XTC 101b plate voltage?

[amiller]

I put a new set of Winged "C" EL34s in my XTC and then set about setting the bias. I have an old printout that someone did specific to the the XTC. The printout says that the XTC's plate voltage is usually around 535v. Using my Weber Bias Rite tool, I checked the old tubes first and the highest plate voltage was only 520v with the lowest being 515v. I put the new tubes in and the highest plate voltage was only 514v with the lowest being 508v. Are these readings normal? Is the 535v stated in the doc I have incorrect?

I did complete setting the bias. I decided to set it a little cool...around 30mA. The amp sounds pretty good to my ear now.

 

[Marshall Freak]

when you adjust the bias, it has an effect on the plate voltage. That said, none of the three I've had were anywhere neard 535.

 

[amiller]

when you adjust the bias, it has an effect on the plate voltage. That said, none of the three I've had were anywhere neard 535.

Yeah, I was thinking 535 sounded high too.

 

[itsme]

How did you adjust the bias? Though the hole on top of the chassis with a small screwdriver, or from underneath? Do you know what Bogner recommends as factory setting? I just got a new one in Feb, and it sounds so good, that when I retube, I want it biased just like the factory.

 

[Dale B]

The ones I've owned were between 525 and 535 depending on the tubes I used.

 

[Dale B]

How did you adjust the bias? Though the hole on top of the chassis with a small screwdriver, or from underneath? Do you know what Bogner recommends as factory setting? I just got a new one in Feb, and it sounds so good, that when I retube, I want it biased just like the factory.

I always pulled the chassis and adjusted it on the PCB where it's labeled. If you buy power tubes for the XTC, make sure you get them in or around the 25 to 30 mA range if the vendor is using a Maxi-Matcher at 400 vdc. You will have an easier time biasing the amp because the bias pot's sweep (range) is very narrow in the XTC.

 

[amiller]

How did you adjust the bias? Though the hole on top of the chassis with a small screwdriver, or from underneath? Do you know what Bogner recommends as factory setting? I just got a new one in Feb, and it sounds so good, that when I retube, I want it biased just like the factory.

I pulled the chassis out and adjusted the bias from underneath. I think Bogner's are normally biased at around 32mA, however, you can go hotter or colder depending on the result you're after.

 

[amiller]

It also depends on the AC wall voltage, in some places it can be high and low in others. Most power transformers are designed for 120v AC input. But most of the wall voltages here are 125v or sometimes higher, and sometimes lower in the 117v ranges.
The 535v may be the highest you would see with high wall AC voltages.

Does my low plate voltage indicate that my house power is below normal? Maybe I should be considering a Furman AR1215 AC Line Voltage Regulator.

 

[Anonymous]

ok lets end this 490 on standby/ 510 with standby off. straight from that crazy guy 12 years ago

 

[Anonymous]

set it to 40 ma and roll as long as you are using winged c svets. dont believe call bogner. have a good day.