I don't know how the H-K tubes fought off microphonics, because they seemed to have thinner glass, but they did. Imported, matched pair Mullards were close and I wondered if H-K had rebranded Mullards.
Later I had trouble ordering matched pairs, and quiet tubes also got harder to find.
I suspect they must have selected them, although I remember going through them and finding the least microphonic pair for the input stage.
I'm not sure who made those 12BY7A, they could well have been imported, mine had an internal black/gray coating on the glass. These also seemed to sound notably better particularly in the first stage than some U.S. ones I tried.
Merry Christmas Kevin!
Those may well have been CBS/Hytron - excellent tubes for sure. Tung-Sols are also quite good. And one more tip - tubes with high Gm do the best job in V1 and V4. RCAs and Sylvanias (as well as the tubes just mentioned) tend to have higher Gm than the most common tubes, the GEs.
This is one amplifier which I regret selling: the matching pre-amp I was glad to see go!
All I did with mine was renew all caps, some wiring and valve bases. It was a super amp in my view and so easy to listen to over extended periods. [It had been when young used as a monitoring amp in Olympic Studios in Barnes and I was lucky to get this (along with x2 AKG 24 mikes many 15" Tannoy drivers (Golds and a pair of Silvers) when the studio was sold to Richard Branson. The Citation II had even been used for bass guitar on a track or two on "Sticky Fingers" recorded at that Studio in its heyday!]
I would certainly buy another if it presented itself near me!
All I did with mine was renew all caps, some wiring and valve bases. It was a super amp in my view and so easy to listen to over extended periods. [It had been when young used as a monitoring amp in Olympic Studios in Barnes and I was lucky to get this (along with x2 AKG 24 mikes many 15" Tannoy drivers (Golds and a pair of Silvers) when the studio was sold to Richard Branson. The Citation II had even been used for bass guitar on a track or two on "Sticky Fingers" recorded at that Studio in its heyday!]
I would certainly buy another if it presented itself near me!
After months of bugging me to sell him one, I finally tuned up one of my Citation IIs and parted with it to a good friend. I included four matched GE Jan 6550A's, four Tektronix matched GE 12BY7A's (drivers) and two other inputs. All were NOS from my personal stock. The PS remains basically stock. Shortly thereafter he invested in some high quality paint (with hardener) that was computer matched for color and painted it. This was several years ago and it's still going strong. No, he's not an audiophile but has the system in his basement shop.
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Thanks Jim! A very Merry Christmas to you too!
I remember the CBS/Hytron tubes as being very good in my amp, as well as some others. I believe my finding on the GE was much the same as yours. I remember selecting higher Gm for the front end tubes. My Citation II was a total rebuild as it was pretty clapped out when I got it, good transformers though. I liked the old MOV KT88 in that amp, something slightly ethereal sound wise with that tube in that amp. The Sylvania 6550 and pre MPD GE 6550A were also very good in that amp. Later GE were gassy enough to cause problems, and early SED 6550B were extremely unstable in this amp, the 6550C was ok if not pushed beyond 70mA IIRC. Ultimately I ended up with EI KT90s which worked very well. (Dating myself obviously) The Citation is long gone, but tubes reign on in my man cave..
The answer to your original question is, yes! It's certainly worth restoring. Someone gave me one less tubes in 1976 I think. I put tubes in it and used in sound reinforcement (remember disco?) and as my home amp for years. It took a regular beating and about 10 years ago it finally smoked. Time to open it up.
The original parts for the PS are no longer available so I put in the PS kit from Jim McShane along with new sockets, tubes, speaker terminals, coupling caps, etc. My wife gave me a set of Gold Lion outputs for Christmas and I got it up. I built a tube analyser and found that my collection of 12BY7As showed two modes. The RCAs and the Sylvanias had 4-7 ma plate current at a given bias and the GEs showed 9-17 ma under the same conditions. So I took Jim's advice and used the GEs in the phase inverter to balance things up.
