rectifier trouble update. (fixed)

[rectofried]

i posted a while back about my 96 recto having volume fluctuations and gain sounding flat with no sustain or harmonics.. i have several recto's and this one sounded like ****.. i figured it needed a cap job or tranformer or something. after giving up on tube swapping i sent the amp to www.andrewsamplab.com in atlanta GA.
he checked out the amp and told me he could find nothing wrong with the amp. but suggested replacing the master volume pots which could cause intermittent volume, and he also noticed that i had tungsol tubes in v3 and v4. he replaced those with the chinese tubes as per mesa.. after such an easy fix i was sure the amp was gonna sound the same when i got it back, but to my surprise the amp sounds amazing now,feedback and sustain are back and the thick tone that made me fall in love with the recto are there in spades. i commend jeff andrews for not fixing a bunch of stuff that prolly didnt need fixing and running up a bill..he is a straight up guy and i will use him again.. now if i can just get my **** loop modded to serial i will be a happy camper..

 

[94Tremoverb]

Russian-made 12AX7s can cause trouble in cathode-follower positions - which both V3 and V4 are, V3 drives the tone stack and V4 the effects loop. The cathode-to-filament voltage rating on them is not good enough, and in a cathode-follower position you can have up to a couple of hundred volts on the cathode, and near zero on the filament. (There can even be problems in phase inverters, where there's typically a few tens of volts.) The result is current leakage - or in a few cases outright failure - which will result in odd tone or loss of volume.

Mesa even uses Russian 12AX7s as stock, you would think that they would have noticed this! I've only come across it with Sovteks usually, but it doesn't surprise me that the Tung-Sols should do it too since they are from the same source - they're not really "reissues", they're just a new Russian tube with an old American name on the outside. I agree they sound good, but probably best to keep them for V1 and V2.

Not making tubes to the proper original design spec is not just a problem with 12AX7s either...

 

[KH Guitar Freak]

Strange. Not to say what you guys are saying about the cathode follower issue as incorrect, but how come I have yet to experience that with my Roadster head and my Stiletto Deuce II head? Just curious to know what you guy might know...

 

[94Tremoverb]

It's pretty rare, even with the Russian tubes - obviously Mesa wouldn't use them if every one was like that. But I've come across this problem enough that I started to see a pattern - every single time, it was a Sovtek 12AX7. It's a pity if the Tung-Sols do it too, because otherwise they are a good-sounding tube.

I'm not a fan of Sovteks - IMO they sound bad, and some of their tubes (the 5Y3 and GZ34/5AR4 rectifiers in particular, as well as the 12AX7s) are not even close to the correct design spec and cause a lot of reliability problems.

 

[fluff191]

Interesting read. I love the bunch of Shuguang Silver Dragons I have, but always fall back to a Mullard in V1 with a JJ in V2 and EH in V3, although I am going to put a Silver Dragon in V2, cause it has alot of bit.

 

[rectofried]

thats why i posted this, i have a roadster and a revision F head that have been using russian tubes for years.the F head since the early 90's with no trouble.. but i have had the intermittent volume drop with 2 other heads, a late 2 channel and an early 3 channel that techs could not find anything wrong with and i continued to have trouble until mesa replaced them..looking back now it may have been the tube trouble since the symptoms are exactly the same. (minus the volume pot). only thing im bummed about is the chinese tubes dont have the clarity of the tungsol imho. below are what i use.
V1= SOVTEK LPS
V2= TUNGSOL
V3= RUBY HG+
V4= RUBY HG+
V5= SOVTEK LPS
since the HG+ are just graded chinese i use those. tube quality is not what it used to be. i put in a new set of tunsol power tubes (6l6) and had those in there about a week before they red plated.so im back to mesa tubes now which i think they are chinese power tubes as well.. my limited number of posts means i didnt check these boards much and missed the mesa bulletin about the tube problem in 08. they should have posted that on their front page on mesa's site.

 

[KH Guitar Freak]

It's pretty rare, even with the Russian tubes - obviously Mesa wouldn't use them if every one was like that. But I've come across this problem enough that I started to see a pattern - every single time, it was a Sovtek 12AX7. It's a pity if the Tung-Sols do it too, because otherwise they are a good-sounding tube.

I'm not a fan of Sovteks - IMO they sound bad, and some of their tubes (the 5Y3 and GZ34/5AR4 rectifiers in particular, as well as the 12AX7s) are not even close to the correct design spec and cause a lot of reliability problems.

I've tried a Sovtek before. Not very good. However, I quite like the Russian 2s in my Mesas. Only replaced V1 in my Roadster with a Mesa SPAX7 preamp valve. I must be tone deaf then... :lol:

 

[mansfieldguitars]

I spoke to a tech at Mesa about the cathode follower issues and he informed me that the problem is in the past. The newer tubes thay supposedly use are said to be fine in a cathode follower circuit. He did not get into the specifics with seriel numbers but stated on new models this is no longer a problem.

 

[rectofried]

hey,mansfieldguitars

is it no longer a problem because they used chinese tubes now instead of russian? or was it a bad production run during 2008 when the mesa bulliten was released?..the last tubes i bought from mesa were chinese...good to hear they got the issue fixed though..

