Which tube does what?

irish_admiral · Post by **irish_admiral** » Sat May 08, 2004 10:19 am

Does anyone know the function of the separate preamp tubes in an AD30R? I generally hear stuff about one tube being in the "drive position", and another being in the "phase inverter" spot that feeds out to the power section? So i've got three 12AX7s in mine. What does each do?

I can't read schematics... Just go in a line from left to right! It goes 3 x 12AX7, 4 x EL84, 1 x GZ34. It prints what each tube is beneath it, and the centre 12AX7 print appears with brackets ( ) around its title. What's the significance of this?

And finally, does anyone have recommendations as to what sort of tube should go in each place?

Don't tell me the best way, just tell me the cheapest way...

spoonie g · Post by **spoonie g** » Sat May 08, 2004 4:56 pm

I've been trying to find this out for a while myself. Not even Orange USA could help me.

One thing, though, when you do find out, be careful when changing out the preamp tubes on these amps; they are mounted to the board, which is a bit flimsy.

spoonie g · Post by **spoonie g** » Sat May 08, 2004 8:38 pm

what about the ad140tc? mine has 4 preamp tubes but no reverb? I have schematics for mine, but have no idea what is what, and Orange USA didn't either.

spoonie g · Post by **spoonie g** » Sun May 09, 2004 4:03 pm

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what about the ad140tc? mine has 4 preamp tubes but no reverb?
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You've got two channels so that's two 12AX7's for each channel.

Can you scan the schematics? Geert Jacobs will put them on the Orange Amp Field Guide.

I seriously doubt it is that simple, plus, I don't know which is the PI, driver, etc. I popped a GT 12ax7m into the closest one to the power tubes thinking this would be the driver, but it didn't make as much of a difference as I thought it should, so I'm thinking maybe that isn't the driver.

Also, I don't have a scanner. I can, however, email them to this Gerrt fellow.

Sooner
OR-AD15-12
Serial No. 001

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irish_admiral · Post by **irish_admiral** » Tue May 11, 2004 12:48 am

Any further ideas as to which preamp valve corresponds to what function on my AD30R?

Don't tell me the best way, just tell me the cheapest way...

fiveightandten · Post by **fiveightandten** » Tue May 18, 2004 1:02 am

I've never been inside an AD-140...but i've worked on an AD-30TC head (no reverb).

The AD-30TC has 2 phase inverter tubes, one for each channel. Each channel has 2 pre-tubes...one for the pre-amp gain stages, and one for the phase inverter.

As for your AD-30R...

Keep in mind that 12AX-7's are "dual triode" tubes. Meaning they are like 2 seperate tubes in one glass housing. If you've got reverb, the signal path goes like this (we'll number each 12AX7 tube or "valve" Vx):

Input>>1st 1/2 V1>>Gain knob>>2nd 1/2 V1>>Tone controls>>Reverb send (the reverb is wired in parallel with the signal path)>>1st 1/2 V2>>Reverb pot>>2nd 1/2 V2>>V3, both sides being used for long tail phase inverter.

So the tubes are being used like this in an AD-30R...

V1- Pre-amp
V2- Reverb driver tube
V3- Phase inverter

Hope that helps.

-Nick

fiveightandten · Post by **fiveightandten** » Tue May 18, 2004 1:06 am

Oh...the GZ-34 is a rectifier tube, which changes the AC wall voltage into DC voltage for the tubes. The EL-84's are the output tubes, which are running cathode based, push and pull.

Also...In hindsight, the 2nd 12AX-7 is probably in () because it's the reverb tube, and not part of the audio path. Also possibly because it's running in parallel (bridged with a 100K resistor that acts as a balance between the dry and aeffected signal).

-Nick

fiveightandten · Post by **fiveightandten** » Tue May 18, 2004 1:09 am

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>
Don't tell me the best way, just tell me the cheapest way...
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But the way...This gets really annoying after reading a few of your posts.

fiveightandten · Post by **fiveightandten** » Tue May 18, 2004 1:22 am

Also...

<img src="http://www.proguitar.de/ProGuitarPreisl ... HTrafo.jpg" border=0>

That's a picture of an AD-30 without reverb. Notice that the 2nd pre-tube is missing. They use the same chassis, and just bolt a metal cover over where the reverb tube would've been.

-Nick

irish_admiral · Post by **irish_admiral** » Tue May 18, 2004 9:32 am

Hah! The tag is a semi-serious autosignature. I'm a student with no money and a lot of debt, so it kind of works out true.

Thanks for the follow up though... i'd just about worked it out by switching different tubes with different sounds within the preamp, but it was good to have it confirmed.

Just for everyone else, for the preamp tubes I think the one on the far left is the drive slot (colours your sound the most... so pick a good tube!), the one in the centre (missing in the picture above) is the reverb, and the one on the right is the phase inverter.

Don't tell me the best way, just tell me the cheapest way...

spoonie g · Post by **spoonie g** » Tue May 18, 2004 3:59 pm

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>
Hah! The tag is a semi-serious autosignature. I'm a student with no money and a lot of debt, so it kind of works out true.

Thanks for the follow up though... i'd just about worked it out by switching different tubes with different sounds within the preamp, but it was good to have it confirmed.

Just for everyone else, for the preamp tubes I think the one on the far left is the drive slot (colours your sound the most... so pick a good tube!), the one in the centre (missing in the picture above) is the reverb, and the one on the right is the phase inverter.

Don't tell me the best way, just tell me the cheapest way...
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yeah, I'd say that's right because I popped a GT-mullard in the far right one on my ad140 and it didnt make as much a sonic difference as I thought it should have. I need to try the left one.

irish_admiral · Post by **irish_admiral** » Tue May 18, 2004 5:56 pm

Yeah, I dropped an old Mullard tube in the drive slot. It was replacing a Brimar one... kind of heard the difference straight away!

Don't tell me the best way, just tell me the cheapest way...

Which tube does what?

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