12ax7 tubes in Hybrid Bass Amps

[NYCbassist]

Has anyone experimented with different 12ax7's in Their Hybrid. I would like to get more Pre-Gain out of my BX500 Carvin. I thought maybe putting in a Groove Tubes GT-12AX7-R2 Preamp Tube. Or I have access to some USA made Tubes. Sovtec has tubes that specifically rate the gain amounts.

I definitely notice a nice tone difference with the BX500 in Tube mode Vs. Solid state. I just want more of it...

[Passinwind]

The BX500 doesn't use the tube in a gain stage, so tube rolling won't do what you want.

[monti2889]

I tried a few tubes in my hybrid, when I had it.
I preferred the Electro-harmonics 12ax7. I believe it was a Russian made tube, but it produced more mid range when compared to the groove tubes 12ax7 (made in china), which seemed to be a little warmer.

I've since gone to solid state "modelling" heads, as I like the versatility and reliability of them. verses worrying if I'm going to blow a tube in the middle of the show.

[NYCbassist]

Originally Posted by monti2889

I tried a few tubes in my hybrid, when I had it.
I preferred the Electro-harmonics 12ax7. I believe it was a Russian made tube, but it produced more mid range when compared to the groove tubes 12ax7 (made in china), which seemed to be a little warmer.

I've since gone to solid state "modelling" heads, as I like the versatility and reliability of them. verses worrying if I'm going to blow a tube in the middle of the show.

I'm thinking that the bypass switch would have me covered if my Tube blew But I was planning on using a Backup just in case.

[Calaverasgrande]

Preamp tubes very rarely "blow".
More commonly they get noisier and weaker until they gradually fade away.
Well made preamp tubes would probably outlast your love affair with a particular amp.
my favorite tubes in order.
RCA 12ax7a short black plate (vintage, expensive)
JJ-Tesla 12ax7a, the older ones especially have a raw muscley kind of response.
Sylvania 12ax7a JAN NOS. I'm not positive these are JAN (military spec) but they were sold as that and sound great.
Groove Tubes 12ax7 HG. Standard Chinese tube, but binned for noise and presumably tone. Very solid and clean, not as shrill as some Sino-tubes.

[bongomania]

Originally Posted by Passinwind

The BX500 doesn't use the tube in a gain stage, so tube rolling won't do what you want.

Also, 12AX7 is already the "high gain" end of the 12A*7 range, so even if you found a 12AX7 that was claimed to be higher gain than other 12AX7's, it will not be a huge difference. Not like the difference between X and the lower-gain tubes like 12AU7, 12AY7, etc.

[Jim C]

Many hybrids don't respond at all to tube changes (SWR SM400)
Mesa Walkabout is somewhat sensitive to tube swaps
Generally, I find either a long plate Telefunken or Amperex as the best choice for my tonal goals

[NYCbassist]

I replaced the GT 12ax7 C with a New Old Stock MIA Penta 12AX7A Today. It didn't help me get any extra Growl with my New Ric 4003. After some research I determined That it's because of where the tube "resides" within the circuit. Well at least I now Have 2 Backup Tubes.
For the record, I definitely hear a slight difference between Tube/SS Mode on the BX500.
Passive Basses just need some "help" overdriving BX500's. I will look into the best option and get something for that.

[bongomania]

I'm sure it's true that there is a difference in sound between the two modes--but the difference is not the gain of the tube in that circuit.

There are a lot of boost pedals, clean and dirty, that will get you the drive you want.