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Citation 12 Amp issue

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Posted on December 8, 2016 at 22:17:06
rockpassion
Audiophile

Posts: 501
Joined: July 9, 2002
Contributor
  Since: January 4, 2006
 Hello all,

I am in need of some help. I have an old Citation 12 that has a blown right channel. It happened when I hooked it up to some speakers on my patio. They played fine until I heard a crackle and saw some smoke coming from my right speaker. I quickly turned off the amp and checked the speaker. I found that a couple of wire strands were short circuiting the terminals. I fixed the short circuit and hooked up the amp. No sound from the right channel. I switched the cables around right to left and still no sound from the left. Oddly enough, the speaker that was smoking worked fine.

So, while I understand this is an old amp is there a simple trouble shooting approach that would help me identify the component that is bad. I only have DVM and can do a limited amount of testing. Although I have built a number of electronic kits, amps and preamps, I would not consider myself a wiz at this.

Thanks in advance.

Richard

 

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RE: Citation 12 Amp issue, posted on December 8, 2016 at 23:14:40
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 Richard
This is a basic dual mono amp with some of the first FET outputs but it's an excellent amplifier. I assume you checked the fuse in the offending channel? If you did,the next thing we want to do is to see if we have the B+ rail voltage going to the output transistors which are mounted on the heatsinks.
Do that and get back to us.It should be 60vdc as I remember.Just check the good channel against the bad one.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Citation 12 , posted on December 9, 2016 at 09:48:27
M3 lover
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Posts: 6599
Location: SW Mich
Joined: May 29, 2005
Contributor
  Since: July 4, 2007
 Richard, I don't know enough to help diagnose your problem (Michael can more than cover that) but I can offer a caution.

Back in the '70s I built a Citation 12 kit (yes, they were offered) and considered it very good driving my large Advents. But then I read about the Double Advent system in TAS and after a brief audition, bought a second pair. I don't recall now how long that lasted but fairly soon the Citation failed. The repair tech said it probably was not happy driving the load of double Advents. I'm not a head-banger so it was not excessive volume, just likely the load.

"The secret of life is honesty and fair dealing, if you can fake that you've got it made." Groucho

 

RE: Citation 12 , posted on December 9, 2016 at 12:56:46
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 His problem was not due to a speaker load because he had a wire that was shorting across the speaker terminals and therefore shut down the amp on one side.The HK Citation series amps were always known for their ability to drive more difficult loads and this goes all the way back to the Citation 2 tube amps.It was very common to find Citation 2s driving Quad ESL-63s and KLH9 ESLs.I think he may have just popped a fuse on the one channel because the smoke didn't come from the amp,it came from the wire strand.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

BJT, posted on December 9, 2016 at 13:53:33
djk
Manufacturer

Posts: 6135
Joined: June 17, 2000

The Citation 12 uses a pair of NPN BJT devices, not FETs.

It runs on about ±40V.

 

Thanks, but, posted on December 9, 2016 at 14:09:00
M3 lover
Audiophile

Posts: 6599
Location: SW Mich
Joined: May 29, 2005
Contributor
  Since: July 4, 2007
 Michael, I understood from the OP his problem was caused by shorting the leads. My intent was to suggest caution with low impedance loads after the repair was made.

However, your information about ability to drive difficult loads may mean my tech at the time didn't know what he was talking about.

To finish my story, I sold the Citation after it was repaired and built a Dyna 400 which drove the stacked Advents with no problems. But it always nagged at me that the Citation likely offered a more musical match, regardless of far less power. But that was decades ago so no matter now.

"The secret of life is honesty and fair dealing, if you can fake that you've got it made." Groucho

 

RE: BJT, posted on December 9, 2016 at 15:20:20
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 Scroll to last page ad look at the outputs.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: BJT, posted on December 9, 2016 at 15:45:01
llwhtt
Audiophile

Posts: 192
Location: SOCAL
Joined: October 28, 2008
 That's Nelson's modified Citation 12, the original was BJT.

Craig

 

RE: BJT, posted on December 9, 2016 at 16:57:16
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 Ah ok.It's been a few years since I've done one and didn't remember the details.
He needs to look at the fuses and then check the rail voltage as he may find a shorted output.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Thanks, but, posted on December 9, 2016 at 17:01:33
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 However, your information about ability to drive difficult loads may mean my tech at the time didn't know what he was talking about.

Not necessarily that.Just sometimes even I thought loads were too difficult for some amps but the citation 12 was a great amp because it's a dual mono and I was looking at a modded schematic with FET outputs. Even the stock amp is a very good amp.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Thanks, but, posted on December 9, 2016 at 18:14:36
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 If it is a stock 12 it shares the main AC fuse. If that is not blown you do not have a dead short. You probably have at least one open emitter resistor and probably a shorted output, they had no current limiting.

I like real RCA 2N3773s for outputs. Some say you can use the 2N3055 but its Vce rating is too low. While most units can handle it, you are exceeding the limits. For drivers I remember a 2N3440 I think and its complementary of which I do not remember the number. Of course you could go ape shit and put MJ15024s in for outputs, which would probably melt the transformers before going bad. Not that bad an idea, they are like six bucks each at Digikey, and since they are a modern part you can probably get them all from the same lot number. Other places have them as well but I have had pretty good luck with Digikey.

None of this applies if it is a Nelson Pass modded unit. Everything is different. The only traces that remain are the power transformers, maybe the filters but I am not sure about that.

 

RE: Thanks, but, posted on December 9, 2016 at 19:45:15
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005



Ive been using the MJ15003 and MJ15004 in most SS amps. I have a lot of the 2N3055s still but use them for regulators.
The citation 12s I worked on have 2 fuses and it's been 3 years since I did the last one. They prolly had earlier versions with one.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Thanks, but, posted on December 10, 2016 at 10:00:25
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 I stand corrected, it has been a long time since I worked on one. Now what the hell was I thinking about ? I distinctly remember working on a dual mono amp and saying "All they share is the AC fuse and power switch".

Still I would recommend a dim bulb tester after the fuse is replaced. Easy to build and saves alot of silicon. Those outputs are alot easier to get and to replace than the drivers. In fact now I remember it took a hammer and punch to get the originals off the heatsinks.

 

Yes, +1 on "even the stock Cit. 12 amp is very good", posted on December 11, 2016 at 16:52:37
Interstage Tranny
Audiophile

Posts: 3063
Location: Eastern
Joined: October 4, 2006
 From the mid to late 1960s, there aren't too many ss amps worthy of that quote. Dynaco and Marantz were also decent, but the dual mono Cit 12 did prove itself rather well. Even today, a good example, simply rebuilt with upgraded caps and some resistors, is a pleasant surprise...

Resto highly recommended !

 

RE: Citation 12 Amp issue, posted on December 11, 2016 at 20:18:04
SgreenP@MSN.com
Audiophile

Posts: 3537
Joined: April 23, 2007
 I hsd a Citation 12 many years ago....I seem to remember it had a fuse(s) somewhere.

 

RE: Citation 12 Amp issue, posted on December 15, 2016 at 15:10:31
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 Ever figure it out ? Is it just a fuse or a major meltdown ?

 

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