I was trying figure out the function of that tap . It's been a mystery for years . Can you see the joint between laminates ? It looks like the varnish runs between them . Is that an air gap or would the air gap be much wider . I don't know what an air gap looks like .

Could be an airgap, especially if there's someting like a cardboard layer between the E and I laminations
Picture is not clear enough.
Generally it's easy to realize an airgap with an E-I core.
Another way would be a shortened center leg.
Not so simple with a band wound core.

I'd prefer not to mix up topics.

[mozz]

Appears to be a air gap on the bottom. The banding has a ground lug soldered to it that ties to pin 7, which would would be my speaker ground. Should not matter.
Fender champ output transformer: primary 330ohms 10H
Philips reel output transformer: primary 310ohms, 9.0 H
So i think i will be fine. If EL84 saturates and sounds terrible, i will rewire to ECL82 and use the triode also.

[Helmholtz]

Appears to be a air gap on the bottom.

Yes, that could be a tiny airgap. OTOH, cutting the core in halves is essential for assembly.

Fender champ output transformer: primary 330ohms 10H
Philips reel output transformer: primary 310ohms, 9.0 H

These numbers are not related to power handling.

[mozz]

I don't know if you can compare sizing of these banded transformer to a regular stand up EI core model.
Frequency Response (all 3 dB): 7½ ips: 40 to 18kHz
So for guitar freq hopefully 4W-5W will be fine. Finishing the power supply now so i should know my B+ tomorrow.

[Chuck H]

Helmholtz caution regarding overcurrent is valid. When these transformers were made the bean counters and the techs were working together with the only tube technology at their disposal. In other words, the unit wasn't likely designed with much over spec tolerance. That said...

For a guitar amp the demand is much lower than a hi fi (or reproduction) amp. I have an amp in my possesion right now using an OT designed for 7591's in a Fisher amp (7500 primary) that I wired at half load (3750 primary) and am using a pair of EL34's. And everything is going fine. In fact two sets of tubes blew up (well, one of a pair of each) while tubing this amp but the OT held up fine and only gets warm in use. I say go for it with the el84. What's the worst that can happen

[mozz]

Well this is a 60's Philips. I don't see any Euro company back then cutting corners as much as a US or Japan made item did. I'm sure there are some which were so bad, no examples are left. Granted some Euro caps i have seen were bad, Franko, some other names. Another granted was, things were done differently over there, you will see odd ways of getting the same results, such as this transformer winding. Maybe those banded transformers were cheaper to make, who knows.

[Helmholtz]

Oh, those band wound cores were expensive and superior performance.
Expensive core (single source: Vakuumschmelze/Hanau, a subdivision of Siemens/Germany) and cost-intensive to make the transformer.
Result was a smaller transformer having the same performance as a larger E-I core type.
Drawback is that a smaller transformer can't take as much abuse as a larger one because of it's smaller surface.

[mozz]

Maybe i shouldn't waste them on a guitar amp?!! I have a habit of finding these old reel to reel machines/radios, cheap, mono or stereo, in bad neglected shape, screws missing, no covers, hardened grease. Some Norelco, Philips, Grundig, Emud, Lowe, some US made. They are always good for parts to build a 5w SE guitar amp.