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Dynaco MKIII tube amp

107.206.132.27

Posted on January 4, 2017 at 20:52:33
DanS
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Posts: 265
Location: EL PASO, TEXAS
Joined: December 19, 2002
From Vintage Vacuum Audio.
Does any one here have any experience with this amp/seller?

 

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RE: Dynaco MKIII tube amp, posted on January 5, 2017 at 08:31:48
airtime
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Posts: 8585
Location: Arizona
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Not familiar with him. Heard of him but not references. If you are concerned why not consider a brand new MKIII for a few bucks more. One that is even better than the original. Better iron, new sockets, everything!!!

 

RE: Dynaco MKIII tube amp, posted on January 5, 2017 at 09:52:02
Palustris
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Posts: 1854
Location: Cape Cod
Joined: September 12, 2008
I have no experience with this vendor. I do have considerable experience with Dynaco gear, however. Those MKIIIs do look as if they are competently rebuilt with Russian and film capacitors in the signal path and electrolytics in the power supply. I am somewhat put off by the negative editorializing about more recent developments in circuit design and power supply capacitors. I would never use Sprague Atoms or Authenticaps in my own gear. Both of these are electrolytics and as a DIYer I have banished all electrolytics from my amps in favor of MKP. Further, I have had Sprague Atoms fail right out of the box.

So in my assessment those amps are probably good mid-fi amps. They will sound good and be reliable, but not exactly what some consider hi-end. The best of the Dynaco resto-mods will break out the two functions of the 6AN8 into two tubes, a pentode and a double triode. By breaking the two functions into two tube you have a huge range of possibilities as to which tubes to use which can substantially increase fidelity. Further, in the 21C. the use of electrolytic caps is like putting bias ply tires on your BMW or Mercedes.

 

RE: Dynaco MKIII tube amp, posted on January 5, 2017 at 10:34:26
petercapo
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Posts: 456
Joined: December 29, 2012
It would be great to be able to have an all polypropylene capacitor power supply, but you'd need a lot of room for that. IMO, low ESR discrete electrolytics are not bad - the Authenticap multisection cans used in the refresh of these Mark IIIs are stuffed with discrete, low ESR electrolytics. If the Atoms are of an appropriate voltage rating, then they could be fine for a while to come - I think it also depends on how old they are to begin with.

 

RE: Dynaco MKIII tube amp, posted on January 5, 2017 at 10:41:47
petercapo
Audiophile

Posts: 456
Joined: December 29, 2012
The original Dynaco Mark III with its original circuit design in place, or its original circuit design with certain enhancements to bring out more of its original sonic potential, can be a very fine sounding amp. Like the other original Dynacos, they may not be "world-beaters," but they get you much of the way there, which was always their value.

The key with the original Dynacos is realizing that after some 50-60 years of service, you need only refresh certain parts. IMO, the original Dynacos do not need a redesign; substituting a different circuit design is not necessary.

Looks like this seller did an extensive refresh while keeping to the original design. If things were done properly, it should be a very fine-sounding amplifier. Upon reading the blurb accompanying the listing, indications seem positive. At the same time, if you have never owned a tube amp before, realize that they generally need more hand-holding than solid state gear.

 

RE: Dynaco MKIII tube amp, posted on January 5, 2017 at 11:30:56
DanS
Audiophile

Posts: 265
Location: EL PASO, TEXAS
Joined: December 19, 2002
Thanks for all you comments and suggestions. Highly appreciated!!
Dan

 

Better iron?, posted on January 5, 2017 at 13:46:03
1973shovel
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Posts: 6773
Location: Greenville SC
Joined: February 25, 2007
Contributor
  Since:
June 17, 2009
I'm wondering how you determined that? Did you measure original A-431 output transformers and compare them against the VTA offerings?

I'm not one to insist that all old Marantz, Fisher, Eico, Dynaco, etc. iron is always better than what is wound today, but I'm curious how you're apparently so sure the VTA iron is "better".

Thanks.




 

You are correct about the output trannies but not the Power tranny, posted on January 5, 2017 at 18:07:08
airtime
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Posts: 8585
Location: Arizona
Joined: February 4, 2003
Ok the Power tranny is a little beefier but the outputs are about the same. Here is the quote off Bob's page.

2. The new USA made power transformer has a higher stack lamination than the original Dynaco power transformer and is rated
for 120 volts instead of 115 like the old design. The two tube heater legs are rated for 5 amps each instead of 3 amps each
like the old design. This beefed up transformer (which has a bottom plate like the original PA-060 to prevent EMI from
the transformer from reaching the audio circuitry) allows the use of KT88 output tubes in place of the EL34 tubes for
a slightly different tonal presentation. Four heavy duty neoprene isolation mounts are used to attach the transformer to the chassis.

3. The A-470 output transformers are brand new USA made custom production transformers. They use the same interleaved/layer winding
technique as the original cloth lead A-470's and incorporate the same high quality M-6 grain oriented laminations.
They are dimensionally accurate to the original design and have a durable heat resistant black epoxy finish.

 

Actually..., posted on January 5, 2017 at 19:26:13
petercapo
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Posts: 456
Joined: December 29, 2012
...this thread is about the Mark III, not the Stereo 70. There wouldn't be room on the Mark III chassis for bigger transformers. Fortunately, the original Mark III transformers are fine as they are.

 

RE: You are correct about the output trannies but not the Power tranny, posted on January 6, 2017 at 04:44:37
1973shovel
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Location: Greenville SC
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June 17, 2009
When people talk about tube amps, the term "iron" is generally used to describe the output transformers, and "power transformer" is used to describe the power transformer.

My intent isn't to disagree regarding semantics, but I felt your statement about "better iron" could be misleading, especially to someone like the original poster who seems to be new at this.

And, as petercapo has already stated, the poster was asking about the MKIII amps, where the power transformers are acceptable.


 

Why paint the bells of the trannies and not the laminations? Doesn't look right? nt, posted on January 6, 2017 at 07:40:33
viridian
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Location: Portland, Oregon
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Nt

 

RE: Why paint the bells of the trannies and not the laminations? Doesn't look right? nt, posted on January 6, 2017 at 09:14:05
petercapo
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Posts: 456
Joined: December 29, 2012
Reading around about how to deal with rust on a lamination stack yields some different opinions.

Some don't want to risk the lams shorting together (or something like that), which might happen if they are cleaned of the rust. Some have said that painting the lams could cause more heat buildup in the transformer.

Others say the lams can be carefully, painstakingly cleaned of rust and painted.

Either way, I would think it is mostly a cosmetic issue.

 

RE: Why paint the bells of the trannies and not the laminations? Doesn't look right? nt, posted on January 6, 2017 at 10:14:33
airtime
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Posts: 8585
Location: Arizona
Joined: February 4, 2003
They were originally varnish at the factory?

 

RE: Why paint the bells of the trannies and not the laminations? Doesn't look right? nt, posted on January 6, 2017 at 10:17:01
petercapo
Audiophile

Posts: 456
Joined: December 29, 2012
I think so.

 

I have painted over 20 with no problems, and no heat build up issues...., posted on January 6, 2017 at 14:49:41
viridian
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Location: Portland, Oregon
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February 1, 2012
agreed there has been a lot of bandwidth used on the painting of lams, just as there has been on cathode stripping and big foot. Practical experience leads me to believe that these are all legendary, but I certainly respect those whose experience runs counter to my own.

And yes, of course it is cosmetic.

 

Absolutely, they all were. Nt, posted on January 6, 2017 at 14:51:54
viridian
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Posts: 3867
Location: Portland, Oregon
Joined: May 26, 2005
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February 1, 2012
Nt

 

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