@grannyring "I was thinking about building one of Latino’s amps. Do you own one and have you compared it to an updated/modified ST70? I was also thinking of just buying an ST70 and updating it using modern day parts in key areas while keeping the output trannys."
I think you will absolutely LOVE having an ST70 (or pair of MKII, MKIII, or MKIV monos) around. Simply put, there’s no other piece of high-end audio that provides as much fun. Not even close. As I recently shifted my base from Philadelphia to Vancouver, I sold off a bunch of extra gear, including 2 ST70s. The guys who bought them often text me about all manner of things. Both had a lot of other amplifiers, solid state and tube, and both constantly tell me how fun and exciting and great sounding the ST70 is. They went out bought soldering irons and the like. And modding / playing with them has re-energized their audio experience. I wholeheartedly concur.
I’ve had originals, modernized versions of the original circuit, and modernized reinterpretations of the amplifier, almost all of which use the Mullard long-tail pair phase splitter / driver, the Latino (actually VTA) kit falling into this latter category. I do still have the VTA and the other boards, as I sometimes solder in different boards to play around, evaluate, etc. I also owned an ST80, not the solid state amplifier of the same name, but the Dynaco attempt at a tube amplifier designed to "fix" everything wrong with the original. These reinterpretations, including the Latino / VTA and the ST80, mostly switch out the driver board for their own design, with the rest of the amplifier remaining as it was. The exception to this are the Dynaco ST80 and Triode Electronic of Chicago, who also redo the power supply as Ralph alluded to. The ST80 also featured a triode / ultralinear switch, that mod I did welcome. I can comment on many of these Dynaco reinterpretations outside of the Welborne kit, which I found interesting and unique, used to have strong interest in, and wanted to try out. But the company went through a lot of ups and downs, and when I wanted to move forward, were no longer shipping any products and a lot of folks who ordered got left holding the bag. Most of these reinterpretations either sound exceedingly similar, or if / when / where they differ in sound it’s because they implement different (i.e. 12AU7 vs 6922) driver tube types from each other.
In my opinion, the most interesting, most fun, best sounding version is the original, updated with modern parts and a couple tweaks to the original design to provide the sort of low-end response we typically demand these days and also protect the 5AR4 rectifier from arcing / blowing at turn on. The total cost of these mods can easily come in under $20. But as they include the coupling caps, you obviously could spend $500 on those parts alone. And for those interested, my power transformer runs barely warm. Not to go off on a tangent, as that’s a discussion in and of itself, and I will leave that for another day, but many who really understand what they’re doing think a power transformer should run HOT for best sound.
That means, although no one has done more for the product over the past decade plus than Bob Latino, you WOULD NOT BUILD a Latino / VTA kit. The reason behind that is you want to go with the simpler and IMO, more interesting and beautiful / less ubiquitous / better sounding cathodyne phase splitter / driver circuit the original employed, and taken over from the guitar amplifier industry. Again, I feel though criticized since the time the kits came out for reasons such as rudimentary / backward, incapable of providing the amount of gain of the Williamson or Mullard designs, and simply employed to save a buck, folks overlooked its inherent superiority for the same reasons as they did with SET designs. I could talk about this all day, but will keep it short and high-level instead of making a deep dive and turning an already long post even longer and more boring. Upon taking a look and listen with a fresh set of eyes, ears, and mind, you find something unique, special, and wonderful. Folks historically dismissed the Dynaco with its slow, syrupy, pipe and slippers sound that represented the typical products of the time after hearing the reinterpretations; most of it came down to a case of comparing apples and oranges. The new amplifiers got built with modern parts, which provide a night and day difference in perceived speed, openness, clarity, and refinement. Build an original with metal film resistors (and good modern caps), and you’ll hear what I’m talking about. After all, that’s what 99% of current transformer coupled push-pull amps do, build a Mullard design with today’s parts. The cathodyne has allowed me to now come to see, and hear, drawbacks of the Mullard design folks never raised previously.
So, if you allow me, here’s a couple of thoughts:
1. Outside of buying something that looks like a truck drug over five miles of bad road with the intent of using those original transformers you mentioned, the days have passed when you could buy an original for a reasonable amount of money. A quick eBay history search shows units with the sort of terribly ugly chassis we all know Dynacos for normally fall into the $400 - $750 range. Again, it’s a good move to go for those great original transformers if you find a decent deal. But I want something that actually looks good in addition to sounding good
2. Bob Latino offers some excellent / modern RCA inputs and loudspeaker connectors that allow you to use the sort of real cables we demand today. I highly recommend getting them from Bob
3. Dynakit Parts offers kits featuring the original circuitry, and again, in my opinion, will produce the best sounding end product. Of course, that means ordering the metal film resistor option used in modern amplifiers NOT the carbon composition of the original Dynaco implementations. In addition to that, Kevin’s phenomenal polishing work on the stainless steel chassis, which obviously forever nixes the issues with discoloration, fading, pitting, corrosion, etc. provide something tangibly better than Bob Latino and Triode Electric. As I’m speaking of several years ago, it’s entirely possible the other two have since upped their games
4. As mentioned previously, you may want to consider implementing a couple of mods. The first protects the 5AR4 from arcing over / blowing during amp turn on. Folks have gone to Bob Latino with his thoughts on this, and after initially hesitating, it seems to now have his full backing. Regardless, blowing a fuse upsets me enough. Blowing my daily drinker JJ or top drawer sound $125 Mullard 5AR4 obviously takes that pain up to a completely different level. I’m not 1000% sure, but I don’t think I detect any sonic degradation from this change. The other mod, coupling capacitors, robs enough of the sweetness and magic of the original that you can surely hear it in A / B listening, but banishes the complaint that the ST70 doesn’t deliver the goods on the bass. It’s a sort of balance you work between the two, adding to one takes from the other. There’s a second mod to improve the low-end that’s pretty brilliant, takes nothing away from any other area of the sound, and costs less than a buck, but the only request of the person who taught it to me was to never publicize it, so I don’t give it out online. Just to tell you how comparable to a modern amp the bass becomes, I’ve scared more than a few bassheads literally almost out of their skins by playing the beginning of a Fiona Apple track through my Fried O subs. By that I mean, the sort of reaction someone working in a haunted house at Halloween dreams of.
More than anything, have fun and good luck!
