Decoding output transformers: strange SE's

[engels]

I've bought a lot of several OT's from very nice gentleman who prefers stereo pairs so he sold me his monos. There are two OT's I'm puzzled with so here they are:

1. Philips OT - quite old, was used with two EL84's. It's heavy, bigger than a regular 18W PP. Everyone thought it's a PP but it's probably a SE. Here's the diagram of what I've measured:



And it looks like this:

the upper terminals are speaker outputs and the left lug is not connected.
so what's the deal with that tap on the primary???


2. A nice pair of Peekel power and output transformers. They're exactly the same weight and size, and each one weighs around 3kg. It looks like it should handle at least 100W in PP. It was used for a church amplifier with one EL34. The power trannie has enough power for two EL34's class A (@190 volts). The OT has primary with two taps (seemingly equal division into 3), the owner was saying it might be wired for PP (??).





so, is it for PP or parallel SE?? or both?

As these will not serve for stereo hi fi I'd love to squeeze as much as possible for guitar/bass amps out of them.

[mcs]

Originally posted by engels
I've bought a lot of several OT's from very nice gentleman who prefers stereo pairs so he sold me his monos. There are two OT's I'm puzzled with so here they are:

1. Philips OT - quite old, was used with two EL84's. It's heavy, bigger than a regular 18W PP. Everyone thought it's a PP but it's probably a SE. Here's the diagram of what I've measured:

Are you sure it was used with two EL84s? Philips often made combined power supply chokes and output transformers, so I guess you have an SE transformer with the 15.9 ohm part being a choke. This was done to reduce hum when using a small/cheap cap in the power supply.

The OT has primary with two taps (seemingly equal division into 3), the owner was saying it might be wired for PP (??).

This could just be a universal SE type. The taps are for different primary impedances. To find the real data you need to measure the voltage ratios. Connect 6-12V AC on the primary, measure the voltages at the different taps and on the secondary. Then the impedance ratios can be calculated.

Best regards,

Mikkel C. Simonsen

[engels]

As suggested, I fed the transformers with AC input and measured the outputs. Here's the results:

the source signal came from 24V tranny. The exact input voltage was 24.6V AC.

1. Peekel OT:

The voltages measured were as following:

primary terminals 1-4 24.6V, secondary 1.0V AC
primary terminals 1-3 24.6V secondary 1.5V AC
primary terminals 1-2 24.6V secondary 3.2V AC
primary terminals 2-3 24.6V secondary 3.3V AC
primary terminals 3-4 24.6V secondary 3.4V AC
primary terminals 2-4 24.6V secondary 1.6V AC

I understand there's no PP, it's a universal SE. All the calculations take the secondary as 8 ohms. Of course, if it's 4 then you divide everything by 2 etc. Here's the diagram with impedances:




2. Philips OT.

this is really puzzling!

primary terminals 1-2 24.6V secondary 0.4V AC
primary terminals 1-3 24.6V secondary 0.4V AC
primary terminals 2-3 24.6V secondary 7.9V AC + buzz

(unfortunately, my tested has only one digit after the decimal point)

and the resulting diagram is like this:



30K primary??? 77ohms choke??? what's this????

And again, the gentleman who sold this said there was two EL84's in the circuit but he couldn't say how it was connected. he thought it was a PP but when we measured it it was not equal division. He had two additional OTs like this which he intended to use for a stereo amp (he had three so he sold one) and the other OT measured the same.

[mcs]

Originally posted by engels
2. Philips OT.

this is really puzzling!

primary terminals 1-2 24.6V secondary 0.4V AC

30K primary??? 77ohms choke??? what's this????

12k primary probably - sounds like an EL95 transformer perhaps? Philips often used 3.2 ohm speakers in their radios - and never (AFAIK) 8 ohms.

Best regards,

Mikkel C. Simonsen

[engels]

12K primary... I'm sure anyone can tell the difference between EL95 and EL84... also, the transformer is indeed very large for one output tube, maybe it's for one BIG tube. I've seen many output transformers made to work with EL95's; the biggest of them was 1/3 size of this one.

Is there some big tube intended to work with 10K load???

[PTSOUNDLAB]

Hello

does somebody knows these transformers ?



Transformer Body 50x40x20 mm


I bought them today, they are sell as Philips/Telefunken transformers 2 vintage output Transformers for Tube Amp EcL82 EL84 o | eBay

I will try them for a funny little 6B4G or 6V6 Single Ended amplifier.

Cordially

Pascal