• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

OEP transformer

Hi everyone
Someone knows about this product?, It seems well done, and fair priced:

OEP T29A05F - PUSH-PULL Audio /Output Transformer for EL84 Valve / Tube Amplifiers

Oxford Electrical Products (OEP) - design and manufacture in Oxford, England. By maintaining a close control over manufacture, OEP ensure that each transformer is manufactured to the very strict specification that their designer intended. The quality of manufacture directly governs the efficiency of the transformer for excellent sound quality and reliability.


PRODUCT SUMMARY - Push-Pull output transformer (10W) for EL84 Valves / Tube application. Amplifier chassis mounting speaker / valve transformer

CHASSIS Mounting
Maximum Power @ 20Hz: 10W

Primary: 7k C.T. with 43% screen taps
Secondary: 4, 8 and 16 ohms
Frequency Response: (+/-3dB): 20Hz - 25kHz
Core Material
Grain orientated silicon steel
Mass: 1.4kg

Made in England, UK.
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It is hard for me to believe +/- 3 dB from 20 Hz to 25 kHz; that is a lot of variation for a small push pull ultra linear EL84 transformer.

If it has the maximum response at midrange (say somewhere near 1 kHz); and the frequency response rolls off smoothly from either side of that (rolls off as it goes to the low frequency and high frequency extremes); then another way to look at those specs is:
+0 dB at midrange frequencies
- 6 dB at 20 Hz
- 6 dB at 25 kHz.

I do not think the OEP can be that bad.
Maybe they built a few prototypes, and they tested good, and they wanted to eliminate the expense of testing each production unit, so they really loosened up the specifications, but did not change the way they built it . . . so it works essentially as good as the prototypes.
Now, nobody can return one for not meeting the new loosened spec, even if the designer did not know how to properly use the transformer.

It might not have enough laminations to put out 10 Watts at 20 Hz.
If it only puts out 5 Watts at 20 Hz, that is -3 dB (and - 6 dB is only 2.5 Watts).
But it should not be more than -3 dB at 25 kHz (certainly not -6 dB).

If I designed an ultra linear push pull EL84 amp (even with no global negative feedback),
Or if I designed a push pull triode wired EL84 amp (even with no global feedback),
It would have a better frequency response over those frequencies than - 6dB, or else I would give away those transformers, and purchase a better set.

And what is the price of one of those transformers?
You did not say.
So I looked online. At ebay, it says that the transformer was designed for guitar amps.
It certainly will work very well in a guitar amp, with the lowest 4 string bass tone at about 40 Hz, and the highest lead guitar frequency tones and their highest harmonics well below 10 kHz, I would say use it.
Now a really harsh effects box might have higher harmonics than 10 kHz, but you would not hear much of that if the guitar speaker rolled off sharply at 7 kHz.

You ought to ask OEP: "Why the loose specifications"?

So, is this for a Hi Fi amp, or a guitar amp?

At the price, I might be tempted to purchase a pair of those output transformers, but then not with the overseas shipping charges.

Have fun building an amp; Hi Fi or guitar.
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