Biasing a Premier 11

[mstrshikadance]

My premier eleven currently has Tung Sol 6550s and it sounds fantastic. I should probably be happy and just leave it as it is.

I do, however, have a perfect set of NOS Svetlana 6550s that sounded fantastic in another amp.

The Svetlanas are hardly used, very low hours, and i never had any issues biasing them in my other amp.

When i moved them into the the P11, that is when all the trouble began.

I was never able to get them biased, and even if i turned every screw all the way to the left, the lights would all stay on. I even moved tubes to different positions, and would be able to bias one slot but not the others.

For fear of damaging something, i removed them, and put the Tung Sols back in and everything is working normally.

Is there something i am missing about how to bias a CJ P11. I am confident these tubes are compatible and i have been able to bias the Tung souls without any issues.

Thanks and sorry for the story!

[AnotherJohnson]

Perhaps they’re not perfect anymore. Tubes can leak and lose their vacuum. Plates and wires can be damaged in transport.

My experience with CJ biasing is that a bad tube can impact the others as it impacts the balance of the circuit.

If a tube is good, and if it is of the same specification, it should bias fine … the fact that there’s no problem with the Tung Sols says the amp is fine. I would look to the Svetlanas to find the problem.

[mstrshikadance]

This was my thought, so i put them into my old amp and was able to bias and use them as normal. So i am stumped.

[AnotherJohnson]

Deus ex machina

[roberto]

This was my thought, so i put them into my old amp and was able to bias and use them as normal. So i am stumped.

Your Premier 11 is more sensitive to the tube gain properties , in other words, the old tubes do not have enough juice to work on it. If you use fresh tubes, probably you are going to be able to adjust the bias. The Premier 11 is detecting that.

When you use the tubes for a long period of time, let's say about 6 to 8th months, and you check the bias pot, you will notice that you must increase a little bit to have them properly biased, turning the screw bias to lit the bias Led. Also, the voltage of the house at night, when the AC line voltage is a little bit stronger, you might have the bias Leds on or flickering, a reason of why you should test your bias Led at night, due to a less energy consumption over all.

Happy listening!

[AnotherJohnson]

I think the Premier 11 LEDs are preset for 57.5 mA.

What is the other amp?

I’m assuming it is one that you bias with either an external meter, like the ARC REF 150, or one you bias with a built in meter, like the ARC REF 75. What current are you shooting for, and how do you know when you’ve achieved it?

[AnotherJohnson]

https://frank.pocnet.net/sheets/049/6/6550.pdf

Here’s the 6550 data sheet.

[AnotherJohnson]

As Roberto points out, different amps run with different bias points. It would appear that the Svetlanas are not up to the Premier 11 bias point at this stage of their NOS life. But they are suitable for the other amp.

If we knew the other amp, the puzzle might clarify.

[AnotherJohnson]

FWIW, the bias current selected by ARC is revealed and discussed in the ARC owners manuals. They make the case for their choice, and advise you to stick to it.

The LED bias procedure is easier, but it’s less clear what you’re actually trying to achieve for bias current. The LED approach is like a go-no go gauge.

[Joe Appierto]

It's strange that particular set of 6550C won't bias properly in the CJ amp. Of the many different tube types I used in my 11A the only ones that wouldn't bias properly (the LEDs were always lit) were the Psvane Black Treasure KT88 and I returned them to the vendor.

[Truth71]

I had the same thing happen with a set of “NOS” Svetlana winged C in a Premier 11a.

[mstrshikadance]

I think the Premier 11 LEDs are preset for 57.5 mA.

What is the other amp?

I’m assuming it is one that you bias with either an external meter, like the ARC REF 150, or one you bias with a built in meter, like the ARC REF 75. What current are you shooting for, and how do you know when you’ve achieved it?

The other Amp is a Willsenton R8.

I bias it using the built in meters.

[AnotherJohnson]

The Willsenton R8 with 6550 tubes is rated for 25 Wpc in triode mode and 45 Wpc in UL mode. The P11 is designed to produce more power. It could well be that the NOS Svetlanas are just not up to the demands of the CJ design. NOS tubes, and used tubes, and even new tubes, are highly variable.

The Willsenton folks in China are likely to be frugal folks because they are producing a well regarded budget amp at a very affordable price. Like Prima Luna, for example.

As Kevin Deal, ARC, CJ and others say, every tube that is produced will be sold to someone. They say their tubes are so expensive because they go through an extensive testing procedure that only the top tubes in a lot can pass.

How do the Tung Sols sound when you use them in the Willsenton? My guess is that you might like the Svetlanas better there because they appear to run in a “low idle wick” sweet spot and the Tung Sols may perform better with idle the wick turned up.

Enjoy them both! You’re lucky to have two amps at different ends of the spectrum.

[mstrshikadance]

Thank you for all the help and explanation.

The Svetlanas sounds great in the Willsenton, much better than the stock tubes provided with the R8. I may move the tung sols over for curiosity, but for right now....enjoying the music.

[AnotherJohnson]

RJ’s technician, who seems to be quite bright, once told him that turning the bias pot clockwise (LED going from off to on) was actually turning the bias current down.

If this is true, then the Svetlanas may be lower impedance than the Tung Sols, leading to the bias pot not being able to add enough resistance to bring the plate’s idle current down to the target. Just a thought. I like meters better than LEDs because you can see and understand what you’re doing.

[mstrshikadance]

RJ’s technician, who seems to be quite bright, once told him that turning the bias pot clockwise (LED going from off to on) was actually turning the bias current down.

If this is true, then the Svetlanas may be lower impedance than the Tung Sols, leading to the bias pot not being able to add enough resistance to bring the plate’s idle current down to the target. Just a thought. I like meters better than LEDs because you can see and understand what you’re doing.

When I tried turning the pot up (clockwise) they would start to run too hot for comfort. I immediately turned the down.

[Big Dog RJ]

Yes, that's correct. My CJ tech did say that but then again there are so many things he's mentioned over the years, that sometimes I'm still trying to figure out what he's referring to. He's way too technical for my tooob brain. So, most of the time whiles he's intently explaining things, about 5-10% I can digest. The balance 90% I've already tuned out!

He always said one thing though, and CJ states the exact same thing in all their manuals; just stick with the tubes that originally came fitted with the amplifier!

However, that's a big No No, in our expert skilled level of being audiophiles... we think we know it all! So, we start experimenting... tube rolling, changing sockets, NOS this and NOS that... oh we just love it! Then something goes wrong... and we blame the brand or the tooobs! Or the bias.
No point going there, just enjoy the item as it was intended.

There are certain mods that can be done, and certain tube types can be used "safely" without causing a sink hole in your neighbourhood... However, my tech's advise on this is just do some research before attempting and really know what you're doing. If you don't know what you're doing then just don't do it! Leave it upto the tech's advice.

Of course I trust him, along with LJ, Ed and now Jeff. None of them have ever given me the wrong advice, and I've never had any major issues with any of my CJ gear, unlike plenty of other gear. Some real disasters but were all eventually fixed! Again, by trusted techies. I guess it's like finding that right Doctor or Dentist, once you've found a good one, you're theirs for life!

Basically, if it "just sounds right" then leave it!
Cheers, RJ