OT, the bigger the better? And which one to choose?

[Gregg]

I think that 'primary' in the above may have been a typo, and that 'secondary' was the intended word; it all makes sense then?

I'm sorry, that was a typo. I meant secondary. If you mess with the primary then Mike would be right.

... if the secondary is in 2 sections then the 4 ohm tap would seem to make no use of one of the sections?

I'm not sure if I understand your question but if you have two same number of turns secondaries and you don't want to rewire them (in parallel) then you can still use one of the halves to drive a 4 Ohm speaker however you won't be able to get full power out of the OT because it won't be able to handle the current. You can use it at low volume levels though.

[pdf64]

Well, assuming say a Drake 784-139 type OT with a secondary having dedicated 4-8-16 ohm taps and a 5 section winding arrangement as jfpamps describes, the primary to secondary coupling etc would be rather different depending on which secondary tap was used then?

[Gregg]

The Drake you mentioned is very good example how a poorly made OT can sound very well. Other Marshall OTs are made in a similar way and some are even less complicated. However by all accounts they sound excellent. Why is that? Well, this is another long thread...
Back to your question. Yes, the coupling is not perfect but I wouldn't call it "rather different". The way secondaries are placed will surely affect the leakage inductance and as a result the frequency response but that's neither good nor bad.

[nickb]

The Drake you mentioned is very good example how a poorly made OT can sound very well. Other Marshall OTs are made in a similar way and some are even less complicated. However by all accounts they sound excellent. Why is that? Well, this is another long thread...

Go one, do tell...

...better to have all the info in one place and I for one would like to know.

[Mike Sulzer]

Go one, do tell...

...better to have all the info in one place and I for one would like to know.

Let's say you want to make an audio transformer for top end stereo. The accepted frequency range is 20 Hz to 20 KHz. For the low end you need enough inductance; for the high end you need low enough leakage inductance. It is hard to achieve both at once. Let's say you succeed in doing this. Then someone comes along and says make me an output transformer for a guitar amp good from 80 Hz to 5 KHz. You laugh and say that is 16 times less frequency range, a much easier task. So you make the inductance high enough to do the job, but not much higher. Then leakage inductance is not much of an issue compared to the transformer you just designed, and so you do whatever is most convenient.

[tedmich]

everything sounds better with a hernia!

[Chuck H]

MM's ridiculous ploys to the less aware are ONE of the reasons I've NEVER used their product. I don't doubt they're good transformers, but it's pretty obvious they care more about marketing than actual product suitability. Why would anyone who knows better spend three times the usual price for a product that clearly epitomizes consumerism over usefulness.?. Ok... The adds have a hot chick. Maybe I should try them? Perhaps a choke upgrade will make me thinner and more attractive

[bob p]

I opened my MM account about 20 years ago, long before they started advertising in the guitar mags. I don't know if you remember it, but I started off by coordinating group buys here so that everyone could get iron at the discount price.

I did two group buys ... the first one was for about a dozen units. It went so smoothly that I did a second one, which involved a lot more units, maybe 3 dozen or so. On that order MM filled the order with all of the crappy seconds and customer returns with cut leads that they had been accumulating in the shop. They screwed me by sending me their seconds because they knew the freight charge was so high that I'd never ship everything back. It was a very shady business deal -- they gave me a great order fill on my first order with them to lure me into thinking I'd get great service, and on the second order they screwed me by unloading all of the shit that nobody wanted.

That crappy shipment put me between a rock and a hard place with the group buyers. I called MM, talked to Paul Patronete in sales, who just shined me on and offered nothing. I ended up talking to the owner (Sergio) who tried to feed me a line of shit about how the transformer splices were made with silver solder and would actually improve the tone. What a load of crap. In the end they made the hollow offer of saying that they'd take the shipment back, but if and only if I was willing to pay to ship the 200 lb of crap from Chicago back to California.

I ended up filling people's orders with the best iron in the lot, and I ate as many of the seconds as I could on my own, flipping most of them out on ebay at a loss. Setting aside any commentary about the stupid ads and the hype, my opinion is that Mercury is a dishonest company led by a man with unethical business practices. I still have an active dealer account with them but I haven't placed an order in 20 years. I'm going to have to be desperate before I'd place another order with them. They're the last place I'd go to buy iron, and I'd only buy from them if I had to have something that I couldn't source anywhere else.

[Gregg]

Chuck, you're absolutely right and I don't have much to add to your comment.
MM=good marketing and that's it. All other of their claims are questionable and that's mildly put.

[bob p]

The JMI era Woden transformer AC30 is 5 sections: 1/4 primary, 1/2 secondary, 1/2 primary, 1/2 secondary, 1/4 primary. The two outside section make one half of the primary and the middle section make the other half of the primary. This way you can get the two halves of the primary well balance for all parameters only using one wire gauge for the primary, which simplifies the winding procedure.

From reading around the subject, this pattern seems to be regard as the most "bang for buck".

