Preamp tubes aren't real bright

[Newc]

Should 2 12AX7s that have been on for 30 minutes look this dim?

This is my in ADA MP1. The tubes in my GSP2101 are about 2 or 3 times as bright after only 10 minutes.

[Danno]

I recently got a new sovtek tube in the preamp section of my marshall head and it didn't seem to light at all, although the amp worked fine. I called the guy who had done the work, and he said that these kind of sovtek tubes don't show very much light at all. Don't know if this helps.

[Cleveland Metal]

Well...

1st: Some tubes aren't that bright. Some are very bright... Depends on design.

2nd: I'm sure there is a more technical explanation, but many preamps just don't send much voltage through the tubes and the same tube won't won't glow in a particular preamp (Mp-1, Marshall JMP-1, Voodu valve) like it would in some other preamp w/big transformers (CAE3+se, sp-77, Mesa recording preamp etc).

Real all tube amps have a LOT of voltage available to tubes. Power tubes see 400-700 volts via the massive transformers and caps. 12ax7s can take something like 300 volts. Most lil preamps just don't supply that sort of voltage, hence the lesser glow.

These preamps, use the tubes in them to flavor the sound a bit, and not so much as "make" the sound.


I look at the Marshall JMP-1, Voodu Valves, MP-1s etc etc, and they have little transformers in them to supply overall power to the whole unit, and I imagine they send enough to get the tubes to function somewhat, but obviously not able to send close to 300 volts.

[Rupe]

I would guess its the tubes if everything souns good to you. The 12AX7's in my MP1 light up as bright as they do in any of my amps.

[Newc]

Thanks all. The tubes are over 10 years old, so I figured it was time for them to die. But if they're not broke, I ain't fixing them

[toejam]

I just got a Carvin V3 head, two of the five preamp tubes are pretty dim compared to the others; one's a Tung Sol and the other is an Edicron EH. The normal brighter ones are two JJ ECC83S and one no-name 7025. I guess someone didn't like the original tubes in it.

[DonP]

Swap the dark tubes for the bright ones and see if it makes a difference.

The glow of tubes are the heaters. 6.3 volts in parallel (or 12.6 volts in series; hence the "12" part of a 12AX7). Plate voltage (300+) has nothing to with the heater voltage.

The hotter the heater, the more electrons fly off the cathode, and the more "stuff" the tube can do (amplify, power).

[Cleveland Metal]

So the the glow is the due heater circuit with a voltage of 12v? And the glow nothing to do with the "up 300v" available in amps?

[Cleveland Metal]

Hmmm, I guess I "kind of" actually knew that, now that I'm thinking of it... Duh...

[DonP]

A 12AX7 has two triodes, each with a 6.3 volt heater. You can wire these in parallel for 6.3 volts or in series for 12 volts. Almost all are wired as 6.3 volts to match the heater voltage of the power tubes. This way you don't need a separate 12 volt and 6 volt heater supplies.

Yes, I was the nerd in the electronics engineering classes (all for the quest of the ultimate distorted tube tone)

Oh, and as far as brightness, it's the same as a light bulb. You can have 40w, 60w 100w light bulbs, but they all run on 120 volts. Same with tubes (which are just fancy light bulbs). Some tubes burn hotter, but for a given tube class (12AX7) they should burn with the same brightness. Differences could account for some tubes sounding better or worse than others. Maybe JJ's burn brighter (but cleaner)? Maybe darker preamp tubes give a better brown sound? Someone should research tube brightness vs. tone.

[Cleveland Metal]

Thanks for waking me up! haha... Not thinking today for sure.

I've seen on I believe tubestore's site where they mention certain tubes barely glow due to design.

Would you agree that tubes thare are not getting the high voltage (up to 300 volts in some amps) for the other areas will not be running up to par?

[Newc]

Ok, I did the side-by-side comparison - MP1 vs GSP2101 - running into both units at the same time via ABY box using my SLS with EMG 85/81.

http://newcenstein.com/mp3/mp1vs2101.mp3

Both preamps set to the following:
Tube Distortion (both have 2 12AX7s and 2 separate Gains/ODs)
Gain 1&2 = Half (5 for the MP1, 5.6 for the 21 since it goes to 11 )
Volume = Half (5 for the MP - goes to 10) (0 for the 21 - goes from -16 to +16)
EQ = 0 (both have + and - so 0 is flat) 2101 has a Global EQ, and that was also set to all 0s
Sends out to the Mixer to bypass the FX sections (preamp-only signal)
Master Volume/Output knobs: 11 o'clock for the MP1, 12 o'clock for the 2101
Mixer channels panned hard left/right.
Levels out of the mixer are Right (MP1)=6, Left (2101)=7.
Input levels into Audition 3 were almost even (the right seems more dynamic (spiky), the left is more consistent - notice the proximity to the -12dB line)




Doesn't sound like the MP1's tubes are bad, so I guess they're just darker by nature. I'm pretty sure the guy I bought it from said it had GrooveTubes in it.

[DonP]

Would you agree that tubes thare are not getting the high voltage (up to 300 volts in some amps) for the other areas will not be running up to par?

I'd agree that if the tubes weren't getting the voltage that the "circuit" was designed to deliver, it wold not be running up to par.

I've created a 2.5 watt micro Marshall with a pair of 12AX7's, a 50C5 and a 35W4. In this circuit, the tubes run with about 160 volts on the plates. It works and sounds good (might need a bigger output tranny for more bass) because the voltages match what the circuit called for.

[Newc]

I've also done a Clean Tube and Fully Saturated/Max Distortion comparison.

http://newcenstein.com/mp3/cleantube.mp3

Settings:
2101
Clean Tube
Gain1: 3
Volume: 0 (middle)
EQ: all 0s

MP1
Clean Tube
OD1: 3
OD2: 3
Volume: 8 (can't be heard well enough below that)
EQ: All 0s

http://newcenstein.com/mp3/maxdist.mp3

Settings:
2101
Tube Distortion
Gain1: 11
Gain2: 11
Volume: 0 (middle)

MP1
Tube Distortion
Gain1: 10
Gain2: 10
Volume: 5 (middle)

Knob and mixer settings same as before.


I should note that I discovered my speakers are wired backwards. In these images and clips, the MP1 is actually on the Left, not the Right. When it comes out of my speakers, the MP1 is on the Right, but in the actual audio clips, it's on the Left.


Looking at the waveform, the 2101 appears to be more dynamic, or the MP1 is more balanced.

The MP1 also hums/hisses loudly when both OD1 and OD2 are on 10.

[metalchurch79]

As stated above some tubes aren't as visibly bright as others are.
I did some tube swapping in Side-B of my Marshall 9200 last month and I thought that some of them looked kinda dim to me, even though they sounded as good or better than some of the other tubes.

I believe that my Sovtek 12AX7's were kinda dim as were the Chinese 12AX7's.
I have (3) 12AX7 Groove Tubes that I'm not using if you want to check them out and see if you like them you're more than welcome to them.
If yours are GT's then they should have a logo on them.

ADA's are noisy as all hell when the Gain is cranked up. My MP-2 was slightly more noisy than my MP-1 because it has more Gain than a stock MP-1.
Does your MP-1 have the 3TM? (3 tube mod) I forgot to look.