The Tube Thread

[oneblackened]

I have had two different quads of preferred series EL34's die in my JCM800 over the last year. The tech who's worked on the amp says he has experienced this before and no longer recommends those tubes. I run my amp loud, and often (twice a week when not on tour). Just a bit of a PSA for anyone considering that specific tube, as the tube store has their annual sale on right now.

That's Chinese tubes for you... I don't trust them, Shuguang is known to put out some real stinkers.

 

[oneblackened]

Couple more preamp tube reviews! This was in a Mark IV and my Dual Rectifier.

JAN GE 12AX7WA: The best way to describe this tube is "big". Dead quiet, too. Somewhat on the warm side of things, but not dull. Distorts beautifully.
Shuguang 12AX7 (1990s stock): Definitely on the bright side of things. These were Mesa branded. Works better in darker amps.
Shuguang 12AX7 (2018 production): Like the older ones, but not as good. Grittier, less clear. I see why people like them, but they're not for me.
EHX 12AX7: Again, Mesa branded. Pretty neutral sounding overall, with a bit of gritty edge like most Russian tubes have. Actually a pretty nice PI tube.
"Northern Electric" 12AX7: Rebranded TJ FullMusic (another Chinese maker) 12AX7. Good sounding tube with a really nice balance and clarity, but the one example I had went very noisy after about 4 hours of use (it's being replaced). Not sure I'd recommend them for the amount they cost each ($48 US plus shipping) when I could buy NOS RFTs for about the same cost without worrying about noise.

 

[oneblackened]

Okay, update on the Northern Electric stuff. The second one has gone bad now too - so yeah, fuck those tubes. Absolutely not worth nearly $60 each.

 

[777timesgod]

Any opinions on the Groove Tube GT-12AX7 ones? They used to be stocked locally in a shop near me and I may look them up again.

 

[efiltsohg]

Any opinions on the Groove Tube GT-12AX7 ones? They used to be stocked locally in a shop near me and I may look them up again.

tested/selected shuguang/new sensor/JJ depending on the part code (-C, -R, -S), not worth the surcharge

 

[777timesgod]

tested/selected shuguang/new sensor/JJ depending on the part code (-C, -R, -S), not worth the surcharge

I was under the impression that they had similar prices. I will keep it in mind.

 

[efiltsohg]

I was under the impression that they had similar prices. I will keep it in mind.

If they are the same price no major reason not to get them... but I'd prefer a Tung-Sol or Sovtek LPS. Last I heard GT-12AX7R was a Sovtek WA which is one of the worst sounding preamp tubes out there

edit: not sure if still accurate by my source says:
GT-12AX7C: Shuguang 12AX7-A
GT-12AX7R: Sovtek 12AX7-WA
GT-12AX7R2: Sovtek 12AX7-LPS
GT-12AX7R3: Electro-Harmonix 12AX7-EH
GT-12AX7S: JJ ECC83

So if you can get an R2 or R3 it might be worthwhile. For me JJ only belongs in a very bright amp

 

[oneblackened]

So Groove Tubes does make a couple of special power tubes... The 6L6-GEs are actually pretty good tubes though they're more 5881s in terms of plate dissipation, and the 6L6GC-CHPs I don't know anything about. I have a pair, but my only 50W amp (my Amelia) is currently on my bench being modded to hell and back.

 

[Descent]

What are the thoughts on JJ's?

I have a hog to retube, the Peavey power amp Classic 50/50. Have to get an octet of EL84s and quad 12ax7s. I wanted to go EH first as I've always had good results with them but JJ price came out to about $120 for all, while if I've gone EH I was looking at $200.

 

[efiltsohg]

I'd stay away from the 12AX7s. JJ is good for power tubes.

If you don't want to change the tone & character of the amp then use what you had in there before

or try new production Tung-Sol 12AX7s for a relatively balanced sounding preamp tube

 

[Descent]

So their 12ax7s are no good?

I'm not sure what the status of preamp tubes are in this amp, probably still good, the power amps' are definitely fading. I'll swap power amp tubes first and if it fixes the issue leave the current ones in there, EH12ax7s I think.

A website was suggesting 12AT7's (ECC81s) for this amp but didn't specify what position. I've always used just straight up 12AX7s in it.

 

[mnemonic]

So their 12ax7s are no good?

I'm not sure what the status of preamp tubes are in this amp, probably still good, the power amps' are definitely fading. I'll swap power amp tubes first and if it fixes the issue leave the current ones in there, EH12ax7s I think.

A website was suggesting 12AT7's (ECC81s) for this amp but didn't specify what position. I've always used just straight up 12AX7s in it.

I found the manual but it was very sparse and didn’t say anything about tubes.

The schematic does call for 12AX7 input stages and 12AT7 phase inverters.

https://www.thetubestore.com/lib/thetubestore/schematics/Peavey/Peavey-Classic50-50-Schematic.pdf

The tubes V200 and V206 are 12AT7’s. The last page is a copy of the pcb layout so you can see which positions they relate to (if it doesn’t specify those numbers on the actual PCB).

 

[Descent]

Haha...didn't know that, been using 12ax7 across all preamp positions for over 15 years

So, I guess what am I missing by running 12ax7 instead of 12AT7 in there?

@mnemonic thanks for the schem, I didn't have that!

