Raising gain on 12AU7 input tube.

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Posted by Cougar (A) on September 27, 2016 at 10:45:47

I need some help to raise the gain on my Driver PCB for my VTA-120. It's the low gain board that I use all 12AU7's but there is not enough gain and I have to turn my preamp up 2x higher to get the same volume level as before.

I don't crank the system but I don't want to turn up so high on the preamp. Can I reduce the value of the Plate resistor to up the Plate voltage slightly to increase gain without causing any other issues?

The plate voltage in this PCB is suppose to see a 135Vdc but I know that can vary depending on what type of Rectifier you are using. I'm using a GZ34 right now but I do have the Weber Copper Can than WZ68 which will give more voltage than the GZ34. I will try before doing any changes in the circuit.

I was looking to increase the plate voltage to about 150-160Vdc from 135Vdc. would this solve my gain issue? I don't need a whole lot of gain like the High gain PCB did before with the 12AT7's.

Also is there a 12AU7 substitute that may have a slightly higher gain that I can plug right in?

Any advice would be greatly appreciated.

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Topic - Raising gain on 12AU7 input tube. - Cougar 10:45:47 09/27/16 (19)

Sounds like from the responses that.... - Cougar 11:03:43 09/28/16 (1)

RE: Sounds like from the responses that.... - FenderLover 15:45:47 09/28/16 (0)

RE: Raising gain on 12AU7 input tube. - Naz 21:26:01 09/27/16 (1)

RE: Raising gain on 12AU7 input tube. - Cougar 10:59:08 09/28/16 (0)

The best solution - Chip647 19:03:26 09/27/16 (6)

RE: The best solution - Cougar 19:41:07 09/27/16 (5)

There is nothing wrong with that - Chip647 20:40:46 09/27/16 (4)

I will put the Weber WZ68 in...... - Cougar 21:17:19 09/27/16 (3)

RE: I will put the Weber WZ68 in...... - Tre' 07:39:38 09/28/16 (2)

I have never had to turn.... - Cougar 10:55:44 09/28/16 (1)

RE: I have never had to turn.... - Tre' 11:12:24 09/28/16 (0)

RE: Measure the voltage in/out of the preamp - Russ57 15:20:14 09/27/16 (0)

RE: Raising gain on 12AU7 input tube. - FenderLover 14:42:03 09/27/16 (1)

Yes, it's the newer low gain PCB. - Cougar 18:54:52 09/27/16 (0)

12AT7... - Ralph 12:48:23 09/27/16 (3)

RE: 12AT7... - Cougar 18:53:09 09/27/16 (2)

RE: 12AT7... - Ralph 10:07:28 09/28/16 (1)

There is one posted on the..... - Cougar 11:23:46 09/28/16 (0)

RE: Raising gain on 12AU7 input tube. - Eli Duttman 11:41:21 09/27/16 (0)

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