Review: Dynaco Mark IV Amplifier

Category: Amplifiers

Want to find a real "sleeper" amp for those of us on a budget? the Dynaco MkIV may be just the ticket to cheapo vintage nirvana! These are monoblock tube amplifiers using a pair of EL-34 as output tubes, a 7199 as the pre-driver and a good old GZ-34 for PS rectification. They put out a real 40watts per side (less in triode, I will get to that in a moment) and were/are spec'd at 10hz-20mhz + or - .5hz with 1% thd at max output and .05% at one watt (where many of us do most of our listening) and have 4, 8 and 16ohm taps for speakers. This is one of the most sought after Dynaco amps due to a simple fact, they each have the same transformer complement as an ST-70 but dedicated only to one side, the result? better dynamic headroom per channel than the already venerable ST-70. Since these were often kit amps you need to check them carefully before buying for good construction techniques but these units are very durable. The normal caveats for hot running, older tube amps remain; watch out for dried up capacitors, think about replacing the orignals even if they measure well, a few dollars spent on better caps can result in much better sound. While you're at it, swap out the resistors as well...why not? the things cost little enough and hot-rodding them is part of the fun. Many pages have been written about how to bring these amps up to date, start at the unoffical dynaco page and then get to work. The sound? well this a VERY GOOD EL-34 PP amplifier! When encountering "modern" designs I still see/hear the strong Dynaco influence, they have the guts to drive a variety of speakers to ear bleeding levels but give you that nice warmth and "truth" in the mid-range many of us crave. This would be a great starter tube amp before jumping into the buck-buck modern amps (Cary, CJ, etc.). With jazz LPs even CDs (they tame some of the digital grunge, some would hide, I would say WHO CARES they sound great!) these really shine, they perhaps lose a little ultimate bass control with large scale orchestral or even modern techno music but the lquidity of the midrange is intoxicating! A word about the triode mod, I have mine set up to switch between pentode operation (traditional for these dynaco units) and "triode" mode, One resitor per amp is all it takes to strap the EL-34s to triode operation. The result is even more luscious mids and half the power in triode. For those of you with Efficient speaker (I have Klipschorns) the triode strapped MkIVs at 20watts give a musical experience that, in my opinion, equals many other modern, much more expensive amplifiers. I have not used pentode since modding them form triode operation. But what the hell, cruise Audiogon and Ebay for a pair of these, pick them up for a song for yourself, plug them in, and begin to laugh histerically as you think about all those others out there not enjoying this level of sound for garage sale prices. Try it, you'll like it!

Associated gear
Click to view my Virtual System

Similar products
Dynaco ST-70, Scott, Marantz, Eico

I remain,
and halleluiah!
nice to see you clueless.
All true but I blew the power transformer and lost one of my good buddies. If anyone knows of a parts set I would be interested.
I think that Joe Curcio is selling replacment trannies. try
regards, tony
Mark IVs are nice, but the specs are NOT as good as cited. Frequency response is +/- .5 dB from 10 Hz to 40 kHz. Power response is from 20 Hz to 20 kHz +/- 1 dB. I bet you found the triode mod made the amps seem louder, even though the power was halved!
I wanted to thank you for your post! I have a pair of Mk IV's that I am going to get updated TODAY!! I felt a little silly using these after buying used a pair of Von Schweikert 4.5's yesterday. I will get these modified and give them a serious listen. Can one also get the same level of results modifying the pas 3 preamp? I used to collect many vintage pieces but always heard that modifying these amps could give performance equal to the lower level Conrad Johnson products (MV 50 etc.) Thank you again for these posts and I will hold my head high!
Has anyone tried Joe Curcio's mods of the MK IV's, and if so what do you think of the mods?
Re: the pas 3 preamp, I have never been impressed by the dynaco preamps, even when upgraded. I think mr. van alstine makes a better dynaco-derived preamp, check him out

re: Joe curcio´s mods...I have no doubt that mr. curcios mods make the dynaco mkIV a better amplifier, improving measured performance and perhaps reliability. BUT I like the amp´s sound, thay is why I bought one...and all those mods curcio mods MUST change the basic sound of the amp, since many change, organically, the circuit desgin of the amp. Cosequently I stayed with upgrades that improved reliability and sound while staying within the original ciruit design.

Part of the fun of vintage amps if working on them...for me progressive modification works better than all-at-once rebuilds, try a particular mods and see if you like it better than before, and on and on until you get what you want.

regards, tony
I can't figure why anyone would want a Dyna MK IV, they go thru power transformers like crazy.........I've never seen one with the original power transformer......I used to rebuild them but not anymore......
I have yet to burn mine out, using it almost ten years and it was old when I got it. problems in other components (these are, after all, vintage units) can stress the power tranny ya know. with all vintage stuff there is a risk of failure of components but I have not seen anything to indicate that dynaco MK IVs are more prone to failure than any other vintage amp, in fact the opposite seems to be true, they are perhaps more rugged. YMMV JMTC ETC regards, T