Swapping the V1 pre amp valve- safe?

[moodyedge]

Can I just swap pre amp valves without anything changing, bias etc?

Ive got some spare SOVTEK 12ax7wb i got for my orange rocker 30 and never used, can I put one of these in the V1 to see if it improves the tone a little? Just wanted to make sure the mesa boogie pre amp valves that are in are not specific to the amp and/or do not differ in any way to the SOVTEK and if I can put one in myself and it be safe. Just the V2 valve Im talking about, not the full set.


I notice in the book it says "each 12ax7 contains two seperate triodes"
what does that mean?


Cheers

 

[mikey383]

Perfectly safe. Just make sure you turn the amp to standby before swapping. I've heard there is no harm in leaving the amp on, but I don't like the loud pop you get through the speakers. No biasing is necessary with preamp tubes.

12ax7s (or any 12a_7) are dual triode tubes, meaning there are 2 "amplifiers" in them. If you look at one, you can see there are 2 plates in each one. Each one of those plates serves a function. One half of V1 is the input stage in the Rectifier series, while the other half of the tube serves the clean channel. One half of the tube can be bad, and the tube will still "work" in some positions.

 

[MusicManJP6]

Perfectly safe. Just make sure you turn the amp to standby before swapping. I've heard there is no harm in leaving the amp on, but I don't like the loud pop you get through the speakers. No biasing is necessary with preamp tubes.

12ax7s (or any 12a_7) are dual triode tubes, meaning there are 2 "amplifiers" in them. If you look at one, you can see there are 2 plates in each one. Each one of those plates serves a function. One half of V1 is the input stage in the Rectifier series, while the other half of the tube serves the clean channel. One half of the tube can be bad, and the tube will still "work" in some positions.

Good answer(s)!

 

[moodyedge]

kool, you know your stuff....I shall try it later.

 

[jimsz]

Here are the various preamp tubes you can swap around giving you variations of gain. For example, I put a 12AT7's in the V6 position which sort of "tames" the high gain output of my DC-3 amp. Some will put a 5751 tube in the V2 (lead) position to "tame" the high gain of the lead channel.

12AX7 / 12AX7A / ECC83 / 7025 / CV4004 = 100% Gain Factor
5751 = 70% Gain Factor
12AT7 / ECC81 / CV4014 = 60% Gain Factor
12AY7 / 6072A = 44% Gain Factor
12AU7 / 12AU7A / 5963 = 20% Gain Factor

 

[moodyedge]

I swapped that valve and when i went to the clean channel (pushed) it made a horrid buzzy kinda muffled noise i i switched it off and put the mesa valve back in.,.,.,..strange

 

[jimsz]

I swapped that valve and when i went to the clean channel (pushed) it made a horrid buzzy kinda muffled noise i i switched it off and put the mesa valve back in.,.,.,..strange

It is a high gain tube, so it's probably not the best position to put it into a clean channel.

 

[mikey383]

I swapped that valve and when i went to the clean channel (pushed) it made a horrid buzzy kinda muffled noise i i switched it off and put the mesa valve back in.,.,.,..strange

It is a high gain tube, so it's probably not the best position to put it into a clean channel.

They're all high gain tubes in a Rectifier.

Sounds like you encountered one of those tubes that I was speaking of earlier, where half of it works and half doesn't.