Just got a Dynaco MK IV and have some questions

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Just got a Dynaco MK IV and have some questions

Postby pgeejr » Fri Jun 14, 2013 6:50 pm

So, I recently got a Dyanco MK IV off of Ebay, for $240, very clean, even came with a hard case, one. When I looked at the tubes that came with it, they appear to be all originals - have Dynaco imprinted on all of them. I noticed that the power tubes were of different size, but still marked EL34/6CA7. I have not done any test to the tubes yet, but if they are good, would these mismatch pair have an effect on the sound quality? Also, why is this monoblock amp not seen too much around for sale?
-Peter
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Re: Just got a Dynaco MK IV and have some questions

Postby kt88pppamp » Fri Jun 14, 2013 9:05 pm

Mismatched tubes degrade performance and if badly mismatched, sound quality. Tube characteristics vary over a statistical bell curve. It is more probable in a sample of several hundred or thousand, they would appear close to what the datasheet says about them. The tolerances of tube characteristics are on the loose side and therefore the fewer of them there are, the more the standard deviations become apparent from the mean (I'm doing my best to communicate this here ;) ). In an absolute worse case scenario, the bias current would be upset pretty severely between the two. I definitely would go for matched tubes having said all that.

The MKIII was marketed as a mono unit. In the early 60's people were going to stereo. I would guess the general technical ignorance of most Americans would not have allowed them to envision two separate amplifiers acting as stereo. Therefore they bought was was sold to them as "stereo" by salesmen and advertising. Therefore most people went with the ST70 as it was a low cost unit, that despite its relatively low output power, was stereo.

Therefore my opinion on the MKIII and it not being as ubiquitous as the Stereo 70 was cost, technical shortsightedness, and marketing. After all, why would anyone buy something "mono" in the age of stereo?

If I were around in the 1960's I would have went with dual mono because I would have been equipped with the insight that dual mono = stereo. Plus I would have liked like the extra power!
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Re: Just got a Dynaco MK IV and have some questions

Postby kt88pppamp » Fri Jun 14, 2013 9:07 pm

Also, how would you know if the power tubes are mismatched? Just because they are of a different size and brand doesn't mean they are mismatched statistically or characteristics wise.
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Re: Just got a Dynaco MK IV and have some questions

Postby pgeejr » Sat Jun 15, 2013 8:06 pm

Well, test the tubes, all but the rectifier tube is good. So I might just go on ahead and replace the board with the poseidon one.
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Re: Just got a Dynaco MK IV and have some questions

Postby kt88pppamp » Sat Jun 15, 2013 9:27 pm

The Poseidon will indeed sound much better than the original driver. In my opinion the original driver was done on the cheap and was only done so to meet a price point. After all, it was Dynaco's mission to provide "affordable" high-end audio. Modified Dynaco circuity in my opinion sounds better than my Mcintosh MC30s. The Macs sound too solid state for me. And the Dynaco was supposed to be the poor mans Mac (lol) .

My only vice with the Poseidon is that it has a semiconductor (LM334), not that will bother you or anyone else. I just have come to realize that it is more fun not to cheat and to use only tubes and passive components, for the engineering challenge. My universal driver uses a traditional long tail phase splitter with an SRPP. When optimized (matched tubes, etc), the circuitry produces similar distortion figures to the Poseidon and the Mcintosh's both. All that needs to be done to make the unit work in a ST70, MKIII, or a high power PPP quad unit is to change around a few of the parts.
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