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hilbert_mostert 15th March 2009 05:52 PM

Output transformers bandwidth/frequency range

I am looking around for affordable output transformers for my EL84 SE diy project. They have to have a good frequency range. I want them to at least match my old Kenwood KA-4002A solid state amplifier (frequency range 18-30.000Hz).

As far as i have found are the following:

1. NTR AU4a ( old louwe trafos ) frequency range unknown ( could somebody provide these details?
2. Edcore XSE15-8-5K, "only" 70-18.000Hz

Does someone know better output transformers? or do i have to buy in the 150,- euros and higher segment? ( Or maybe push-pull is a better idea, these are around ~70,- euros.

Does anybody have comments on this?

Thanks in advance,


vuki 15th March 2009 06:04 PM

elettronica novarria

Ty_Bower 15th March 2009 06:11 PM

These 8k Transcendar output transformers might be something to consider. The shipping costs will be higher to Europe. I've used his 5k transformers with a single ended EL34 amp, and was very pleased with the results.

SpreadSpectrum 15th March 2009 06:23 PM

18Hz-30kHz. Is that 3dB down? If you want at least 18Hz-30kHz you may want to consider building a push pull amp. If frequency response is your driving requirement, an SE amp with air-gapped cores will not be the best choice.

Jeb-D. 15th March 2009 08:00 PM

Keep in mind, the edcor's bandwidth spec is at rated power. If you run it at a lower power, the bandwidth will be wider. Also, if your not paranoid about adding a little NFB, you can further increase bandwidth.

Tubelab_com 15th March 2009 08:16 PM

As stated the Edcors are rated for reasonable performance at 15 watts. The stated frequency response is probably realistic for operation at that power level. I have made some measurements on the XSE15-8-5K at low powers using a 300B tube. The type of tube has a very small effect on the frequency response. The current has a greater effect on the low frequency response and the distortion. These transformers would be a good choice for an EL84 SE amp.

Measurements at 1 watt: frequency response is 8.3Hz to 45.9KHz with 50mA, and 16.6Hz to 45.6KHz with 80 mA.

hilbert_mostert 15th March 2009 08:17 PM

I think the output will not exceed 5Watts, its for an EL84 amplifier, just one EL84 tube in the channel ( with ECC8(3/2/1) preamplifier tubes.

It is good to know this, is there a website which has a list of transformer producers in Europe? I have found one but a lot of pages are already gone.

Thanks so far!

hilbert_mostert 15th March 2009 08:40 PM


We posted on the same time.

I have a pair of B&W loudspeakers ( V201, 8ohm impedance, 50watts and a frequency response of 59Hz-22KHz ). Is that also on maximum level? or is that below that level?

I think iŽll go for the Edcor trafos, they are brand new and I think that is better compared to buying components that have been on the shelve for a long time. It also saves me some money which I could spend on better capacitors and loudspeaker connectors etc..

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