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Vintage threads from the first ten years

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Re: 5E3 Volume Comes on Fast

2/20/2005 7:44 PM
Greg Simon Re: 5E3 Volume Comes on Fast
It could be that they used an audio taper pot instead of a linear taper pot?  
2/21/2005 12:12 AM
Casey Sackett

I had a Vicky 5E3, have built a few, and have played through a couple real Fender 5E3's. The volume came up just about the same on all of them.  
Just my observations.  
2/21/2005 10:28 AM
Bruce /Mission Amps

I've worked on and played with many Victoria 5E3 amps and real vintage ones. They all do the same thing and some are better/worse then others.  
It seems to be the nature of the beast.  
However, I agree it's the amp's biggest complaint.  
It would be nice if someone would come up with a 3%-5% audio taper pot.  
The newest MOJO taper pots MEASURE a 15% taper (plus/minus 2%-3%) and all my kits use the heavy duty 3/8" bushing, dampened, Alpha pots which are also MEASURE 15% taper (plus/minus 2%-3%).  
Whether either is Audio or Log taper, nobody can/will tell me.  
It's a bit funny though, I have hundreds of other vintage audio pots (not 1Ma) that have shallow tapers in the 7%-10& range.  
Maybe someday I'll be able to afford a 10,000 piece purchase of custom made pots with radical tapers like that.  
2/28/2005 3:51 AM
Dave H

The volume is nearly flat out at half rotation on a 15% taper pot. If you never need to turn it above half way the 1M pot could be replaced with a 750K resistor in series with a 250K 10% log pot. That would reduce the volume jump but it still wouldn’t be as good as a 1M pot with the output taken from the wiper.  
2/21/2005 4:31 AM
Chris @ CMW amps

I did experience a slightly more pleasing range with the MojoTone pots compared to Alphas and CTSs.  
2/21/2005 12:00 PM

A couple of quick points:  
12AX7 or 12AY7 ? the 12AX7 has more gain and will tend to distort earlier. In Weber's schematic, the plate resistor is changed to 68K to counteract this and give roughly the same performance with a 12AX7 that the original had with a 12AY7.  
Some "Audio" pots are 10% (-20dB) at half rotation, some are 30% (-10dB). There are other variations I'm sure. Find ones with the most dB attenuation.  
Some possible remedies:  
Change the cathode arrangement on the input triodes to individual unbypassed resistors.  
Remove the cap on the second stage cathode.  
Install a resistor in series with the cap that connects the input tube to the pot. Something like 47K or 100K.
2/23/2005 8:14 AM

Or, you could use a good attentuator to get more range and leave the circuit as-is. I like the Dr. Z Air Brake, but it's expensive. Some guys like the mini MASS, but it cuts the highs a little much for my taste.
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