Which preamp tube to play with

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Bottle Rocket
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Which preamp tube to play with

Post by ehehat » Sun May 27, 2018 5:18 pm

Sorry guys. I’m sure it’s been covered here but I couldn’t find it (and yes, I searched). What preamp tube slot will have the biggest impact on tone? It’s usually V1 but looking at the layout all the gain stages are V2 and V3. Would those have a bigger impact or is V1 still the way to go?

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Mark II
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Re: Which preamp tube to play with

Post by dtrax » Fri Jun 08, 2018 11:29 pm

V1a (first half of the triode) is the input stage for all channels on a Recto. So anything that happens at that stage will be amplified the most, and generally the reason why it's said to have the most influence on tone. Preamp tubes are cheap, see for yourself.
Ibanez '98 RG7620 (EMG 81-7H, 60-7H)
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Mark III
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Re: Which preamp tube to play with

Post by woodbutcher65 » Sun Jun 17, 2018 1:07 am

I do two specific tests of all tubes that I put in a Triple Wreck, or ANY amp, for that matter.

First I check tubes for gain and stability. Stick the tube in V1 on the Recto (dual or triple) and set it to the green channel, pushed mode. Crank EVERYTHING on that channel but the master and output. Plug a guitar in and play while SLOWLY rolling the guitar volume from zero to full. Listen to how smoothly the distortion rolls in. If it "gates" then it's not a good enough tube. Not for that position, anyway.

I've found that for some reason, V1 pushed is the toughest test for testing preamp tube gain. No other tube socket makes greater demands on the tube.

Very high gain tubes may go unstable and you may even get a "wah effect" (actually it's the Miller Effect) as your guitar's volume approaches max. Generally speaking, the higher the tube gain, the more pronounced the "volume wah" effect will be.

Second, I switch to the red channel, set all six red controls to 5 (middle of their range), switch to Modern, and swap tubes around in socket V2 to check for tube noise level.
I do this by setting up my sound level meter in front of the speaker and picking a specific reasonable and comfortable test volume level to test at. I have chosen 73 decibels as my target.
The meter is set to "c" weighting and SLOW response.

First, I take a preamp tube that I consider to be a decent one, not my quietest and not my noisiest, stick it in V2, and will use this specific tube as my reference.

I remove the original knurled output knob and install a knob that has a numbered skirt on it, like any knob found on a Mark series amp.

I set the output level to 5 and then slowly roll up the effects send (effects loop ON but no effects connected) until the sound level meter reads 73 dB of noise.

Oh...this is important....nothing is plugged into the amp's input jack. We're testing tube noise, not trying to make guitar sounds.)

Now, I turn the output level down to 0, flip the standby switch to standby, remove the tube in V2, and install a tube to be tested in the V2 socket. Flip the standby switch to operate
in about 10 seconds or wait a little longer if you want.

While doing this test on your tubes to be tested, leave EVERY control on the amp alone except the output control. Leave all the others alone because any of them can affect the consistency of your results.

Slowly turn up the output control and watch the sound level meter. When it reads 73 dB, read the number setting on the output knob. After you remove the tube you'll mark that number on the tube with a sharpie. A higher number means a tube that has less noise. It's only a relative value, relative to your reference tube you started with, which has a value of 5. (Mark the tube as your reference, say R5 with a Sharpie.)

If you have a tube with crusty pins, clean them. I dip the pins in muriatic acid for a few seconds, then rinse them off very thoroughly. But do this quickly or acid fumes will be sure to eat the painted markings off the tube. Just cleaning the tube pins well can add a whole number to the tube's noise level setting. (lower noise floor for that tube)

About every 3 tubes you test, retest your reference tube. This is to ensure that nothing drifts as the amp warms up and stabilizes. If there is drift, adjust for it using the effects send level control.

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