Good budget tube amp?

A few more things I should have mentioned regarding the "true blue" pop-classic: Proper NOS 7199's are a must -- they are generally considered pricey -- so carefully investigating the condition of these in any ST-70 you're considering is important. A minor mod to accept NOS 6GW8's (pricier)in this position is considered by some enthusiasts to be the high end way to go. Substituting a pair of top-shelf input loading resistors such as Caddock is dead simple and can clearly improve the sonics in a well sorted out tube amp for the price of a solo dinner at Appleby's. And don't think the kind of gold binding post mods you commonly see around are improving the sonics: more likely, the opposite, cable-fitting issues aside.

BTW, Trelja, do you think some folks in Kevin's network would want to take on some of the refurb work I alluded to in my initial post at a keen price for tube newbies? THAT would simplify this path greatly for Rossbernstein and others.

Any Cayin or VAS, used, of course.

Seakayer, you are incredibly knowledgeable about this vintage gear. This year, though I've not acted on it, I've been more than a bit curious regarding the Eico HF-87 you mentioned. My hat's off to you...

I happened to recommend the "original" Dynaco circuit as I find there to be a purity in that Concertina front-end that is overlooked/underestimated by most. Rather, I see it as one of those situations where simpler can be better. I fully admit that mine represents the minority opinion, and that more elaborate (VTA/Latino, KTA, Dynaco's own 1990s tubed ST80, etc) front-ends, most of which employ a classic Mullard long tail pair driver stage are considered to be a major improvement by most. As you said, budget played a huge role in design, and obviously, less parts translates into an easier fit into a budget.

Again, tipping my hat to you, your point on the 7199 is spot on. With Sovtek tubes, I consider the Dynaco to be, at best, an average product, and I'm not even sure it reaches that level. Install a pair of Sylvania or RCA, and the amp comes alive.

But, to answer your question, while the individuals should be contacted, the impression I get is that some of them are more oriented toward a new build. That said, there are a whole lot of folks out there who can get an old Dynaco right.

By the way, one final point - I often see folks make the statement that today's circuits are the reason for the superiority of today's tube amplifiers. That is absolutely incorrect. With an incredibly few exceptions, today's amplifiers employ the circuits of yesterday; there are no two ways about that. The difference is the implementation of today's products, both parts and things like higher bias (we are not as conscious of the economics of tube life today). This is why a Dynaco ST70, built with today's metal film resistors and better caps can outclass a lot more current tube amplifiers than most would believe.

I very much take your point on the Concertina, Trelja, but here's the rub: the Concertina, or split-load style of phase splitter & driver, really is not properly used "naked" driving a Class AB output stage, or with any sort of output stage where you are going to be drawing much grid current. This is because the frequency balance between the two phases -- which interacts in various complex ways with other characteristics of performance -- depends crucially on the plate circuit and that of the cathode in the Concertina seeing EQUAL IMPEDANCES at all times.

Contrary to audiophile mythology, in a circuit where the two loads are effectively kept close in value and stable, the output impedances of the splitter, top & bottom, hence the "drive" characteristics of the two halves, are VIRTUALLY IDENTICAL. Not so in a Stereo 70 trying to push out nearly 35 watts into most real world speaker loads. How many "respectful" ST-70 mods retaining this splitter arrangement, but operating in pure Class A, where neither OP tube cuts off, have you seen -- preferably with grid chokes, etc, to handle the grid current? None, I bet. This is why D.T.N. Williamson added a LTP driver stage after the phase converter in his classic design... at the expense, because of multiple poles in the now more complex circuit, of marginal stability vis-a-vis the global loop feedback -- which itself interacts with complex, dynamically changing speaker loads. D.T.N. got it pretty much right -- others didn't.

Thus, some Williamson copycat amps of the '50's, being adulterated by cheaper, slightly wonky or inconsistent output transformers and such, could be -- and STILL ARE -- very dicey performers. The Heathkit W4-M is an example. It will work fine with a LTP converter and a simpler front end circuit.

Their are ways to stick some band-aids on these problems, but you know, why not get it right?

By contrast, a little EL-84/7189 amp with Concertina, running Class A or close, at 10-12 watts out, can sound excellent in ways a stock Stereo 70 never can. So, I have the doggone cutest little refurbished Fisher SA-16 on the way to me now to add a little reinforcement to my point! And I have, I guess, a very nice ST-70 refurb with the stock front end for sale (in theory).

Music reference RM-10. Magical little tube amp. I run one upstairs with totem model 1 sigs and joule la 150 and it sounds very very nice.