Pair of Dynaco Mark VIs .... Worth a try?

Haven't had a lot of luck with tube amps. Mostly use SS, MosFet, or hybrid. I do like the sound on the hybrids with the tubes in the driver circuits.

I may have a shot at a pair of stored, low-hour (20 to 25) Mark VIs. Is the basic design a sound, reliable one?

I expect to replace a few caps, etc., but I don't want to have to do a complete rebuild, just to correct original design deficiencies.

I was thinking I might have to look at older McIntosh monos before this opportunity presented itself.

Your thoughts? Thanks!

Greg

cgregory4 wrote:Haven't had a lot of luck with tube amps. Mostly use SS, MosFet, or hybrid. I do like the sound on the hybrids with the tubes in the driver circuits.

I may have a shot at a pair of stored, low-hour (20 to 25) Mark VIs. Is the basic design a sound, reliable one?

I expect to replace a few caps, etc., but I don't want to have to do a complete rebuild, just to correct original design deficiencies.

I was thinking I might have to look at older McIntosh monos before this opportunity presented itself.

Your thoughts? Thanks!

Greg

The mK VI is a good design. After check/adjust bias you don't have to do anything until the tubes
needs replacement.

That is what I am looking for -- something that doesn't have to be rebuilt to enjoy it.

What sort of tube life should I expect from the four output tubes?

Is the bias easy to adjust?

Thank you.

Greg

If you want something easy to use and trouble-free then you may want to stick to solid state. If you don't mind doing a little homework on tube amps and providing some occasional TLC then go for the MkIVs. They are great little amps.

Power tube life is affected by a few things: idle current (aka-bias current), Rectifier life, and quality of manufacture. If I'm not mistaken original Dynaco specs ran the power tubes a bit on the hot side with 50mA of idle current per tube. You can ensure longer life by running them around 35-40mA and it shouldn't affect the sound.

I've had a lot of bad luck with newer rectifier tubes. I've heard NOS rectifiers can be great but they can cost quite a bit more. Either way, if the rectifier goes south it can take your power tubes with them. Fortunately you don't have to go with a tube rectifier. A Weber Copper Cap or couple of UF4007 diodes do a great job turning AC to DC.

If you get good tubes then you can go a long time without any problems. Get a good voltmeter and read up on tube amps. There's lots to learn. Remember the guts are running with hundreds of volts and can be very dangerous. Good luck!

Are you talking about MkVI (6) as the OP stated or MkIV (4) as assumed by the respondents? Two quite different amplifiers! The MkVI is not what I would describe as a "great little amp". The biggest issue with the Mk VI is the virtually unobtainable 8417 output tube situation.

On the other hand, if you are talking about a pair of MkIV (4), they are essentially a slightly modernized ST-70 divided onto two chassis.

Ah, those Roman numerals got me. I was talking about Mk4 amps. I don't know anything about the Mk6's

corndog71 wrote:Ah, those Roman numerals got me.  I was talking about Mk4 amps.  I don't know anything about the Mk6's

"Are you talking about MkVI (6) as the OP stated or MkIV (4) as assumed by the respondents? Two quite different amplifiers! The MkVI is not what I would describe as a "great little amp". The biggest issue with the Mk VI is the virtually unobtainable 8417 output tube situation."

Thank you both, gentlemen, for your comments.

The advice on the Mark 4s seems applicable to me, however, but that's why I came here -- for good counsel. I hear the 8417s run 'hot', so why not play with the idle current? -- apparently the plate life would benefit. Also, the use of solid state rectifier devices seems prudent. All these can be done easily. So, again, why is the Mark 4 advice not applicable?

I know the 8417s are difficult to acquire, but the original tubes have very few hours. In addition I've located 2 sets of quad-matched replacements -- in the event I commit to the Mark VIs.

So ... With spare tubes, some prudent poly cap upgrades, simple rectifier insurance, and refined bias adjustments -- why would the Mark VI not be a "great little amp'?

My time on this planet is short -- the glow in the night of a reliable tube amp powering a pair of my efficient JBLs or Klipsches would take me back to the days when I was a 'pup', and a cheap Heathkit tube receiver cost me every penny I could make in a year on my newspaper route. It would be a fine feeling.

Sincere thanks, and please offer up more comments,

Greg

cgregory4 wrote:That is what I am looking for -- something that doesn't have to be rebuilt to enjoy it.

What sort of tube life should I expect from the four output tubes?

Is the bias easy to adjust?

Thank you.

Greg

To check bias you need a digital voltmeter and a screwdriver.
See the manuals description ( you will find the manual in a special thread )

When the tubes has past their first hours they will most likely be stable ( but do check
once in a while, each month or so, don't bother adjusting small changes).

Tubes will last 2-5 years depending on frequency of use, when buying new make sure its
matched pairs from a reputable vendor.

** Ohh it's Mk6 ! Well, you don't need anything but a screwdriver according to the manual.
( i have never listened to them, the Mk6 is unusual in scandinavian).
They use 8417 tubes which are scarce and expensive, they can be rebuilt to kt-88 at
the cost of lower sensitivity.

Having the chance to get pair of Mk6 in good shape is a lucky event ! Grab it !

The Dynaco MK6s are Monos...........tube rectifier are not used in theses amps...I had a pr in the 90s
The ACV to day is higher... in the wall of most homes its 120-126....this well push the B+ way up
Like 580-600v
...I have found like others that 480 on the B+ is the sweer spot sound wise an to get good life out of the output tubes....
I got the amps to re-work for output tubes like KT88sKT90s...an to day it would be KT120s...i never cared for the sound of the 8417s....  there sound to me....made tubes Sound like a bad SS ...other well have there own take?
I dont see the MK6s as plug an play tube amps.....an if you looking to drive Klipsch or JBls..
You only would ever need  50-60 tube watts...not the over a 100+ watts...an to get the B+V an Noise down...you well have to re-work the amps....Good luck an have fun with tubes....in 2014 hehe...gofig




Thanks for the site Bob........

there is plenty of info on the web concerning replacing 8417 type tubes with modern type tubes
here's one article to start with (specific to a Quicksilver amp, but can be applied to the Dyna MK6)
http://www.triodeel.com/8417.htm