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 Post subject: V5 - AT7
PostPosted: Tue Jan 30, 2018 11:34 am 
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Mark III
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I was swapping out my 6V6s with a set of yellow color coded EL34s last weekend. I also decided to move my SPAX7 from V1 to V2 and added another SPAX7 to V3. While I had the chassis out of the head shell, I pulled V5, the AT7. The pins were kinked and bent. I had never pulled this tube before and was very surprised at it's condition. I had already thought of replacing the stock AT7 with an NOS JAN Phillips AT7, which I immediately did once I saw the condition of the stock tube. Still trying to figure out how the tube got that way. I would initially think it was how I pulled the tube, thinking the socket would straighten the pins just from being in place. But, I pulled that tube out with one smooth, straight pull. Baffling...

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 Post subject: Re: V5 - AT7
PostPosted: Wed Jan 31, 2018 7:47 am 
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Mark III

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<confusing fake news deleted>


Last edited by mace on Wed Jan 31, 2018 9:57 pm, edited 1 time in total.

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 Post subject: Re: V5 - AT7
PostPosted: Wed Jan 31, 2018 11:07 am 
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Mark III
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Not only does my manual specify an AT7 in V5, on the chassis there is "12AT7" written in like a metallic sharpie right below the V5 socket. I believe the RA series also required an AT7.

The amp has functioned fine during this first year of ownership, which is good. I was just surprised at the condition of the pins on the tube itself.

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 Post subject: Re: V5 - AT7
PostPosted: Wed Jan 31, 2018 12:27 pm 
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Mark IV
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mace wrote:
Well, that’s interesting. If everything is working I wouldn’t worry about it too much. Although, it would bug me on a new amp. :)

I was surprised that the TC-100 uses an AT7 because the TC-50 does not. I thought the gain structures were the same and only the power sections different? I guess not.


Both TC-50 and TC-100 use the 12AT7 in V5. Thanks!

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 Post subject: Re: V5 - AT7
PostPosted: Wed Jan 31, 2018 9:57 pm 
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Mark III

Joined: Sun Feb 02, 2014 11:51 am
Posts: 179
Authorized Boogie wrote:
mace wrote:
Well, that’s interesting. If everything is working I wouldn’t worry about it too much. Although, it would bug me on a new amp. :)

I was surprised that the TC-100 uses an AT7 because the TC-50 does not. I thought the gain structures were the same and only the power sections different? I guess not.


Both TC-50 and TC-100 use the 12AT7 in V5. Thanks!


Oh my. I double checked the pdf manual before posting. I need some new glasses. Indeed. AT7 in V5. :shock:


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 Post subject: Re: V5 - AT7
PostPosted: Thu Feb 01, 2018 6:48 am 
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Triple Recto

Joined: Fri Feb 22, 2013 7:31 am
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Location: North Carolina
Yes, the TC series uses a 12AT7 in V5 position. Do not use other as this is a cathode follower circuit used for the Send driver or level attenuator. the RA100 also uses a 12AT7 (but location is different) but same circuit. I have had my RA100's much longer than either of the TC amps so the circuit it quite stable as it is basically the same. I have briefly tried other flavors of the 12AT7 but I personally like the stock tube.

As for the bent pins, best to use a different tube just in case the damaged pin may break off inside the tube socket.

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 Post subject: Re: V5 - AT7
PostPosted: Thu Feb 01, 2018 3:29 pm 
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Mark III
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I fired up the TC50 with the yellow color coded EL34s, the SPAX7s in V2 and V3 and the JAN 12AT7 in V5. I had also just replaced one of my speakers in my Recto Vertical 2x12 (long story, but the top speaker was not a V30 when I got the cab. Now there is a WGS Veteran 30 in the top slot with a MB V30 on the bottom). I have the treble and presence both set close to 9 o'clock on both channels 2 and 3 since I find the amp to be a bit on the bright side. First impressions is that it sounds a little fizzy - nothing I experienced with the amp before. I think that is more due to the WGS speaker since it's brand new and the V30 is broken in. I suspect that will diminish over time. No issues with bottom end whatsoever. My bass is set to about 1 o'clock and the mids are set to about 10 o'clock. I may switch back to the original stock gray color code tubes just for a comparison. Probably should have left those in first...oh well.

I do think the SPAX7s slightly tamed the high end, but the fizziness from the new speaker sort of brought it back. Time will tell. I was able to crank it up close to gigging volume and there really wasn't much of a change in tone.

Just for kicks, I flipped the Tight switch and cranked up the bass a little. That seemed to accentuate the mids more than anything. Since I rarely do any alternate tunings, I think I will stick with normal for a while.

I won't be putting the stock Mesa AT7 back in. Those bent pins made my decision for me.

