Noisey tubes

[pbman1953]

Last night while using my bass amp a Fender Super Twin being used as a bass bead. By chance, I hit the input jack an there was a crackle around the jack. Then I tapped the face of the amp and he the static still was there. Two tubes were noisy by a soft tap. The V2 & 3, a RCA 12AU7 and a RCA 7025, both are original tubes to the amp. I had a Tung sol 12ax7 which I put in the 7025's spot and all I had for the AU spot, for a lower gain,  was an AT -GE tube.


Can I keep the GE in there or should I get another AU?


Thanks

[sluckey]

I like to use the correct tube.

[tubeswell]

Last night while using my bass amp a Fender Super Twin being used as a bass bead. By chance, I hit the input jack an there was a crackle around the jack. Then I tapped the face of the amp and he the static still was there. Two tubes were noisy by a soft tap…

Are you sure it’s the tubes and not a loosely touching input Jack tip switch contact? If you’re sure it’s not the Jack, it could be the tubes. But check the Jack tip switch first (by closing the tip switch contact firmly with your finger) to see if the ‘crackle’ stops.

[pbman1953]

Yes, I' m ruling out the jack because I spent some time to swap out tubes, then tap tap. Plus with out an installed jack the noise was evident by tapping the face plate near the jack. The pre-amp tubes are right behind the jack


At this point the crackle is gone. Totally quiet




Any suggestions for a 12au7?

[sluckey]

I have a bunch of NOS 6189, which is a ruggedized version of 12AU7 made for the military. Electrically identical to 12AU7, but more shock/vibration resistant, which means less microphonic.

I could sell you some if interested. One sleeve of 5 tubes for $50 plus $10 for USPS flat rate shipping. The small flat rate box can hold two sleeves (10 tubes) so shipping would still be $10.

Price for individual tubes is $15 each plus $10 flat rate shipping.

Send me a PM if interested.

[scstill]

I have a bunch of NOS 6189, which is a ruggedized version of 12AU7 made for the military. Electrically identical to 12AU7, but more shock/vibration resistant, which means less microphonic.

The 12ax7 comes in a long plate and short plate version. I read where the short plate is less susceptible to vibrations/microphonics. Claimed better for guitar amps. True?
Does the 12au7 have similar short and long plate versions?

At times I have experimented with a 12au7 replacement for the 5E1 12ax7 to get a lower gain amp.
Had heard that it is not a problem, do you see any risk?

[Esquirefreak]

No risk, but you'll get alot less of everything. Ans my experience is that 12au7/ECC82 tend to sound rather bright when used as a gain stage. I'd suggest trying a 5751. The GE "5 stars" 5751 is a really good tube, IMO.

/Max

[scstill]

I forgot to mention that I built an amp that used 12au7 as output tube (single ended parallel plate)
two stage preamp using 12ay7, 6CA4 (ez81) rectifier.  Circuit based on Rob's "deluxe micro" although this one is point to point. Runs through a vintage 6x9 ceramic Jensen. Housed in an old Silvertone tweed radio cabinet. Vol, Master and Tone controls. It is surprisingly loud in the house, much bigger thru a 12. Great tone, low noise.

Unfortunately my website is down for a few more weeks, so can't share the build, but it was a lot of fun.