Problem biasing Premier 140

[kve777]

My new-to-me Premier 140 was playing at low volume (Premier 17LS2 preamp, Tekton Pendragon speakers) and I heard a loud POP on the right speaker. I looked at the tubes, V7 was red-platting(maybe others) I also saw bias light on V10. Shut it off immediately. Today I tested the output tubes, no shorts, reasonably serviceable test results. Reinstalled tubes, biased the left channel, no problem. Right channel won't light any LED's, dialed all the pots to max. Any thoughts before I tear into it? I am no novice to tube gear. I have a TV-7D/U tester calibrated by Dan Nelson, A couple of Sencore PR57 variacs, lots of Tektronix scopes, Tek sig gens and Fluke meter. I have the schematic. I figure it's a bias/grid issue, but C-J isn't as simple as a 60's organ amp. Common issue?

Also- Thinking of changing to Tung-Sol KT120's. Any Yays or Nays?

[admin]

First, welcome to CJO. Great to have you with us.

Are you still getting sound from the right channel? Did you check the fuses? If you think it's a bad tube, you can try substituting one tube at a time from the left channel and see where you get issues. That could help identify the tube at least. If the tubes are all ok then you will have to open up the unit,.. although that wouldn't be a bad first step to check for any obvious component damage/burn marks.

[joeinid]

Welcome to the forum, sorry you are having problems. Please keep us updated. I’m interested in the outcome.

[kve777]

Sound from both channels, still. Tubes are OK. Just can't bias the right. None of the four LED's will light in any potentiometer position.

I have to get a Carver TFM-45 off my bench before I can open up this one.

[admin]

Probably not the factor, but any chance the voltage in your home is substantially off of 120V? It can cause the tubes to be outside of biasing range.

[AnotherJohnson]

I know Jeff told Roberto this, but t sure seems like a red herring.

How far off could it be? Certainly less than 10%.

Seems like the adjustment range could deal with this. Maybe an active power line conditioner could solve the problem.

[kve777]

It's only Right channel. Left Biasing normally. My voltage is fine. Plugged into a Power Wedge.

[AnotherJohnson]

It's only Right channel. Left Biasing normally. My voltage is fine. Plugged into a Power Wedge.

And it is fixed to one position regardless of tube installed?

[AnotherJohnson]

If you are well versed in tube electronics, you are well aware of the need to discharge capacitors before poking around. There are potentially lethal voltages present.

You can generally drain them by grounding them. But if you’re not sure how to do this, it is better to be safe than sorry. Don’t be the ground path yourself. It could be your last act.

[AnotherJohnson]

CJ no longer provides schematics to the general requester. Maybe liability is as much in play as intellectual property protection.

Some years ago Chinese sourced electronics “based on Conrad Johnson” started showing up on eBay. Krell replacement cases also started showing up. I don’t know if they’re still being offered, but this sort of theft is not a victimless crime. EBay won’t help unless the company that’s being knocked off threatens legal action.

[kve777]

I have purpose built capacitor drains. All four tubes in the right channel will not bias.

[AnotherJohnson]

[roberto]

Hola kve777,

How the amp is doing? Did you have a chance to check the fuses? Usually that's only the problem. Don't look at them, test for continuity. Remember to take one side out of the fuse holder.

Happy listening!