Changing tubes in Pro Junior

[rjs6700]

Is it as easy as pulling them out and putting new ones in?

Getting a new cabinet for 12in speaker and thought I'd put new JJ's in at the same time.

[Riscchip]

I believe a Pro Jr. is fixed bias, so you will need to have the bias tested and potentially swap the bias resistor to change the power tubes.

The preamp tubes you can swap out without any adjustment.

Since you're talking JJs, you could always try contacting Eurotubes and see if he knows the factory bias range of your amp. He could then sell you a set would work with the stock bias setting. This isn't ideal, though, because things may have changed since the amp was new, or if the amp was previously owned, someone else may have changed the bias resistor already.

Alternately--and I may be wrong here--I think Fender uses pre-rated tubes like GTs these days? If you went with those, you may be able to find a set that Fender guarantees to fit the stock bias setting on your amp. But they wouldn't be JJs, unless Fender is using those now.

[boogieplaya]

Huh? Pro Jr. Is simply plug'n'chug..

[SatelliteAmps]

Even if a company guarantees matched or pre rated tubes, they should be checked every time you change them by a tech or with some sort of meter. Too many times have tubes shown up that aren't what they were supposed to be.

[Riscchip]

Huh? Pro Jr. Is simply plug'n'chug..

How so? The Fender amp field guide says it's fixed bias:

http://www.ampwares.com/ffg/pro_jr.html

[SatelliteAmps]

Fixed bias.

[brad347]

Huh? Pro Jr. Is simply plug'n'chug..

nope.

It is non-adjustable fixed bias, but it should have a bias adjust. IN fact, I have modified mine so that it does, and can be properly biased.

It's very warmly biased from the factory, at that, with most EL84s.

You could definitely burn up tubes in there if you don't at least check it.

[rjs6700]

I emailed Eurotubes.com for clarification (very quick response by the way).

They say the tubes are plug and play with no bias adjustment needed.

[brad347]

Sometimes people confuse "no bias adjustment needed" with "no bias adjustment possible with the amp in stock form."

This is one of those times.

[deeval]

I have had mine for 10 years and still never biased and have changed several tubes over the years,never burned or red plated,I,m sure it would be good to check bias,but they seem to work fine.:phones