Building a 5F6-A

[nosaj]

+1 to this. But I've never built a 5f6a. So while I agree about the Hammond transformers I have no first hand experience with this model amp. I read in one of the Weber books that the original Triad 5f6a transformers were labor intensive being paper bobbin and seven interleaves. I think someone here debunked this once but it sticks in my head because I can't imagine Gerald pulled that out of his butt and printed it in a book. Hammond doesn't offer anything like this. Not even Mercury does. Pretty much all the Bassman transformers you'll find are just standard Fender transformers with a Bassman footprint. If the seven interleaves on a paper bobbin thing is true then this would be a boutique transformer made made for special customers that want something authentic. And pricey. Not knowing how far this project is intended to go I didn't suggest any transformers.

Were good enough for traynors and heavily built.
nosaj

[Chuck H]

Marketing. something he did no one else would attempt therefore building mystic ....Common amog scammers and conmen (only recognize this because I've been listening to a lot of podcasts lately on cults).
nosaj

Yes. Well Gerald was known for it to be sure. I called him out here once on a lie I caught him in regarding a speaker design. People thought I was talking about Ted Weber and I took a real beating for it (even though I wrote "Gerald" in the post). Ted Weber is/was respected WRT speaker design for good reason. So...

I did my own research since I prefer not to rely on uncredited internet information. The original 5f6a OT was a Triad 45249. I found some old listings where the sellers took DCR measurements. Each was consistent with the other with the primary halves being about 42 ohms and 48 ohms respectively. Assuming a typical wrap wire gauge that should mean about fifty or sixty feet more wire on one half. So even for my rudimentary understanding of magnetic components I'm calling BS on the interleaving. Which would mean Gerald DID pull that notion out of his butt.

[Chuck H]

Doing more research... It seems like anyone on forums who thinks they know anything about the Triad 45249 says they are interleaved. These are mosrly posters that come across pontificant like they have their pinky out and they never say anything about actual specs. None of the transformer clone makers (Mojo, Mercury, etc.) say one way or the other regarding interleaves.

With the difference in DCR between the two half primaries it doesn't seem "to me" that the original Triad 45249 was interleaved WRT to it's primary. OT's with interleaved primary halves are typically very close in DCR. Possibly the primary and secondary are interleaved in the Triad 45249? Discuss?

[Helmholtz]

There's no direct relation between DCR difference and interleaving, though using 4 primary sections would allow to make resistances equal.
And a few Ohms difference are totally insignificant considering that the DCR is in series with the k-Ohm impedance of the primary.
Rather, interleaving is used to improve coupling and thus lower the leakage inductance, which matters for HF response and stability with NFB.

All the Fender OTs I mentioned above measure very good and close. Makes me assume they all use the same construction.
The have low leakage (between 5mH and 8mH) and rel. high primary inductance (def. more "Hifi" than a 50W Marshall OT).
By comparison of data with OTs of known construction I'd say they have at least 5 sections, probably 3 primary sections and 2 secondary sections.
Even cheap OTs typically have 3 sections (secondary sandwiched between 2 primary sections.)

[Tom Phillips]

Interesting discussion.
I have never had a failed classic 4X10 Bassman or Super Reverb OT cross my bench. If it ever happened, I'd be tempted to unwind and document it. Then what? I have more than a lifetime of projects in the queue. It's ironic that all my personal amps need attention including my HiFi equipment but I spend all my bench time on other people's amps.

[Helmholtz]

What counts is measuring results (performance) and not how this is achieved (construction/interleaving).

[Bob M.]

Well, I know Gerald Weber and I find him to be straight ahead, a good guy. He he's not above praising his own products; he's proud of his amps. He's continually experimented with different ideas like using aged pine for cabs. That's how these things progress in the amp field; someone tries something new. I don't own any of his amps but the ones I've played or worked on sound good, as do the amps most boutique makers build. Sometimes these amps just have to be played thru by the right player.

