Billy Zoom's Jet Set

Tube question


Just replaced the el84 tubes in my main amp, a Vox ac10c1

The amp started sounding like crap. The power tubes were microphonic.... made some interesting sounds all on their own.

Replaced them with a pair of Mulllard el84s. The amp sounds very good now. My question is... should I replace the preamp and inverter tubes at this time? I gig often and crank this little amp up most of the time. How long do pre-amp tubes last in a little 10watt beast?


Good preamp tubes can last decades. Many (if not most) vintage amps that still work have originals in them. Power tubes - especially EL84s - are driven hard - in the Vox designs. They might want to get swapped from time to time. New production usually way earlier than old ones.


I have observed preamp tubes getting microphonic fast enough -- still work ok tho. True enough about 6BQ5 aka EL 84 original Vox designs being run pretty hard


Agree with above. If the amp sounds good leave the preamps alone.

Out of curiosity, are the Mullards old British tubes or new production?


New “Russian” made


Good tubes...if used continuously...should last at least 50 years. Never replace tubes that are working fine because there's no reason to, and the replacements probably won't be as good. Just because tubes unplug doesn't mean you have to keep fiddling with them. Get some good NOS tubes, and then leave them alone.


New “Russian” made

– Hipbone

If you’re interested, I can send you a pair of old stock European tubes. A chance to compare the new Mullards with some old Amperex/Telefunken tubes.


If you’re interested, I can send you a pair of old stock European tubes. A chance to compare the new Mullards with some old Amperex/Telefunken tubes.

– Powdog



There are two sides to this story depending upon how the amp has been used. If you play that AC10 clean at relatively low levels then I go with Billy.

If you drive it to insanely high distortion levels on a daily basis then you'll wear out the tubes......first the EL84 power tubes then later the 12AX7 first preamp then the others so then I go with DCBM.


I do run the amp hard.... I gig often.... it is loud for 10watts, there are times I won’t mike it for small outdoor shows.
So it doesn’t surprise me the tubes called it a day.


OK, if you push the amp hard, then replace the output tubes every twenty years, and replace the overdrive 12AX7 every 10 years. But modern tubes get worse every year. On my touring amps, I replace filter caps and output tubes every twenty years, just to be safe.


And, if you have to use new tubes, get the cheapest OEM type Sovteks...they're better than the Mullard, Tung-Sol, Genelex, etc which are also made by Sovtek.


Maybe BZ, but I've tried the standard Sovtek 5881 tubes in my Carr Rambler and got nowhere. Talked to Steve Carr who suggested the TAD matched 6L6 Sovteks and that really was what I wanted to hear.

I guess his amps are set up with these tubes in mind?


Tube tone is totally subjective,what sounds good to me,may not sound so good to you.One factor that is certain is durability.Old stock tubes,even used old stock will out last new production by years,if not decades.I've got an old Ampeg Gemini II from the 60's,I bought it used in '71 with the original Bugle boy preamp tubes.I used it hard in the 70's and 80's.Put a bass speaker in it and loaned to a friend who used it for piano thru the 90's.My son has been using it for bass for about 10 years.The Bugle boys are still going strong.I have been amassing old stock tubes since the early 80's and have a couple hundred preamp tubes and have no reason to change the tubes in that amp.If you can find old stock tubes that were used in radio and stereo applications they will likely be like new,as they are not driven hard in these units.Power tubes are a different story as they are driven harder in guitar amps,but old stock is still more durable.I had a pair of Genelex KT66's I got at a ham fest for $50.Put them in an amp I built for my son who gigged with the amp for over 5 years.He wanted to change them just because it was his main amp and wanted to be sure it wouldnt shit the bed on a gig.I sold them to an audiophile for 350 bucks,thats what he offered after trying them out,not what I was asking for them.Old stock tubes rule,I wont use anything but.


In my opinion, the differences in tone you can experience from the entire sweep of tubes (from modern to vintage to American to foreign) is very little compared to the tone variations you can get from simple mods to your amp. Basically swapping out the value of a 10 cent capacitor will give you worlds of difference compared to spending hundreds on vintage NOS tubes. That being said I DO value durability and reliability with tubes and there is something to be said for the quality of NOS American tubes vs. modern stuff coming out of China. But if you are looking for the best bang for your buck in terms of reliability and ability to handle high plate voltages and current....check out Russian military EL84 tubes....sometimes labeled "EL84M" or "6P14P" tubes. They are great and they can handle the really hot bias that Fender Blues Junior and Pro Junior type amps are set at.

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