I have a Harman Kardon Citation II. It is a very problematic amplifier. It is my suspicion it was constructed incorrectly. When I first obtained the amplifier, it sounded horrible. I had to trace the circuit with a schematic and make corrections. There were many mistakes.
I believe this amplifier never sounded good, because of mistakes made during construction. Therefore, it has been stored unkempt in garages and attics, and has probably never been used.
The tube sockets need to be replaced, many components need repair, and it needs re-tubing. Some of the 12BH7s have blue ionization clouds when running.
The bias on the 6550s is way too hot. I suspect it is because the amp was built for 115VAC and my power is usually 121VAC. Last week, the 6550 output tubes went into runaway and blew a fuse. I need to do some component changes to modify the bias circuit to modern voltages.
So here’s the question: is it worth the money to rebuild the amp to original condition, or should the whole circuit be redesigned?
Here’s another way of asking the question: is spending money to rebuild the original driver circuit using six 12BH7 pentodes better or worse than designing and building a new driver circuit?
There's people who say they hate the Citation II, and there's people who say they love the Citation II. Which one are you, and why?
I believe this amplifier never sounded good, because of mistakes made during construction. Therefore, it has been stored unkempt in garages and attics, and has probably never been used.
The tube sockets need to be replaced, many components need repair, and it needs re-tubing. Some of the 12BH7s have blue ionization clouds when running.
The bias on the 6550s is way too hot. I suspect it is because the amp was built for 115VAC and my power is usually 121VAC. Last week, the 6550 output tubes went into runaway and blew a fuse. I need to do some component changes to modify the bias circuit to modern voltages.
So here’s the question: is it worth the money to rebuild the amp to original condition, or should the whole circuit be redesigned?
Here’s another way of asking the question: is spending money to rebuild the original driver circuit using six 12BH7 pentodes better or worse than designing and building a new driver circuit?
There's people who say they hate the Citation II, and there's people who say they love the Citation II. Which one are you, and why?
Yes.........a new year surgical case........I did the same for my amp, found the chassis in a skip and recovered it. Are you sure about the front end and phase splitter tubes, on my sch it's a 12BY7A all round. Big difference......
The citation 2 has DC multiple feedback loops between O/Pstage tube anodes to phase splitter. There are also alot of 0.47uF 600V caps in it.. (pricy).... I'm not against this but there are many simpler UL push-pull circuits around which operate equally well and some better. In most high power fixed bias circuits, there is no failure interlock, i.e if for nay reason the neg volts goes down, the output stage can operate with reduced power or shut down, as it's easy to write-off the pricy output tubes. In addition the Citation 2 has a HT doubler power supply and that I don't like. I don't have values for the mains tranny not HT details but probably 450-470V B+
In your case, the list of faults can be high and is high. The UL stage is attractive and can stay intact, similiar output powers obtainable to KT88. If you are staying with the original and opting for a refit, and hoping for the best then all original components, pots, (used for neg bias) and caps should be replaced with new as also tubes
If it was my amp I would change the circuit. The output trannies are gold dust. For absolute simplicity, you could do as I did some time ago, butcher an orig GEC KT88-50 circuit and fit a higher power output stage and mains tranny in lieu.
The good common mode performance of the ECC82 triode drive as used in the GEC 88-50 circuit has enough guts to drive pair 6550's at 500V and is dirt simpler, when compared to the complex arrangement used Citation 2.
If it was my amp......the surgury to a simpler and more reliable version would be inevitable.
