NOS preamp tube advice

[CraigP]

Hi all,

I recently bought a SamAmp Vac 40 amp - it is a billed as a Fender inspired (think Blackface meets Tweed) 40 Watt, 2-channel, all tube amp. It has a novel attenuation system where different small light bulbs are used to reduce the wattage going to the power tubes. The result is that you can run the amp at 4 watt, 9 watt, 20, or 40 watt settings without changing the tone. What changes, of course, is the amount of clean headroom at each setting. There is a very good (albeit long) review from Anthony Stauffer at the Stevie Snacks website: http://steviesnacks.com/gear-videos/samamp-vac-40-series-2-demo.html

So far I am really loving the sound. The attenuation system works as advertised, and its takes pedals very well. What I am a little less happy with is the overdriven sounds, both on the clean channel when pushed and the overdrive channel. To me, it sounds too harsh. I mostly play at lower volumes, so I think (perhaps incorrectly) that I am mainly hearing preamp overdrive and not power tube overdrive. The preamp for each channel is composed of an electroharmonix 12ax7 and a 12au7 tube, and the phase inverter has a 12at7. There is no reverb. I am thinking to replace some of the preamp tubes with some nice NOS tubes.

My first question is: Which preamp tube replacement is going to give me the most change in tone? NOS tubes are not cheap, so "rolling" all 5 tubes seems like a new way to drop a ton of cash. Would changing the first tube at each channel (V1) have the most impact? Looking over the web, this seems to be at least one thought. I am thinking of replacing the 12ax7 at the gain channel for a NOS Brimar CV4004, and the 12au7 in the V1 spot of the clean channel with a JAN GE 6072A. In general I am looking for crystal clear Fender cleans and smooth, creamy overdrive -- not too much to ask is it?

[LostArt]

it is really difficult to answer this question.

all the tubes interact together.

I have tung sol 12at7wa's that are a military spec that sound great.

In most of my amps I use used telefunken 12ax7's that are way out of spec but just sound good.

just changing the first tube in each channel may help.

this is a situation with having a bag of tubes and an afternoon to experiment is a ton of fun.

[Jakeboy]

Agree with Lost Art.....tubes do interact......but put a quality tube in V1..... In all my amps, that slot "colors " the tone more than any other preamp tube.

Good power tubes too....especially if you want power tube distortion. What are the power tubes? 6v6s or 6L6s?

[Lockbody]

Sam is the local amp tech at my favorite haunt, and everything he's ever done for me for either my Boogies or Fenders has been top notch. He does love those EH tubes, though, and that's about all that the store gets in.

I always look forward to playing through any of his amps that may be sitting on the floor when I go in there. You definitely got a good amp.

[CraigP]

It has a pair of 6L6GC for power tubes, probably EH as well. I had heard that the new production power tubes are actually pretty good and that old power tubes may not have a huge impact on tone? In general, I am liking the EH tubes that are in it now, but just want to warm up the overdrive a bit.

[jisham]

I REALLY REALLY REALLY like the RFT 12AX7s, especially in V1.

[CraigP]

Lockbody -- you must be from Alabama then? Sam of SamAmp has really been great to deal with. When I first got the amp, it had some issues with picking up interference of some sort in my house. He worked through the issue and ended up sending me a grounded valve shielding sleeve that slid over the two V1 tubes. Intereference problem solved and the tone seems better all the way around. He always answers my emails -- though I do agree that he seems to like the EH tubes. He didn't seem to have much enthusiasm for swapping in some NOS preamp tubes.

[Lockbody]

Lockbody -- you must be from Alabama then? Sam of SamAmp has really been great to deal with. When I first got the amp, it had some issues with picking up interference of some sort in my house. He worked through the issue and ended up sending me a grounded valve shielding sleeve that slid over the two V1 tubes. Intereference problem solved and the tone seems better all the way around. He always answers my emails -- though I do agree that he seems to like the EH tubes. He didn't seem to have much enthusiasm for swapping in some NOS preamp tubes.

Yep, in Birmingham. Sam is a super nice guy and does great work, but it doesn't take much research to see that the EH tubes are just "meh" tubes compared to others, even at the same price point. While I like SED=C= 6L6s a lot more, the EH 6L6GC aren't bad, but I haven't liked the 12AX7s in any amp I tried them in, plus I thought they were noisy. Sam will tell you, though, that the EH are as good as anything out there, and you really won't gain anything by replacing them. He's also not big on power tube matching, either.

