Modern Day 12AX7s

[Soulcrusher_X]

Re: Modern Day 12AX7s

Okay if a 12AU7 is acting as a phase inverter - I had to look all of this up and yes, my amp is a push-pull - does it in effect halve the wattage assuming I balance the difference out in biasing the power stage? I ask because we got burned out of our house in August and are temporarily in an apartment where even 40 watts is too much. It'd be desirable to be able to max my master volume, keep my tone and hopefully have managable overall volume.

(been trying to trade a Line 6 Spider IV 150w for an HT-5 stack on craigslist but so far no takers.) Thanks. -Rod-

Nah, it doesnt work that way. The power section is still pushing out that 40 watts regardless if its being fed a clean or dirty signal by the PI

 

[misterwhizzy]

Re: Modern Day 12AX7s

The JJs and Chinese tubes have always lasted. I dont think Ive ever changed one out due to failure.

Interesting. My JJs last forever too. They sit in a drawer and stay exactly the same all day.

That's not entirely fair. The long-plate JJ I've got sounds all right. I feel like it doesn't have much treble detail, but it's good as a follower stage to tame highs a bit.

 

[Soulcrusher_X]

Re: Modern Day 12AX7s

I usually use the jj 803 long plate as a PI tube. In my MKIII and Splawn it added quite a bit of detail and articulation. In my old PV XXX, jjs were great because that is a really bright amp. Otherwise, I always use a TungSol in V1 in front of a JJ or two.

 

[Gunny47]

Re: Modern Day 12AX7s

I gotsa try me some 5751s in me Fendres!

 

[USAPatriot]

Re: Modern Day 12AX7s

Nah, it doesnt work that way. The power section is still pushing out that 40 watts regardless if its being fed a clean or dirty signal by the PI

That's unfair! :naughty: Okay...I need to replace my EL-34's soon anyway and the bias setting is supposed to be 50mv. Is there any ramification to the circuit if I drop that voltage? Thanks. -Rod-

 

[misterwhizzy]

Re: Modern Day 12AX7s

That's unfair! :naughty: Okay...I need to replace my EL-34's soon anyway and the bias setting is supposed to be 50mv. Is there any ramification to the circuit if I drop that voltage? Thanks. -Rod-

You'll be looking at current on that measurement rather than voltage. I'm pretty sure EL34's aren't going to work properly at 50 mV. Also, usually when you bias cold, you'll get a cleaner power section, which you may or may not like. When you bias it hotter, the power section is easier to drive into breakup. And this is a general rule, because the PI may have a lot to do with the power section's breakup characteristics, depending on the amp.

 

[jeremy]

Re: Modern Day 12AX7s

I gotsa try me some 5751s in me Fendres!

im a big fan of using one for v2 in fender reverb amps, a deluxe reverb in my case. i plug straight in atleast half the time and it pushes the balance of preamp vs pi/power tube distortion a little more to the right

 

[Gunny47]

Re: Modern Day 12AX7s

im a big fan of using one for v2 in fender reverb amps, a deluxe reverb in my case. i plug straight in atleast half the time and it pushes the balance of preamp vs pi/power tube distortion a little more to the right

Noted dude - thanks! This'll be a good spring break project! What musicians do on spring break :cool2:

 

[ErikH]

Re: Modern Day 12AX7s

JJ's for my Marshall head and EH's for my Vox Valvetronix AD50VT. I've had EH's and even Sovtek's in my Marshall but the JJ's just sound soooooo much richer and a lot quieter when I roll the gain up higher on the amp.

 

[PRSfan nym 1985]

Re: Modern Day 12AX7s

Okay if a 12AU7 is acting as a phase inverter - I had to look all of this up and yes, my amp is a push-pull - does it in effect halve the wattage assuming I balance the difference out in biasing the power stage? I ask because we got burned out of our house in August and are temporarily in an apartment where even 40 watts is too much. It'd be desirable to be able to max my master volume, keep my tone and hopefully have managable overall volume.

(been trying to trade a Line 6 Spider IV 150w for an HT-5 stack on craigslist but so far no takers.) Thanks. -Rod-

as I said earlier get an attenuator or a different amp, you aren't going to make that amp work in an apartment without an attenuator (that is literally the only way to drop the output level of the amp while crankin it), trust me I live in an apartment and I have tried dozens of different tube/SS amps. I know what works and what doesn't.

Small tube amps are still pretty loud, I doubt the HT5 will be much better for your apartment playing. You won't be able to crank that either without pissing the neighbors off.

 

[glassman]

Re: Modern Day 12AX7s

Okay if a 12AU7 is acting as a phase inverter - I had to look all of this up and yes, my amp is a push-pull - does it in effect halve the wattage assuming I balance the difference out in biasing the power stage? I ask because we got burned out of our house in August and are temporarily in an apartment where even 40 watts is too much. It'd be desirable to be able to max my master volume, keep my tone and hopefully have managable overall volume.

I know others have already answered this for you but I thought I might chime in and tell you why.

A 12AU7 in place of a 12AX7 in the PI roughly cuts the "drive" in half...but, the amp will still put out its full rated output or at least very close. What the 12AU7 gives you is the ability to turn up the master a little bit more to get a little more thickness to the tone. If you want to crank it all the way up...you're out of luck. But seriously, I don't know anyone that can crank a 40 watt amp in a typical performance environment. If you do, your stuck with an attenuator. If you set your stage volume at a typical level, a 12AU7 may be able to mimic the behavior of your amp at a lower volume.

