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Post subject: Blues JR. Can I find an audio taper pot for the Gain/Volume?
Posted: Fri Aug 30, 2013 9:27 am
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Aspiring Musician
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BillM has an audio taper pot for the Master, but it's 50k and the gain/volume control is 1M.
I typically run the Master volume wide open (it just sounds better this way), but this makes the Volume/Gain control hard very sensitive to the smallest change around the 2-3 range.
Is there a 1M audio taper pot (same snap in form factor) that I could replace it with?


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Post subject: Re: Blues JR. Can I find an audio taper pot for the Gain/Vol
Posted: Fri Aug 30, 2013 9:49 am
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The gain/volume control (NOT the Master Volume) already is an audio taper pot.

http://support.fender.com/schematics/gu ... ematic.pdf

http://support.fender.com/schematics/gu ... _Rev-D.pdf

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Post subject: Re: Blues JR. Can I find an audio taper pot for the Gain/Vol
Posted: Fri Aug 30, 2013 11:29 am
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I was afraid of that. Well shoot.
I guess I will just have to deal with it or figure out a way to get the same tone when the master isn't on 10.


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Post subject: Re: Blues JR. Can I find an audio taper pot for the Gain/Vol
Posted: Fri Aug 30, 2013 12:51 pm
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Try a lower gain 5751 or 12AY7 in V1.

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Post subject: Re: Blues JR. Can I find an audio taper pot for the Gain/Vol
Posted: Fri Aug 30, 2013 3:20 pm
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I already have a 12AY7 in V1 and a 12AT7 for the phase inverter. (V2 is a ECC832 with the cathode follower mod).

My assumption is the master is reducing some high end much like the volume control of your guitar can kill some of the sparkle.
I'm not sure if I had this issue before all the changes from stock. Is this typical?


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Post subject: Re: Blues JR. Can I find an audio taper pot for the Gain/Vol
Posted: Fri Aug 30, 2013 3:34 pm
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Sorry. Can't help you there.

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Post subject: Re: Blues JR. Can I find an audio taper pot for the Gain/Vol
Posted: Sun Sep 01, 2013 6:07 am
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Perhaps a 12AX7 or 5751 in V1. It seems that you have too many low gain tubes with the lineup that you have now. You start off with a very low gain 12AY7 in V1, then a high gain half then a low gain half in V2, followed by another low gain 12AT7 in V3 (PI). Increasing the gain in V1 might be your best bet, maybe even a little more gain for V3 also, like a 5751. I like to turn up my master and set the volume at about 3 for a good clean tone. The 12DW7 in V2 is probably perfect for the Cathode follower mod, but you might even try a 12AX7 there too.

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Post subject: Re: Blues JR. Can I find an audio taper pot for the Gain/Vol
Posted: Sun Sep 01, 2013 9:55 am
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shimmilou wrote:
Perhaps a 12AX7 or 5751 in V1. It seems that you have too many low gain tubes with the lineup that you have now. You start off with a very low gain 12AY7 in V1, then a high gain half then a low gain half in V2, followed by another low gain 12AT7 in V3 (PI). Increasing the gain in V1 might be your best bet, maybe even a little more gain for V3 also, like a 5751. I like to turn up my master and set the volume at about 3 for a good clean tone. The 12DW7 in V2 is probably perfect for the Cathode follower mod, but you might even try a 12AX7 there too.


OP is complaining that even with the current tube selection, the volume control (not master) is too twitchy at low levels. Putting a 12AX7 back in V1 will only compound that issue. I also don't understand why BillM recommends a 12DW7 for the cathode follower mod. The cathode follower is a unity gain stage and works quite well with a 12AX7 in the 59 Bassman. I would suggest a 12AY7 in V1, 12AX7, in V2, and either a 12AX7 or 12AT7 in the PI.

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Post subject: Re: Blues JR. Can I find an audio taper pot for the Gain/Vol
Posted: Sun Sep 01, 2013 10:15 am
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I can definitely play around with some tube changes.
I guess I have hesitated to do that because it sounds so good with the current setup (just hard to control).
Just played out yesterday and someone came up and commented on how good my guitar sounded (and he wasn't even a guitar player)


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Post subject: Re: Blues JR. Can I find an audio taper pot for the Gain/Vol
Posted: Sun Sep 01, 2013 1:54 pm
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bluesky636 wrote:
...OP is complaining that even with the current tube selection, the volume control (not master) is too twitchy at low levels...


I think that problem is because of the low gain input of V1, followed by a high gain first half of V2. It's as if the signal from V1 isn't driving V2 very well until the volume gets up a little, then it starts really conducting suddenly. But, it's just a thought, I could be way off. :?:

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Post subject: Re: Blues JR. Can I find an audio taper pot for the Gain/Vol
Posted: Sun Sep 01, 2013 3:19 pm
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shimmilou wrote:
bluesky636 wrote:
...OP is complaining that even with the current tube selection, the volume control (not master) is too twitchy at low levels...


I think that problem is because of the low gain input of V1, followed by a high gain first half of V2. It's as if the signal from V1 isn't driving V2 very well until the volume gets up a little, then it starts really conducting suddenly. But, it's just a thought, I could be way off. :?:


I think you're close, but .....

You need to take into consideration that the OP's amp has the BillM cathode follower mod:

http://billmaudio.com/wp/?page_id=141

The schematic is a little unclear, but what BillM has done is insert the low gain half of the 12DW7 between the output of V1A and the high gain half of the 12DW7 (V2B), wih the tone stack in between.

In the 5F6A Bassman, the cathode follower is used to drive the heavy load of the tone stack which then drives the PI:

http://ampwares.com/schematics/bassman_5f6a.pdf

So the BillM mod has a cathode follower driving the tone stack which then has a gain recovery stage following it. The cathode follower keeps the tone stack from loading down the circuit and cutting the gain but then a gain stage follows which boosts the gain even more. Personally, I think it is all too much and is probably the reason BillM recommends using the 12DW7.

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Post subject: Re: Blues JR. Can I find an audio taper pot for the Gain/Vol
Posted: Mon Sep 02, 2013 4:04 am
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Crap! That's what I get for not looking at the schematic. :lol: I had the 12DW7 halves reversed in my head, thinking that the high gain half was first in the signal chain. Thanks for clearing that up for me bluesky636. I was really thinking of the rare 12WD7, which has the gain factors reversed for the halves. The 12WD7 is the tube that I've been wanting to try in the HRDlx.

As for the OP's problem..... maybe some tube swapping? :?:

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