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

[shocki]

Unless other circuit components are the same, especially the amp's filtering, B+ voltages etc., how can you be sure the OT is the only thing contributing to the less farty bass? I'm not saying a larger OT doesnt help, but Fender's can get farty bass at high volumes. There's several threads on this, even on the old Ampage board.

I think you are talking about the Valvetech ? I don't know 100% of course.The Valvetech Homepage was relaunched some weeks ago. On the old site he was actually saying he used a beefed up OT so the bass stays tight at higher volumes if I remeber correctly.

[jpfamps]

OK, but there's a point where going larger doesn't help, and in some amps the original amp's character gets lost. I had put a Deluxe Reverb OT in my Princeton. Definitely a difference, but an improvement? Didn't sound like a Princeton, so the original OT went back in. So for some amps, the original (presumably smaller OT) gives the amp it's characteristic sound. (at least in part) We're not talking HiFi here.

The difference may not be due to size as the Deluxe Reverb OT (6.6k) and the Princeton Reverb (8k) present different impedances to the output valves.

[JoeM]

The difference may not be due to size as the Deluxe Reverb OT (6.6k) and the Princeton Reverb (8k) present different impedances to the output valves.

Yes, good point. And the B+ in my Princeton is actually higher than the Deluxe. The DR OT is substantially larger than the PR, so the greater amount of iron is definitely a large factor.

[Alan0354]

I myself just change out the big OT of my Bassman 100 to a smaller one. Mostly because of the weight. You can "make" the amp sound the same by working on the other components. I just don't like the huge heavy OT. It is sitting in my garage floor now!!!

I never like the Bassman 100 for guitar. It was just cheap, I only paid $250 at the time. If you look at the normal channel and trace the signal path to the output, it is very much same as Twin Reverb, but the Twin sounds nothing like that. It just has a booming or tubby sound that is not good for guitar.

[JoeM]

Yes, that's one drawback for tube amps, all that iron makes them heavy! I have Super Reverb that just spends it's time in the closet. Very heavy. I just don't need that kind of volume anymore.

[Gregg]

An extreme example the other way would be the new toroidal OTs, with an unbroken magnetic circuit of grain-oriented steel that saturates hard with only a few tens of milliamps unbalance. Hi-fi guys like them, but they never caught on for guitar amps, I wonder why?

AFAIK hi end toridal PP and power transformers (like Plitron for example) have a tiny air gap to prevent that. I've seen lamination manufacturers to offer air gapped toroid cores so it shouldn't be a problem anymore.

Bigger OT's are not for every amp. Want a muddier Mesa DR? I think I'll skip.

[jpfamps]

well for instance I've built an 18W marshall but used Weber bigger, non-interleaved OT. It had too much bass and too little treble. Tone control didn't seem to do much. I then put a GDS/Heyboer OT which is wound like the old OT's that 18W used (and is a bit smaller), and it sounds just right

I'm sure you could change other components to achieve the same frequency response, but that would mean..... research *shudder*

The original 18W transformers have quite a lot of interleaving.

I've got a winding pattern somewhere, and from what I remember it's more complex than the "standard" 5 layer pattern used in the larger Marshall Drake OTs and the Vox AC30. At least some of the additional complexity is to optimize utilization of the secondary windings.

I think Marshall only made the 18W for a couple of years at most and weren't they mail order only?

Regardless, Marshall simply used an off-the-shelf 18W RS "hi-fi" transformer as it wasn't worth getting any "cheap guitar" transformers specially made.

[Alan0354]

Sounds like nobody think that the interleaving has advantage that cheap old OT cannot match with some tinkering!!! I keep questioning this because we want less than 10KHz response, and I don't think power is too hard to get anyway. So you miss 10% power through leakage, so what. Now a days, people keep going low power, not the other way around. I can't see any occasion you want 4 6L6GC running. 30 to 50W is good for most concert hall already. I have to say from experience the Deluxe is a little under power in some occasion, but my Vibrolux is just good enough even in the days of walls of amplifiers in the late 60s and early 70s.

[jpfamps]

An extreme example the other way would be the new toroidal OTs, with an unbroken magnetic circuit of grain-oriented steel that saturates hard with only a few tens of milliamps unbalance. Hi-fi guys like them, but they never caught on for guitar amps, I wonder why?

Kevin O'Connor's London Power amps sport toroidal OTs.

Can't really comment on their efficacy as I haven't tried one (nor heard any sound samples), however I can see DC imbalance being a major issue in a guitar amp (or indeed a hi-fi amp).

Speaking to someone who winds toroidal mains transformers, interleaving becomes a major issue due to the fact the hole in the middle of the transformer soon gets full of insulation.

[Alan0354]

I am into audiophile......to certain extend. I think I would stick with solid state for that. There are some very good amp out there, I particular like the YBL power amp.

[loudthud]

Kendrick amps sells an OT ( 2112AHR, $305.00 ) with an 11 way interleave. GW told me it uses a 40W core and claims it makes a pair of 6V6s sound like 50W.

[Chuck H]

Kendrick amps sells an OT ( 2112AHR, $305.00 ) with an 11 way interleave. GW told me it uses a 40W core and claims it makes a pair of 6V6s sound like 50W.

He told that to everyone in his publications. I did speak with him about it (just try and shut him up). He's VERY enthusiastic about what he does. I've been jonesing to try one. But at that price it's not going to happen.

[Gregg]

I can tell you from experience that even a 5 layer design (Sec-Pri-S-P-S) will get you easily well above 20kHz with leakage inductance below 10mH for a 4k/50W OT so more interleaving than that may be considered as and overkill for guitar amps. However all this is subjective and matter of taste so the best way to figure it out is to get a Hi Fi OT and make some listening tests for yourself.

[jpfamps]

I can tell you from experience that even a 5 layer design (Sec-Pri-S-P-S) will get you easily well above 20kHz with leakage inductance below 10mH for a 4k/50W OT so more interleaving than that may be considered as and overkill for guitar amps. However all this is subjective and matter of taste so the best way to figure it out is to get a Hi Fi OT and make some listening tests for yourself.

We use 5 section transformers for guitar amps and are very happy with them.

The mains issue for hi-fi (as Steve points out) is that having a higher upper limit to the transformer bandwidth increases the phase margin when applying negative feedback, although I guess this could also be an issue in guitar amps which traditionally employ less negative feedback but also have poorer transformers.

Another issue with guitar amps is that are regularly driven hard into clipping, and a transformer with high leakage inductance would presumably be more prone to large inductive spikes, and ringing. This could certainly compromise reliability, but may also have detrimental sonic effects.

The most sophisticated hi-fi transformers (for push pull operation) these days are wound on split chamber bobbins. One half of the transformer with interleaving is wound on each side of the bobbin. This ensures that both sides will be very well matched for resistance, capacitances and inductances.

[Gregg]

We use 5 section transformers for guitar amps and are very happy with them.

Note that in my previous post I meant a single wire 8 Ohm secondary (the middle one) coming from the 4 Ohm tap (only 4 and 16 Ohm secondaries are in parallel) so it's not even a "classic" 5 section OT.

The most sophisticated hi-fi transformers (for push pull operation) these days are wound on split chamber bobbins.

And not only these days. I've seen connection patterns for the windings of such transformers and I instantly got headache...