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alaskanaudio 18th September 2002 02:09 AM

Modifications for HK Citation II Power Amplifier
 
This last year I acquired a HK Citation II power amplifier in fair condition. It works just fine but the resistors mounted to the turrent style terminal boards sure get hot and cause a unpleasant odor when the boards they are mounted on start heating up.

I would like to potentially upgrade this amplifier to use modern parts, keeping the circuit original, or use a different circuit design. If I keep the circuit original I would like to replace the turrent style terminal boards with new ones. The tube sockets will likely be replaced in either case.

Does anyone have any information on where tube sockets and fiberglass terminal boards can be obtained? Or perhaps have information on existing modifications to the HK Citation II power amplifier?

I'm in no hurry to attack this project at the present time, but at some point I would like to turn this amplifier into a reference standard for push pull tube amplifier performance.

If anyone has a HK Citation II power amplifier and is interested in doing this type of work to their amplifier I would be more than happy to share information I obtain or generate. I have not built a tube power amplifier since about 1978 and it may be a nice break to get away from solid-state designs for a while.

Johannes Fassotte
Alaskan Audio

Brett 18th September 2002 06:30 AM

JF,

Jim McShane, a regular poster on the AA tube boards does a lot of refurb and mod work on these particular amps. Sorry I'm not on my PC (it died) so I can't give a URL, but a quick search on Audioasylum will find it easily.

Tagstrips:
http://www.tubebuilder.com/ptp boards.html
http://www.tubesandmore.com

Sockets:
http://www.tubesandmore.com
http://www.triodeel.com
http://www.tonywelsh.com
http://www.partsconnexion.com
http://www.hndme.com
http://www.angela.com
and heaps more I can't think of off the top of my head. Sockets are easy to get in a whole variety of flavours depending upon your budget and excessiveness. Octals and 9 pins shouldn't run more than a few bucks each.

If *I* were you, I'd either restore it with new tagstrips (maintain original layout), new sockets and tubes, and replace any suspect caps. Or, use the reputedly excellent OP transformers and make something else, leaving the chassis as it is, so it can be restored later. These are becoming less common and more valuable all the time. The CitII uses a number of nested feedback loops which might give you some greif if you go too far from original values. I heard one in my system about 2 months back, and it left me less than impressed. Use the OP trannies and make something good, but the PSU uses a doubler supply IIRC, so I'd toss that and use a full wave damper diode choke input.

Cheers

fdegrove 18th September 2002 04:07 PM

HK
 
Hi,

I can't agree more with Brett.
Don't smash your heritage,restore it.
Absolute value aside,I feel Harman Kardon,Fisher,Scott amongst others were pioneers in the field.
If you don't have the circuit diagram.I'm sure someone has a Photofact to help you out?:cool:

Rgds,

buglehead 18th September 2002 05:25 PM

I have recently finished a complete parts replacement on Citation II and have found the original construction manual to be a very helpful resource. If you are serious, I can mail you a copy.
The turret strips are one of the few things that I did keep. The organization created by using these strips, and the routing of the wires in the original was probably brought about by the need for ease of kit construction. Many manufactured products of this era are jumbled messes of PTP wires and components. The wire routing was somewhat less than optimum in my view, because of this need for ease of construction, but the internal layout is very nice.
I made use of the space in the power supply side of the chassis to install solen polyprops to replace electrolitics of same value. Most people would choose to replace these with electrolitics of larger value. I also kept the voltage doubler in an attempt to keep the circuit as original as possible(no major alterations like adding trannies). One alteration I did make was to eliminate the outermost feedback loop. I think I found the mod list on Kevin Kenned'ys? web site. If I were to make another mod it would be a regulator for the B+ created by the voltage doubler, as the B+ has crept up because of higher AC voltages these days, a because of lower voltage drops from modern components.

I recommend replacing elecrotolitics and diodes ASAP.
This is a lot of work but probably worth it. As said before, the output transformers on these are very good.
Hope this helps,
Joe E.

alaskanaudio 19th September 2002 12:45 AM

Thanks for the info
 
Brett,

Thanks for refering me to all the links you posted and also the postings by Jim McShane on the AA forum.

fdegrove,

I will likely keep the original chassie, but don't know whether to keep the original circuit or not. There is so much feedback in this design that it bothers me a little bit. I like, and usually use multiple feedback loops but I understand that the Citation II has more overall feedback then any other tube amplifier. This of course is allowable due to the outstanding output transformers. It seems to drive my Sound Lab A-1 electrostatics just fine even in its present aged condition.

buglehead,

I would like to get a copy of the construction manual. I have found a copy of SAMs repair manual for the Citation II and have found it usefull. The construction manual however would be great to find out exactly where all the parts go if I decide to keep the original circuit. If I dont then it would be nice to have it in the Citation II file. If it is ok I will contact you by Email and give you my address.

Johannes Fassotte
Alaskan Audio

fdegrove 19th September 2002 12:55 AM

Johannes,

I think we just meant:treat it with the respect it deserves.
If you decide to restore it to original status there's a lot of help out there,diyAudio forum included.
Feedback doesn't scare us one bit...
Although the Kardons get complicated,here we have all the skill you need.
;)

Rgds,

GaryB 21st September 2002 12:07 AM

Citation II mods
 
I can second the recommendation of Jim McShane and his services. He provides lots of good advice and parts for those wanting to upgrade HK amps. His website is:
http://pages.prodigy.net/jimmcshane/
Another short but good page describing some mods to the Citation II is at:
http://members.bellatlantic.net/~vze...cles/ots7.html
I've been using a modified Citation II amp for the last few years and think its a great amp. I modified it according to the suggestions in the 2nd link. I also changed the outputs to KT-90s and triode wired them. I upgraded most resistors to Mills, changed the coupling caps to Hovlands, and replaced the 9 pin tube sockets. I found that changing all power supply electrolytics was required to get rid of the last bit of grain from the amp.
Sheldon Stokes has some notes on this and has designed a circuit board that makes changing the caps a bit easier. Take a look at:
http://www.quadesl.com/schematics.shtml

---Gary

alaskanaudio 21st September 2002 03:24 AM

Thanks for all your help
 
I have contacted Jim Mcshane via the link that GaryB provided at; http://pages.prodigy.net/jimmcshane/ for a complete high quality rebuild kit for the Citation II power amplifier.

After much consideration I decided to keep the circuit the same and do a total rebuild and parts upgrade. This is the only way I can think of to properly evaluate the performance of the original design of this well respected amplifier.

Thanks to all for the help, input and links that have been provided.

Johannes Fassotte
Alaskan Audio

Brett 21st September 2002 04:50 AM

Johannes,

Please don't forget to let us know what you think of it when the mods are complete and it's in your system.

Cheers
Brett

alaskanaudio 9th October 2002 05:43 PM

Parts and Info have arrived
 
I have received all the parts I ordered from Jim McShane and also the the assembly manual that buglehead sent me. Now all I have to do is find the time to do the work.

Thanks buglehead for the information you mailed me.

John Fassotte
Alaskan Audio


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