Tube experiment

[jnoel64]

I've already put Mesa 6V6 power tubes in and REALLY dig that tone. I also put a Mesa SP12AX7 in V1 just because I had one. I also have 2 NOS JAN Phillips 12AT7WC lying around as well as a Tun-Sol 12AX7. I just received 2 Mullard CV4004 which I wanted to test in V3 and V4 since those 2 positions feed the gain stages for Lo and Hi. Since I had the back panel off and the tube cage pulled out, I decided to put the Tung-Sol in V2, the Mullards in V3 and V4. Then I put the NOS 12AT7s in V5 and V7. Stock, an AT7 is in V5, so there wasn't much change for that slot. But after reading so much about the PI tube and what a swap to an AT7 might do, I gave it a shot. Normally, I like the Sovtek 12AX7LPS in the PI slot.

With those changes in place, I noticed a much brighter, open clean on channel 1. That adage about removing a blanket from the front of the amp really rang true in this case. I had to back down the treble and presence. Still, the openness and chime was very noticeable. Channel 2 had less gain. The jury is still out on whether or not I like that. But, with some tweaking on the tone knobs, I got a very distinctive Angus Young tone from the Back in Black album. I thought about putting my BB preamp in the mix, but didn't out of laziness and the desire to hear just the amp.

Channel 3 lost just a touch of gain, but, more importantly, I found I also lost a little definition. The touch sensitivity was all still there, but it turned slightly mushy. Tweaking the tone knobs helped a little, but I think I may go back to the LPS in the PI slot or I may try pulling the Mullards first since they are a warmer, creamier tone and that could mush things up a bit. Hopefully the clean channel will retain the sparkle I got and I am thinking the Tung-Sol had more to do with that. So many tubes, so little time....

I've done a similar swap in other amps, and liked what I got in those. But no 2 amps have the exact same tone path. As always, tone is subjective and YMMV.

 

[bandit2013]

I would highly recommend tying out a JAN/GE or JAN/Phillips (if you can find one) 5751. I have experimented with one in all of my amps. I was impressed on the character when used in V2 on the Roadster with the rest as stock Mesa tubes. Used it in V1 on the Mark V. The first one I bought I dropped it when installing into a practice amp (broken glass does not make a tube sound better). Had to get another one but when I put it into a Stiletto I must have installed it in a cathode follower circuit as the silver getter flash immediately turned black. Also burned up a few other tubes in that amp so I returned it......traded for an RA100 Combo. JAN/GE phillips will add some brightness, may reduce gain but not as dramatic as a 12AT7. Actually I have used 12AT7 in the later gain stages of the Mark V which killed the notch filter sound and improved tone considerably. For some reason I feel if you step too far from the intended the tube may run hotter. Also with some circuits in the amp, the plate voltages may be too high for the NOS tubes.

Another tube to get if you can find them, NOS Mesa 12ax7a with square foil getter (Chinese). Those are much better than the current versions (they have the small chrome or silver plate clip on the plates with a few mica spacers separating the getter from the plates.
These look like the same tube.....
http://www.dougstubes.com/preamp-tubes/12ax7-ecc83-7025/nos-chinese-12ax7-80-s-90-s.html

 

[jnoel64]

The 2 AT7s I put in the TC-50 are in the FX loop driver slot and the PI slot. After re-reading about the PI slot (from here: http://www.guitaramplifierblueprinting.com/files/Phaseinverter.pdf), I wanted to see how the output signal would be affected by the AT7. I was never out to reduce any gain, and both of those slots shouldn't really affect the preamp gain at all - provided I understand the TC-50s tube layout correctly.

I've used some NOS 5751s in other amps, namely a Carvin V3M, but still chose AY7s instead to keep that amp's gain under control. And, when it comes to 5751s, I definitely do not care for JJs. Many people do, but, to me, they are dull. Tubedepot has some JAN GE 5751s for about $70 each, and thetubestore has them for $50 each. I hope to swap V2 and V3 out tonight and see what happens. I tend to deal mostly with tubedepot or thetubestore over Doug's. When I first got my Dyne, I asked Doug's about a decent tube cocktail for that amp, and he told me to use the same as the kit for the Mark V. The tube layout for the Dyne and Mark V are nowhere similar, aside from V1, so I was really confused as to why that would be his recommendation. I suspect he had never seen the tube layout for the Dyne.

For now, I am going to try putting the original tubes back in V3, see what happens, and maybe switch V4 as well, or flip those 2 around. I can't say I am completely dissatisfied with my current experiment, I just want to see if I can improve it a touch, and it simply may be to put the stock tubes back in V3 and V4.

I also plan to gig the amp this coming weekend, but that band will only need the clean channel, and I am very much in love with my clean tone right now. The Tung-Sol added some beautiful sparkle to the clean channel that really opened up the tone even more than it already was. I may have to bypass my BBE at the gig.

 

[bandit2013]

Depending on the position, I found the 12AT7 to be warmer in tone but it matters what amp it is going into. Used in V4 and V5 of a Mark V it darkens the tone a bit and really cuts the thin ice tone but with some loss in compression. I do not mind the JJ preamp tubes. The ECC 803S long plate is not bad, may have a lower gain than the short plate version ECC83 but works well in the PI position. If the amp has a separate tube for the reverb circuit, the Mullard 12ax7 Reissue long plate works well there. Also would do good as a PI tube as it is similar to the Sovtek LPS tube but with more gain. Also works good in the front end as it helps to cut some treble if the amp is too bright (depends on the amp and how the tube is driven). Some of the Mesa amps do voltage shifts on the plate circuit to alter the characteristic of the tube for specific effect. Mark V ramps up voltage on selected preamp tube circuits in tweed mode. Probably why the amp tends to get brittle when using full power.

I would agree that the Carvin V3M needs to be tamed but I found that drop in bias was the key to making it sound great (factory setting was way too high). Mullard EL84 with a full complement of Mullard CV4004. That little 50W amp sounds as good as my Mark IV did when channeled though a 412. Also used 12AT7 which did improve tone a bit. I generally use the V3M as a practice amp on the clean channel and drive it with a Boss GT-100. That amp I leave at my friends house and it is much easier to carry than any of my Mesa amps. If something were to happen to it, I will not be totally bummed out about it.

Current make of the 5751 are not as good. Actually I found the JAN/GE 5751 to sound better then some 12AX7.
As for Doug's, I stopped using him a while back but once in a while he may have something of interest. The tube store is my primary for alternates to Mesa tubes. I will get Mesa tubes from Sweetwater. I have made requests for specific color coded power tubes and they will do what they can to get them for you.

Good luck with your tube rolling.