Tube Rolling w/Crack

[cddc]

I wanted to have a few backup 12AU7 varieties around and I thought I’d try a new production tube  to see what the difference might be for myself. It’s a Northern Electric 12AU7. The music sounds good but there is a faint hiss that my RCA clear top doesn’t make. I don’t know if a few hours of burn will make it settle down. For now it’s a $40 experiment that I probably won’t repeat. Also in my bag of tubes were the orange painted RCA above, a GE JH 5814 and an RCA black plate 5963, which all together cost less than the NE.

New production tubes are a waste of money. I'll never waste a dime on these garbages.

[jivex5k]

New production tubes are a waste of money. I'll never waste a dime on these garbages.

I see a general consensus about this, but wonder if there has been anything besides subjective analysis.

I decided to have some fun last night and recorded the amp's output using two different tubes. One was an RCA 6080 that the kit came with, the other was a Sovtek 6AS7G.
Now this was using a mono guitar cable, so it's only comparing one channel.

I'm not even certain it works that way, but I believe the tip would touch the left channel, and the sleeve would touch the right channel, and the ground of the jack. The input jack is mono so it would only grab the left channel.

Anyway, I got the sovtek from here: https://www.partsconnexion.com/TUBESVT-68351.html

I was getting a new pot and knob already from that store, figured what the hell I'll try a new tube. I think it's new production, the description says new.
It sounded thinner at first, but after a while seemed to become fuller. It's pretty subjective though, more of a feeling like I said before.

So I recorded the amp playing a song with each tube, ran a frequency analysis. I've attached the picture.
The top line is the hold of the highest amp for a given frequency, the bottom is the average. I played the same song for the same amount of time on each.

It seems like the sovtek has slightly better seperation of frequency response? You can see at the very start there's a clear separation in the low end, where the RCA is smoother.
In general this seems to follow across the other frequencys, around 100 you can see the RCA is smoother again.

Anyway, not sure it means much but it was fun to do. I don't know much about this stuff really but it sure is neat.

From an objective standpoint, the sovtek solved a lot of microphonic issues I had with the RCA tube.
From a subjective standpoint, I swear the RCA still sounds a little richer, but I think it's in my head. The sovtek today seems very rich though... it's so subtle it's hard to tell.

I should get someone to help me do a blind test.

[Paul Birkeland]

For measurements like that, you want to use periodic noise that itself would have a flat frequency response. I'd also try to get the level up to about the 0 line.  I would also do this with no headphones plugged in, and with the newer version of the Crack, you'd want a 1/4" to 1/8" adapter plugged in to defeat the shorting function of the output jack.

If the Crack was -60dB at 10kHz, we wouldn't sell very many 

[jivex5k]

For measurements like that, you want to use periodic noise that itself would have a flat frequency response. I'd also try to get the level up to about the 0 line.  I would also do this with no headphones plugged in, and with the newer version of the Crack, you'd want a 1/4" to 1/8" adapter plugged in to defeat the shorting function of the output jack.

If the Crack was -60dB at 10kHz, we wouldn't sell very many 

Hmm yes, I was looking for some frequency response test audio but couldn't find anything. I guess a noise that plays across all frequencies at the same level would work?
I'm clearly out of my element here...

I picked up a 1/4" TRS to 2 1/4" TS cable. My interface has 2 1/4" mono jacks for recording, this should allow me to record both channels out of the amp's headphone jack, no?

EDIT-
I found this page: https://www.audiocheck.net/testtones_highdefinitionaudio.php
"flat freq response" was the phrase I needed to find it. I'm guessing the white noise would work well for this purpose.

[mcandmar]

Try Right Mark Audio Analyser (RMAA), does everything for you by playing a frequency sweep, and then measuring the response, distortion, noise floor etc.

Start with a loopback cable and get the level dialled in to 0db and you should be seeing very close to a flat frequency response, then put an amplifier in the loop, set the volume control for the same level and measure again.  You can see in the example my cracks response was at the limit of my test setup, except the distortion was order of magnitudes higher, but in a nice tubey way

Download from here https://audio.rightmark.org/download.shtml , i prefer to use the older v5.5 of the software.

[jivex5k]

Try Right Mark Audio Analyser (RMAA), does everything for you by playing a frequency sweep, and then measuring the response, distortion, noise floor etc.

Start with a loopback cable and get the level dialled in to 0db and you should be seeing very close to a flat frequency response, then put an amplifier in the loop, set the volume control for the same level and measure again.  You can see in the example my cracks response was at the limit of my test setup, except the distortion was order of magnitudes higher, but in a nice tubey way

Download from here https://audio.rightmark.org/download.shtml , i prefer to use the older v5.5 of the software.

Oh cool, thanks!

[cddc]

I see a general consensus about this, but wonder if there has been anything besides subjective analysis.

I decided to have some fun last night and recorded the amp's output using two different tubes. One was an RCA 6080 that the kit came with, the other was a Sovtek 6AS7G.
Now this was using a mono guitar cable, so it's only comparing one channel.