I still have quite a few really good RCA and other 12AX7s but they aren't going to last me forever

I run RCAs in V2 & V4 of my Super Reverb. They've been in there a long time (20+ years) and test pretty low (~50% of original TC)...but that's how I like them! I've put new tubes in recently ("new" ones and NOS RCAs) and hated the response...way too much bass, too sterile and a rough break up. The old RCAs will stay. I have a stash of old Mullards for a Plexi build (actually my interpretation of one) I have planned for the spring (for me). Great minds think alike!

 

[Bludave]

Re: Modern Day 12AX7s

I use whatever my amp tech puts in. He has never failed me and my amps always sound like a dream when I get them back from him.

 

[USAPatriot]

Re: Modern Day 12AX7s

You'll be looking at current on that measurement rather than voltage. I'm pretty sure EL34's aren't going to work properly at 50 mV. Also, usually when you bias cold, you'll get a cleaner power section, which you may or may not like. When you bias it hotter, the power section is easier to drive into breakup. And this is a general rule, because the PI may have a lot to do with the power section's breakup characteristics, depending on the amp.

Dunno what to say about your second sentence. The bias setting for the HT-40's power stage is 50mv. I may (or may not) be the only person ever to have gotten that directly from Blackstar, who otherwise refuses to release the specs to anyone other than their "authorized technicians". I'm not one of those, obviously, and it took me 2 months of arguing with them and Korg to get that figure as well as "D36". Shrug. The preamp on the HT-40 has WAY more gain, with good tone, (new JJ's in it) than I need and your dire description above actually suits me because I play relatively clean, with the HT-40's gain at about 8 o'clock, 9 max. I push the master volume over for tone, not more gain. This is how I'll be playing probably for the rest of this year and I still have the GT-10 here for when I want to change patches. The patch I've been using for the last 6-8 weeks is the only one I have that doesn't use the GT-10's preamps, ie, it's the only one using only the HT-40's, and I like it. I've got a very expensive delay/tuner/volume pedal cuz right now, that's all I use it for :eyecrazy:

Anyhow, thanks to everyone for your thoughts. I have to replace those EL's regardless, so I may as well try and get what I want from the swap. -Rod-

 

[USAPatriot]

Re: Modern Day 12AX7s

I know others have already answered this for you but I thought I might chime in and tell you why.

A 12AU7 in place of a 12AX7 in the PI roughly cuts the "drive" in half...but, the amp will still put out its full rated output or at least very close. What the 12AU7 gives you is the ability to turn up the master a little bit more to get a little more thickness to the tone. If you want to crank it all the way up...you're out of luck. But seriously, I don't know anyone that can crank a 40 watt amp in a typical performance environment. If you do, your stuck with an attenuator. If you set your stage volume at a typical level, a 12AU7 may be able to mimic the behavior of your amp at a lower volume.

Thanks for your reply, Glassman. I'm just going to think on it awhile. Since the tubes have already been replaced, it's a project for later and who knows, maybe we'll actually be out of here and back into the house by the time I think it through. 7 months and the house hasn't even been torn down yet, much less rebuilding started. Real reason I replied...just had to type for while here...is that the wife saw your avatar and said, "Who's THAT?" LOL. -Rod-

 

[misterwhizzy]

Re: Modern Day 12AX7s

The bias setting for the HT-40's power stage is 50mv. I may (or may not) be the only person ever to have gotten that directly from Blackstar, who otherwise refuses to release the specs to anyone other than their "authorized technicians".

That's cool. Tell you what. Put your multimeter on 200 mV and measure it. Let's see what it says.

After that, put it on whatever you have that's more than 20 mA, and let's see what that says. You don't have to believe me. You can actually test it.

 

[STRATDELUXER97]

Re: Modern Day 12AX7s

I know others have already answered this for you but I thought I might chime in and tell you why.

A 12AU7 in place of a 12AX7 in the PI roughly cuts the "drive" in half...but, the amp will still put out its full rated output or at least very close. What the 12AU7 gives you is the ability to turn up the master a little bit more to get a little more thickness to the tone. If you want to crank it all the way up...you're out of luck. But seriously, I don't know anyone that can crank a 40 watt amp in a typical performance environment. If you do, your stuck with an attenuator. If you set your stage volume at a typical level, a 12AU7 may be able to mimic the behavior of your amp at a lower volume.



I run RCAs in V2 & V4 of my Super Reverb. They've been in there a long time (20+ years) and test pretty low (~50% of original TC)...but that's how I like them! I've put new tubes in recently ("new" ones and NOS RCAs) and hated the response...way too much bass, too sterile and a rough break up. The old RCAs will stay. I have a stash of old Mullards for a Plexi build (actually my interpretation of one) I have planned for the spring (for me). Great minds think alike!

Thanks buddy....In my 66 Pro Reverb I currently have Black Plate RCA 6L6s and pretty much all RCA 12AX7s and a Mullard 5AR4...Just a wonderful sounding amp overall....I did some nice stuff inside of it and the Webers in it are great also...My favorite and overall go to amp...Bought it for $50 back in like the late 80s off our drummer at the times dieing Dad.. ;o)