• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

True amplifier Identification Please..

mcgarick

mcgarick

Super Member
Hi Everyone, there's a pair of tube monos for sale in my neck of the Woods..
These are advertised as Dynaco Mk III , But I don't think they are the originals, Not that, that would turn me away...
Can anyone here Identify these blocks from their re-creator??
Thanks in Advance..
Also, what would be a going price?

1790733387776.png
 
Register to hide this ad
Looks like a not-stock Mark III. Offhand I don't know the board but 100% its not the stock 6AN8 driver.

The rectifier situation I'm puzzled by though. Thats definitely a 5AR4, Chinese is my guess, but the thing next to it looks like one of those Weber "copper top" rectifiers that usually replaces a vacuum rectifier. No can cap, so the filter caps must be underneath, possibly on a circuit board, hopefully not just in a big messy lump of parts. I'm sort of curious whats going on with the rectifier situation, maybe the copper top is doing the actual rectification, and the 5AR4 is just serving as a delay? Thats a very expensive way to do it, a cheap TV damper diode and some common silicon diodes would do that every bit as well for a lot less money. Four 1N4007 or a pair of some higher voltage rated diodes to do the rectification, damper just for slow-start.
 
Thats one driver board I haven't seen yet for these Mklll's. I haven't seen a 12AX7 used before in these amps. Wouldn't a couple 12AU7's get the job done?
It looks like it might have CCS as well?
If the price is right, it could be worth it. You could always put new stock style driver boards in it from Dynakit, or boards from Tubes4hifi if you wanted to.
My guess was that the 5AR4 is being used as a delay device as well.
The coppertop rectifier has a thermistor inside, so it does have a bit of delay already. They work fine. I have those parallel push pull amps that are just Mklll's with twice the output that I have the Coppertop's in them and haven't had any issues.The added 5AR4 isn't really needed in those Mklll's.
 
could do a pair of 12au7, or a pair of 12ax7, depends on the configuration really. All depends on how much gain is needed or wanted. With 4 triodes available there are also multiple options here. One of the tubes as a long tail pair, one triode from the other as a voltage amp is the most common and most simple. The extra triode could potentially be rigged as a CCS but the lazy way is to do nothing with it. Available voltage becomes your problem there with tubes, though there is a negative DC supply available that could be used to compensate for that.

Can also cascode the first twin triode to make it like a pentode, which is basically the original Mullard driver circuit.

Then you have the possibility of a Williamson, though that would typically be med-mu tubes.

I'm sure there is something else that could be done with 4 triodes that I haven't had enough coffee to come up with. Cross-coupled maybe? Nobody besides ARC really uses that though, and all of the schematics I've ever seen using it have a gain stage in front of the four triodes in the inverter. Does anyone do SRPP driver stages?
 
You must log in or register to reply here.
Back
Top Bottom