Harman Kardon Citation III-X questions

rudedogg

AK Member
Hey guys, i acquired this filthy HK tuner while drinking with a friend last evening. I probably would have passed on the purchase if completely sober.....but the price was right and i felt pity for the thing. So, he offered it up, and i now own a Citation III-X! Lol. I did a quick dim bulb test with the rectifier removed, and the bulb (100 watt) dimmed down very nicely. Next i added the rectifier back in, and left all the other tubes in as well, and again DB tested. This time the bulb dimmed out almost completely, but after about 30 seconds, started to brighten slowly to about half brightness, so i powered it down. Is that a fail? Or just normal activity as the tubes begin to conduct? I will recap, but i kind of want to see if she passes signal at least before spending some money.
Btw, i started to clean up the chassis a bit, it was/is covered in nicotine and dust and grime! I'm pretty amazed at how nice it is coming along.
 
I think it passed the dim bulb test. I had one of those several years back and about all I did with it was replace the rectifier tube as it caused a dreadful hum. Mine was just mono if I recall correctly and was sent along to another AKer before I could do much with it.
Hook up something for an antenna and try it out. Use the db tester, at least initially, it should have enough juice for the tubes to operate. Also, there is a volume knob on there which I would turn down to start with just to limit the output.
 
Thanks mibag6. I believe it passed also. I hooked it into my system with an antenna and on the DBTester. It all lit up, I got a little static and nothing else. I believe my dim bulb is limiting current and voltage just a tad too much for full operation. Here is the belly, looks great, save for the nuts a little mouse hid inside! LolFE6D8D5B-4E96-4C4F-B4CF-9DB2F4B40BF5.jpeg
 
Yup, it all looks familiar to me because I got one in somewhat worse condition for $40 last summer. There are schematics for it that show voltages and resistance readings to ground from each tube element, so troubleshooting is not all that bad unless you have to get into the MPX adapter that is crammed with components. Mine had an open screen resistor on the last 6AU6 IF stage and a broken dial cord. A lot of the tubes tested weak, so this thing was probably on all the time. Mine also had a bad 6CW4 nuvistor that I replaced and it needs an alignment. Yours may be in better condition but it should be fun to track down any ailments it has. One thing you will find is that the two tuning capacitors are not synchronized in any way, so they can get out of sync with each other.
 
Well, I tested the rectifier. It’s good. Tested all the front end tubes.. some are weak. I did not test the 12ax7s and mpx tubes yet. The tuner all lights up, no excessive heat from the filter caps etc, but no sound or response from the meters at all...hmmm.. nothing in the belly looks obviously stressed or broken. What does the nuvistor do??
 
The 6CW4 is the first RF amplifier stage, so if that goes bad, the signal gets no farther except in local mode. You have a local-distant switch which biases the 6CW4 into cutoff in the local position and the signal goes to the second stage via the neutralization network in the local position. There are a few other weird design features in this set.

The AFC uses an NE-2 neon lamp as a voltage regulator for the AFC diode.

The supply to the oscillator and 1st IF screen has no decoupling other than the capacitor to the bottom of the 1st IF transformer.

The IF stages are bridge neutralized by having the screen bypass capacitors go to the bottom of the IF plate winding. My Fisher KM-60 uses the same design.

You may find some deviations from the published schematics with the inclusion of a stereo decoder plug that is 11-pin rather than the 8-pin shown on the schematics. There is a diode detector network similar to the one for interstation muting but of opposite polarity whose output goes to the MPX section and this is not in the published schematics. The stereo light that is shown to come from the selector switch in the published schematics actually appears to come from the MPX decoder.

The published schematics omit the value of C74 at the signal input to the MPX decoder. It is 0.01 µF 5% because it is part of the SCA filter tuning capacitance.

Whether by accident or design, someone had replaced the last 6AU6 stage plate supply resistor in my unit with a 120 ohm rather than the designed 1200 ohm resistor.

Someone has added a capacitor across the cathode resistor for the first 6AU6 stage, so this and the last item may be someone's attempt to hot-rod the IF stages.

My tuner is badly misaligned, so it is not a good example of how the unit should sound but I will get out my trusty SG-165 at some point, I just have a lot of things to do. How did I ever find time to go to work before I retired? It takes a large signal (from a signal generator in my case) to get the meters to move, so dead meters may not be dead after all.

The Citation III was featured in the April 1961 issue of Radio Electronics. It was the winner of the Electronics Illustrated shootout of 11 FM tuners in the November 1961 issue. It beat all other tuners in harmonic distortion and signal-to-noise ratio and came second in most other specifications. It was the most expensive in the test and it still commands a high price today. No one was looking to pinch pennies in this design except maybe on the cheap wafer tube sockets and the corroded antenna input terminal strip. The dial cord idlers have plastic bearing inserts – something I have never seen elsewhere. You can find these articles here:

http://www.americanradiohistory.com/
 
Thank you for responding. I am pretty much a novice tech. I can and have recapped my amps, set bias and idle etc. and aligned a Dyna FM3! Lol. I really would love to get this beast up and going. I know the transformer is ok, I checked voltages there. Tubes are “fair” I suppose.. rectifier very strong.. gotta do some research and figure this thing out, I really want to hear it! Any help/suggestions at all appreciated! Should I get a new nuvistor to start with?
 
I tested the Telefunken ax7s and they pegged my meter! That’s good news if I can’t get her going I suppose. The resistors I checked thus far are good, along with a few voltages...gotta be something simple. I hope!
 
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