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 Post subject: Re: V5 - AT7
PostPosted: Thu Feb 01, 2018 4:05 pm 
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Mark III
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I couldn't resist, I put the gray color code EL34s back in. The fizziness diminished. Not 100%, but maybe 90%. I know my ears are old and tired, but there was a definite difference.

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 Post subject: Re: V5 - AT7
PostPosted: Thu Feb 01, 2018 5:31 pm 
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Mark III
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It looks like I should have put the SPAX7s in V3 and V4 instead of V2 and V3. I think I will do some rolling this weekend and try some Mullard CV4004s, too.

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 Post subject: Re: V5 - AT7
PostPosted: Thu Feb 01, 2018 10:03 pm 
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Triple Recto

Joined: Fri Feb 22, 2013 7:31 am
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Location: North Carolina
clean channel is V1 and V2 only has three gain stages and the tone stack sits between the first two gain stages, that typical Mesa - fender style of circuit.

CH2 and CH3 use V3 and V4 only. Ch3 is a three gain stage circuit, similar to CH2 on the Mark V V3A ->V4A-tone stack -> V4B. CH3 is a 4 stage circuit V3A-> V4A->V3B -> tone stack ->V4B

If you think of the gain stage sequence, it may help you choose what preamp tube to stick where. Not sure if this amp is using a cold cathode circuit, if it is I would assume it to be in V3B position and effective for Ch3 only. I would have to open it up and look. Why I think this, the TC-100 has more bass on CH3 and is quite similar to the Roadster (sort of). Ch2 sounds more lie the crunch on CH2 of the Mark V (sort of). This is just a guss, no confirmation yet. May just be your typical gain stack like usual.

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 Post subject: Re: V5 - AT7
PostPosted: Fri Feb 02, 2018 11:06 am 
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Mark III
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One thing I failed to keep in mind: the yellow color coded EL34s were supposed to be new, never used. According to my father, he had those as spares for the Road King, and never used them. But, I have to take many things he says with a grain of salt, lol! At any rate, normally when I install new power tubes in any amp, I like to leave the amp on for a 24 hour period - fully on, not in standby mode. I did not do this with the TC50 and those power tubes may have needed a good 20 hours or so to break in. I may try them again, but first I want to tube roll a little bit in the preamp section. I am still a little embarrassed that I mixed up V2 & V3 for V3 and V4. I had the manual out and was checking it before I did my swap. Total failure on my part.

And, of course, there is still the new Veteran 30 to keep in mind. That will take some time to break in and smooth out.

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 Post subject: Re: V5 - AT7
PostPosted: Mon Feb 05, 2018 12:27 pm 
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Mark III
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Because of the tube layout, I confused V2 and V3 with V3 and V4. In other words, I had the SPAX7s in the correct places I wanted them to be: V3 & V4. So, I swapped both of those out for the Mullard CV4004s. But, I also decided to go ahead and do a full burn-in with the original stock grey color coded EL34s, so no sound test yet. I will probably do another burn-in with the yellow color coded EL34s. Then, both sets should be fully broken in and I can make a better sound comparison. I also found a pair of Mullard RI 12AX7s that I completely forgot about. I have a suspicion that tube rolling in the TC 50 isn't as profound as with other amps I own. That's definitely not a complaint. It would save me hours of experimentation.

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 Post subject: Re: V5 - AT7
PostPosted: Tue Feb 06, 2018 9:28 pm 
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Mark III
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I put Mullard CV4004s in V3 and V4. I got what I hoped for! No more fizz and a nice boost to the low mids and bottom end. My TC50 has a definite thump now. I didn't lose any clarity on the high end, either. Just no more fizziness. I've got some JJ ECC803s coming to try, too. But I think I will stick with this setup for a little bit. However, I will definitely put my yellow color coded EL34s in for an overnight burn-in and see if there are any improvements to to those tubes.

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 Post subject: Re: V5 - AT7
PostPosted: Fri Feb 16, 2018 11:14 am 
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Mark III
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I finally got a good test with the yellow color coded EL34s. After installing them, I left my amp on for a good 24 hours. Yesterday, I was able to crank the amp up to gig volume. There is a slight difference in tone between the yellow and grey color codes. The yellows were a bit "softer" sounding to my ears. But, at gig levels, it's not as noticeable as with lower volumes. I have yet to try out the ECC803s because I really like how the CV4004s sound in V3 and V4 and couldn't stop playing. Not sure I even want to test the JJs for a while.

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 Post subject: Re: V5 - AT7
PostPosted: Fri Feb 16, 2018 6:21 pm 
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Triple Recto

Joined: Fri Feb 22, 2013 7:31 am
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The ECC803s will have a less notable gain than the CV4004 or the stock Mesa tubes. If you have a Tung Sol, try that in V3 and keep the mallard CV4004 in V4 (tone stack is on the last gain stage). That is what I have the TC-100. I have all stock tubes in the TC-50.

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