2. amps-preamps
  3. 194571-191137

KT88 Tubes

I am new to tube amps having acquired a Harmon Kardon Citation II about a year ago. A little while ago I started experiencing one of the channels dropping out and an occasional loud pop. Today I noticed one of the KT88 tubes glowing purple where the rest glow orange so I have assumed that the tube has gone bad. As I bought this amp used, I have no idea of the age of the tubes. So I have a couple of questions. First, should I replace just the two tubes on the bad channel with a matched pair, or should I replace all 4 tubes with all 4 being matched. Second, any recommendations for good quality KT88 tubes? Any other thoughts or ideas would be appreciated. 

russbargmann
rwwear
2,898 posts
 

I have a pair of Citation II's that I run in mono. If your amps haven't been rebuilt, I recommend the McShane power supply kit before using the amp.http://www.mcshanedesign.net/  These are wonderful amps but need to be updated to perform safely and at their best.

yzfr1mike's avatar
yzfr1mike
16 posts
 

It's possible the problem is bad capacitors in the channel where the problem shows up. How old is the amp? If you don't know the history of the amp, I would take it to a repair shop and purchase new matched tubes before using the amp. The problem could damage your speakers, which would be a disaster for all of us.

I had a similar problem on my Sonic Frontiers Power 2 amp. It turned out to be a cap in that channel.

Capacitors on the power supply are

yzfr1mike's avatar
yzfr1mike
16 posts
 

Capacitors on the power supply are the electrolytic type and degrade with time. Bad Power supply caps are a problem that affects all amps with time of use.

russbargmann OP
2 posts
 

All, Thank you for the responses. I have found someone recommended by Jim McShane to completely go over the amp and preamp (Citation I). They will come back good as new (or better).

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