LP66S Problem(s)

[Dsper]

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,

Dsper

[AnotherJohnson]

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,

Dsper

Regarding your #1, it is not uncommon for a bias adjustment on one tube to affect another tube.

Regarding #2, get a set of new tubes. The manufacturer mix isn’t nearly as big an issue as the hodge podge of tubes of unknown history. Get a known set of high quality.


Regarding #3, see response to #2.

Regarding phone calls to CJ, it’s a very small operation and they are presently focused on the roll out of new flagships ART 88 and 108A). They don’t have the horsepower to trouble shoot an old amp with tubes of suspicious history over the phone. They’ll be happy to sort it out for you if you send it in. It will probably cost around $800 plus tubes if you count shipping, new box for the return, insurance, etc.

[Dsper]

Thanks for the advice AnotherJohnson. I posted my questions on another site and got the same advice to purchase another set of tubes.

[AnotherJohnson]

Do the small tubes too. Pops and intermittent sound is often originating there.

[admin]

I think AJ nailed it on the head. Considering the age of the unit I personally would replace all the tubes so I know that I'm good to go. It's the low hanging fruit. There may also be some tube degradation but not complete failure.

[Dsper]

Hi all,

I had checked the small tubes earlier and today installed a brand new set of four EH 6550 power tubes and the problem is continuing.

I start playing music and the the sound stops on the right channel and then there is a thump followed by buzz as the power comes back. Does this every few minutes.

A user on another forum who has access to Jeff at CJ, said he spoke to Jeff who suggested to write him as note via "contact" on the CJ website. I did that this PM so we shall see,

I appreciate the suggestions and interest.

Dsper

s new set of

[AnotherJohnson]

Intermittent ground?
Cold solder joint?

[admin]

Perhaps a cap failing?

[roberto]

That's a temperature resistor problem. It opens while working hot, and when the resistor goes to a lower temperature, it makes a contact again. Usually located at the B+ small tubes. it is a 5 watts 20K or around these ohms resistor. Difficult to track.

[roberto]

I forgot, there is one for each channel.

[AnotherJohnson]

That's a temperature resistor problem. It opens while working hot, and when the resistor goes to a lower temperature, it makes a contact again. Usually located at the B+ small tubes. it is a 5 watts 20K or around these ohms resistor. Difficult to track.

So it acts like a cold solder joint, but is a failure of the resistor itself.

Maybe you could track it by poking with a wooden chopstick when it works, like you might do to find a cold solder joint.

[roberto]

or a freezer spray, when it is not working, this freezer colds the resistor and if it is, then it will start to work.

[AnotherJohnson]

or a freezer spray, when it is not working, this freezer colds the resistor and if it is, then it will start to work.

I forgot about that option. It is a very good method.