To each his own, I guess. His opinion on tubes, won't keep me from taking my amps to him in the future.

[CraigP]

Well, if I was in the business of making amps, I might also look for a source of consistent, modern tubes, which may be EH. Perhaps if he was doing lots of individual amps, then he would customize with more expensive and less consistently available NOS tubes. It can't hurt (except for my wallet) to roll a bunch of tubes in the V1 positions and see what happens.

[crunchee]

I stumbled across this article yesterday, when I was looking for info on 12AU7 and 12AY7 tubes in V1 in old Fender amps. There's useful nuggets of info about tubes throughout, but YMMV, since not everyone uses old Fender gear:

http://thetubestore.com/earfenam.html

Edited to add more, including an article on Marshall amps, again YMMV:

http://thetubestore.com/inonfenlatbl.html

http://thetubestore.com/inonmaram.html

http://thetubestore.com/gainfactor.html

[CraigP]

Well, my new tubes arrived today. Put a NOS Brimar CV4004 in the V1 slot at the Gain channel (V2 is a EH 12AUY) and then a JAN GE 6072A in the V1 slot of the clean channel. Tone? Well, it is changed but perhaps not as dramatic effect as I would have thought. On both the clean and gain channels, the tone just seems a bit smoother. No fizz and the highs do seem "rounder". The odd thing that I am finding is that the new tubes respond very differently to my various pedals. Lately I have been almost exclusively using a AnalogMan Sunface fuzz pedal to get some nice tones with my start. But with the new tubes, that pedal sounds all dark and muddy. Very weird! It's tone is altered with either the clean or gain channel. Tubescreamer and Fulltone Plimsoul also seem a bit darker with the new tubes. One thing I haven't been able to try yet is to really crank up the volume and see how it opens up -- maybe tomorrow after the wife goes to work...

[CraigP]

Problems solved. With the new tubes, all that was apparently needed was to increase the clean headroom a bit by changing the amp from the 4 watt to the 9 or 20 watt setting. Now the clean and overdriven tones are crazy great. Pedals do what they are suppose to do, including my SunFace fuzz which is now doing great stuff for my Strat. My old tubescreamer yields this wonderful "woody" overdriven tone on the 2/4 positions. Wow. This SamAmp vac40 with these preamp tubes loves my strat.

[JohnnyB]

Tone? Well, it is changed but perhaps not as dramatic effect as I would have thought. On both the clean and gain channels, the tone just seems a bit smoother. No fizz and the highs do seem "rounder".

If your experience is anything like mine, you may find that these subtle differences have more impact than is immediately apparent. You're describing the removal of an artificial layer of electronic grunge from your signal path. What remains is a more honest expression of your playing and your musical intentions. Although first listen doesn't sound like a night-and-day difference, that difference is more of a musical value (dynamics and expression) than a sonic one (higher highs, lower lows, etc.). Over time you find this type of improvement (e.g., NOS tubes) draws you deeper into the music and makes you feel what you're playing more strongly. This in turn spurs you to play better, with more dynamics and expression. Ultimately it can result in playing in a more emotional way that draws the crowd into your performance.

Pretend your new tubes aren't there and see what happens to your emotional state while you play and how that affects your playing.

[Armitage]

Yeah, diiferent brands of new tubes should be transparent, indistinguishable from each other... but they're not, yet the differences are usually subtle. One might be brighter, more sizzly, or fatter another even shrill, but not a huge deal. It's more a fine tuning thing. More like the difference between fresh and really old strings... or maybe different pickups.

Now comparing new tubes to old worn ones is another thing altogether.

[CraigP]

Great thoughts and insights. I think I see (hear) exactly what you are saying. Already I feel like I am worrying less about little things about my tone and enjoying what I am playing. Need to put some NOS tubes in the remaining two slots...

[Jimbilly]

While you're out tube hunting, don't overlook the 12AV7s, which are pretty similar to 12AY7s and 12AT7s (somewhat lower gain than 12ax7, but nowhere near as low as a 12au7, 12ay7s are V1 in real 59 bassman). At the ham radio swap meets and elsewhere 12av7s are mostly overlooked.