simple science project

[212Mavguy]

Voicing the amps in my modest stable via tube and speaker swaps is a routine for me that I really enjoy. I was cruising around eBay and saw an adapter for putting a 6sn7 preamp tube into a 12ax7 socket. So I bought two of them. They arrived yesterday. I had two of those tubes lying around, one was a well used Tung Sol, the other was a NOS Sylvania. So I inserted them into their adapters and went to socket them in V1 and v2 of my Ceriatone HRM D-clone. The socket sides that the shields slip over were too tall for the pins to insert, I was stymied for about 30 seconds until I remembered a 5755 to 12ax7 adapter project that required a socket saver often used in tube testers. A socket saver looks like a plastic tube base with pins coming out the bottom and the same pattern as a socket on top. With this used as a spacer inside the amp's tube socket, I was golden, but I only had one of them. So I yanked out the long plate RCA/Wurlitzer organ tube in v1 and swapped in the 6sn7.

 

In this amp V1 is for the clean channel, V2 is cascaded, adds on after V1, then on through the circuit.

 

The gain knob operated as if the 6sn7 has about 60-70% of a strong 12ax7. The tone exhibited more of the fundamental, and there was no mush at pick attack at higher gain settings. I heard less of the pick attack and more of the note and harmonics just seeming to pop off the strings. Note definition along with sustain were wonderful. I did not have microphonic problems with either example of 6sn7, mainly because I had the tubes in something other than a combo amp. Overall there was a feeling of increased girth along with chime when compared to 12ax7 tones in the clean channel, and when switched over to the dirt, the tones were rich and round. There seemed to be more dynamic response in volume to pick attack than 12ax7's or other nine pin preamp tubes.

 

Then I went to swap the adapter into V2, the dirty channel tube. I wanted to hear what would happen when the 12ax7 smacked the 6sn7. All the things that made the amps of Howard Alexander Dumble gush their fountain of distinctive, signature tone seemed to be even more evident after the swap. The girth of the tones in the lead channel, already full, became even more so, there was no mush at the pick attack, just a sweet, smooth expression of what ever happened between the fingers and strings. Harmonics are abundant, and there is abundant, well defined, gorgeous crunch with sufficient gain. But what really set this situation apart was the single note stuff. I'm not skilled enough to do chordal jazz melodies or Chet Atkins style picking like so many of you HOC'er monster players can do. I'm lucky to struggle through simple improvised single note phrases using mostly down strokes on a 3mm stubby pick... But with that limited skill set this amp seemed to go like the proverbial fat lady at the opera, man, does the voice sound SO good! And thinking about the theory of it, it makes more sense to put a microphonic-prone tube later in the tone chain than V1.

 

I haven't done that swap into the PI yet, because on many Dumble clones the two sides of the driver tube are balanced in their output to the two sides of the power tubes' section by a small pot mounted right on the eyelet board, I'd have to remove the chassis to get it just right. I'm familiar with what the effect of PI tube swap will be, It will affect all tones of the amp with the response and tone color of that tube…like V1, except that a tube that is too microphonic for a V1 spot MIGHT work in a PI position and the overall effect on the tones of the amp is less affected from PI than V1.

 

Now that socket adapter and socket saver has me thinking of some of the other amps in the stable...

 

Anyway, the experience was both very positive and relatively inexpensive to try. Vintage old stock 6sn7's are fairly easy to find on eBay. Demand for those tube types is very slight and the tones from the two I've tried were worth the time and money to know about first hand. YMMV.

 

 

[FredZepp]

Interesting stuff. It's a great moment when a tube change makes a dramatic difference for the better.

Can't say that I've used a 6sn7 , but it sounds like ones you had laying around had some magic left in them , especially with a 12ax7 in front.

[212Mavguy]

Yes, and it's an eminently affordable way for a tube amp head owner to go from store bought copies to original and personal tones…why spend all the chasing time going after some one else's youtube or other muse? It was so easy to get the parts, and without the swap the tones are already delicious in this particular case. Old stock 12ax7's sound better than the new stuff to most ears, and the amp had them in it to start with.

[rockabilly69]

Good one Mav, I might have to try that trick in my Boogie!

[212Mavguy]

Many Boogies use a preamp shield/clamp over the whole row of 12ax7's, you can just leave it loose or remove it. Octal pre's can get pretty microphonic in combos…I'd do it with that Frenzel head of yours if you still have it.

[rockabilly69]

Many Boogies use a preamp shield/clamp over the whole row of 12ax7's, you can just leave it loose or remove it. Octal pre's can get pretty microphonic in combos…I'd do it with that Frenzel head of yours if you still have it.

Yep I still have the Frenzel head which is mated to a Boogie 4X10 cab. That's what I play my Wurlitzer piano through in my studio:)