Only my opin!
rich
The citation 2 has DC multiple feedback loops between O/Pstage tube anodes to phase splitter. There are also alot of 0.47uF 600V caps in it.. (pricy).... I'm not against this but there are many simpler UL push-pull circuits around which operate equally well and some better. In most high power fixed bias circuits, there is no failure interlock, i.e if for nay reason the neg volts goes down, the output stage can operate with reduced power or shut down, as it's easy to write-off the pricy output tubes. In addition the Citation 2 has a HT doubler power supply and that I don't like. I don't have values for the mains tranny not HT details but probably 450-470V B+
In your case, the list of faults can be high and is high. The UL stage is attractive and can stay intact, similiar output powers obtainable to KT88. If you are staying with the original and opting for a refit, and hoping for the best then all original components, pots, (used for neg bias) and caps should be replaced with new as also tubes
If it was my amp I would change the circuit. The output trannies are gold dust. For absolute simplicity, you could do as I did some time ago, butcher an orig GEC KT88-50 circuit and fit a higher power output stage and mains tranny in lieu.
The good common mode performance of the ECC82 triode drive as used in the GEC 88-50 circuit has enough guts to drive pair 6550's at 500V and is dirt simpler, when compared to the complex arrangement used Citation 2.
If it was my amp......the surgury to a simpler and more reliable version would be inevitable.
Only my opin!
rich
I’m looking at the original schematic – I made a typo – it is the 12BY7A pentode.
I see six different feedback mechanisms:
-big global feedback from output transformer to input stage
-local feedback from grid 2 of input stage to cathode of input stage (capacitor C1 and C18)
-local feedback from plate of positive phase splitter tube to grid of the positive phase splitter tube
-local feedback from plate of negative phase splitter tube to grid of the negative phase splitter tube
-semi-global feedback from positive 6550 plate to negative phase splitter grid
-semi-global feedback from negative 6550 plate to positive phase splitter grid
Yowza! I haven’t calculated all the gain from the 12BY7A stages, but it appears this amp employs heavy feedback. Based on this information, I’m guessing when it functions properly, it will sound like a solid-state amplifier.
I see six different feedback mechanisms:
-big global feedback from output transformer to input stage
-local feedback from grid 2 of input stage to cathode of input stage (capacitor C1 and C18)
-local feedback from plate of positive phase splitter tube to grid of the positive phase splitter tube
-local feedback from plate of negative phase splitter tube to grid of the negative phase splitter tube
-semi-global feedback from positive 6550 plate to negative phase splitter grid
-semi-global feedback from negative 6550 plate to positive phase splitter grid
Yowza! I haven’t calculated all the gain from the 12BY7A stages, but it appears this amp employs heavy feedback. Based on this information, I’m guessing when it functions properly, it will sound like a solid-state amplifier.
The message getting across seems to be the same........It did forget to mention that it's worth studying other circuits before deciding on a complete re-design. Okay most 50 watt amp driver circuits have enough umph to provide the drive for 100Watts.
Looking at the HC2 circuit there seems an awful lot of electrolytics in the power supply stages. If they have been mouldering for years in the back of a garage then they are well past their useful life. I can't make out the SS diodes, make etc, but this an area for improvement.
To design philos'y, alot of US amp designs did make alot of inverse feedback and sharp cut off pentodes, unlike in europe where more straightforward designs prevailed.
I don't know the noise figure for the HC2 but with all that internal feedback it could be quiet perhaps around -85dB or better .........most other P- amps are around -70dB; in other words, if you want to detect the background noise, it is just about disconcernable. perhaps someone with a spec of the HC2 could come forward.
My experience using pentodes ((as longtailed phasesplitter drivers.....is .. I don't like them) ) is that ageing characteristics are more likely to effect the operating conditions when compared to using triode stage configured as a common mode driver. So what happens in practice? Most of these longtailed phasesplitters require an AC balancing pot for symmetrically balancing the output stage drive (as unsymmetrical drive ends up as higher THD.. )
Who knows how to set it up ? I do; but one shouldn't really be expected to **** about with it. The simpler and common-mode approach as used in Williamson configuration and others does solve this problem. The drawback.....overall lower gain = mid 20dB, however if you use a concertina phasesplitter before this with a 30dBgain stage then things look reasonable. There is an advantage in not having too much stage gain in the middle driver stages ..so to speak of..as this can bring the noise of the previous stage up. That's why most amps using the concertina and paraphase phase splitters have noise figures around the 70dB @below full o/p.. The paraphase splitter (ECC83) as used in the GEC 88-50 configuration is also worth examining for simplicity.
