![ab763 bandmaster ab763 bandmaster](https://images.reverb.com/image/upload/s--MrTVyeMK--/f_auto,t_supersize/v1542747431/e2qoljywrhnbzglxw566.jpg)
The more clean headroom you need, and the more often you play, the more often you need to replace them. There is no single, correct answer how often you should replace them. Some people change power tubes every year, others keep them for 40 years. You need to adjust bias of these tubes when changing them or the rectifier tube. These tubes mean a lot for tone and headroom. If you want to lower the clean headroom you may use 12ax7 in this position. If you seek maximum clean headroom make sure you have a new and fresh tube here. It plays an important role for the clean headroom. Phase inverter tube. This tube is used by both channels and a part of the power amp section of the amp. Never using the tremolo or just the normal channel? Pull this tube. You may very well use cheap and old tubes in this position. It is needed to make the tremolo work and has no effect on the tone of the amp. This tube is only in use in the vibrato channel. Never using the vibrato channel? Pull this tube. You will then hit the V4 tube much softer and the signal comes cleaner out of the preamp stages.
![ab763 bandmaster ab763 bandmaster](http://www.ggjaguar.com/68bmast.jpg)
If you want less preamp gain out of this tube, insert the V1 tube and use 12au7 or 12at7 in the V2 slot in stead of the standard 12ax7. If you want more preamp gain out of this tube, you should pull V1 to achieve a hotter signal out of the V2 preamp tube. We recommend to use high quality tubes here. Old tubes may result in lacking lows or highs. If you have hum or noise issues, the tone will suffer directly.
![ab763 bandmaster ab763 bandmaster](https://images.reverb.com/image/upload/s--2W0QLMX---/f_auto,t_large/v1602273446/maf3ircvpkeksvpkowag.jpg)
As the 2’nd gain stage in the preamp section this tube is just as important for the tone as the V2 preamp tube. This tube is only in use in the vibrato channel and for two different purposes. Reverb recovery and 2’nd gain stage for the vibrato channel. What is reverb after all if not a lot of noise? If you for some peculiar reason own a vintage Fender reverb-amp and play strange music without reverb (!), we recommend you to pull this tube. It is not important to have a high quality, fresh and totally noise-free tube in this position. Both channels will work fine without this tube (just without reverb if you’re using the vibrato channel). It runs a strong current into the reverb tank. This tube is only in use in the vibrato channel, but even so, it means nothing for the dry guitar tone of the vibrato channel or the normal channel. Hence, you will achieve preamp distortion earlier. The stronger tube you have the more you will push the next preamp gain stage of the vibrato channel. If you are like us and use only the vibrato channel, you should pull the V1 tube (see for more info). It operates identically to the V1 tube, just for the vibrato channel. If you have hum or microphonic issues, this will be blended into the amp tone and become a problem. It is important that the V1 tube is a high quality tube with little noise. The headroom is determined only by the phase inverter, power tubes and rectifier tube. The clean headroom is not affected by the V1 tube. If you play the amp at maximum volume, you’ll achieve more distortion and screaming tones with a strong tube that has a high voltage gain factor. The stronger tube you have the more you will push the power amp section. A weak, old and worn out V1 tube will give you a dull tone with potential lacking lows or highs and you might have to set the volume knob relatively high to achieve a certain volume. This tube is very important for the tone and how sensitive the volume knob is. This tube amplifies the guitar signal immediately after it enters the jack input of the amp’s normal channel. We start from right to left, amp seen from behind:
#Ab763 bandmaster pro#
Some of these amps are the Deluxe Reverb, Vibrolux Reverb, Pro Reverb, Super Reverb, Twin Reverb, Vibroverb, Bandmaster Reverb. Let’s explain what the different tubes do in the common AB763 blackface & silverface amps with two channels, reverb and tremolo.