 

[efiltsohg]

You'd probably get different volume and slightly different distortion character from swapping the type PI tube

 

[DudeManBrother]

Haha...didn't know that, been using 12ax7 across all preamp positions for over 15 years

So, I guess what am I missing by running 12ax7 instead of 12AT7 in there?

@mnemonic thanks for the schem, I didn't have that!

They are actually quite different. AT’s have an mu of around 60, peak heater-cathode value of 90v, a plate resistance of 11k-ish and a plate dissipation of about 2 1/2 watts and roughly quadruple the bandwidth of an AX: mu of 100, peak heater-cathode value of 200v, plate resistance 60k, and a plate dissipation of 1.2 watts... to name a few differences. You get lower plate voltage and much higher current draw than the design called for. In general, when a 12at7 is per design: the high end suffers with a 12ax7, and the low end isn’t as tight. 12at7’s are inexpensive. You can get RCA NOS tubes on the cheap.

 

[Konfyouzd]

Noob question...

Do you guys find an amp / cab that gets you close to the tone in your head then experiment with tubes for fine tuning or is it another process entirely for you guys?

I've only recently started messing w tube amps and I currently have more than one cab and a few speakers so I was planning to play around w that but was also curious about tubes since (on YouTube) they sometimes seem to make big differences and other times not so much.

 

[Descent]

They are actually quite different. AT’s have an mu of around 60, peak heater-cathode value of 90v, a plate resistance of 11k-ish and a plate dissipation of about 2 1/2 watts and roughly quadruple the bandwidth of an AX: mu of 100, peak heater-cathode value of 200v, plate resistance 60k, and a plate dissipation of 1.2 watts... to name a few differences. You get lower plate voltage and much higher current draw than the design called for. In general, when a 12at7 is per design: the high end suffers with a 12ax7, and the low end isn’t as tight. 12at7’s are inexpensive. You can get RCA NOS tubes on the cheap.

Thanks. I'll order a pair to compare.

I've been running that amp for over 15 years, never had issues with 12ax7s in all preamp positions.

Broke down and got two NOS Jan Phillips 12at7s. They were quite cheap, hope they're good. Also will experiment with some new AX7s in the preamp section of my Mesa Mini Recto just for kicks - JJ, EH, Sino (Shuguang?), Groove Tubes.

@Konfyouzd - it really depends. I am quite happy with all my tones, but I like to experiment. The Mesa for example is a bit noisy-ish on high gain, so trying to see if I can tame that somewhat.

My other amp, I looked for preamp tubes that have less low end as it is really wooly. I ended up with the shoddiest (supposedly) Chinese tubes that had awful rating from hifi people, and these took off some of that loose low end that I needed out. Also they provided higher gain as that amp was a bit low in that dept.

The power amp that I am retubing right now, basically the idea is to go as clean as possible, although with what I can afford that's a tall order.

My amp repair man and tube guru told me just now that JJs are absolute garbage...so I am now wondering whether I should return them.

 

[efiltsohg]

Noob question...

Do you guys find an amp / cab that gets you close to the tone in your head then experiment with tubes for fine tuning or is it another process entirely for you guys?

I've only recently started messing w tube amps and I currently have more than one cab and a few speakers so I was planning to play around w that but was also curious about tubes since (on YouTube) they sometimes seem to make big differences and other times not so much.

Yeah basically. I would look at speakers & cab construction first, then variety of power tube (if you can rebias), then preamp tube make/models, and power tube make/model last since it will make the least difference for modern high-gain amps

 

[efiltsohg]

My amp repair man and tube guru told me just now that JJs are absolute garbage...so I am now wondering whether I should return them.

not sure why he thinks that as they are the ONLY current production power tubes that can reliably handle high plate voltages

 

[DudeManBrother]

Thanks. I'll order a pair to compare.

I've been running that amp for over 15 years, never had issues with 12ax7s in all preamp positions.

Broke down and got two NOS Jan Phillips 12at7s. They were quite cheap, hope they're good. Also will experiment with some new AX7s in the preamp section of my Mesa Mini Recto just for kicks - JJ, EH, Sino (Shuguang?), Groove Tubes.

@Konfyouzd - it really depends. I am quite happy with all my tones, but I like to experiment. The Mesa for example is a bit noisy-ish on high gain, so trying to see if I can tame that somewhat.

My other amp, I looked for preamp tubes that have less low end as it is really wooly. I ended up with the shoddiest (supposedly) Chinese tubes that had awful rating from hifi people, and these took off some of that loose low end that I needed out. Also they provided higher gain as that amp was a bit low in that dept.

The power amp that I am retubing right now, basically the idea is to go as clean as possible, although with what I can afford that's a tall order.

My amp repair man and tube guru told me just now that JJs are absolute garbage...so I am now wondering whether I should return them.

Quality amps thankfully use higher tolerance components than the design minimums. You might notice a quieter, punchier amp once the 12at7 goes in. The Jan Phillips are fantastic. I have one in the PI spot on my Ultra Lead, and use them in all my old Boogies that spec’d an at7 for the reverb tube.

And JJ’s suffer from QC like every other tube being produced. Just buy (any new tube) from a good tube specialty store that adequately tests each tube. It’s still not a guarantee that the tube will last, but it’s the best option now adays.