Conrad Johnson LP66s Problems

Hi All,

I am looking for advice before sending my amp to Conrad Johnson for repair.

I am at least the second owner of the amp and it is all original as far as I know. I have not opened it to look inside.

Recently the amp has been behaving funny:

1. when I go to bias a new set of tubes, a red warning light will flash but not for the tube I am biasing. Used to be only the red light for the specific tube would flash. This can happen on any of the four positions. I keep adjusting each tube and eventually this stops. Is this normal or a sign of a problem? 

2. I start it playing. Occasionally, one channel will go out and then come back on with a thump. A while later, it will do this again. It does this with tubes from three different manufacturers - 6550's and KT88's. I have started trying to rotate tubes and it seems I can move this problem from the right to left channel, but because I only have four tubes from each manufacturer, I cannot figure out which of the two tubes it is. Can 6550 tubes from two manufacturers be intermingled to figure this out?

3. It does not make sense to me that all three sets of tubes would start to exhibit this problem at the same time. All three sets of tubes are used...but I am thinking there is wrong with the amp?....

Advice and suggestions, please. I have tried to contact CJ but get routed through a help desk and then I get a call back a couple of days later from a customer rep and a not a tech. Not making much progress....

Thanks for listening, 





keep us posted on your CJ repair experience.


Happy Listening!


I start it playing. Occasionally, one channel will go out and then come back on with a thump. A while later, it will do this again

I know you are discussing an amp, but I recently had this exact problem with my tube preamp, especially the awful thump.  Like you, put in new tubes and same thing happened.  Was about to send my unit for repair when I decided to ask the distributer if there was a repair facility they recommend.

The distributer said before sending it in that the problem may be caused by a loose tube pin socket and there are two ways to check this; One is to gently pinch the socket sleeve using small pliers to make the pin contact tighter.  The second is also quite effective but easier to do. Simply bend each tube pin slightly inward and outward for better contact with tube pins slightly bent in opposite direction. The point is to create more tension inside the socket holes for a firmer grip.

I couldn't believe it worked like a charm. Used the second method which took all of minute.

As a side note, it is remarkable how much more robust my old school preamp tubes including Telefunken, RCA and GE are built compared to newer Psvane tubes, especially the pins.  I was not careful and one of the Psvane pins broke off, no chance of it happening with the NOS tubes.

@celloover, dsper, I spoke with the factory today. Jeff asked that you use the website "contact" and send a message and he will get back to you.

Thank you for that!

I installed anew set of EH 6550 power tubes today and the amp is still doing the same thing. The sound stops on the right channel and then there is a thump and then a buzz as the power comes bac. Doers this every few minutes..

I will contact Jeff and see what happens. 

I appreciate everyone's interest and suggestions.

Thanks for listening,



For anyone who might be wondering, Jeff at CJ responded to me by saying my LP:66S needs to come in for repair if i have inserted new tubes and the problem still happens...

Did not comment on what could be wrong and what it might cost...

Leaves me so warm and fuzzy...





Being a 2nd owner (at least) it is certainly time for a Tune-Up (no pun).

Keep us posted on your experience with Jeff at CJ.


Happy Listening!