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VAA-70MK2 Dynaco clone?

V

viridis

New Member
Greetings all,
I can buy a Chinese St-70 kind of clone (kinda rip-off) for $150.00 locally and it supposedly works fine. I own and regularly use a couple Dynaco Classic series and an LK72B so no, I don't need it, I probably shouldn't buy it, and I hear they are junk but something is pulling me. Am I just in for aggravation or is there hope of making it sound better than a cheap solid state amp?
 
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Regardless what the uninformed say there are a lot of very, very good tube amps coming out of China. Do you have a brand name, manufacturer of the amp? That would help some of us who know about Chinese tube amps tell you if it is one of the good ones.
 
I've done a little research on this amp and it was manufactured by Shenzhen Audio Labs in the late nineties. The reviews I've read indicate a lot of problems but there are ways to fix it to a usable amp. I don't know that it will ever be as musical as I'd like but the draw is still there....Just checking to see if anyone has heard a modded version.
 
The big magic in any tube amp are the transformers. Almost anything else can be corrected for, but if the transformers suck there is only so much you can do about it. If the transformers are a decent clone of the original Dynaco iron, its probably a solid amp. Honestly for that cheap I'd be tempted just to see how it does. Some real quick research seems to indicate the driver circuit is probably very similar to the original ST-70 using a pentode/triode tube.
 
Just realised what one it is. The output transformers on those are a weak spot, and they benefit from some upgrades to resistors and caps. I would holdout for something better. Or use it as a base for upgrading, if you can get it cheap enough it might be a good platform to modify.
 
Welllllllll, just to be an enabler ... You would get a chassis, a power transformer, tubes, probably a choke (i assume), a volume pot, tube sockets, binding posts, input sockets, etc. etc.

Get a VTA board and new output transformers from someone like Bob Latino, get to it and put it all together, and hey presto, a much better amp.

But, hey, that's what I would possibly do.
 
Now you've done it! I'll give the seller a call tomorrow and make the deal, providing it's in as good as condition as I've been told by messaging. Many, many thanks for the input. I'm glad this forum is here. And hey, No Money, thanks for the push. I'll post when I get it up and running to my liking. Or, maybe it'll drive me nuts and end up for sale again.....
 
Spot on, Gadget. I'm a fan of the cheapest way out. Save the change for more audio gear, right? I have read several posts and a couple reviews and though the OT's seem to be troublesome, I'll check the circuit for other upgrade
 
So, I got hold of someone here who knows about these (and lots of other tube related stuff). They were copies of a Dynaco ST 70 for sure, with a few "local" modifications. He says the output transformers were not very good, especially with treble response. Some transformers were better than others. I get the feeling quality control was a bit hit and miss at the transformer winding shop.

I still reckon, at a good price it's a good base for a project.
 
Thanks for the effort! I guess the consensus is check it out, upgrade/mod where needed and give it a long listen. If nothing else, I'll get back to the bench and have a lot of fun, hopefully without spending vacation money. Thanks again!
 
Also possible if the transformers are marginal at this power level, they could be acceptable to build a lower power amp around. Just a thought if you do end up replacing them with better.
 
viridis said:
Greetings all,
I can buy a Chinese St-70 kind of clone (kinda rip-off) for $150.00 locally and it supposedly works fine. I own and regularly use a couple Dynaco Classic series and an LK72B so no, I don't need it, I probably shouldn't buy it, and I hear they are junk but something is pulling me. Am I just in for aggravation or is there hope of making it sound better than a cheap solid state amp?
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Do not buy Chinese , in my humble opinion. You already have a couple dyna's. Save yourself $$ & a headache
 
You're humble opinion is well valued, Rick, so if I make the jump and the amp drives me nuts, your post will haunt me! As NoMoney pointed out, I'd still have a pretty nice chassis and, from what I read last night, a decent power transformer for a Marshal style guitar-I play, but badly. I figure that for the money, I can use the Eico ST70 iron I have in my shop (ok, basement)
with this chassis to put together a nice amp. I've got a lifetime supply of 7591, 6gm5 and 7868 NOS tubes so may as well use 'em. Lifetime isn't what it used to be so maybe three lifetimes.
 
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