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MKIII Retrofit to Double P/P
Dear Rodents,
I have a few Dynacos in storage but need 100w/c. If I wanted to add another pair of KT88s or 6550s (4 per mono side) to make a double P/P Mark III, (physical placement considerations not withstanding) what do I need? Do I need to change the OPTs? How about the Power Xfrs? Will I need more current capabilities? Maybe I'm just oversimplifying, hope not. Your opinions will be most appreciated. Cordially, west |
#2
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#4
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In article ,
west wrote: Dear Rodents, I have a few Dynacos in storage but need 100w/c. If I wanted to add One version of this was called the Sovereign 120 and was published in an article by Halfer in Radio-Electronics magazine in the late 1950's. It required a different power and output transformer, plus 4 6550's or KT88's rather than 2. The driver board was the same as the MK III. The output transformer hasn't been made (at least by Dynaco) since the 1970's; I bought the last 4, 2 which I used and two which went to Bill Conrad and Lou Johnson when they were building test beds prior to launching their amplifier line. If you really want 120 wpc out of a Dyna tube amp then it may be easier to find some Mark VI's rather than update the MKIII. I don't think you can push 120 pwc through the MK III transformer, certainly not at the frequency extremes. If you don't need a low output impedance, and really want a tube amp, I have seen variants of the Futterman H3 transformerless designs that were capable of much more than 120wpc output. Since these don't use output transformers (and sounded very nice driving full range ESL's; I've never heard one driving anything else) they would be less expensive to build today than designs with transformers. The 250wpc Futterman amplifier was made by Lucius Morris in DC, under an agreement with Futterman. I heard them driving double KLH Nines ca 1975. Mike Squires -- Mike Squires (mikes at cs.indiana.edu) 317 233 9456 (w) 812 333 6564 (h) mikes at siralan.org 546 N Park Ridge Rd., Bloomington, IN 47408 |
#5
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"west" wrote in message news Dear Rodents, I have a few Dynacos in storage but need 100w/c. If I wanted to add another pair of KT88s or 6550s (4 per mono side) to make a double P/P Mark III, (physical placement considerations not withstanding) what do I need? Do I need to change the OPTs? How about the Power Xfrs? Will I need more current capabilities? Maybe I'm just oversimplifying, hope not. Your opinions will be most appreciated. Cordially, west What would happen if you ... ...."parallel" two units to serve as 1 channel in a, sort of, master/slave configuration? ....strap speaker ground of the master to speaker ground of the slave. ....strap speaker out of the master to speaker out of the slave. ....unsolder one end of both power tube coupling caps from the slave at the phase inverter side. ....reconnect the unsoldered ends to the respective points from the master phase inverter. ....disconnect the slave feedback circuit from the 16 ohm tap. I'm not sure what to do with the slave's lower KT88 pin 4 feedback, via the 390mmF cap (is that 390pF?), to the 6AN8. Maybe the master B+ needs to be connected (via a resistor?) to the slave B+ so both are sagging and surging indentical. I guess the latter won't be necessary when both power stages and power supplies are "matched" close enough. .... and if you apply signal to the master unit..... Now, master as well as slave deliver the same voltage to the load, but, if master and slave are closely "matched", only half the usual current each. IOW, master and slave "see" double the speaker impedance each, so to get double the power to your speakers you'll have to move the speaker connection one tap up. So, if the Infinity (was'nt it?) has 4 ohm, you'll have to drive it from the paralleled 8 ohm tap etc. BTW, there's a lot of guessing going on here, maybe it's just a crazy idea. I've never tried this, lacking stacks of Dynaco's or stacks of anything else :-( But I reckon it could work, and, if it does, it might save you some iron and glass. In history relationship between master and slave has been troublesome. I wonder, and am curious, about that in this case. Keep me posted if you give it a go. Rgds, Jan. |
#6
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Other Rodents have already clarified that it is not advisable to do
Frankenstein-like surgery on a glorious Dyna. I'd just suggest to use all Your amps together in bi/tri-amplification with bi/tri-wiring. I'm sure You can sort all Your stuff in order of available power to make it fit the speakers needs in a reasonable way. Say, a SS for bass, the Dynas for mid and some other one (I'd suggest a SE if available) for highs. This will provide about the power You're talking about. As per the preamp/electronic crossover... well, a chance "to boldly go where no man has been before." Ciao Fabio "west" ha scritto nel messaggio news Dear Rodents, I have a few Dynacos in storage but need 100w/c. If I wanted to add another pair of KT88s or 6550s (4 per mono side) to make a double P/P Mark III, (physical placement considerations not withstanding) what do I need? Do I need to change the OPTs? How about the Power Xfrs? Will I need more current capabilities? Maybe I'm just oversimplifying, hope not. Your opinions will be most appreciated. Cordially, west |
#7
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"Patrick Turner" wrote snip I can only suggest that the Dynacos be left alone, and thus they will retain their value, and that a better solution is to devote some time to a new pair of mono amps. The MkIII are a decent PP amp in their own right; Yep. ppl will kill to get a pair in good condition... Well they can kill me then - I've got a pair (240V) in superb, original condition, working perfectly and sounding great. See halfway down this list: http://www.apah69.dsl.pipex.com/item...emsforsale.htm :-) |
#8
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"Fabio Berutti" wrote in message ... Other Rodents have already clarified that it is not advisable to do Frankenstein-like surgery on a glorious Dyna. I'd just suggest to use all Your amps together in bi/tri-amplification with bi/tri-wiring. I'm sure You can sort all Your stuff in order of available power to make it fit the speakers needs in a reasonable way. Say, a SS for bass, the Dynas for mid and some other one (I'd suggest a SE if available) for highs. This will provide about the power You're talking about. As per the preamp/electronic crossover... well, a chance "to boldly go where no man has been before." Ciao Fabio But Fabio, I only have 1 input to the speakers. What you are espousing sounds ideal, but how do I do it practically? Incidentally, I have a daughter who graduated from West point with a degree in Chemistry & minor in Nuclear chemistry. She was talking about after her military obligations to maybe go to the University of Bologna to study medicine. You went to Univ of Roma for Chemistry? west "west" ha scritto nel messaggio news Dear Rodents, I have a few Dynacos in storage but need 100w/c. If I wanted to add another pair of KT88s or 6550s (4 per mono side) to make a double P/P Mark III, (physical placement considerations not withstanding) what do I need? Do I need to change the OPTs? How about the Power Xfrs? Will I need more current capabilities? Maybe I'm just oversimplifying, hope not. Your opinions will be most appreciated. Cordially, west |
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