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In the world of vintage vacuum tube kit amps that are push pull and 15 watts or less in output, How would you rate the little transformers? Integrated amps included. I was wondering about Dynakit, Heathkit and Eico and how they would compare. There is not much said that I can find about the Heath and Eico (Wee) transformers. Thanks......Mark Korda
I have a bunch of their 7189 amps and a beautiful old brass faced 600 tube rectified receiver.
Are we talking about two amps that use the same tubes and have the same impedance transformers? Or are we talking about a transformer for EL84's compared to one for 6550's? Very different thing.
I'll assume we are talking about two transformers rated for the same tubes, the same loads, and same output power. Lets say a 10K to 8 ohm 15 watter for EL84's.
What does a physically larger transformer typically give us? More inductance....which lets us play lower bass at higher power levels. Most units will do the quoted 20-20khz at one watt but few will do it at full rated output power. One could say the more inductance the more the high end has to suffer as a gross general comment.
So perhaps if you don't intend use more than a small fraction of it's rated power....and you don't need low bass....then a smaller transformer will suffice....and might even do better on the highs.
But there are some other very important factors. Some to do with the transformer and some to do with the audio circuit.
Feeding a 5 hertz signal into any OPT at any reasonable power level is going to saturate the core. One needs to design the circuits so there is an absolute sharp cutoff at some point. Best to have one on the high end too.
Now lets think a bit about how a transformer is made/wound. You are going to have something like a 2,300 turns of small gauge wire in the primary and maybe 98 turns of heavier gauge wire on the secondary (I am not going to do the math to make this realistic but it is close enough). This wire is going to wound on a single bobbin. It is push pull so you have to have an even amount of primary windings. You need the same number of turns for each tube and the same DCR. You also want to completley fill the window in the EI core.
So you wind the first primary (P1) on the bobbin. Then you wind the secondary (S1). Then you wind the second primary (P2). All of these windings go on top of one another and in a vintage transformer there is paper insulation between them. Now the astute reader will see that the length of wire for winding P2 has to be longer then P1. Therefore DCR can't be equal. Maybe we don't care because we have made no provision to balance current in the output tubes. Maybe we don't have a phase splitter that always provides equal and opposite drive to the output tubes? Maybe those issuses are a far greater error than the difference in DCR in the transformer. So why pay for a better transformer?
Now what could we do to make matters better? Suppose that we had two different bobbins so that P1 and P2 could be laid down first with equal turns and DCR. Then S1 was split in half between the two bobbins (S1 and S2).
Bottom line, good transformers might have better material for the core (grain orientated high silicon), might have a different core shape (C-core), might have several primary and secondary windings (P9 and S7), might lay down primary and secondary windings together rather than on top of each other (bifilar). Etc, etc, etc:) Way more stuff than I know about. Rest assured the really good stuff is way top secert!
But again, if you aren't going to make the amp circuit good enough to make the transformer the weak link why pay for a better transformer? Besides, sometimes it is the imperfections that make something special and more appealing. And that might be why you are here instead of enjoying some solid state amp:)
......partial to the Acrosound TO370. Mikey doesn't care for them, so I imagine that these are all matters of taste. Enjoy the project!
Without specific current knowledge of the transformers themselves, I have to believe that the iron in these Heath EL84 basic amps was good. Their performance reflected it.
Russ, great lesson, thats what I wanted! Keep it coming anytime I'm all eyes and ears.
Eli, always on the ball!
Russ, I am using a Heathkit AA-32 in my small living room and love it. As what you said Story I also have a subwoofer in play with the AA-32 and seem to look at an amp like the Heath W-5 with the giant Altec transformer as over kill. The cheap bastard in me has me wondering about smaller transformers and which ones you guys like. Thanks...Mark...lately the HF-14 and HF-12 Eicos are peeking my interest more than Nina Hartley!
I'm no engineer but how do smaller trannies fair with easier loads. using small very efficient speakers and low watt systems vs. less sensitive speakers and trying to pump out 20+ watts???
Sort of the right tool for the job kind of thing?
I rewired the socket to power a McIntosh C8 preamp and nicely drove a 12 inch Altec in a Karlson enclosure.
Dave O'Brien, who conducted the McIntosh amplifier clinics, spoke well of the UA2 and included a chart of it in his book as an example of a good amp.
Mark, are you of the opinion that the better vintage transformers are superior to today's offerings? No judgement in my question, just curious.
Sadly, IMHO, I would say the engineers who understood audio circuits knew little about transformer design and the engineers who made transformers knew little about audio circuits. This typically lead to a transformer being built as cheaply as possible to meet a given "spec". Had things been different I suspect we would have seen more C-core's instead of E-I's....and maybe more split bobbins.
Sorry but I don't know which audio brands used which transformer brands. So I'll just name some transformer brands below. There are many other quality ones as I'm just going by memory. In many cases a given company will make transformers of vastly differing quality.
Western Electric, Partridge, Triad, Chicago, UTC, Peerless, Thordarson, Acrosound, Stancor, Freed, Sowter,......probably wouldn't look down my nose at Telefunken, Phillips, or Siemens....no idea who made the Sansui OPT's...maybe Tango??? but they were good.
So no shortage of names. IMHO the key is understanding the "spec" they were built to, the trade offs in transformer design, and ways to spot a better product. For example, I'd say one with UL taps and more connections for different ohm speakers is a better unit (because it is more likely to have more primary and secondary windings).
both power amps and integrated (same OT) were great. IIRC Eico had no ultra-linear taps like the Dynaco, but all other things being equal, I preferred the Eico to the Dynaco (EL-84 PP).
It's a tradeoff between bass energy and mid to treble 'openess'. Guess which one usually wins?
I'm waiting for the rest of the story Story. Who wins?.....Mark K.
Hi Mark - pick your candy - some people like deep, strong bass (although I do dig that bass), but after hearing what a great OT can do with just the right amount of windings, I chose mine. Unless you go $$exotic, some of the older plain jane iron is just amazing. And there are other ways to make up the slight loss. Enjoy
all the best,
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