So - Sounds great. I had an opportunity to blind A-B it with a Mac 275 with friends. Everybody preferred the sound of the Cit. In fact, it blew it away, and the Mac was in good shape. The Cit is a classic for a reason. If you fix up a Cit II you have something that will sound better than just about any "high end" amp made and for about 10k less money.
I woudn't F*** around with it very much. Stu Hegeman did some real witchcraft with feedback in that amp and I can't think of anything to do with it that would make it better. As it is, I can drive it to well over 100 watts a channel without detectable distortion. (I didn't measure the distortion as I didn't want to run the amp at that power for long enough to measure it.)
The only thing I would advise you to do is to check for components that have changed value and replace any worn out hardware. Should last another half century with no problem. BTW, Jim McShane is a wealth of resources and advice. The world is a better place with him in it.
P.S. I also used the Cit II to drive a cutting head cuz the sound was better than what came with the lathe. Made the records sound deep and clear. Just hooked up the 16 ohm terminals to the 500 ohm head windings. Worked just fine.
-Rich
The original parts for the PS are no longer available so I put in the PS kit from Jim McShane along with new sockets, tubes, speaker terminals, coupling caps, etc. My wife gave me a set of Gold Lion outputs for Christmas and I got it up. I built a tube analyser and found that my collection of 12BY7As showed two modes. The RCAs and the Sylvanias had 4-7 ma plate current at a given bias and the GEs showed 9-17 ma under the same conditions. So I took Jim's advice and used the GEs in the phase inverter to balance things up.
So - Sounds great. I had an opportunity to blind A-B it with a Mac 275 with friends. Everybody preferred the sound of the Cit. In fact, it blew it away, and the Mac was in good shape. The Cit is a classic for a reason. If you fix up a Cit II you have something that will sound better than just about any "high end" amp made and for about 10k less money.
I woudn't F*** around with it very much. Stu Hegeman did some real witchcraft with feedback in that amp and I can't think of anything to do with it that would make it better. As it is, I can drive it to well over 100 watts a channel without detectable distortion. (I didn't measure the distortion as I didn't want to run the amp at that power for long enough to measure it.)
The only thing I would advise you to do is to check for components that have changed value and replace any worn out hardware. Should last another half century with no problem. BTW, Jim McShane is a wealth of resources and advice. The world is a better place with him in it.
P.S. I also used the Cit II to drive a cutting head cuz the sound was better than what came with the lathe. Made the records sound deep and clear. Just hooked up the 16 ohm terminals to the 500 ohm head windings. Worked just fine.
-Rich
So from what I've read, there is overly too much of the amps gain tied up in overcoming feedback (for lack of a proper technical term). Somewhere, I read, cranked out the numbers and was really amazed at the amout of feedback. They claimed the amp my suffer from it.
My question is this, what might be better to drive the amp with? To give it more gain?
Is it possible to use a mosfet type cricuit to drive the amp properly and overcome some of the gain lost in feedback?
I'm curious has anyone tried it? Experimented with it?
Doable?
If so to what performance level?
Cheers,
Sync
My question is this, what might be better to drive the amp with? To give it more gain?
Is it possible to use a mosfet type cricuit to drive the amp properly and overcome some of the gain lost in feedback?
I'm curious has anyone tried it? Experimented with it?
Doable?
If so to what performance level?
Cheers,
Sync
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No idea what you are talking about.. 
The stock amplifier has plenty of voltage gain, referred to the 16 ohm taps around 28dB under load, about 3 dB less referred to 8 ohms. (Given constant output power.)
http://www.quadesl.com/pdf/cit2_pfacts.pdf
The stock amplifier has plenty of voltage gain, referred to the 16 ohm taps around 28dB under load, about 3 dB less referred to 8 ohms. (Given constant output power.)http://www.quadesl.com/pdf/cit2_pfacts.pdf
I have to agree with Kevin. Sure, there's some incredible feedback both global and local and only Stu Hegeman could have gotten away with it. It's made up for by using pentodes (12BY7A) for the input and phase inverter, which have much more gain than the triodes other amps used. Or you might say the higher 3rd order distortion of the pentodes is made up for with lots of negative feedback.