I'm not even certain it works that way, but I believe the tip would touch the left channel, and the sleeve would touch the right channel, and the ground of the jack. The input jack is mono so it would only grab the left channel.

Anyway, I got the sovtek from here: https://www.partsconnexion.com/TUBESVT-68351.html

I was getting a new pot and knob already from that store, figured what the hell I'll try a new tube. I think it's new production, the description says new.
It sounded thinner at first, but after a while seemed to become fuller. It's pretty subjective though, more of a feeling like I said before.

So I recorded the amp playing a song with each tube, ran a frequency analysis. I've attached the picture.
The top line is the hold of the highest amp for a given frequency, the bottom is the average. I played the same song for the same amount of time on each.

It seems like the sovtek has slightly better seperation of frequency response? You can see at the very start there's a clear separation in the low end, where the RCA is smoother.
In general this seems to follow across the other frequencys, around 100 you can see the RCA is smoother again.

Anyway, not sure it means much but it was fun to do. I don't know much about this stuff really but it sure is neat.

From an objective standpoint, the sovtek solved a lot of microphonic issues I had with the RCA tube.
From a subjective standpoint, I swear the RCA still sounds a little richer, but I think it's in my head. The sovtek today seems very rich though... it's so subtle it's hard to tell.

I should get someone to help me do a blind test.

Measuring and analyzing the output signal is too complicated to me. But several things I need to point out:

1. The Sovtek 6AS7G is not new production, they are NOS Russian tubes. Though I've never bought any Sovtek branded 6AS7G tubes, I have several Svetlana 6H13C tubes (Russian equivalent to 6AS7G), and they look identical to your Sovtek. I believe they are from the same Russian factory.

2. You paid too much for your Sovtek ($48  ), Russian 6AS7G tubes normally cost $10 a pop plus shipping from Ukraine/Russia, that's what I paid.

3. NOS Svetlana 6H13C/6AS7G is a decent tube for the price, large soundstage and good bass performance. For $10 I'd pick up a Svetlana 6H13C any day than a crappy RCA 6AS7G. IMHO RCA 6AS7G is the worst 6AS7G tube ever manufactured, muddy nothing but muddy 

[greenneedle]

The adaptor I am using to put a 6sn7 in the 12AU7 socket has quite long pins so it doesn't seat flush like a 12AU7 does.  Is there any problem with clipping 2mm off each pin so it will seat properly?

[cddc]

The adaptor I am using to put a 6sn7 in the 12AU7 socket has quite long pins so it doesn't seat flush like a 12AU7 does.  Is there any problem with clipping 2mm off each pin so it will seat properly?

I don't see any problem cutting the pins. Just make sure you smooth the cutting edges with some file or sandpaper so that they won't scratch the socket, I think.

[jivex5k]

Well I was a bit bored today, searched around for some tubes for fun.
Picked up this bugle boy for 25 bucks: https://www.ebay.com/itm/254626346257

I started searching Mullards at first, was surprised to see them selling for around 500 bucks.
Crazy high prices, I'd rather spend that on SEX kit, or maybe some DIY synth stuff.

Eurorack stuff looks interesting, lots of DIY. Modular stuff sounds pretty good on this amp too, listening to some tracks right now. The highs, they're high but they are airy....? They aren't harsh, and modular stuff can get pretty freakin high pitched. The bass too... man, it really thumps on some songs in a really good way.

It would be a lot of fun to build my own synth and run it through the amp.

[Paul Birkeland]

Here are some Mullard 12AU7s for under $50:
https://www.ebay.com/itm/1-x-12AU7A-ECC82-Mullard-Hammond-Tube-Very-Strong-Balanced-3-Available/283991231062?hash=item421f324a56:g:j2EAAOSwR6NfRuok
https://www.ebay.com/itm/Mullard-Hammond-12Au7A-Vacuum-Tube-Measured-100-90-Gm-on-Amplitrex-1967-Gf2/282981215782?hash=item41e2feae26:g:nfEAAOSw~19bCC5u

[jivex5k]

Here are some Mullard 12AU7s for under $50:
https://www.ebay.com/itm/1-x-12AU7A-ECC82-Mullard-Hammond-Tube-Very-Strong-Balanced-3-Available/283991231062?hash=item421f324a56:g:j2EAAOSwR6NfRuok
https://www.ebay.com/itm/Mullard-Hammond-12Au7A-Vacuum-Tube-Measured-100-90-Gm-on-Amplitrex-1967-Gf2/282981215782?hash=item41e2feae26:g:nfEAAOSw~19bCC5u

Oh cool, thanks PB! Picked one up

[Colonl_Charisma]

Hi all,

I am wondering if changing the input tube makes a difference in the sound of the Crack. If it does what is the input tube that you all enjoy? I tried googling this question, but every thread and article seems to focus on the power tube.

[Paul Birkeland]

IMO the 12AU7 makes the bigger difference.

[Colonl_Charisma]

Thanks PB! That’s good to know.