50s RCA 2A3 vs new JJ 2A3: electrical differences?

[mhardy6647]

Sovtek 2A3s have served well in my experience with 'em; but the ones I have were very early production (1990s). The worst thing I can say about them is that they're kind of bland sounding compared to many other 2A3s. Actually the next-worst thing I can say about them is that their filament design doesn't allow much glow to be seen.


Long exposure photo of one taken by my son many years ago in a Bottlehead Paramour. In normal light, the filament glow is barely visible.

They're perfectly OK tubes, though -- indeed, during some amplifier issues recently, they were a nice, solid, go-to while I was troubleshooting. I've run them recently in both of the two different flavors of 2A3 amplifiers here, in fact.

 

[maxhifi]

I guess the easy way to put it is I've never met a 2A3 I didn't like, including the lowly valve art of years past. I may try Sovtek some day too, but I have three sets of output tubes already and they're all testing as new, so why bother?

One thing I noticed about then OP's amplifier is the bias meters appear to be reading kind of high. Just to be sure these amplifiers are intended for, 120VAC, and not 100V, right?

 

[mhardy6647]

I concur about the ValveArt, FWIW. They were cheap ($20 a pop back when my Paramours were new) and they sound, and look, good.


DSC_0001 by icouldbeahero, on Flickr
another of my son's long exposure photos

 

[grantray]

I guess the easy way to put it is I've never met a 2A3 I didn't like, including the lowly valve art of years past. I may try Sovtek some day too, but I have three sets of output tubes already and they're all testing as new, so why bother?

One thing I noticed about then OP's amplifier is the bias meters appear to be reading kind of high. Just to be sure these amplifiers are intended for, 120VAC, and not 100V, right?

The bias meters have since been reset to zero when powered down. The amp is specifically built for US 120v. That stated, the right power tube is currently running a touch over 70ma and the left is s hair under 70ma. What that says about the tubes, I can't say.

 

[maxhifi]

The bias meters have since been reset to zero when powered down. The amp is specifically built for US 120v. That stated, the right power tube is currently running a touch over 70ma and the left is s hair under 70ma. What that says about the tubes, I can't say.

The schematic says 60mA is normal, all it means is the tubes are strong, and in good health. I wouldn't worry about it, but it's at the high end of the normal range. Once they're worn out it will probably read 45 or 50mA.

 

[Poultrygeist]

I have a pair of the RCA 2a3 tubes but in my Bottlehead/Lowther system I prefer the less expensive Shuguang 2a3C

I also have a pair of Valve Arts and they don't come close to the Shuguang C.

My only experience with JJ was with a pair of EL84's that didn't last a year.

 

[grantray]

The schematic says 60mA is normal, all it means is the tubes are strong, and in good health. I wouldn't worry about it, but it's at the high end of the normal range. Once they're worn out it will probably read 45 or 50mA.

Thanks Max! That's exactly the info I've been lacking. Now I'm going to dig into the schematic to see where you got the info that 60mA is normal. I'm slowly learning my way down the rabbit hole of capacitance and resistance

 

[grantray]

Got the JJ 2A3-40s installed and set the bias. Like the grey-plate RCA 2A3s, they're operating closer to 70mA, but the JJs aren't quite as strong on the meters as the RCAs. The sound, though, is better. Not worlds better, but better. Not better midrange (although likely just as good once the tubes burn in), but more impact in the low frequencies, and more headroom on the high frequencies. Again, not huge, but noticeable and enough to make me rethink the chase for NOS as the penultimate. When/if the 12AX7 and 12AU7 long-plate Mullards ever go south that are currently in McIntosh C20 I run for my preamp, I just might be looking for new, not new old stock.

 

[maxhifi]

Got the JJ 2A3-40s installed and set the bias. Like the grey-plate RCA 2A3s, they're operating closer to 70mA, but the JJs aren't quite as strong on the meters as the RCAs. The sound, though, is better. Not worlds better, but better. Not better midrange (although likely just as good once the tubes burn in), but more impact in the low frequencies, and more headroom on the high frequencies. Again, not huge, but noticeable and enough to make me rethink the chase for NOS as the penultimate. When/if the 12AX7 and 12AU7 long-plate Mullards ever go south that are currently in McIntosh C20 I run for my preamp, I just might be looking for new, not new old stock.

The bias?

Anyway glad you got it going, I use JJ 2A3-40 tubes for hours a day, and have no interest or temptation to experiment more with other tubes. For the preamp stuff, you'd be hard pressed to beat NOS, in that realm if you want to go new I'd be tempted to get shuguang 12AX7 and 12AU7 before looking at JJ.

 

[grantray]

The bias?

Anyway glad you got it going, I use JJ 2A3-40 tubes for hours a day, and have no interest or temptation to experiment more with other tubes. For the preamp stuff, you'd be hard pressed to beat NOS, in that realm if you want to go new I'd be tempted to get shuguang 12AX7 and 12AU7 before looking at JJ.

Ha. I'll get out of the new-baby/no-sleep fog one of these days. I thought hum, but the fingers still typed bias. Alas.

For preamp, I won't be rolling anything new in until the Mullards die. The next project for this rig is designing and building a custom audio cabinet to protect all those shiny knobs, buttons, and tubes from curious little pudgy fingers. I'm mighty tempted to mount both the C20 and MR67 on a single walnut face that's protected by panes of sliding frosted glass. We'll see.

 

[maxhifi]

Ha. I'll get out of the new-baby/no-sleep fog one of these days. I thought hum, but the fingers still typed bias. Alas.

For preamp, I won't be rolling anything new in until the Mullards die. The next project for this rig is designing and building a custom audio cabinet to protect all those shiny knobs, buttons, and tubes from curious little pudgy fingers. I'm mighty tempted to mount both the C20 and MR67 on a single walnut face that's protected by panes of sliding frosted glass. We'll see.

That's really how they were meant to be installed. Make sure to read the instruction manuals about ventilation and how to mount in a panel.

Those old Mullards in your preamp will probably last many years, there's no sense worrying about them, although It is kind of nice to have some spare tubes on hand in case you need to troubleshoot, I always like to have a full set of spares at the ready.

 

[grantray]

That's really how they were meant to be installed. Make sure to read the instruction manuals about ventilation and how to mount in a panel.

Those old Mullards in your preamp will probably last many years, there's no sense worrying about them, although It is kind of nice to have some spare tubes on hand in case you need to troubleshoot, I always like to have a full set of spares at the ready.

Yeah, I'm not planning on fiddling with preamp tubes for the C20 any time soon.

Definitely working off the specs for the cabinet, and I won't be building it myself. I know a couple master cabinet builders here in SF, and I'll be handing the the design off to one of them after we make sure the details are all worked out. Since you mention ventilation, the poor ventilation of the components' original cabinets is one of the major reasons why I'm designing a custom solution. The little walnut boxes sure look cool, but they're the equivalent of wearing a down feather straight jacket on a desert summer day for those transformers and tubes.