are tweaker 40 & 88 cathode biased?

[jamme61]

I'm guessing cathode ( I don't see bias adjustment on back) which is it? Thanks

 

[Ian Egnater]

They actually are not. It's adjustable bias with internal test points.

 

[bluesstrattone]

They actually are not. It's adjustable bias with internal test points.

can bias probes be used for the 40 , at what mv or ma should these run at, and where is the bias pot?

 

[Ian Egnater]

You can use bias probes on the internal test points. The bias pot is internal on the new Tweakers, and is on the power tube board. It should be set at 65mV (+/- 3mV).

 

[jamme61]

I wish the bias was on the outside like, the other Egnater amps. I always thought that was a great feature and was hoping the rest of the amp MFG's would start doing it. It's also very dangerous inside tube amps.

 

[sweetrock]

I wish the bias was on the outside like, the other Egnater amps. I always thought that was a great feature and was hoping the rest of the amp MFG's would start doing it. It's also very dangerous inside tube amps.

Agree , +1 !

 

[talltxguy]

Gotta agree with the other guys on a great idea about bias test points. Not so good though having it inside the amp.

On a different note, my Tweaker 15 is the first cathode-biased amp I've owned, and I love it. For you folks running the 40 and 88, how hot are you running your tubes?

 

[bluesstrattone]

You can use bias probes on the internal test points. The bias pot is internal on the new Tweakers, and is on the power tube board. It should be set at 65mV (+/- 3mV).

The bias probes are the tube socket kind that have a male
End that goes in the amp socket and the tube goes on the
Female end.

Let me ask you a question Ian,
Can the 40 run on 6v6 instead of 6L6s?

 

[Ian Egnater]

You can use bias probes on the internal test points. The bias pot is internal on the new Tweakers, and is on the power tube board. It should be set at 65mV (+/- 3mV).

The bias probes are the tube socket kind that have a male
End that goes in the amp socket and the tube goes on the
Female end.

Let me ask you a question Ian,
Can the 40 run on 6v6 instead of 6L6s?

Ahh, I understand which type you are using now. In that case, yes just divide the total number I gave you in half(+/- a few mV) for each tube. As for 6V6's, you can use them, but not every brand will work. They need to be rated for 450V, which a lot of them are not. We do know that JJ's are, and I'm sure there are other brands we haven't tested. Just make sure to find out the rating for the tubes from the manufacturer before you use them.

 

[jimmyt]

Hey Ian,

Is the 65mvDC(+/-3) recommended setting a 50% plate dissipation setting?
The reason I ask is I just checked the bias on my new Tweaker 40 with Ruby's and it was set at 98mvDC which is equals about 68mA or 70% of plate dissipation.
I'm changing out the power tubes and really need to know if this setting is safe and ok to use. I'm putting in SED winged "C" 6L6GC tubes rated at 30 watts. My plate voltage at the standby switch reads 446vDC. So, if I set the bias at 98mvDC or 68mA which is a 70% plate dissipation, will this be ok?

Thanks.........Jimmy

 

[Ian Egnater]

Just for some clarification, are you reading 98 mV with your bias probe on one tube, or using the internal test points and measuring the pair of tubes?

 

[jimmyt]

I'm using my volt meter reading accross the two points on the amp board. This reading gave me 98vDC. The mA reading came from bias probe off of one tube.

 

[jimmyt]

To further clarify, I measured the 98vDC at the two internal test points on the amp board with both tubes in and connected to a speaker load as well. Thanks

 

[Ian Egnater]

To further clarify, I measured the 98vDC at the two internal test points on the amp board with both tubes in and connected to a speaker load as well. Thanks

Hate to keep asking questions on this, but just to clarify, was this on the stock tubes, or new ones you had put in? I am assuming the stock ones, but I always have to ask. We have already addressed this in testing, to make sure the bias is being double and triple checked now though.

 

[jimmyt]

This was with the stock Ruby tubes. Bruce has e-mailed me and explained the mvDc & mA differences. I understand totally now. The reading was high with the stock tubes though. Everything is great now - thanks!