The interleaved transformer thing has been around a while now. Some people weight it more than others. It's not like only interleaved transformers sound great and all other sound bad; it's a matter of degrees. In my builds, I use some interleaved trannys and some not, depending, but all the amps I build (for customers or myself) sound pretty darn good before they leave my shop. Amps are complex and I find there's no one answer to making a great sounding amp. Unfortunately, people are many times looking for the one easy answer.

I'm still looking for transformer recommendations from experienced people in the know.
Thanks,
Bob M.

[Helmholtz]

I use some interleaved trannys and some not...

Did you verify?

I don't have own experience with Hammond OTs, but I can definitely recommend original Fender SR and BM replacements.

[mozz]

He passed away if you didn't know.

[Chuck H]

Well I didn't hope to offend anyone with my commentary on Gerald above. I can counter my above statements by saying that the two times I talked with him he was friendly and very enthusiastic. Enough so that "I" had to end the call. And both those calls were regarding his parts that I was purchasing. And those performed and sounded very good. So while he was, by nearly all accounts, a known grifter that never seemed to affect his passion for the amps.

[Chuck H]

Helmholtz
I don't know enough about the construction of transformers to say anything definitive. So I digress. And I know the dcr isn't the critical performance measure for balanced performance of the half primaries. What I do know is that based on what I read there is a lot more wire on one half of the Triad 45249 primary than the other. And this is usually an indication of a more simply wound transformer where all of one half primary is wound before all of the other half is. And that interleaves usually make for more equal wire "length" for each half primary. Which can be detected reasonably by measuring dcr.
I think what you said was not so much that I was wrong but more that the whole picture wasn't evaluated. Which is true.

[Helmholtz]

The difference between 48R and 42R is only 14%. Simple, smaller OTs can have a difference of 50%.
With 5 section interleaving, the innermost primary section will have lower DCR than the outermost.
But as there's also a part of the primary in the middle, the DCR difference between primary halves will be lower than with only 2 primary sections.
As said, it would take 4 primary sections and "cross-wiring" (as with a 7-fold interleaving) for identical DCRs (i.e. without using heavier wire for the outer part).
I don't think the Triad 45249 has 7-fold interleaving but I'm quite sure it uses 5-fold interleaving.
The only OT using higher than 5-fold interleaving I measured is a Marstran replica of an RS JTM45 OT.

[Bob M.]

Loudthud,

I found my notes on my 2010 build of a 5F6-A, which I call my mini-Bassman, as it has a smallish cabinet with one 12" speaker.

The B+ is 442Vdc. It has a solid state rectifier and I used a thermistor for a soft start-up. It has an ultra-linear output transformer; I was interested in experimenting with UL output transfxs just around this time. It has a pair of NOS GE 6L6GC tubes from the 60s. The amp is not here at this time but I remember I was buying lots of Hammond and Heyboer transformers around this time so the power transfx is most probably one of these brands. Not sure on the make of the UL output tranny but I researched it carefully at that time and I am happy with my choice. I had a lot of problems/updates to do after the initial Rev 1 build was complete. Too much gain, way too bassy - too much low end. I used a 12AY7 at V1 and a 12AT7 for the PI. I tuned the right amount of lows to highs by a number of the usual ways, but mostly by coupling cap choices. After a few iterations, I got it right and I've used this amp a good amount in the subsequent 14 years with no repairs or no need to change/mod/update anything else. Turned up, it's a real screamer, but it also has a great lower volume clean sound, very distinctive without any master volume or similar gain reduction techniques and I have great control going from a clean sound to an overdriven one just by using the volume control. I'm very happy with it; a successful build. I hope that answers most of your questions.
Bob M.

[loudthud]

It seems to me that if i was winding a transformer, making a tap in the middle of a layer would be a pain. So I would opt for an even number of primary sections. consider the original Hammond 1600 series, the ones with the oddball secondarys. The primary has the UL taps so while the layers aren't exactly equal, they can be split up nicely into four sections. The secondary would split up into three sections. Two with equal number of turns for the 4 and 16 Ohm series-parallel and a third layer for the 8 Ohm tap, probably slightly heavier wire but fewer turns. Seven layers

Bob M. I was just wondering out loud if the choices you made on the clone build were satisfactory and could be used again. Will you be using a rectifier tube on this build ?