Monday, September 29, 2008

Review: Classic Dynaco Tube Amps - Upgrades and Mods

Tube be or not tube be... sorry... couldn't resist. The picture you see here shows a pair of restored, original factory assembled Dynaco Mk III amplifiers. I purchased this pair from a neighbor who had them stored in has garage. He needed some cash and I was looking for some tube equipment to sweeten up my stereo system.

With a little help from my friends I cleaned up these amps, replaced old selenium rectifiers, installed new power supply capacitors and of course installed all new tubes. James Demeter and Kevin from were both generous in providing their expertise and encouragement. Kevin also supplied replacements for the original Dynaco can type capacitors. These replacements increase the capacitance and voltage rating of the original power supply caps. That makes the power supply safter and it also give you a performance boost. Kevin sells complete kit amps that are excellent replicas of the original Dynakit amps. Like the original Dynakits the prices are reasonable and the quality is first rate.

Dynaco amps were some of the most popular hifi amps ever sold. Their popular models include the Stereo 70, Stereo 35, Mark III, and Mark IV. These amps were sold factory built or as kits. I was fortunate to get a pair of the 60 watt Mk III amps that were factory built. The original workmanship was good and they didn't need a whole lot of work. The sound of these amps is lush and sweet. You know right away these aren't your typical transistor amplifiers. Voices and instruments take on a three dimensional quality that brings the music alive.

There a folks such as self-proclaimed Dynaco guru Dynaco Doctor aka Joe Curcio who will tell you that the Dynaco amps perform poorly unless modded. Curcio audio has for sale a number of "upgrades" that he promises will allow you to realize the "full potential" of your classic Dynaco amp. It makes me wonder how these amps became bestselling classics in the first place without any help at all from Mr. Curcio and his fellow tube gurus. Could it be that they sound pretty darn good with the stock circuitry designed by David Hafler? Are the commercially available mods really going to sound better than the classic Dynaco sound? 

My buddy Dennis and I have, between us, built most of Mr. Curcio's designs and we've each been disappointed with the final results. The tube magic was lost. The modified amps may measure well but they they sound somewhat cold and uninvolving. It's also worth noting here that the Dynaco amps are collectable and that they are most valuable in their stock form. Perhaps monetary value is significant as an indicator of optimal sound quality–it depends on who you listen to.

Curcio is now advertising some newly designed mods. He says these mods will preserve the tube sweetness of the original Dynaco circuits. We exchanged some emails and he persuaded me to place an order. However, after thinking it over, I cancelled the order and opted to keep my Mk III amps stock. The 6922 tube driver stage favored by Curcio may be accurate and may measure well, but 6922 tubes tend to sound cold compared with the original Dynaco drivers. If you're dead set on modding your vintage Dyncaco amps, there are a number of popular mods available these days. You can do some Googling and you will find the commercially available Curcio Audio mods, the Roy Mottram mods and the Poseidon mod plus all kinds of DIY mods. 

In my opinion, David Hafler got some things very right in the original Dynaco designs. Therefore my advice is to do only what is necessary to keep them running well and then sit back and enjoy the magic. (By the way, be warned... when I cancelled my order for Joe Curcio's Mk III upgrades, he deducted a whopping twenty percent "restocking fee" from my refund. When I complained about that his response was adversarial bordering on belligerent. He doesn't deal with returns graciously.)

I'm using a Conrad-Johnson PV5 preamp and my Mk III amps to drive a pair of Thiel CS 2.2 speakers. While Thiel's are not considered to be especially tube friendly these CS 2.2's sound great with the Mk III's. There is plenty of power to spare. 

If you are fortunate enough to own a pair of Klipsch horn loaded speakers, you should seriously consider finding or building a tube amp. Many music lovers consider Dynaco and Klipsch to be the path to musical nirvana. Kevin from tells me the Dynakit Stereo 35 paired with some highly efficient horn speakers is some of the best sound he's ever heard. The Klipsch forums are another good source of info about Dynaco amps.

The original Dynaco designs are among the best tube amps ever made. You can buy better tube amps, but you had better be prepared to spend a whole lot of money. If you absolutely must have the best of the best and you can afford it, then look for some Conrad-Johnson tube hifi gear. If you are willing to believe that you can convert a Dynaco amp into an amp that rivals the very finest amps that money can buy then Joe Curcio and the other Dynaco gurus will be glad to take your money. Although I haven't tried every possible mod, I would urge you to be skeptical of these claims. They sound too good to be true and in my experience that's usually a sign that they probably are too good to be true.

In the meantime consider this: In the world of tube amps, second best is still a darn sight better than just about anything else available. If you are fortunate enough to stumble across an old stereo Dynaco tube amp or a pair of Dynaco tube monoblocks my advice is to restore them, keep them as original as possible, and enjoy them for their classic sweetness and richness. I guarantee you will rediscover your favorite music and hear subtleties and shadings you never noticed before.

As a musician I believe that the perfect is the enemy of the good. Before you blow your hard earned money on expensive "upgrades", hear what the original Dynaco amp designs can do. I'm willing to bet that if you do that, you'll stop right there. It doesn't get much better. So save yourself some money, skip the mods, and spend your extra cash on some new recordings. Music is one of life's greatest pleasures and even more so when you play it through some great classic tube amps like the Dynaco Mk III's.


