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Acquired a Pair of Dynaco MK IV Clones As A Fun Diversion

M

Mister Pig

Pigamus Maximus
Brought home a pair of the these amps that were built by a respected amp builder. This was a project he did 10 years ago and recently refreshed. Used new transformers, updated pre driver boards, and some very nice power supply caps. The quality of the build is very nice and well laid out, even for one of his earlier projects.

I am not wild about the side panels, but new ones can be cut, and they are pretty simple. I should be able to cut new planks and just have to pass the sides through a router table to make a rabbit joint on one side, and both sides. The plates of the amp chassis will all screw into into the edges.

All in all, seems like a very nice little pair of amps.
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Nice find! Those appear to be decently made and finished. If you're serious about cosmetic improvements, maybe also get rid of those circuit boards. I've never understood why the Dynaco clones didn't replace the board with a nice aluminum panel and sockets wired point to point.
 
The Mk.4 was a nice looking amp. I have always been thinking that as monoblocks built around the A470 opt, a clone should be built with enough room to support a proper power supply and tube rectification. 6W4's for example, and of course add a proper LC filter...which means higher AC input to the filter( but 6W4/6AU4 could not care less about that sort of voltage ). The original profile; all in a line is Right...IMO.
cheers,
Douglas
 
I rebuilt a Stereo 70 with oem upgrades for my covid quarantine project, and acquired a VTA 70 custom build to compare.
Don't recognise the board in yours, it is neither but I will be interested in your take on these.
 
Pio1980 said:
I rebuilt a Stereo 70 with oem upgrades for my covid quarantine project, and acquired a VTA 70 custom build to compare.
Don't recognise the board in yours, it is neither but I will be interested in your take on these.
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I believe it's a Triode Electronics board as that is where the transformers come from also
 
a single triode and a 12A*7 I'm guessing? 6AV6 is half a 12AX7, 6AT6 is half a 12AT7. 6C4 would be half a 12AU7. That would make perfect sense if its half the usual Triode ST-70 board. Those run three twin triodes, one for each channel as a long tail pair phase inverter and half of one tube for a voltage amp.
 
gadget73 said:
a single triode and a 12A*7 I'm guessing? 6AV6 is half a 12AX7, 6AT6 is half a 12AT7. 6C4 would be half a 12AU7. That would make perfect sense if its half the usual Triode ST-70 board. Those run three twin triodes, one for each channel as a long tail pair phase inverter and half of one tube for a voltage amp.
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Supposed to be a very good alternative classic Mullard 5/20.
Higher gain with more gfb than the standard newest VTA amps, otherwise similar, afaik.
 
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Pio1980 said:
Assume the outputs are A-470 type then?
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Yes those are the output transformers. Now I don't know what these transformers cost 10 years ago, but I just looked them up on the Triode site and what the current cost of the transformers is basically what I paid for the amps. I knew when I was given the price it was more than fair, but I didn't realize it was that good. These were built by the fellow who does all the custom builds for Bottlehead orders, this was one of his earlier projects that he just refreshed. Power supply has Solen caps, the boards have Auri Caps, and I suspect the other hardware is also going to be sourced from Triode Electronics.

I don't have a plan on what I am going to do with these amps quite yet. I do have an under the radar SS pre amp that sounds remarkably good that is not being used. I could pair them with these and have the start of a decent little system. The only problem is I don't have a place to put them, as if I tried to use them in another room I am afraid my wife will bury me in a shallow grave in the back yard.
 
gadget73 said:
a single triode and a 12A*7 I'm guessing? 6AV6 is half a 12AX7, 6AT6 is half a 12AT7. 6C4 would be half a 12AU7. That would make perfect sense if its half the usual Triode ST-70 board. Those run three twin triodes, one for each channel as a long tail pair phase inverter and half of one tube for a voltage amp.
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Looks like two twin triodes, guessing 12AX7, maybe sections paralleled, and maybe 12BH7 LT splitter.
 
To pick a nit, none of these variants without the basic Laurent driver topology are actually Dynaco clones, the only thing Dynaco being the A-470 OPTs. They might otherwise be Marantz tube amp clones as Mullard 5/20 variants, tho others like Eico also used similar driver topology.
 
Pio1980 said:
To pick a nit, none of these variants without the basic Laurent driver topology are actually Dynaco clones, the only thing Dynaco being the A-470 OPTs. They might otherwise be Marantz tube amp clones as Mullard 5/20 variants, tho others like Eico also used similar driver topology.
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I hear what you are saying, you expect a clone to be an exact copy. In this case its more like "inspired" or an updated version of the Dynaco MK IV circuit since it uses the Triode Electronics boards on the front end of the circuit.

So to call it a clone is a bit of a stretch, but it is based on the Dynaco iron and back end of the circuit.
 
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Mister Pig said:
I hear what you are saying, you expect a clone to be an exact copy. In this case its more like "inspired" or an updated version of the Dynaco MK IV circuit since it uses the Triode Electronics boards on the front end of the circuit.

So to call it a clone is a bit of a stretch, but it is based on the Dynaco iron and back end of the circuit.
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Nonetheless, they should provide at least decent performance, at best, "keepers".
Fwiw, I much prefer EH 6CA7s to EL34s in all these type amps I've used.
Viva Tubes had them matched for a reasonabe price, last time I checked and bought two matched quads.
 
I think the driver ckt is a cascoded 12AU7 input voltage amp into a 12BH7 LTP splitter with a CCD on the long tail.
That should sound pretty decent.
 
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