Matched power amp tubes

alexc said:

While on the subject of matching power tubes ...  and their transformers ..

The Dynaco output transformers are sometimes said to be 'more' tolerant of 'power tube imbalance'  ..  at least by some modern vendors ...

So what would it be, in the design/manufacture of the dynaco, that improves this property ?

....

As I understand the dynaco, it differs from most in that it uses (more) interleaving with (more) complex interconnections.

ie. more interleaved layers with paralleling of reverse-phased sections (and what not). Possibly better 'balanced' halves in the primary ? (maybe even less balanced!)

The cores and other basic properties are pretty similar -  I don't think any exotic materials are used in either ..

Click to expand...

I can venture three possible explanantions;

• The laminations are not perfectly butt-stacked, which reduces the global magnetic permittivity, thus making the core less sensitive to DC, but also decreases the inductance at the expense of LF response, which may be compensated by increasing the number of turns, which in turn increases leakage inductance, at the expense of HF response or would could be compensated by more complex interlleaving. That would account for making the xfmr less sensitive to DC unbalance.
  
• The circuit is under heavy NFB. That would account for making the whole circuit less sensitive to AC unbalance (not only the xfmr). 
  
• The mmktg dept has put a lot of effort in the BS factor. 

from Kittleson's interview with David Hafler.

gridcurrent said:

from Kittleson's interview with David Hafler.

Click to expand...

That was a "new" technique when Hafler patented it, but now it is quite commonly known, although not often implemented because it requires particular attention to the starts and ends, since some are on the right, when the others are on the left. In addition, any connection problem can be detected only when the xfmr is assembled.
this technique does not lend itself easily to automated manufacturing.
The advantages are less leakage inductance and less parasitic capacitance.

@AlexC, Gridcurrent and Abbey

Thank you guys for sharing your thoughts about the output transformers. It is a bit hard for me to judge what transformers to get... the Edcors are way cheaper than the Sowter equivalent so a natural question must be if the Sowters are worth the extra money... i.e are they that much better? Am I capable of hearing any differences? To mention a few thoughts.

best regards

/John

Many of the traffo choices are very high quality  ...  across the price spectrum.

Some are better in some aspects, some are more expensive and some may sound better!

It depends on where you  are  build-wise, and how experienced an end-user you are have .. and what budget.

...

I'm not sure I could tell the difference by ear in more than a few cases ...  but I like to think I really can hear a specific output traffo choice ..  in a few cases for sure.

...

I think it's fair to say, the quality league kind of starts with Edcor, then increases in expenditure  up the Hammonds and the Triode Electronics dynaco types ... further up to the Sowter at the start of the top shelf players.

Not to mention the Mercury Magnetics in the premium instrument amp field, as well as Magnetic Components at the more affordable end of authentic stuff.

A world of old stock vintage choices too  can be a great choice, particularly for more interesting build types.

Me, I like them all  8)

Thanks Abbey and others' for your well presented info regarding possible optimisations in the dynaco types 

I have read the vtv articles with Hafler  ...  a good read for sure.

Of course, another interesting maker is Electra-Print 

Good reputation for meeting customers needs, doesn't skimp on the 'heavy iron'  ...

They seem to be able to do most things transformer wise, including the more esoteric stuff  ...  like big triode SE.

They have some interesting winding techniques in some models ...  for low 'intermodulation' distortion ... addressing similar things as  from Abbey's description above, I think.

reverse winding goes way back,  farther than Haffler, but if you want to make a living selling boutique audio you have to be a good salesman,

reverse winding will not cancel the dc amp-turns, if it did, then your ac would cancel also.  google right or left hand rule.

a magnetic field can only be built one way or the other, the sense of the current relative to the core must be the same to be additive,

you can use non grain lams in .018 gauge to raise your ac and dc saturation levels,  and it is cheap. 

Partridge made some good output transformers, they knew how to split the primary up, probably came from experimentation,

MacIntosh made some good output transformers with cathode winds and quad filar winds,  but that market has changed in a big way, 

Fisher made some nice medium range iron, you can get a junker x 100  of evilbay and get the some of the  best EL84 transformers ever made,  93 EI lams, (15/16" tongue)  why not just skip up to 100 EI which is much more common and probably cheaper?  they wanted to get it just right.

Altec Peerless 15036, what a beast! fat stack of 175 EI which is insane for an 80 watt amp,  all done with #26 wire, quad wound secondaries, 5 section primary, (wtf?) with a rev wind thrown in plus a cherry on top in the way of 4 lams of nickel alloy in the middle, try buying 175 EI in 80 Ni !  does the Ni do anything special? probably not, these guys were out to showoff to each other because they knew the competition was gonna do a break down on their stuff,


edit: never mind on the X-100, prices have gotten out of hand, this rusty hulk is going for $800, i got one from Kittleson for 150 back in the day, he used to hang out with Eric Barbour on Duane Ave Sunnyvale at the VTV shop, i got to go in that shop and was amazed at the vintage gear that was stacked up, the most impressive was the PA system for a drive in movie , huge chunks of iron needed as car speakers were not out yet, full of giant PCb capacitors, lord have mercy,  Fisher iron-best guitar amp you could ever make can be built around these and some Amperex Bugle Boy tubes from the 50's

I've been listening to a mid60s japan el84 integrated amp I refurbed last diy season ....  first couple of days of all-day listening, in my houses' winter 'warm room'  ... typical 'fisher' style ...

Hooked it up to my mid 90s tannoy system 8 concentrics : wowee !  typical listening from 3m away or so .. prolly doing 5Wrms most of the time .. heavy class a  ..  at low thd ... at that low-ish level ...  big bass (relative to 5W that is) and snappy, well define to boot ... 

Just sounds so alive!  I can vary the global nfb nicely for additional control. My rework with new 5751 and the 6P14Pev (super el84) really ended up worth the time to go thru it all....

I also have a mesa preamp rack which really comes alive into the el84 pp amp   It can get bad ass and huge sounding pushed all the way up ... around 12Wrms at 3%  is a cranked as I go without hearing protection.

..

Anyone had experience with old organ traffos ... baldwin, hammond and the like ..  for pp el84 or 6V6 ?  I think they could be very nice in an instrument amp, perhaps even hifi.

Most of the good old stuff, that once was affordable, is now approaching the cost of new good manufacture .. at least way down here, after shipping an taxes ....  One can occasionally be lucky though!