20th Shiva has a fixed bias range?

  • Thread starter Thread starter richedie
  • Start date Start date
R

richedie

New member
I noticed in biasing tubes in the 20th Shiva, I can't bias any tube above 29. It seems they fix the bias with a 29 max.
I ended up having to order my tubes with a hotter grade because I prefer my bias to be 30-36.

Anyone else experience this too?
 
Rich, there's a resistor attachd to the bias trim pot that can adjust it's operating range. Email bogner for more info.

I know that I had to snip a resistor, going from KT88s to EL34s, and that opened up the range. There's probably more you can do with other value resistors.

Something's really weird if you can't bias EL34s above 29.
 
I had the same issue with the 20th XTC. 6l6 and maxed out at 28
 
richedie":3eo699aa said:
Yes all my el34s max bias at 29 in this amp.
Click to expand...

Lol. Not a fixed bias amp man, you just gotta understand what your doing when your doing a bias of working on any tube amp. Measure your bias resistors. But be carefull. A bias trim pot means an amp is adjustable. Take some component measurments or I'd recommend a tech if your not familiar with the Shiav's death power. That cap by bias resistor with kill you in a heartbeat. Just keep writing down your amp list again. PW-Modded-Shivafier. Lol
 
Adambomb":1bmags0w said:
richedie":1bmags0w said:
Yes all my el34s max bias at 29 in this amp.
Click to expand...

Lol. Not a fixed bias amp man, you just gotta understand what your doing when your doing a bias of working on any tube amp. Measure your bias resistors. But be carefull. A bias trim pot means an amp is adjustable. Take some component measurments or I'd recommend a tech if your not familiar with the Shiav's death power. That cap by bias resistor with kill you in a heartbeat. Just keep writing down your amp list again. PW-Modded-Shivafier. Lol
Click to expand...

Sure thing But I have been biasing tubes in my amps since the 80s. I talked to Bogner tech and the bias is set so you can't bias a tube beyond about 29mA. I can't get any of the power tubes in the Shiva past 29mA. There is a resistor you can cut which will open up the bias range.
 
You must log in or register to reply here.
Back
Top