Question about the Bogner Ecstasy 101b bias/plate voltage.

[MoistTowelette]

I was planning to change tubes in my 101b. I picked up some gold lion kt77s. I noticed some cyclic squealing whistling and the plate current looked way too high. I put the original JJ E34ls back in and the noise went away but the the current was still very high. It was in Class A mode and the current and plate voltage was 69 mA and 464V. This seems crazy high to me. Putting it class AB mode the plate voltage went up to an expected 527V with a reasonable 29 mA. I checked the bias on the other tube pair and it was similar. Is it normal for these amps to change PV when switching from class a to class ab? The tubes aren’t redplating and I haven’t noticed any issues for the month or so I’ve owned it. Also, does the whistling cyclic sound from the kt77s sound like a bad tube? I just received them in the mail.

 

[glpg80]

101B mandates 115V wall voltage for class A operation. If you’re running 120+ in class A you’ll have bias runaway or redplate without room to correct it.

Power tubes can be microphonic just as much as preamp tubes, but it’s far less common.

 

[MoistTowelette]

101B mandates 115V wall voltage for class A operation. If you’re running 120+ in class A you’ll have bias runaway or redplate without room to correct it.

Power tubes can be microphonic just as much as preamp tubes, but it’s far less common.

Hmm. What's the best way to get clean 115V? I live in a old apartment building and the power sucks here.

 

[glpg80]

Hmm. What's the best way to get clean 115V? I live in an old apartment building and the power sucks here.

I’d run a power conditioner from the wall and then into a variac which the amp can then plug into. If you run the power conditioner into the variac it’s not the end of the world but not how I’d run it.

There’s something called a brown box which lets you set the voltage you want if you don’t want to use a variac. Try googling it.

 

[Geo]

I’d run a power conditioner from the wall and then into a variac which the amp can then plug into. If you run the power conditioner into the variac it’s not the end of the world but not how I’d run it.

There’s something called a brown box which lets you set the voltage you want if you don’t want to use a variac. Try googling it.

I have been running my Metro build for years like this. Works perfectly fine.

Also 527v is not extraordinary.

 

[Scot]

101B mandates 115V wall voltage for class A operation. If you’re running 120+ in class A you’ll have bias runaway or redplate without room to correct it.

Power tubes can be microphonic just as much as preamp tubes, but it’s far less common.

This.

I experienced your same issue w/my 101b and red-plated a power tube not realizing (and fully appreciating) what affect even slightly higher wall voltage can have on a tube amp. Especially the xtc as they seem to run pretty hot to begin with. A variac solved my problem, and more. My amps never sounded as consistent (and good) as it does now since feeding it the voltage it wants. When running in Class A, I also get similar odd readings to yours (eg: 79 +/- ma). I’ve come to dial down to 115 in Class A, per glpg’s advice, and have been staying pretty close to my amp ready to shut down should a valve start going stupid, but that hasn’t happened since pulling back on wall voltage.

Jorg at HQ went through alot of this with me at the time and said my amps kicking ass just the way it’s supposed to and not to worry, he said to just enjoy it. As Geo points out 527v is not extraordinary for the xtc and that will also fluctuate with tubes. I have a set of =c=’s that run around 550 and they sound great. Good luck.