Jump to content
Gibson Brands Forums

Changing tubes in a Vox AC4TV


Twiz

Recommended Posts

Hey gang, one of the gifts Santa brought me was a gift card from my favorite Pgh music store. I decided to get some new Electro Harmonix tubes for my AC4TV. I've done some research on changing the tubes out, and it looks really easy. I know to be extra careful so I don't shock/kill myself. I was just wondering if it will need biased. I couldn't find anything on the Vox website stating that biasing would need done, but I figured I'd ask some of you guys since I know you have more experience with this stuff. Thanks for any info.

 

DSC_7987_100dpi.jpg

Link to comment
Share on other sites

I would say not as it is most likely a Class A....

 

Actually this brings up a good topic... I think overall people make a much bigger deal out of biasing than needs be. Unless something has drastically changed in the amp ( like a blown resistor/cap or diode in the bias circuit) just replacing the tubes is generally not a problem.

 

Most tubes of the same types ( regardless of brand) have the same approximate bias range. The overall idea of Biasing is to put the tubes in a Class A/B amplifier in an optimal idle state to prolong tube life and compensate between the differences between the 2 or 4 power tubes overall. If the amp only has one trim pot then the bias is gonna be set at a " compensational" setting which is kind of inaccurate at best anyway.

 

That doesn't mean they will produce the optimal tone ( to your ears) at that bias voltage. Most bias adjustment pots won't take the tubes out of a "Safe operational" range regardless of where you set it. The more you adjust it one way the more gain and earlier power tube distortion you will get which will reduce the tube life faster depending on how much you play. Turn it the other way and the tube will stay cleaner and the tubes will last a bit longer.

 

I'm for tone so I just check that the bias adjustment does not take it out of a safe range ( this would be where you are burning up the plates) and use my ears to find the point where I think they sound the best. This method isn't for everyone but it's what I do...

 

 

Hopefully the tubes are pretty well matched to begin with. THe optimal solution would be to have an adjustable bias for each tube then you can compensate and match pretty much any set of tubes...

 

 

End of Rant....

 

 

Regards,

 

 

Andy

Link to comment
Share on other sites

I think that is a single ended single EL<mumble> 4, so I'd say it is of a fixed bias.

 

And I agree, the only time to adjust bias is usually the first time you work on an amp. They are set cold at the factory, tubes last longer that way. Other than that, once you bias an amp it usually needs it no more.

 

rct

Link to comment
Share on other sites

Thanks guys. It is a Class A, so I guess I don't have to do anything except put the new tubes in there...sweet. I appreciate the info. I'm just learning about amps and how they work now (I'm reading a book called 'Amps! The Other Half of Rock N' Roll' by Ritchie Fliegler). It was kind of confusing at first, but it's starting to make sense. Thanks again.

Link to comment
Share on other sites

That Vox AC4TV is a great amp. I love them so much, I have all of three combo versions, the AC4TV mini, AC4TV8 and the AC4TV10. Hmmm.....I just had a thought. Perhaps, I should do a youtube demo comparing all three? Of all the three, the AC4TV8 is no longer made and rumors has it the AC4TV mini is being discontinued as well. Very brief production on both of these amps, perhaps these two will become collectors?

Link to comment
Share on other sites

That Vox AC4TV is a great amp. I love them so much, I have all of three combo versions, the AC4TV mini, AC4TV8 and the AC4TV10. Hmmm.....I just had a thought. Perhaps, I should do a youtube demo comparing all three? Of all the three, the AC4TV8 is no longer made and rumors has it the AC4TV mini is being discontinued as well. Very brief production on both of these amps, perhaps these two will become collectors?

 

You should do one if you get a chance. Your demo vids are great.

 

Yea, I really like mine. I run a 4X10 cab with it sometimes. It sounds awesome.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...