Logically, I might have expected a transformer without negative feedback to have more sections as the frequency response of the amp is not extended by negative feedback, however with guitar amp design then logic is often sacrificed at the altar of economics.

The Tiny Terror uses a similar 5 section design, as do the Drake transformers used in Marshalls from the late 60s onwards.

The Twin Reverb also uses a 5 section transformer, but the interleaving pattern is slightly different: 1/4 secondary, 1/2 primary, 1/2 secondary, 1/2 primary, 1/4 secondary. I think this arrangement was used as the transformer still benefits from having a 1/2 section on the outside, and as Fender don't tap the secondary winding, there is no issue with utilization of the transformer properly.

Incidentally, the JMI-era AC30, Marshall 50W and Fender Twin all use the same sized core for the transformer.

Partridge transformers used in Hiwatts etc, have a more complex interleaving arrangement. John Chambers from Champ Electronics did explain this to me a few years ago over the phone, but I have failed to remember the exact details. I do remember that the 50 and 100W version have slightly different arrangements.

The Orange Tiny Terror is an interesting circuit.

The PT has selectable "15W" and "7W" taps so that the user can switch between B+ of 322VDC and 237 VDC.
The OT is a 5-section design of decent quality.
Overall, the OTT is a nice amp for it's price point, and the quality of the iron is good. the amp offers that nice "glassy" EL84 chime if you run it clean, and it has that cascaded distortion thing going on that lets you get some nice overdrive sounds at very reasonable volumes.

Of course, if you read the hype, the first thing that you're supposed to do after paying $350 for your amp is rip out that crappy OEM iron and spend another $350 on the MM upgrade kit! The transformers have orange-colored endbells!

Mercury Magnetics -- Orange "Tiny Terror" Upgrade Kit



Here's a funny video that features the guy I referenced in my previous post on guitar.

All things considered, I think there are many other suppliers that can give you great sounding iron without the hype, without the price hike, and without having to deal with a shady sales and half-assed customer support.

[nickb]

Let's say you want to make an audio transformer for top end stereo. The accepted frequency range is 20 Hz to 20 KHz. For the low end you need enough inductance; for the high end you need low enough leakage inductance. It is hard to achieve both at once. Let's say you succeed in doing this. Then someone comes along and says make me an output transformer for a guitar amp good from 80 Hz to 5 KHz. You laugh and say that is 16 times less frequency range, a much easier task. So you make the inductance high enough to do the job, but not much higher. Then leakage inductance is not much of an issue compared to the transformer you just designed, and so you do whatever is most convenient.

Sorry Mike. The question was directed toward gregg. I was referring specifically to the Drake transformer mentioned What exactly is so horrible about it? I've never measured one or taken one apart. I'm genuinely interested.

[frus]

Now I'm gonna switch over to the modded amplifier, set up with much more gain...

[SoulFetish]

I think that 'primary' in the above may have been a typo, and that 'secondary' was the intended word; it all makes sense then?
.

Oooooooh. Yeah, now I see..... pdf, I've been going over this in my head for a day and a half and you just saved me from the post I no longer have to write. I've been going over different calculations of inductance, impedance ratio, how it would affect bandwidth, etc; wondering why the hell this would make any sense to do at all (and what manufacturers wind output transformers to be configured in this fashion?!! Was this common?).
But, he seemed pretty convinced, (and I'm fairly new at this) so figured I must be missing something
Thanks for picking up on that. What a relief.
It did lead me to question something I want to make sure I understand correctly. On a Transformer with two separate primary windings which can be connected in series or parallel (lets say, as found on a mains transformer designed for dual voltages), does the primary inductance differ when connected in series vs connected in parallel? Here is a drawing.



This is how I understand it now, so please correct me if I'm mistaken:
- It would think the primary inductance would be less when connected in parallel, because the shorting action at the ends of the coil would "electrically" cut the turns in half and double the diameter or the wire (This is certainly the case in other parallel conditions.) If the reflected impedance were to stay the same, if would create a problem as the lower primary inductance would not be able to pass the 50/60hz under the same load conditions. But the parallel connected primary has a lower reflected impedance than the series connection, and does not require as high a primary inductance in order to pass the 50/60Hz. So it works is the simple answer.
Does that my question and explanation make sense? I apologize if this is over simplified, but I don't have the accompanying formulae committed to memory yet and it's late. I want to sleep at some point tonight So if you can let it slide this time, I'll make it up to you guys.

Now, I can tell myself "It was only a typo... it was only a typo...."

[bob p]

Now I'm gonna switch over to the modded amplifier, set up with much more gain...

But he said that the amps have identical tubes and speakers, and only the transformers were different! I guess he just forgot to consider that the knob settings might be different... LMAO.

It's sad that the numbskull from Premier Guitar let them get away with that kind of blatant misrepresentation.

[frus]

well he did mention that, apart from transformers, the mod kit contains "some resistors", so it's apples to oranges in any case

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