AD30VT Tube

[marnold]

The Fret's third birthday reminded me that I've had my AD30VT for about three years too. That's how I came across this site in the first place. This may seem like a dumb question, but I've never owned a tube amp before. How would I know if the AD30VT's tube had died? I assume that with a solid state pre and post amp, the amp would continue to function relatively as normal. I don't think you can actually see the tube through any of the vents to see if it is still glowing. It's not like I beat on my amp or that it's really moved anywhere, but I don't know what the life expectancy of these tubes is supposed to be.

[tunghaichuan]

I was able to find the schematic online:

http://www.westebbe.com/Vox/AD15_30Servicemanual.pdf

It doesn't look like the tube's anodes are operating at very high voltage (15-30v if I'm reading the schematic right. The tube is operating at starved plate voltages and is there to add some distortion.

The limiting factor is the filament voltages. The closer the voltage is to 6.3v (or 12.6v depending on how the tube is wired) the longer the tube will last. A 12AX7 tube operating at 6.3v will last decades if the plate voltages are low enough (< 250v or so).

If the amp sounds the same as it always has, I wouldn't worry about replacing the tube. If the distortion gets kind of weak, or the sound changes a lot, then you may look into getting a replacement.

tung



The Fret's third birthday reminded me that I've had my AD30VT for about three years too. That's how I came across this site in the first place. This may seem like a dumb question, but I've never owned a tube amp before. How would I know if the AD30VT's tube had died? I assume that with a solid state pre and post amp, the amp would continue to function relatively as normal. I don't think you can actually see the tube through any of the vents to see if it is still glowing. It's not like I beat on my amp or that it's really moved anywhere, but I don't know what the life expectancy of these tubes is supposed to be.

[duhvoodooman]

+1 on what Tung said.... :AOK:

[tunghaichuan]

Forgot to add:

I don't know much about your amp, having never seen or played one but if I had to guess, I'd guess that the tube in your amp is of Chinese origin. Chinese tubes can be kind of hit and miss. As I stated earlier, you may want to listen for tell-tale signs that the tube is going.

The strange thing about starved plate voltage circuits is that some tubes work in them, and some don't. I remember experimenting with tubes in a BK Butler/Tube Works Tube Driver back in the 90s. Russian tubes would not work in that device. Chinese tubes worked and sounded great. I remember calling Tube Works (they were located in Denver back then) and asking about this and they confirmed that the current crop of Russian 12AX7 did not function well in their starved plate devices. FWIW.

tung

[tot_Ou_tard]

The thing about the tubes in Valvetronix amps is that they have a trim adjustment that is set at the factory to get the right input level into the AD converter which follows it.

You can adjust this yourself on Valvetronix amps etc with an LCD display: Blue series, Tonelabs but NOT the AD cheesegraters.

Well, you probably can still adjust them, but the ones with an LCD display allow you to put them into tube trim mode. Then you can use a jeweler's screwdriver to adjust the trim & the display will tell you when you've got it right.

I don't believe the type of tube matters all that much, but the trim does if you want to get the maximum amount of precision from the AD converter without clipping.

I'd stick with the tube that you have.

My Tonelab has a Groove Tube Mullard 5751 in it that I adjusted as above, but my AD30VT has the stock tube.

[tunghaichuan]

My Tonelab has a Groove Tube Mullard 5751 in it that I adjusted as above, but my AD30VT has the stock tube.

Just out of curiosity, what tube comes stock with the AD30VT?

tung

[just strum]

I recall reading an article about replacing the tube and/or something in the preamp. If I can locate it, I'll post. Has anyone gone on the valvetronix forum to see what they might be able to provide?

[tot_Ou_tard]

Just out of curiosity, what tube comes stock with the AD30VT?

tung
My recollection is that it is an Electro-Harmonix.

[duhvoodooman]

Tung:

Mine came with an Electro-Harmonix 12AX7EH. I put in a GT 12AX7-M Mullard Reissue, but damned if I could hear any difference.

Marnold:

My advice is, unless you are dissatisfied with the tone or perceive a definite change in the sound, leave well enough alone. BTW, the tube is also a big PITA to change....

[tunghaichuan]

Tung:

Mine came with an Electro-Harmonix 12AX7EH. I put in a GT 12AX7-M Mullard Reissue, but damned if I could hear any difference.



That is probably because running the tube at low voltages puts it outside linear operating region. The good news is that any tube will do (if it works). You can use a "hole filler" with no ill effects.



Marnold:

My advice is, unless you are dissatisfied with the tone or perceive a definite change in the sound, leave well enough alone. BTW, the tube is also a big PITA to change....

Good advice, I hadn't considered that.

tung

[ShortBuSX]

...I've had my AD30VT for about three years too. ....This may seem like a dumb question, but I've never owned a tube amp before. How would I know if the AD30VT's tube had died?
It's not like I beat on my amp or that it's really moved anywhere, but I don't know what the life expectancy of these tubes is supposed to be.

If youve had the amp 3 years, celebrate, do yourself and that amp a favor and replace that single solo lonesome tube...its dirt cheap...buy 2 of em...itll cost you $20 and you both will be happier!
Buy a JJ's tube and buy an EH tube...you likely like one over the other a lil more, and then youll have a good back up.

If youre able to tap on the tube, with like your finger nail or a pencil erasure, if its bad youll hear it through the speaker...of course itll have to be on though, and youll certainly have to remove the back, but then youll also see how it sounds as an open back.

You will notice a difference with a new tube...and its cheaper than a new speaker.

[marnold]

My advice is, unless you are dissatisfied with the tone or perceive a definite change in the sound, leave well enough alone. BTW, the tube is also a big PITA to change....
I had heard that about the tube change as well. Recently I thought I had noticed slightly more overdrive (as in what I thought was pristinely clean now has an ever-so-slight bit of dirt). That may be due to the fact that now that I'm in the basement I can turn the amp up far louder than I could in my tiny office on the main floor.

[tot_Ou_tard]

I had heard that about the tube change as well. Recently I thought I had noticed slightly more overdrive (as in what I thought was pristinely clean now has an ever-so-slight bit of dirt). That may be due to the fact that now that I'm in the basement I can turn the amp up far louder than I could in my tiny office on the main floor.
Rawking in the church basement?

Right-on Rev!

[marnold]

Rawking in the church basement?

Right-on Rev!
Well, parsonage basement, but yeah :)