Studio 22+ factory bias setting

[tonejam]

Can anyone tell me what this is? I've been emailing Mesa, but so far they've given me no info.

 

[talltxguy]

I can't see Mesa giving out bias information! They will tell you to use their tubes to be safe.

I ended up purchasing a multimeter along with a bias probe that measures bias and plate voltage.

 

[Authorized Boogie]

The Studio 22+ has a plate current of 390v. Typical bias range for EL84 in Class AB at 390v is approximately 21-22mA. There will be some variation depending on line voltage and individual tubes used.

 

[tonejam]

Thanks, "Authorised Boogie", and others, for replies.

I have purchased a kit so I can bias it myself. I've owned the amp since new. The amp has had a few mods over the years, including a bias adjustment pot. It's nowhere near as loud as it used to be, and I'm curious to see if its had a major bias change (which is why I need to know what it was originally).

I'm a little surprised and disappointed at Mesa's attitude. Not very helpful, and I've been singing their praises for years.

 

[McBarry]

Tonejam,
I'd have a squizz at the PCB and see if any joints look suspect, ESp around the EL84's.
I think I recall U said U thought yr 22 was OK for heat-affected joints, but I'd be wanting to definitely exclude it as it's a simple fix and reasonably common, relative to use of course..

Dave

BTW: Authorised Boogie - thx for the bias info - heaps helpful ! DB

 

[TiPiMods]

The original Bias Setting on the 22+ is much higher. Mine was dissipating around 11-14 Watts, depending on the tubes. It destroyed a wonderful NOS Brimar Set within a few month. I cooled down the bias setting with some resistor so it is near 8 Watts now.

 

[tonejam]

WOW!
I actually got a reply from Boogie.
It said......"the Grid Bias on the power tubes should be at -12"...... anybody know what that means?

 

[TiPiMods]

That means the negatative voltage between grid and ground should be -12V.
But be careful, it seems that you dont know too much about electronics. The high voltage in tube amps can kill you!!! If you are unsure what to do, you should take the amp to an experienced technician.
plus: the right bias voltage depends on the tubes you use, so a better way to bias, is to measure the current flowing through the tube and calculate the plate dissipation (plate voltage times plate current) it should not exceed 80% of the maximum dissipation (max 12W for a EL 84)

 

[tonejam]

Thanks Tipimods, that's what I ended up doing. Although, after doing a lot of internet searches, It appears that Boogie biases these little suckers around 120%, but are reluctant to discuss it.