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Post subject: some very basic tube questions...
Posted: Fri Jul 11, 2014 2:48 pm
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I've been playing tube amps for almost 50 years, but just recently started actually thinking about the things (the tubes that is, not the amps), anyways I have some old and new tube amps and some very basic tube questions: I have a bunch of 12AX7, ECC83, and 7025 tubes of different ages in different amps - I've heard these are all interchangeable - are any 'better' than any others? - I'm looking for a very clear - rich sound - lots of shimmer and bass without distortion. I've also heard that old tubes can be very good.. or bad. I have a '60's Gibson Hawk that has the original 3 Lowery 12AX7 tubes - I've tried them now in my '65 RI and '68 Custom Deluxe Reverb and they sound great but a little microphonic. Is it okay to mix preamp tubes of different types and ages? My Silverface Reverb Unit has 3 7025's, can I try these in different amps without messing up the way they sound in the reverb unit? I figure that not returning them in the same order would change the sound of the unit...? Do the preamp tubes in the SuperSonic 112's burn channel take a special beating 'cause of the distortion? If I'm looking for a clean, rich sound - doesn't have to be especially loud - what might a good choice for the Deluxes' V1 or V2 tubes? If I were to get new power tubes (6BQ5) for my two old Gibson Hawks, would I need to worry about the amp bias? I love bright, splashy reverb - any ideas for good tubes? Why does the Fender Reverb Unit (at least the Silverface version) use 7025's and the reverb amps use the 12AT7? Whew...OK Thanx!!


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Post subject: Re: some very basic tube questions...
Posted: Fri Jul 11, 2014 4:07 pm
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I don't claim to be a tube or tube amp expert. But I'll try to answer some of your questions.
The 12AX7 vacuum tube is a high-gain dual triode amplifier. The "12AX7" designation is an American civilian (IEEE) designator for this tube, while 7025 is a US Military designator and ECC83 is the European designator for the same design dual triode tube. 12AT7 and 12AY7 are similar dual triode tubes but have lower gain specs. My understanding is that they can replace the 12AX7 in almost all instances, but that you will lose gain that is usually intended by the designer of the circuit.

Most people run their tubes until one dies and just replace the dead one, continuing with the other old ones until the next one dies, replacing only the dead one. Other's will replace all preamp tubes when one preamp tube dies and likewise do with the power tubes.

I do not like to keep old tubes around because I don't organize or keep records on them as to what amp it came out of and how many hours are on it, yadda, yadda. I fear putting an old tube into a perfectly good amp and burning up something else in the circuit. And if one of my power tubes die, I replace them all.

The circuit design in the Burn channel of the Super Sonic, or a Marshall, or Mesa Boogie, etc. is designed so that the audio signal on the control grid (input) of a preamp tube is so large that it completely cuts off the peaks of the output signal of the tube. The larger the input signal the more the output signal is clipped and the more distorted it sounds. Even on a clean amp like the Twin or Deluxe Reverb, you can crank the volume enough to make the output tubes clip causing a pleasing distortion sound.

I suggest replacing tubes with the ones the manufacturer designed for that circuit. It's OK to replace 12AX7 with ECC83 or 7025. I wouldn't use 12AY7's etc. You'll change the sound.

As for power tubes, basically the same advice. Replace with the same thing the manufacturer designed the circuit to use. And yes, the bias should be properly set for the new tubes.

There are mods so that an amp that uses 6L6's (American amps) can take EL34's (Marshalls, etc.). I don't recommend such mods, especially on classic old amps like it sounds like you may have. If you want a British sound, buy a British amp. (or buy a Mustang amp!)

By the way, I've been playing since 1963.

Of course, you will find a few on here who disagree with me. Opinions are like bellybuttons...everybody's got one :o)


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Post subject: Re: some very basic tube questions...
Posted: Fri Jul 11, 2014 4:26 pm
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By the way, check this out if you want to experiment without doing real mods to your amps:

http://www.yellowjacketstc.com

They manufacture tube adaptors for your power tubes. I have a pair for 6L6 tubes like most Fender amps use. You remove the 6L6's and plug in these yellow tube sockets that then take EL84 power tubes. I tried them in TRRI and didn't like the sound, but it turned my 85 watt TRRI into a 18 watt beast! I removed all four 6L6's and plugged two Yellowjackets into the outside tube sockets. I could have left the two inside 6L6's in and maybe liked the sound, but didn't bother. I just removed the Yellowjackets and re-inserted the original tubes and got that beautiful Fender Twin sound back.


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Post subject: Re: some very basic tube questions...
Posted: Fri Jul 11, 2014 10:25 pm
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My 2 cents.
I have Tons of ax7's mostly vintage and have tried/own most current production.
The very best tubes of these types were made in the 50's, in terms of strong output, longevity, and to a high degree...microphonics.
Starting in the 60's transistors made tube manufacturers believe in their mortality, and quality spiraled down from there.
When you find non microphonic, strong tube from this Golden era, its a keeper.

I don't for the most part buy the concept of "sounds" from one brand of tube over another.
Its all about maintaining spec output and reliability.


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