At the end of the day anyone can look at all this and compare like for like, I'd put it forward; that the THD +IMD of the HC2 is probably no different to other tube amps which have far less internal gubbins which probably sound better. < Simplest is always the best and less likely to play up >...>any more ??
I'd abandoned many designs which offered darned good bench results, also on paper; but the amp sounded subjectively different when finished. In the end I went back to the simplest configurations and I'm more than happy with them....
rich
Looking at the HC2 circuit there seems an awful lot of electrolytics in the power supply stages. If they have been mouldering for years in the back of a garage then they are well past their useful life. I can't make out the SS diodes, make etc, but this an area for improvement.
To design philos'y, alot of US amp designs did make alot of inverse feedback and sharp cut off pentodes, unlike in europe where more straightforward designs prevailed.
I don't know the noise figure for the HC2 but with all that internal feedback it could be quiet perhaps around -85dB or better .........most other P- amps are around -70dB; in other words, if you want to detect the background noise, it is just about disconcernable. perhaps someone with a spec of the HC2 could come forward.
My experience using pentodes ((as longtailed phasesplitter drivers.....is .. I don't like them) ) is that ageing characteristics are more likely to effect the operating conditions when compared to using triode stage configured as a common mode driver. So what happens in practice? Most of these longtailed phasesplitters require an AC balancing pot for symmetrically balancing the output stage drive (as unsymmetrical drive ends up as higher THD.. )
Who knows how to set it up ? I do; but one shouldn't really be expected to **** about with it. The simpler and common-mode approach as used in Williamson configuration and others does solve this problem. The drawback.....overall lower gain = mid 20dB, however if you use a concertina phasesplitter before this with a 30dBgain stage then things look reasonable. There is an advantage in not having too much stage gain in the middle driver stages ..so to speak of..as this can bring the noise of the previous stage up. That's why most amps using the concertina and paraphase phase splitters have noise figures around the 70dB @below full o/p.. The paraphase splitter (ECC83) as used in the GEC 88-50 configuration is also worth examining for simplicity.
At the end of the day anyone can look at all this and compare like for like, I'd put it forward; that the THD +IMD of the HC2 is probably no different to other tube amps which have far less internal gubbins which probably sound better. < Simplest is always the best and less likely to play up >...>any more ??
I'd abandoned many designs which offered darned good bench results, also on paper; but the amp sounded subjectively different when finished. In the end I went back to the simplest configurations and I'm more than happy with them....
richQuote:
I'd rebuild the original circuit. It's not for nothing that this amp became a classic.
SY is 100% correct here. Unfortunately you ended up with a bast**d unit that wasn't wired correctly. Very simple solution, undo it all and rewire it paying close attention to what the hell your doing. When you do this you will be VERY pleased with the result. Its easy to point the old finger and question why a circuit was designed a certain way. Have some faith as our fore fathers that designed tube circuits and paved the way for us knew what the heck they were doing. The amp is a classic! Restore it and enjoy it or sell it to me and I will give it a good home.
J
I'd rebuild the original circuit. It's not for nothing that this amp became a classic.
SY is 100% correct here. Unfortunately you ended up with a bast**d unit that wasn't wired correctly. Very simple solution, undo it all and rewire it paying close attention to what the hell your doing. When you do this you will be VERY pleased with the result. Its easy to point the old finger and question why a circuit was designed a certain way. Have some faith as our fore fathers that designed tube circuits and paved the way for us knew what the heck they were doing. The amp is a classic! Restore it and enjoy it or sell it to me and I will give it a good home.
J
The place to go for Citation information is http://pages.prodigy.net/jimmcshane/ - schematics, specs, etc.
Jim sells kits of parts to rebuild these, and he rebuilds them too.
In good working condition, it's probably worth $800 and up, mostly depending on external cosmetics. Unlike the Macs, modifications won't hurt the value that much - but you'll find it hard to beat the original.
