Harman Kardon Citation II Rebuild

[mayfly]

Gregg,  If this thread really belongs in off-topic (as I'm talking about a stereo amp), please feel free to move it.  But I figure that the Dead used Macintosh amps for their live rig, then it's possible that this monster might have been used in the same way.

ok Kids!  What weighs 70 pounds, has three stupid large transformers, delivers 60x60 watts from a quartet of 6550/KT88 tubes, has a frequency response of 10Hz to 100kHz at the 3db down points, and has not been made in over 40 years?  That's right:  One of these suckers:

So here's the thing.  I've got one.  I've actually had this one for 20 years.  It was the heart of the audio lab in the EE department at the University of Alberta in the 60s and 70s, and was given to me (that's right - a gift) when I was finishing up my BSc in the late 80's.  

I didn't know anything about tubes at the time.  When I got it home I fired it up and tried to bias the tubes - but ended up with one in thermal run way.  I unplugged it, put it on the shelf, and left it there....

... Until now.  A buddy of mine is into vintage audio and agreed to make some vintage type speakers using modern drivers if I got the old girl running.  So we're gonna do it.

 

[mayfly]

So this baby was used in a university lab for 20 years.  Folks who know these amps know they came as a kit.  Chances are that it was well made and taken care of at the beginning of it's life, then gradually over time it was abused and hacked up more and more.  taking the cover off did not disappoint:

The power supply caps had been hacked over, and it was obvious that one or more had burst over the life of the unit.  But that was not all:

It was obvious that the thing had seen a lot of heat.  There are scorch marks on the chassis, many wires were blackened, and the output tube jacks are black with gunk.  I knew then that a partial rebuild would not do the trick.  Old components that had seen a lot of heat, even if working now, could fail at any time.  If I wanted to see the thing run, I need to do a full rebuild.  And by that I mean replace everything.

 

[Death by Uberschall]

I like projects like these!!  :icon_thumright:

 

[Super Turbo Deluxe Custom]

The frequency response had me reeling.  10 Hz?  That goes pretty darn low.  So low, most bass speakers won't even let one appreciate that.

 

[Patrick from Davis]

Heat and carbon comp resistors?  Eeek.  They tend to crumble when you remove them if they get too hot, now how do I know that...  The can caps should be replaced, but you are well aware of that.  Then there are a couple of caps visible, quite a number of ceramic jobs.  Those seem to take a beating, but are not the highest fidelity.  Mumble, mumble, mumble.  The over all parts count doesn't seem to high, so replacing everything should not be to big of a problem, other than minding your p's and q's when getting the replacements.  Looks kind of like a VHT 2150 without the anodized purple aluminum.  What a fun project.
Patrick

 

[blue313]

It's nice to open up a stereo amp....and not think you're looking at a laptop with all the PCB's

Cool project!

 

[Super Turbo Deluxe Custom]

Of the people on this board, you are certainly one of the most qualified to undergo this task.  The people that understand this stuff say that tube technology is inherently simple.  No doubt you will replace the correct cap values with better quality caps.  I can't forsee anything that wouldn't make this better than when it was new.  However, 70 lbs. just for an amp, it may not travel much.

 

[mayfly]

Thanks for the votes of confidence folks.  We'll see if I actually pull this off.

Here's an update.  I pulled the capacitor mounting plate and all the caps, diodes, and other hardware off of it.  The capacitors were junk, but I kept some of them for fun ... the ones that were not covered in goop that is.  Here's the plate after a little cleanup:

The plate is designed for Mallory style 'FT' twist mount caps.  I wanted to stay as original as possible, so I ordered up some newly manufactured versions from Antique Electronic Supply.

Then I took one of the turret boards off.  I figured I'd do one side, then the other to have a visual reference. Here's what it looks like partially disassembled:

aaaand here's the turret board:

Check out the size of those caps on the back!!

 

[mayfly]

Allright, time to address that turret board.

Looking at the caps on the board, one of them is a 4uf/450V electrolytic.  And it's on the bottom, where it's completely inaccessible.  This annoyed me to no end.... until I figured out that I could replace it with a Solen Poly cap.  And I even had some!

Here's a shot of the board comparing the old caps to the new:

And here's a shot comparing the Solen to the original electrolytic cap:

This is the only cap that has increased in size over the last 40 years  :icon_biggrin:

 

[mayfly]

Last night, I stripped the board to the bone and cleaned it up.  I made a quick jig to hold the board steady while working on it:

Here's the parts as they came off the board.  I'm keeping them for historical reasons:

and here's the board, all stripped (except for the jumpers) and cleaned up:

 

[Wana_make_a_guitar]

I've no idea about any of this, but it's interesting.

 

[mayfly]

The rebuilding as begun! Here's the board with the new caps and jumpers on.  I'm following the original assembly manual order to ensure I don't miss a step. 

The new caps are a hell of a lot smaller than the old.  So much so that the leads are almost not long enough!  That's garden variety heat shrink on the leads BTW.

 

[Alfang]

Mayfly, your the man

 

[Mor Paul]

Hey, um, Trevor...
My watch stopped working, and I was wondering...
:icon_jokercolor:

 

[dbw]

Sweet

 

[dbw]

The frequency response had me reeling.  10 Hz?  That goes pretty darn low.  So low, most bass speakers won't even let one appreciate that.

It's a hifi, I think that kind of low end response is expected for hi fi equipment.  Gotta get a woofer to hear it!  :guitaristgif:

 

[Super Turbo Deluxe Custom]

It's a hifi, I think that kind of low end response is expected for hi fi equipment.  Gotta get a woofer to hear it!   :guitaristgif:

I know, but most subs I've seen have the low side of frequency resonse in the 30s Hz range.

 

[OzziePete]

I've no idea about any of this, but it's interesting.

+1.  :sad1:

Of the people on this board, you are certainly one of the most qualified to undergo this task.  The people that understand this stuff say that tube technology is inherently simple.  No doubt you will replace the correct cap values with better quality caps.  I can't forsee anything that wouldn't make this better than when it was new.

Mayfly, your the man

And agree also!   

 

[blue313]

It's a hifi, I think that kind of low end response is expected for hi fi equipment.  Gotta get a woofer to hear it!   :guitaristgif:

I know, but most subs I've seen have the low side of frequency resonse in the 30s Hz range.

You should see the subs that the sicker audiophiles use.  Some use them for serious home theater as well.  10-30Hz is a reference sweep for them.

 

[OzziePete]

It's a hifi, I think that kind of low end response is expected for hi fi equipment.  Gotta get a woofer to hear it!   :guitaristgif:

I know, but most subs I've seen have the low side of frequency resonse in the 30s Hz range.

You should see the subs that the sicker audiophiles use.  Some use them for serious home theater as well.  10-30Hz is a reference sweep for them.

A note that low at volume might end up being the mythical 'brown' note, lol....... :laughing7: Would be like a punch to the guts.