Toob Time

[kbp810]

Came across a couple of used RCA 7025's today that seem to have plenty of life left in them and decided to put them in my Ampeg J-20 Reissue

 

I put them in V1 and V2, left the stock Sovtek in V3, and am quite impressed with new tone! It really tightened up the bass (though I recently also replaced the rectifier with a modern jj gz34 which also seemed to help out there), brought some extra life into the mid's, and overall added some really nice warmth and creamy crunch to the tone! To further compliment them I just ordered a matched pair of NOS Jan Phillips 6v6's, can't wait to hear how it all comes together

 

Not that the tone didn't already sound great on this amp; I just always feel the need to continually tinker with things along the quest for the holy grail of tone...

[slider313]

That amp runs 6V6 pretty hot. Do you have a bias meter? Be sure to check your bias as to not cook a set of NOS 6V6's.

[212Mavguy]

That amp runs 6V6 pretty hot. Do you have a bias meter? Be sure to check your bias as to not cook a set of NOS 6V6's.

 

+1, definitely!

[kbp810]

+1, definitely!

 

Yep on the bias meter... also considering an adjustable bias mod I saw in another forum (I think I recall seeing your name amongst that thread slider)

 

Last thing I would want to do is fry tubes (or worse) - especially NOS's

[slider313]

I was actually running mine with a pair of the new Tung Sol 5881's. Yes, that amp "likes" the RCA 12ax7a/7025 tube. I've had good luck with a strong 12at7 in the phase inverter position also. It gives the amp a little more clean headroom and chime.

[kbp810]

I was actually running mine with a pair of the new Tung Sol 5881's. Yes, that amp "likes" the RCA 12ax7a/7025 tube. I've had good luck with a strong 12at7 in the phase inverter position also. It gives the amp a little more clean headroom and chime.

 

Sorry to bump my own thread, but my wife got me a Zoom H2 recorder for V-Day so thought I'd share a clip of the re-tubing efforts (random bits and pieces)

 

Slider, I ended up following your tip above and tried a 12at7 (NOS Mullard) in the phase inverter position - that was excellent advice, I think it really brought it all together

 

I'll go ahead and apologize in advance for the sloppy playing - also wanted to note, there are a few times when it seems to sort of flubber out - this is from the mic and not the amp, haven't quite found the right balance of distance and sensitivity settings when recording yet ...

 

http://dl.dropbox.com/u/3272872/STE-004.mp3

[212Mavguy]

I listened to your clip, and noted a very nice full tone. Way to go! You have recieved some great advice too!

 

It is fun as can be to collect vintage tubes, roll them and listen to their tonal characteristics. You can voice an amp for a particular guitar or speaker cab for instance. The ability to adjust the bias of the output section has a huuuuuge effect on the tone from the same set of tubes, you can get quite a wide variety of tones with adjustments from bias pot(s). The topic of how to bias correctly is quite a can of worms, there are a lot of philosophies espoused on the net.

 

I like Chris Siegmund's way...use your ears. Now of course that means staying within reasonable limits of where the tubes need to operate with regard to their idle current. Too hot and you will see red hot plates, shorter operating life, and muddy distortion where tones ought to be clean, too cold and you will get thin and nasty, but starting from a cold setting and bumping it up a couple millivolts/milliamps at a time you will find at least one sweet spot zone that satisfies you within that tube's operating limits. In 6v6, new production or old stock, there is a lot of variety to choose from, and most are sorta affordable.

 

And as long as they draw similar plate current in your amp, you can mix brands of a similar tube type and obtain the tonal characteristics from each type blended together much in the same way that some players mix different speakers in the same cabinet. I know these words might cause disagreement in some of the more technically and theroretically minded ones here, but my repeated experience has been positive in that regard with no amp failures at all, and I have several very nice amps as well as a collection of a few hundred vintage tubes to roll in them. The same tube(s) can sound slightly different in different amps, preamp or power section types. Hope this helps.

 

Peace.