Jim sells kits of parts to rebuild these, and he rebuilds them too.
In good working condition, it's probably worth $800 and up, mostly depending on external cosmetics. Unlike the Macs, modifications won't hurt the value that much - but you'll find it hard to beat the original.
Rich,
Found this old post of yours. If I can ask you to scratch your brain,
or at least show us what mods you did. It might be worth considering
for me.
Got your notebook handy? or pics? or Schematics?
I'm sure I"m not the only one who would appreciate it.
Sync,
Just refurb your "Deuce" ala Jim McShane.
The only vintage amps in the same league as a Cit. 2 are by McIntosh. Frank McIntosh and Stu Hegeman were anything but stupid. Modern parts allow us to jack up the performance of the vintage wonders, but the original circuit designs should be respected.
Just refurb your "Deuce" ala Jim McShane.
The only vintage amps in the same league as a Cit. 2 are by McIntosh. Frank McIntosh and Stu Hegeman were anything but stupid. Modern parts allow us to jack up the performance of the vintage wonders, but the original circuit designs should be respected.Love it.
Does yours have a bias meter on the back? If not, it was a factory build. The Kits had meter and pots for bias and balance. (This may have changed in subsequent years.)
The II's were susceptible to high capacitance / inductance in speaker wiring, so avoid coiling long speaker wires. Set your bias and balance from time to time with the wire wound resistor on the speaker terminals. I don't know how to install a meter and pots if it's a factory build.
You might consider upping the voltage rating of the bias resistors. You might derate the fuse which usually blows only after the bias resistors burst into flame.
I benched mine vs. a McIntosh (at a Mac clinic) and the distortion and noise floor were several factors of 10 below the Mac. Fancy test equipment.
I always liked the sound, reserve power and speed of the amp.
Sounded like it had a much higher damping factor than published, especially when listening compared to Macs and Marantz of the time, i.e. controlled speakers better.
I wouldn't mess with the circuits but new caps would probably be a good idea.
There are no right or wrong answers to this. The amp is a classic and as such rebuilding to the original will retain its value. Altering the circuit will seriously detract from its value. As in many kit amps the final results were dependent on the builder's skill, and with the C2 being a more complex design it was easier to make mistakes. Of course that leaves you to completely rebuild it to original or something else.
Sound quality is very subjective, especially with "classic" equipment. If you have a preference to a particular circuit then using the HK2 transformers will probably give you very good building blocks. After all the amp is yours and you can do whatever you want with it.
I have rebuilt 2 of these both to the original circuit but one has non stock power supply. I like the sound but I prefer the sound to some of my single ended amps. And perhaps to me, keeping the C2 stock serves as a reference to a different type of tube amp circuit. It certainly is the pinnacle of an all pentode tube amp. A definite "one of a kind" design.
You might also look for cold solder joints.
Back the day of Heath, Dyna and Harmon Kardon, there were plenty of bad soldering jobs. It could be cold joints, where you can see a crystallized instead of shiny appearance, or a gob of solder that doesn't engulf the connection, or even a solder "bridge" between posts. Or a good mechanical connection not made before applying solder, or even acid core solder, which might show as oxidation at the leads.
You can often assess the skill of the assembler with a quick glance, because there are many cases of ALL bad solder connections.
With the military circuit boards and their soldering posts, these bad joints can be easily fixed by reheating and maybe adding a bit if resin core solder. Maybe a solder sucker would be a good tool to use if you need to start over.
mikapen, DAK808,
Thanks for your input, but the original question was posted 12 years ago...
Kashmire even hasn't been online here for 2 years (how is that possible? is there a cure for tube-aholism?)
Still an interesting question though: how does the CitII perform to modern amps (vacuum or otherwise).
Thanks for your input, but the original question was posted 12 years ago...
Kashmire even hasn't been online here for 2 years
(how is that possible? is there a cure for tube-aholism?)Still an interesting question though: how does the CitII perform to modern amps (vacuum or otherwise).
mikapen, DAK808,
Thanks for your input, but the original question was posted 12 years ago...
