#1
so i was looking for a mod to smooth out the overly dog bark like breakup on my palomino (crate) v16. it was suggested to me that i could use a 12at7 for the phase inverter preamp tube to smooth the transition from clean to crunch to saturation. well i popped one in and it did the trick wonderfully and without affecting the apparant volume or usable distortion enough for me to mind at all. the only thing is that i noticed that the glow from the power tubes changed and it seems like they are a bit dimmer but theres a bluish color coming out. my understanding is that that color instead of reddish oarnge would indicate a much higher heat level inside the power tubes but as i understand the 12ax7/ecc83 should be directly compatible with the12at7/ecc81 and operate basically the same but with different tonal characteristics. do any of you tube afficionados know if this effect on the power tubes is normal and also are the two preamp tube types 100 percent compatible? the amp didnt seem to get any hotter than normal and its working fine but any input would be valuable. oh BTW the power tubes are medium sovtek el84 s and theyre less than a month old.
#2
First off take the 12AT7 out of your phase inverter. Whatever the amp called for originally you want to keep there, which should be a 12AX7. Try using the AT7 in one of the gain stages. It will probably sound best in the second stage, but experiment to see what you like best.
#3
Quote by Matt420740
First off take the 12AT7 out of your phase inverter. Whatever the amp called for originally you want to keep there, which should be a 12AX7. Try using the AT7 in one of the gain stages. It will probably sound best in the second stage, but experiment to see what you like best.

will it hurt it to leave it in. i really like the sound im getting. i wouldnt even mind going through power tubes twice as fast if i could keep getting the sound im getting out of it now. i just dont want to fry the amp itself or turn it into a once a week tube eating monster but i would really like to leave it like it is and keep getting the tone its giving me.
#4
That's funny, In my 1977 Ampeg VT-40, a couple of the (12(?) in total) tubes glow blue. Some glow red.
Just realized something, If all my tubes all blew at once, it would cost me around 200 dollars to replace them all. My guess is that is going to happen soon, because the tubes have not been changed since 1977...
..I was watching my death.
#5
Quote by MichaelOfCanton
will it hurt it to leave it in. i really like the sound im getting. i wouldnt even mind going through power tubes twice as fast if i could keep getting the sound im getting out of it now. i just dont want to fry the amp itself or turn it into a once a week tube eating monster but i would really like to leave it like it is and keep getting the tone its giving me.


It probably won't really hurt the amp, but the 12AX and AT7 are a bit different.

12AX7
Has a plate current of 1.2 milliamps

12AT7
Has a plate current of 10.0 milliamps, ten times that of the 12AX7. It also has much higher transconductance .

That won't really hurt anything, but it will make your power section react differently, and I'd feel better with a 12AX7 in there if it was my amp. There are several variants of the 12AX7 that have lower gain.

I'd keep the recommended tube in the P.I. , and try swapping the gain stages to tailor your sound. Maybe a 12AU7 in the input stage, or second stage. I don't like the sound of the 12AT in any of the gain stages though.
Last edited by Matt420740 at Nov 18, 2009,
#6
Blue glow in the power tubes is quite common and not a problem.
Chances are it was there before and you just started noticing it.
Either way, it's just the residual gas in the tube ionizing. Completely meaningless.
Meadows
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#7
sweet !! ! !! ! ! thanks guys. someoneyouknew, after you mentioned it i realized that my last tube swap for the power section was only a few uses ago and i never really looked lovingly into my cooling vent at the tube glow since the swap. its wiered though ive never seen blue and ive been through another set of sovteks and never noticed a difference other than the sovteks show less glow than the groove tubes that came with it originally. guess you learn something new every day. thank you much gentlemen for easing my valve loving soul in letting me know that the new sweetness i have found is something i can keep. im about to go spread the word to the palomino owners guild. just imagine the collective joy...
#8
BTW, 12AT7s sound like total crap if you run them in the preamp and distort that stage (too much grid current). Sound great as a phase inverter though, shouldn't be any problems with the sub.

Try a 12AV7 in the phase inverter, it's my favorite there...
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