Anonymous said...

I totally agree with you, Alan, about not changing the stock Dyna's. I recently aquired a Stereo 70 unmodded and after some cleaning up, and checking of transformers, etc. I carefully fired it up and quickly took some voltage readings in all the important places. I was amazed to find that everything checked out near as dammit to spec! Amazing for an amp of that age. I left it running for half an hour just make sure that it stayed on track and then put some music thru it. Now, I have had a lot of different valve amps in the past, includig four or five of my own, but the stereo 70 sounds as good as any of them. I don't buy vintage stuff to resell, I buy it to use and I'm definitely keeping this one. What a star !

don said...

I am a Dynaco Mark III 'holic'. If I add up all the MkIIIs Ive own, then its around 12 mono blocks. Now, I only own 3 sets (6 mono) of MkIII’s. One set is factory wired mint museum all original condition that I keep boxed up. The 2 other sets follow the original circuits, but I do upgrade the following:
Filter/ bypass caps to 700v 100uF (very important, the original 525V are a ticking time bombs).
The 3 coupling capacitor (0.1uF, 2x0.22uF)
The 2 matched pair resistors 100k and 47k ohm, and the diode.
I do change all other capacitors to its original spec, and I make sure all resistors are in acceptable range.
I consider what I do are maintenance but not mods. I do enjoy the original circuit. And, I don’t care much about these new mods circuits. But, there is a modernized version of the williamson type amplifier by dynaco that uses the A-431 transformer. Now, I might try that but then again, its uses EL-34 tubes which are harder to find.

Reed said...

Hey - great post!
what are the power output tubes in the Mk.III?

Minneapolis, MN

Alan Acuff said...

Thanks for your kind words Reed. The standard output tube for the Mark III is the KT-88.

DrBob said...

Nice website!! I wish I could A/B my current MKIIIs with the original 6AN8 topology! After several ventures, I have settled on the Posiedon board by Shannon Parks and use AudioCap capacitors and cbs-hytron 12au7 type tubes with Sylvania bp 12ax7s. German mfg. Authenticaps have replace the old power supply caps and rhodium flashed Cardas speaker binding posts are mounted on the back. All wire has been replaced and not one hole has been drilled into the chassis. Hafler sure knew what he was doing, and Brian DePalma contributed to the design. An old PAS has been totally re-worked over the years to accommodate a 12AU7 typology and an RCA Orthophonic phono stage has bee installed. Blackgates, etc. and the Cardas outputs have been installed. This rig drives Zu Druid mains and an upgraded old pair of M&K 2-1b subs...absolutely seamless soundstage with great hf information and heft. Again, wish I could a/b this rig with a similarly upgraded but unmodified original pair!!

DrBob said...

Nice review of the work of this genius. I wish I could a/b my current incarnation of the MKIII with the old 6AN8 topology. After a number of driver board trials, I settled on Shannon Parks "Posiedon" with the 12ax7/12au7 combination (NOS Sylvania and CBS-Hytron bp), AudioCaps, and all new wiring. German mfg. Authenticaps replaced the weak old cancap power supply firecrackers. A totally renovated PAS of purist persuasion outfitted with a 12au7 design and a RCA Orthophonic phono stage from the old 1950's RCA tube manual completes the electronics. I replaced the cheesy rca outs with Cardas w/ rhodium flashing and did the same for the MKIIIs, which also now have Cardas speaker binding posts. NO CHASSIS DRILLING HAS BEEN DONE. This all drives Zu Druid mains mated seamlessly with an old pair of M&K 2-1b subs (raised on 10"Lovan stands). Better people than I are surprised by their sonic beauty. But again, I would like to A/B these with a simple upgrade of originals!

bluesboy said...

Hi Alan, i am in possession of a Dynaco Mark III guitar amp!! While i can locate loads of info on the Mark III hi-fi amp, i am unable to find any info on the guitar amp. Any help from you or your readers would be great.

Alan Acuff said...

Bluesboy, you may have an old Sunn guitar amp. Their early guitar amps were built using Dynaco Mk III amplifiers.

Thijs said...

About the upgrades concerning original Dynaco equipment....
Some people just like that more distant, clean... call it 'cold' sound if you like. Personal, I like the warm tube like sound, but definition and clarity mustn't be compromised. So to some these really are upgrades, lifting the performance more to today's standard. And I'm not saying the standard is always best.

Blog do Zé Pardini said...

Dear Allan,
I Am in Brazil and I Have a pair of MKIII monoblocks, original design and circuitry. I had modified only the components and parts quality, with fast diodes, ribbon couplig capacitors, regulated power supplies at the input stage and output too, regulated and separated bias circuitry,...original circuit was keeped !! Nice sound, also, the eater power supply has a dedicated transformer...I keep in my mind that MODs..ok.,at the point that today´s pasts quality is really good, only this.
Best wishes for anybody who likes The Nice Audio from Tubes.
Jose Pardini