Anyone here able to help with Tube positions? Not sure where pre or power tubes go. Mainly the 12AU7 or 12AX7?
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2013 Ampeg V-4B 100W Reissue Pt2
- Thread starter Chef
- Start date
The positions are labeled on the back of the head
Here's the manual as well http://www.ampeg.com/products/classic/v4b/images/V-4B_OM.pdf
Thank you! I remember know seeing them.
Looking at amp from the rear is the drive 12AX7 on left of the 12AU7 or one of the two on the right of the 12AU7. Basically where is the position of the 12AX7 drive section compared to the 2 power 12AX7?
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Congrats. SCORE! Great rig. . the V4B thru the SVT810
Haven’t posted in a wile...picked up the Ricky a month ago and finally did some Rick O Sound this evening . Ran one v4b bass heavy thru the 810 and the other v4b gain all the way up, mostly mids and treble thru the 610. Very cool effect, sounds mean as all get out! Going to try it with distortion pedal next time but the v4b gain turned up does a good job. I’ve slaved both v4b’s before but never split the signal like this. Be fun to do this at a live show but it be a lot to move...will see!
Hey! I want to play too! Here's a couple of mine.
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Last time I checked. . A "couple" means 2. You've got what's commonly referred to as a hoard! 
VERY sweet collection there.
VERY sweet collection there.
That sounds like a lotta fun! And the sheer schlep factor is the ONLY reason I've not done it with my 4003.
Congrats!
The 12AX7 closest to the input jack is your first gain stage, the next one in order should be the second. These are your input gain and tone stack tubes. The third 12AX7 is the phase inverter, the 12AU7 the driver tube. There is a block diagram layout in the manual.
Michael Schreiber
Commercial User
Hm... isn't the 12AU7 the inverter?
According to the schematics, on page 14, the 12AX7 drives, while the 12AU7 inverts:
http://www.ampeg.com/products/classic/v4b/images/V-4B_OM.pdf
That would be in line with what @beans-on-toast explained, a couple of years back here:
If the block diagram layout is accurate then no, the 12AU7 is not the phase inverter. Look at the second half of the lower 12AX7, the phase inversion happens there. The plate of side A feeds side B, plate and cathode feed each half of the 12AU7 with inverted signals (inverted from plate, in phase from cathode). The 12AU7s are used to drive the power tubes, as they're plate output it would be inverted again, but the signal split is in the second half of the 12AX7. I don't have the full schematics of the new V4 so it's possible the diagram in the manual is inaccurate.
In the Invalid Link Removed the 12AU7 was a floating paraphase inverter in which case yes, the 12AU7 was the PI.
Also worth mentioning, the block diagram in the manual follows the design of the ampeg V4BH and is more similar to the SVT PI/driver arrangement than the original V4. As I said, it's entirely possible that diagram is not accurate.
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Michael Schreiber
Commercial User
Shoot, you are right. I should have had a closer look at the schematics. Thanks for the hint!
If I may take the opportunity; do I understand it correctly that the preamp and direct out both have inverted polarity compared to the original input signal - which takes a path through three halves of 12AX7 each taken from the plate - and for the DI finally followed by two non-inverting op-amps?
Again since I only have the V4B-RI block diagram from the manual and V4BH schematics I'm making assumptions, but yeah it looks like there are three plate stages before the cathode buffer.
Michael Schreiber
Commercial User
Yes, of course, I mean only by reading the schematics; just wanted to know if I interpret that diagram correctly.
Thank you very much!
The V4BH schematics are available here: Link Removed
The schematics are drawn differently but the V4BR and the V4BH preamps are basically the same. The wattage of some of the resistors in the V4B are higher, bumped up from 1/4W in the V4BH to 1/2W in the V4BR for example. This helps the V4BR to be quieter.
The schematics are drawn differently but the V4BR and the V4BH preamps are basically the same. The wattage of some of the resistors in the V4B are higher, bumped up from 1/4W in the V4BH to 1/2W in the V4BR for example. This helps the V4BR to be quieter.
