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DVDHack 11th January 2004 08:41 PM

SE Output Transformers
The general thoughts I'm picking up is that the Output Transformer is te key ingrediant in a SE 300B design.

Would some of you care to comment about the virtues of some of the beter known brands.

Smaller suppliers

I'm thinking Tamura cause I want to do this once and they seem to have the best rep so far but their cost is several times that of a Hammond.

On smaller suppliers that you can't get a reference for eg I tried with Black Art OTF but no one has used them. How do I know if the TF is any good - its a bit expensive to "give it a try".

Please discuss and Many Thanks

Mikael Abdellah 12th January 2004 08:28 AM

I ordered mine from Sowter. Unbelievably good service and even better transformers. You can't go wrong with Sowter! :judge: :D

Mike C 13th January 2004 11:34 AM

Odd rambling reply ...
First, 'DVDHack', how about letting us know your first name; DVDHack is so impersonal!

Some may argue against the OPT being 'the' single most important aspect of a SET, but I think all will accept its importance.

The problem with your request is that few of us have been able to do much direct comparison, as good OPTs are expensive. So you may have to gather as much info as you can, of whatever type, and filter it; that's what I did.

My experience is limited to ONE 300B SET, and ONE type of OPT, so what the hell do I know?
Well, that OPT is Lundahl, and results are excellent. No way can I say it's the best, I just don't know.
I suggest you research the point here; and also on Tube DIY Asylum where you'll find hundreds of posts ... most saying their choice is the best, which is where you have to apply that filter. :)

I have some specific points for you to consider.

It's suggested that, when plotted logarithmically, the total bandwidth of most good OPTs is surprisingly similar in magnitude.
Comparing two with upper limits of say 30kHz and 60kHz, you'll often find that the second one has a higher low frequency cutoff. So don't just take an impressive hf figure as a single figure of merit.

Of somewhat dubious value! It depends how the measurements were done. Possibly, measuring an OPT at very low power can give very high upper frequency measurements that cannot be met in use.
So, reliable descriptions of sound 'character' may be of more use.

Many designs use about 3kohm, perhaps 2.5kohm, impedance for a 300B. However, there can be benefits from using a higher impedance of say 5kohm; less distortion.
However, a lower impedance of say 3k will give more power. About 8 watts. I guess it's often used by professionals as, if the 300B's are run hard, they can just about claim 10 watts (at say 10% thd) and double figures has *so* much more street cred than a single figure wpc!
A 5kohm OPT will give about 6.5 watts at the point of clipping, compared to 8 watts or 8.5 with 3kohm. Possibly a good trade off for less distortion; something to consider, as the difference between 6.5 and 8.5 is really not a lot.
Oh, and 6.5 watts of pure SET sound, delivered from a really solid PSU, is a hell of a sight more powerful than you'd expect.

Good luck; keep feeding us your ideas.

Zoran 14th January 2004 12:17 AM

If You want realy good OT go to "Bartolucci"
and of course Sowter have best quality price value and always good english sound...

DVDHack 14th January 2004 04:26 AM

Well that's two for Sowter at least.

I take your point on lack of comparability unless you've owned a few but I got the impression that several people had gone through the process of Hammond and Piltron etc and formed an opinion.

There are references on the web stating people had "upgraded" their amp with better OTF but how do they know they are upgrading unless there is some sort of quality hierarchy?

I can't readily compare the sound so I am concerned I may miss the potential of Valve without ever realising it. I could spend a great deal on poor components and never realise.



Brett 14th January 2004 10:49 AM

Hola Ralf,

Try Lundahl. They are excellent and quite reasonably priced, and there is an Australian distributor who's good to deal with. As there is a shipment about to arrive (I have another order in), there may be a 4 week leadtime if you ordered them soon. I've tried the Hammond PP varieties and they suck compared to the Lundahls. I've used lots of them, and compared them to a number of other brands, so I have a good reference point to comment from*. , specifically the 1663 (3k:8), probably around $A250ea (BUT check the pricing with Control Audio)

Control Audio Pty Ltd
Mr. Rick Dowel
Level 6, Westfield Towers
100 William Street
AU-Sydney NSW 2000

Phone +61 - (0)2 - 9368 7100
Fax +61 - (0)2 - 9368 7199

A second choice, and another one to recommend is Lancroft.

I have some of these too, and they're excellent.

* Caveat: can't give specific advice on SE OPT's as I don't build SE amps, but have built lots of PP's.

Mike C 14th January 2004 11:22 AM

These brands seem to have a good reputation:
Tamura, Tango, Magnequest, Lundahl, Plitron, SJS (used by Border Patrol).

At this level, differences in performance are probably not going to be great, and may be explained to some extent by how the passband is set relative to the audio spectrum; some oriental models with extended high frequency may, possibly, have a less extended bottom end. You may be able to make an intelligent choice if aware of this.

I tend to suggest that Lundahl set the passband pretty evenly on the spectrum, favouring neither highs nor lows. In conjunction with a 300B with extended top and bottom (TJ mesh plates), results seem good to me.

There are two suppliers in the Netherlands who produce amorphous core OPTs that appear to be of very high quality, worth a bit of research. I am very tempted to try these myself in a new SET project .... possibly to be called 'Sindy' and I'm sure people can guess why.

Given the lowish dollar, you might check pricing on the better ones from the USA?
Or see what's going on US Ebay for the far eastern makes (but avoid one particular US seller with many adverse comments on Tube DIY Asylum!).

Ouroboros 14th January 2004 12:05 PM

I had a couple of custom SE opts made by Sowter to work with the big DA100 100W triodes. The transformers perform very well.

The only possible problem might be that they don't LOOK all that special!


Mikael Abdellah 14th January 2004 02:49 PM

I think my sowter-trannies looks sexeh! :hbeat:

KlausB 14th January 2004 04:29 PM


Originally posted by Brett

Try Lundahl. They are excellent and quite reasonably priced.

I fully agree. I made excellent experience with Lundahl line transformers. :nod:


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