Jet City JCA20HV biasing question

not_the_dj

Picked up one of these yesterdays (from the classifieds here), very impressed so far. 

I've just downloaded the manual and it seems to be contradicting itself with regards to the need to bias it when changing valves.

The manual is from here: http://www.jetcityamplification.com/#!20hv/c1s1p

It states: JCA20HV is a Fixed-bias amp which allows you to “plug and play” EL84 power tubes without needing a bias adjustment.  

But then also: ·       Class A/B, Fixed Bias (Internally Adjustable)

I thought that a fixed bias amp was the sort that needed biasing when changing power valves.

@ICBM are you familiar with these?

digitalscream

That's...disappointing. From what I know, they do have to be rebiased when you change valves - as do all their other amps.

olafgarten

not_the_dj said:

Picked up one of these yesterdays (from the classifieds here), very impressed so far. 

I've just downloaded the manual and it seems to be contradicting itself with regards to the need to bias it when changing valves.

The manual is from here: http://www.jetcityamplification.com/#!20hv/c1s1p

It states: JCA20HV is a Fixed-bias amp which allows you to “plug and play” EL84 power tubes without needing a bias adjustment.  

But then also: ·       Class A/B, Fixed Bias (Internally Adjustable)

I thought that a fixed bias amp was the sort that needed biasing when changing power valves.

@ICBM are you familiar with these?

I think the adjustment may just be to make it hotter or colder rather than a necessary adjustment.

digitalscream

OK, just had this back from Doug @ Jet City:

Doug said:

Hi buddy. 

You do NOT need to adjust the bias on the amp when you change the power tubes! 

 D.

not_the_dj

digitalscream said:

OK, just had this back from Doug @ Jet City:

Doug said:

Hi buddy. 

You do NOT need to adjust the bias on the amp when you change the power tubes! 

 D.

Great, thanks for checking.

digitalscream

No worries. I'm now sorely tempted by a pair of Mesa EL84s. £30 for a pair seems like a decent deal, given that I'm used to paying £20+ each for 6L6s.