It must have been done skillfully cuz every time I try to use NF it makes the program kind of dead sounding. Good numbers on test equipment but muffled sort of. A subjective thing. The Citation doesn't do that. Best sound I've heard.
Also, TBH, I didn't notice much difference when I replaced the thirty year old GE 6550s with new Gold Lion KT88s. Just a little more power wide open, which I never use. I'd be interested to hear if someone else has experience with that.
It must have been done skillfully cuz every time I try to use NF it makes the program kind of dead sounding. Good numbers on test equipment but muffled sort of. A subjective thing. The Citation doesn't do that. Best sound I've heard.
Also, TBH, I didn't notice much difference when I replaced the thirty year old GE 6550s with new Gold Lion KT88s. Just a little more power wide open, which I never use. I'd be interested to hear if someone else has experience with that.
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Age isn't necessarily a big issue, the number of hours of operation and how hard they were pushed is more relevant. A higher quality tube may also last longer operated within its ratings than a comparable but cost engineered competitor. The pre MPD GE 6550 was a pretty high quality tube. (I still have some I use in projects from time to time)
The 12BY7 exhibits high gm. That "speed" protects against HF error correction signal induced slew limiting. Hegeman, a most competent engineer, understood RF circuit designs and applied that knowledge to an audio problem.
Of the 36 dB. or so total NFB in a "Deuce", only a few are present in the outer, global, loop.
Of the 36 dB. or so total NFB in a "Deuce", only a few are present in the outer, global, loop.
Funny you should mention that. I had the preamp also and gave it away. The little Radio Shack transistor phono preamp sounded better. I never heard anybody else say that and they go for a small fortune on ebay. I tried reworking the RIAA filter but it didn't help. Even the line stage didn't sound so good. I suspect the culprit was all those 12AX7s. I used to respect them in some of the recording I used, but when I got rid of them in a home brew preamp the sound got much better - I mean a lot better. Other people have described the 'X7 as "miserable". I didn't used to agree with them, but I do now. (I scrapped my PAS; 5751s didn't help.)
How old was the Cit I you are talking about? A lot of people forget that the youngest Citation I (or II) in the world is over 50 years old. The power supplies are often shot, the switches are all dirty, and so on. Once properly rebuilt they are a very good preamp with a very good phono stage.
How good something is is a matter of opinion, but I've NEVER heard anyone say a Citation I was not a fine preamp until this post.
Oh, Hi Jim,
It wasn't a I it was a IV it turns out. I gave it away in the early 80s. The stats were wonderful - bandwidth, distortion, equalization, etc. but it wasn't as lively as the other preamps I used. I tried tubing it but it didn't help much. The phonostage didn't even didn't sound as good as the front end of a Scott 99B I had. Like I said, I never tried upgrading it. We didn't have the internet and I didn't know about you. I'm sure you have a dynamite upgrade for it.
BTW, the Cit II you helped me restore is running great. I recently kicked a Mac275s a** with it in a blind competition. Made me feel good.
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Citation I Preamp
Wow,
That reminds me I have a CitationI all bundled up and half finished.
Well I need to finish it with McShane's kit purchased long long ago.
Then when I put it in service I can pull the ARC SP3-A1.
I want to mod it slightly by putting in a PSA Servo Filter,
new balance pot and some other minor circuit changes.
It had the power supply rebuilt upgraded years ago and it's
still running strong. But never hurts to make stuff better.
Now I've got to research the PSA Servo Filter.
Cheers,
Sync
Wow,
That reminds me I have a CitationI all bundled up and half finished.
Well I need to finish it with McShane's kit purchased long long ago.
Then when I put it in service I can pull the ARC SP3-A1.
I want to mod it slightly by putting in a PSA Servo Filter,
new balance pot and some other minor circuit changes.
It had the power supply rebuilt upgraded years ago and it's
still running strong. But never hurts to make stuff better.
Now I've got to research the PSA Servo Filter.
Cheers,
Sync
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