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In Reply to: RE: HK Citation 2 rebuild questions posted by Michael Samra on April 19, 2015 at 09:54:41
"If you are going to butcher a nice clean vintage unit... I couldn't go along with that."
That's your choice. It's my opinion that stripping the iron off a '60s amplifier and rebuilding it in a modern chassis isn't butchery. Didn't I read somewhere that Jim McShane used to do that with the Cit II amps? Correct me if I'm wrong.
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Buy Chinese. Bury freedom.
Follow Ups:
" Didn't I read somewhere that Jim McShane used to do that with the Cit II amps?"No, ABSOLUTELY NOT!! I would never do that, period. If you did read it it was either totally mistaken or a complete fabrication. IIRC a guy by the name of Mike Moffat - who was later of Theta fame - did that though.
Edited - I stand corrected, it was Bruce Moore. The mixup came about because I am currently considering purchase of a basket case Cit II that was indeed reworked by Mike Moffat - I got the names confused. Thanks for the correction.
Edits: 04/19/15
OK, I'm corrected too. :) It was a long time ago that I read that piece, must have mixed up the names.
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Buy Chinese. Bury freedom.
IIRC, Bruce Moore made a 120 monoblocks that used Citation II output iron.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Jack
Depending on the amp,that would be your choice but would you butcher a mint condition Mac Mc275 just to get the iron?
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
Well, if your position is going to be based on a MacIntosh, using words like "mint" and "butcher", there's nothing to discuss.
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Buy Chinese. Bury freedom.
How about a clean factory built Citation 2? I don't think you would butcher that either.
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
I've seen some that the only thing worth salvaging on them is the output iron. The power transformers on the Citation II are not the best to begin with. Many of those amps ran so hot the potting material literally melted out.
I kind of wished the Citation II was allowed to be designed with a pentode output. I think that wold have made a very good amp even better.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
" The power transformers on the Citation II are not the best to begin with."
I don't agree at all, IMHO those transformers were top shelf stuff. What about them was substandard?
"Many of those amps ran so hot the potting material literally melted out."
Often the heating was due to the trafo being on an amp that needed work. And early on H-K got crazy with the bias spec of 100 ma. per tube. So the transformers were worked VERY hard in many cases. But even many of those trafos that were not well treated are still running just fine today, 50+ years later.
IMHO those trafos may have been assassinated by other amp issues but they very rarely failed on their own. We've seen some issues with the bias winding in the last few years, but that's it.
If I were to get another HK Citation II, I would have to seriously consider a newly made power transformer with more reserve (overkill) to help out performance. I'm sure the original quality of the power transformer is fine. It's more the fact that it was run HARD near its limits for a lot of years, so many of them are stressed.I also wonder if a pentode output would have been better in the long run.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Edits: 04/19/15
and they don't generate a lot of heat unless people leave old leaky caps in the unit that stress the power trafo..The Heath W6m also uses a doubler and as far as the Citation 2 running hot,that was true back in the day when they were biased at a 100ma per tube..With the McShane mods and the reduced bias on the tubes,they run much cooler than before.
I wasn't a fan of doublers either until I realized their wonderful attributes..Do you realize the power transformer in a doubler has fewer turns of wire that is thicker and heavier and therefore has a lower impedance secondary.
The biggest reason for doublers back in the day was the price and availability of higher voltage and higher current silicon diodes.I wish they would use them again.
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
Edits: 04/22/15 04/22/15
Always good when you provide some good insight, Mikey. Valid points to consider.
Having said that, I still prefer not to use a voltage doubler. I'm also not a fan of cathode bias. To me, fixed bias is a better technical solution, especially in the DIY world.
I never cared much for the sound of the Mac's you mentioned. Always thought the Citation II sounded better. I have always wondered what the Citation II would sound like as a all pentode design.
Give me fixed bias pentode output any day.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Interesting: Marantz 8 and 9's also used voltage doublers. Doublers were quite common in the old days. For modern designs, Quicksilver has almost totally ( i haven't see all his designs) gone over to a doubler system.What is interesting is Mike has used the doubler for B+ supply for the front end tubes ( 600 volt B+ = 300 volt at the half way point) or for the screen 2 taps. This, in effect, enables him to run a non ultralinear output and also enables his amps to be stable running anything from a 6L6 to a KT 120
Edits: 04/19/15
All the smaller HKs I'm rebuilding have doublers. They work very well, and I wouldn't hesitate to design one into new gear. That's a useful trick regarding the 1/2 B+ tap. Of course, it can also be done with a FWB if the PT has a center tap.
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Buy Chinese. Bury freedom.
It's just economics, in the old days, it may be fine to "butcher" an amp for its irons, but these days, an original un-molested amp of certain makes is worth a lot more than the irons. So in most cases, it does not make sense to do so anymore. Anyone continue with the practice of "salvaging" is either got more money than sense or just "out of the loop".
"Anyone continue with the practice of "salvaging" is either got more money than sense or just "out of the loop"."
Really? How about 40- or 50-year-old integrated amps with worn out pots and switches that can't be replaced, faceplates faded and scratched, and virtually every part needing replacement, including NLA capacitor cans, riveted-in tube sockets and banks of rear-panel jacks? Then there are those awful tone control PECs, sub-optimal bias designs and phono preamps that by modern standards bordered on "defective" even when they were in new working condition. Gimme a break. Anyone who strips this iron and uses it to create a modern, high performance system has done the audio world a favor.
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Buy Chinese. Bury freedom.
+1
You make many good points, however, we are not talking about beater units of pedestrian origins... Citation II, like most of Hegeman's designs are collector items, unless they are completely beyond repair, why would you want to strip them for parts? With some exceptions, these units could be brought back to life with some TLC, they are a part of electronics and American history, I think they should be perserved and appreciated as they are.
Unless you have a rare factory built that is in clean or mint condition,I let those alone.OTOH,a Dynaco ST70 turns my stomach in stock electrical condition.They are so anemic in every way they pretty much have to be modded to get real performance out of them.This is why there are so many aftermarket parts available for them,sort of like the small block Chevy.
The early ones had undersized power transformers and then you have that single GZ34 that struggled because it is being run close to its limit in that amp under dynamic conditions..The Knight KB85 used two GZ34s which made much more sense.They also used much more filtering than the Dyna ST70 which was a measly 90uf total.
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
Of course, I'm referring to amps in the condition I described. MOST are now in that condition or worse, due to age. I have no qualms about converting any of them into modern tube amplifiers, and I have a dozen or so in storage just waiting their turn. :)
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Buy Chinese. Bury freedom.
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