Changing Vox AC30 Tubes

admin · Post by **admin** » Mon Jun 23, 2003 1:50 am

Don: I will be changing my Vox AC30 tubes in the near future. Do you have any recommendations as to what tubes I should use?

admin · Post by **admin** » Mon Jun 23, 2003 11:16 pm

Further to my question about replacing tubes, I found the following Tonequest article to be of interest.

admin · Post by **admin** » Tue Jun 24, 2003 5:49 am

Don: Is the ECC82(12AU7) tube used for the Vibrato Circuit?

ric480 · Post by **ric480** » Wed Jun 25, 2003 3:17 am

I've read that article before. The author (Mike K) is well known as a source for NOS tubes. His web site is http://www.kcanostubes.com and I've done business with him a few times.

Why are you changing your tubes, Peter. It may be that a change of power tubes only is necessary. Preamp and rectifier tubes (especially the old quality ones) can last a long long time. I still use (from time to time) 5 of the 6 original RCA preamp tubes (7025 aka 12AX7, 12AX7A, 12AT7) that came in my '74 Super Reverb. My experience is far from unique.

toneman · Post by **toneman** » Fri Jun 27, 2003 6:41 am

Peter; John maybe quite right on this. Usually with an AC-30 all that needs changed are the EL-84's.
I would recomend the Ei Elite's for EL-84's. The Ei factory use to be owned by Phillips which also owned M<ullard and several other tube manufacturer's. They seem to have alot of the same tooling/build as the old Mullard's did.
The Elite series features a beefier build and gold plated pins!
I've come across many old AC-30's that just needed new output tubes and maybe one or two preamp tubes. Rectifier's don't need replacing unless they stop working.
The ECC82(12AU7) is indeed for the VibraTrem circuit.
Since the EL-84's work the hardest in those amps, it's best to start by replacing those first. If your amp still sounds dull or lacks sparkle then replace the preamp's. You should be able to get years of use out of good preamp tubes.
Mark Sampson, when he ran Matchless, use to recomend replacing the EL-84's about once a year with amp useage of 10+ hours a week. he said that if the amp sounded dull or lacked the high end it use to have, then replace the EL-84's before doing anything else.

admin · Post by **admin** » Thu Jul 03, 2003 7:23 am

Don: I just put new Ei Elite EL-84s in my Vox AC30 and there is a very big difference. The sound is much fuller and the clarity and the high end has certainly returned. I will see if there is any change in them over the next couple of weeks.

admin · Post by **admin** » Sat Jul 05, 2003 4:10 am

On the basis of some research I have done on the "settling in" of new tubes, it would seem that approximately 24-72 hours of playing time is a rough estimate.

toneman · Post by **toneman** » Sat Jul 05, 2003 7:30 am

Peter; I think we sometimes forget that tube componets are totally assembled by hand and I'm sure each one is just a bit different for the next one even if the same person is building the plate structure. When you put in a set, each one will take a while to adjust to voltages and settle. Usually, it's been my experience that it a tube is still working right after about 20 hours that it will remain pretty stable. If tolerence/longevity is really critical I'll buy them already burned in for 24 hours and then matched. E-H/New Sensor calls this their "Platnium Match". costs a bit extra but have found it's money well spent.