 

[MrMarkIII]

Somewhere there's a service memo from Mesa on this. Russian = bad, Chinese = good for cathode follower positions.
Oh, found it:

"Most (but not all) Mesa/Boogie amplifiers have one or two “cathode follower” tube stages in their preamps. Tube selection is CRITICAL in these stages.

Specifically, in a 12AX7 tube used as a “cathode follower”, the voltage difference between that present at the cathode, as compared with the heater voltage, can be withstood or tolerated by certain types of tubes, whereas other tubes will fail. The failure of a “cathode follower“ tube will cause sound dropouts or signal loss.

For the past few years, Mesa has been using two types of 12AX7 tubes: ones originating in Russia (Sovtek EH), and ones originating in China. The Russian (Sovtek) tube is NOT reliable as a cathode follower. Of the tubes Mesa is using today (March 2008), ONLY THE CHINESE 12AX7 IS RELIABLE AS A CATHODE FOLLOWER."

GUITAR / BASS AMPS WITH CATHODE FOLLOWERS:

Lone Star & LS Special: V3
M-Pulse: V2
Stiletto: V3 & V4
Venture: V2
Road King I: V3 & V4
Big Block 750: V4
Road King II: V3 & V5
Titan: V4
Roadster: V3 & V5
M2000: V2
Dual & Triple (2ch or 3ch): V3 & V4
Bass 400+: V2
Tremoverb: V3 & V4

 

[R_ADKINS80]

Th 3 new preamp tubes that Mesa sent me for this problem are thir relabeled JJ's. I was having problems with huge volume loss when flipping to spongy. My amp was shipped with four chinese tubes in v2-v5 and a russian in v1. Even though it had the chinese tubes in the cathode follower possitions it still had the problem even with switching the tubes around. As soon as I put the new Mesas in the problem was gone. Also it doesn't have the problem when NOS tubes are used either.

 

[rectofried]

Th 3 new preamp tubes that Mesa sent me for this problem are thir relabeled JJ's. I was having problems with huge volume loss when flipping to spongy. My amp was shipped with four chinese tubes in v2-v5 and a russian in v1. Even though it had the chinese tubes in the cathode follower possitions it still had the problem even with switching the tubes around. As soon as I put the new Mesas in the problem was gone. Also it doesn't have the problem when NOS tubes are used either.

what recto do you have ?..2 or 3 channel ?

 

[the_wallcrawler]

GUITAR / BASS AMPS WITH CATHODE FOLLOWERS:

Lone Star & LS Special: V3
M-Pulse: V2
Stiletto: V3 & V4
Venture: V2
Road King I: V3 & V4
Big Block 750: V4
Road King II: V3 & V5
Titan: V4
Roadster: V3 & V5
M2000: V2
Dual & Triple (2ch or 3ch): V3 & V4
Bass 400+: V2
Tremoverb: V3 & V4

Do we know if the Single Recs have this issue? If the other Rectos do I would assume so.

 

[fluff191]

I have a 2088 Dual Recto with all Russian tubes in it. Aftermarket EH's in fact. Should I change out V3 and V4 with the Shuguangs that I have?

And what kind of volume drop are we talking about? Cause after an hour or two of band-volume use, I swear the tone changes slightly and the volume drops just a little.

 

[rectofried]

my volume dipped a little or sometimes alot depending on how long i had the amp on..tone would sound harsh and highs were cut. and gain would cut back as well. i would try the chinese to see if it makes a difference. i know it did on mine. so far i jammed for 3 hours at pracice and it held up with no issues.
before i couldnt go 30 min.

 

[kingston11]

most amps I have played exhibited this behavior in a band setting. usually in such a loud setting for an extended period of time, you wont be able to hear the highs, and your gain will feel turned down a bit. Like listening to the radio on the way home from a concert. Or maybe I missed the point to this thread entirely. lol.

 

[fluff191]

most amps I have played exhibited this behavior in a band setting. usually in such a loud setting for an extended period of time, you wont be able to hear the highs, and your gain will feel turned down a bit. Like listening to the radio on the way home from a concert. Or maybe I missed the point to this thread entirely. lol.

That is exactly what my amp does. Its like after an hour you find yourself saying "man, is something laying in front of my amp?"

Just today I put the stock Chinese tubes back in all the position except for V1. Havent had the problem since.

 

[Soma]

Can't add much to this except to say my tremoverb had the same issue; after an hour or so of moderate volume playing the tone thins out and volume drops. Replaced 3 and 4 with chinese tubes and good to go. A shame though, because the chinese tubes do the same thing, thin out the tone :?

Cheers.

 

[rectofried]

im gonna try the mullard reissues in those spots, since doug and the tube store said they would hold up in those slots.. they got to sound better than the chinese...i tried the russians again today at bedroom level just to see if it was a fluke or bad tubes..but i got the same issues within a few min. of playing.. this has got to be critical in the 2 channels or something..i remember having this trouble out of several 2 channels over the years.