we have duplicated the circuit from our ST70 modification onto a PCB that will fit the Dynaco MK3 mono amplifiers.

MK3 bare PCBs are $60 a pair Compatible with Dyna MK3 & VTA M125 includes shipping to the US	a pair of PCBs with parts kit is $95 Includes shipping within the US NOT including tubes	If you'd rather have the boards assembled and ready to install, it's $60 for our labor total price $155 the pair
NEW 6SN7 OCTAL DRIVER Compatible with Dyna MK3 & VTA M125 the bare PCBs are $65 a pair Includes shipping within the US	a pair of MK3 OCTAL PCBs with parts kit is $109 Includes shipping within the US NOT including tubes	If you'd rather have the boards assembled and ready to install, it's $60 for our labor total price $169 the pair
add an additional $90 for 4 - JJ 12AU7 tubes	add an additional $140 for 4 - EH 6SN7 tubes	add an additional $280 for 4 - EH KT88 tubes
add an additional $120 for 4 - Tungsol 6189/12AU7 tubes	add an additional $200 for 4 - Tungsol 6SN7 tubes	add an additional $300 for 4 - Sovtek 6550WE tubes

four Mundorf EVO oil caps, high-end upgrade for the outputs four caps for $70	optional - upgrade the on board power supply caps this is 4 - 100uF 400v caps instead of standard 4 - 47uF caps $15	new 550v quad cap 80-40-30-20 KTL-25 $80 plus $6 shipping
bias meters (replace octal socket) MK3 For use with VTA driver board only $50 for two pairs KIT $85 for two pairs assembled/tested	bias test points (replace octal socket) $20 pair	Triode-Pentode switch kit $30 for two amps
dual speaker posts $16 pair - note these use standard 3/4" spacing fits ST70 and MK3 only IN STOCK	new TRIPLE speaker posts $20 pair note these do NOT use standard 3/4" spacing and must be used with single plugs or terminals, fits ST70 and MK3 only IN STOCK	original type Dynaco switch (power, mono-stereo) $4 each (only with orders over $20 total)

here's a review from one of our many customers . . .

Roy,

This is a great-sounding circuit. 
With your circuit, one of the first things I noticed was that different recordings are clearly different, 
indicating to me that the amplifier is neutral, rather than colored. I was surprised by dynamics in music 
that I hadn't noticed before, especially in classical music. 
This circuit seems able to render complex passages and dynamic variations that made the original circuit 
sound sluggish. I am a trained classical pianist, and I also play Hammond Organ, other vintage keyboards, 
and trumpet, so I know what instruments sound like in real space. The original Dyna circuit made acoustic 
guitar sound "good," but also a bit unnatural--as if the player were playing an acoustic guitar that was 
twenty feet wide. With your circuit, it sounds like someone playing an acoustic guitar right in front of me.

Your circuit is especially wonderful for the MkIII, which I've never thought was a very good-sounding amp 
to begin with. It always seemed kind of grainy/grungy even with upgraded parts. 
The new circuit cleans up the highs and gives the midrange both clarity and natural richness.

I did do a little tube-rolling last night. I swapped some Telefunken ECC81s in place of the Mullards. 
It's hard to say which I like best. The Mullards seem more dynamic, the Telefunkens, a bit smoother.

My brother, for whom I built these, was wowed by them. He says he's going to have to get some speakers 
that will do them justice. I'm playing them into a pair of KEF 104/2s that I think are one of the best speakers 
for tube amps. This new MkIII is very well matched to them and drives them with apparent effortlessness.

Best,
David A.

here's a full rebuild I did summer of 2021

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here's some photos of a newly built MK3-octal

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