Output transformers (why Heyboer?)

[Justin]

I understand that selecting the right output transformer to design around is one of the most critical components in voicing an amp. Can anyone shed some light on why Heyboer seems to be the output transformer of choice for trainwreck clone builders? Do they possess certain sonic characteristics or electrical values that work well in a wreck circuit? Or is it the fact that the company will work with a customer and their custom specifications where other manufacturers won’t. After looking at the real trainwreck homepage (www.trainwreck.com) listing of amps I see that Ken did use a Heyboer for the power transformer on one of his amps along with a mix of other vintage and new ones. From what I understand (I could be wrong) Ken used to go through loads of transformers and pick out his favorites by ear and didn’t use the same one every time. Has anyone tried Triad, Schumacher, Thoradson, Hammond Merit, ADC, Dynaco, Acrosound or any of the other vintage transformers out there? What about Mercury Magnetics? Does anyone know of other outputs that Ken used besides Heybour and where to possibly find them (old equipment salvages?)

Justin

[Moose]

The reason for Heyboer comes down to two things. They alreadyhave a design to his spec, and they are extremely responsive when it comes to working with folks like us. Since they have that spec design, some folks here worked with them on impedances and laminates to get a great sounding transformer, so they're now a good source. Since they're so great to work with, I like supporting them and that's why I had no problem ordering in larger quantities so we have stock available.

You are right about transformers varying. Mr. Fischer used a range of primary impedances and some different vendors. What that tells you is that there's no single holy grail and that you should get the best you can, but that you should also use your ears to tune things to taste.

I'm sure MM might wind you a 'wreck style OT, but they don't have one on their Axim menu. They are also quite expensive for one-offs, though they get significantly cheaper if you want to order 5 or 10 lots. I love MM trannies in some applications, so if you're willing to spend the scratch to develop one with them, I can't imagine you'd get anything less than a spectacular product.

[toddyjoe]

I recall reading a discussion on the Blue Guitar website that Mr. Fischer used Pacific trannies in some of his Express amps. There is a post from Mook in a text file there that indicates the same and identifies Pacific's manufaturer code as 1052. Of note, Pacific makes an output transformer with an available 6.6K primary.

I also seem to recall a discussion somewhere online that suggested Express transformers all have a very unique mid response compared to other output transformers. I notice that Pacific output transformers have a difference frequency response range compared to transformers like Hammond. Hammond and other companies offer a 30Hz to 30kHz range, whereas Pacific is something like 20Hz to 20kHz. This difference in range could give Pacific transformers a different frequency response overall and even in the midrange.

Vibroworld sells Pacific output transformers like this as replacements for Marshall 2xEL34 and 4xEL34 amps. I am wondering if these trannies might also be a good option. Of course, the pricepoint (over $100 for an output transformer) is not as attractive as Heyboer.

[Moose]

You know, they might be good transformers. If you're willing to pony up the cash, I bet they sound great. Of course, most 50watt iron that's super high quality tends to cost that, including MM marshall trannies, OEI, etc. I've used them all in one build or another and don't feel the extra $30 was wasted.

I do want to address the frequency response. Most hi-fi transformers have more extended response than your average guitar amp tranny. For two reasons. Cost and we just don't need it. Most of our fundamentals are a couple KHz or below and you have to get in to the gazillionth order harmonic to reach 30Khz. Add to that the fact that guitar speakers roll off pretty shaply starting between 4KHz and 8Khz (depending on the driver) and you see excessive range becomes less of an issue.

I make this point really to emphasize that MOST guitar amp transformers aren't going to be super wide bandwidth.

[toddyjoe]

Moose, I agree with your good points about frequency bandwidth and transformers. I guess I was wondering (out loud) if the fact that Pacific trannies have a different, i.e. lower, efffective range than other trannies might affect frequencies within these limits. In other words, if Pacific's limits are 20Hz to 20kHz and Hammond's limits are 30Hz to 30kHz, do these transformers react or respond differently at 82Hz (low E string) because this is closer to Hammond's limit than Pacific's? If so, maybe there is some stone unturned by us homebrew builders regarding Mr. Fischer's reputed search for output transformers with a specific mid-range response. Like I suggested, I am just thinking out loud here and certainly have not looked into this very deeply.

[Tweedguy]

I just built a 5E8A Tweed Twin with a Heyboer OT. I thought I could improve the tone with a Mercury OT but was disappointed. The Heyboer had way more harmonic detail and the tone was usable no matter how I turned the tone knobs. With the Mercury, the amp was only playable with both tone controls set between 8 and 10. The overall sound was flat and plain except for a bit more highs.

I emailed Heyboer and asked how they're OT's were made and they told me that they're wound on a paper bobbin just like in the 50's. Mercury Magnetic's use a thick plastic bobbin (keeping the windings further away from the core). Obviously there are other things that will determine the sound of a OT but I think the paper bobbin is key to Heyboer's sound.

Mercury's website says there is no difference when using plastic vs. paper bobbins. I'd say that would be true if they were the same thickness, but Mercury's plastic bobbin is ALOT thicker than a piece of paper.

Does anyone have a verdict on the paper vs. plastic bobbin controversy?

[Tweedguy]

I just built a 5E8A Tweed Twin with a Heyboer OT. I thought I could improve the tone with a Mercury OT but was disappointed. The Heyboer had way more harmonic detail and the tone was usable no matter how I turned the tone knobs. With the Mercury, the amp was only playable with both tone controls set between 8 and 10. The overall sound was flat and plain except for a bit more highs.

I emailed Heyboer and asked how they're OT's were made and they told me that they're wound on a paper bobbin just like in the 50's. Mercury Magnetic's use a thick plastic bobbin (keeping the windings further away from the core). Obviously there are other things that will determine the sound of a OT but I think the paper bobbin is key to Heyboer's sound.

Mercury's website says there is no difference when using plastic vs. paper bobbins. I'd say that would be true if they were the same thickness, but Mercury's plastic bobbin is ALOT thicker than a piece of paper.

Does anyone have a verdict on the paper vs. plastic bobbin controversy?

[VacuumVoodoo]

Does anyone have a verdict on the paper vs. plastic bobbin controversy?

Plastic (nylon being most common)) needs less thickness than paper for same HV isolation thus windings are closer to the core on plastic bobbin.

You should be more concerned with laminations and isolating lacquer thickness, carbon and silicon content, cold vs. hot rolled steel, post roll heat annealing etc.

[jaysg]

I just built a 5E8A Tweed Twin with a Heyboer OT.

Multi tap or just 4 ohms? Recall the HTS number?

[Tweedguy]

It's just the 4ohm tap. All I know is the Mojo Tone part Number 767.

[Tubetwang]

I have a 60's Pacific 4,8,16 ohm OT in my Express.

It came from an old P.A. amp. Can't remember wich one now, Western Electric maybe?

I used to be able to pick up 60's P.A. amps for around 50$...

I'd keep the knobs, tubes, trannies and recycle the rest...