Kashmire even hasn't been online here for 2 years
Still an interesting question though: how does the CitII perform to modern amps (vacuum or otherwise).
Yes of course. But it remains searchable forever and current ideas about the Citation are important because they are, well, current.
That is incorrect. EVERY Cit II had a meter - the early ones had a larger and nearly square meter, the later ones had a horizontally oriented narrow meter. BTW, the easiest way to tell factory built units is that they used rivets to attach the tube sockets, RCA jack plates, etc. where the kits used screws/nuts.
I'm sorry, but that also is not true. The Cit II in proper operating was (quoting H-K/Stu Hegeman) "absolutely stable with any load". My experience bears this out.
I assume you are referring to the cathode resistors, the 15 Ohm 1 watt pieces. I recommend a change to 18 Ohms 2 watts. I also recommend a reduction in the bias current (as did H-K after a while). I use 80-85 ma with good quality KT-88s.
These amps are now over 50 years old, and they were sophisticated units to start with. They ran hot under the chassis. They are INCREDIBLE amps.
Rebuild it fully, and you'll have a great amp for years to come.
Jim, I assembled about 10 of these back in the day, as part of a little Hi-Fi business I established to help me through college. (My majors were Music, ME, Acoustics and Computer Science.) I was in contact with H-K fairly regularly about the earlier versions, including discussions about inductance/capacitance in speaker wires.
My practice was to make initial installations with overly long 12 ga wire because i knew I would be rearranging speakers, amps, furniture and even entire rooms to get good sound. Later I would cut the wires to a final length. Sometimes I would have a 30' wire coiled to reach only 10'. Some of the amps got fried and needed to be re-wired.
H-K agreed with my observations about possible instability with capacitance / inductance with that practice, and although I don't know if they made any design changes (I doubt it), I abandoned that practice and cut various lengths of shorter wire during placement testing. My incidents of runaway Citations nearly quit. H-K acknowledged.
Although I never saw a Citation II without meters, the earliest manuals showed that configuration for factory built units. My thought was that, early on, H-K wanted to make the ownership of "separates" (a new concept then) appear to be a simple experience. You are right about the rivets on factory units.
I have worked on multiple 100s of them and my experience is as I previously described it. My comrade Don Sachs has also worked on 100s of them - his experience is like mine. But there's no point in arguing about it.
That's all I can say.
I've worked on a much smaller number (maybe 20 or so) but can confirm that all factory assembled units I've seen were exactly as Jim describes.
No stability problems with any that were working properly, but heard rumors from older HIFI folk of stability problems in the first generation units. (I owned one for a long time)
I ended up running mine at about 75mA - 80mA per tube. I had some original HK branded 12BY7A which seemed a bit less microphonic than bogey 12BY7As. I seem to recall I picked them up at a hamfest in NH for about $12 total for a full set in 1990 or so. Mine came to me thoroughly broken, but otherwise complete sans tubes. I ran MG1.4s and later MG1.6QRs which it did pretty effectively.
No stability problems with any that were working properly, but heard rumors from older HIFI folk of stability problems in the first generation units. (I owned one for a long time)
I ended up running mine at about 75mA - 80mA per tube. I had some original HK branded 12BY7A which seemed a bit less microphonic than bogey 12BY7As. I seem to recall I picked them up at a hamfest in NH for about $12 total for a full set in 1990 or so. Mine came to me thoroughly broken, but otherwise complete sans tubes. I ran MG1.4s and later MG1.6QRs which it did pretty effectively.
Not arguing, Jim - just providing some information from the early '60's. I may even find the doc's I am talking about, because i am about to sort through a few boxes of '50s and '60s manuals and literature. I'm also looking for that stash of NOS tubes that went missing two moves ago. Here's hoping.
I respect what you have been able to do to keep these beauties alive and kicking. I'll probably place an order with you when I get my bench up and running again.
I respect what you have been able to do to keep these beauties alive and kicking. I'll probably place an order with you when I get my bench up and running again.
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