5E3 Variable Boost Mod

[Shawnobi]

Hi,
I want to mod my 5E3 based build to have a boost, though a pot rather than a switch.
This is what I am thinking of implementing. Does anyone have a better suggestion or can see an issue with my plan?
Thanks in advance.

[Enzo]

The main issue I see is you already have a 25uf cap bypassing that cathode. Adding another 0.68uf in parallel will do nothing. I don't have my calculator, maybe 3% tops? The difference between 25uf and 25.68uf.

A real 5E3 has a 12AY7 input tube, a 12AX7 would have higher gain. Then you could add a pot, but dial it down to the original level as "normal", then turn it up for some boost. Just a thought.

[Shawnobi]

The main issue I see is you already have a 25uf cap bypassing that cathode. Adding another 0.68uf in parallel will do nothing. I don't have my calculator, maybe 3% tops? The difference between 25uf and 25.68uf.

A real 5E3 has a 12AY7 input tube, a 12AX7 would have higher gain. Then you could add a pot, but dial it down to the original level as "normal", then turn it up for some boost. Just a thought.

Hi Enzo,
I already use a 12AX7 in that position. What I want to be able to do is dial in some pre-amp distortion for lower volume playing.
Are you suggestion use a pot instead of the 820R cathode resistor to drop the value?

[Shawnobi]

Actually, reading around it seems a master volume mod will do a better job of it. Only involves swapping the 1M resistor with a 1M pot Pre PI.

[Chuck H]

A master volume mod won't include any of the good power tube clipping at lower volumes. In fact, you won't get much distortion without power tube clipping with that amp. Which means that distortion = loud WRT that model. I think your best option would be an attenuator.

[Shawnobi]

A master volume mod won't include any of the good power tube clipping at lower volumes. In fact, you won't get much distortion without power tube clipping with that amp. Which means that distortion = loud WRT that model. I think your best option would be an attenuator.

Wanted to avoid that really. Same way I want to avoid have a pedal sat in front of the amp on the floor as the amp mostly lives at home. Thanks for the suggestion though.

[copperheadroads]

I just added this master volume mod to my newly built 5e3
https://robrobinette.com/5e3_Modific..._Master_Volume
using a 1 meg audio pot I've installed it on the back where the ext speaker jack use to be ,I'm not really impressed ,it goes from hardly any sound to about 1/2 volume right away turning the rest of the way increases slightly .also it sounds kind of anemic untill it gets up to almost full volume .
I think i will reverse this mod . I really like this amp cranked with a Boss SD 1 boosting it .

[Chuck H]

That's not a surprising outcome. I tried to warn against it in post #5. This is why I suggested an attenuator. That the amp doesn't start sounding good until the master is almost maxed is a clue. I understand that you want to avoid an attenuator... If what you want is master volume type amp then a 5e3 was a bad choice. If what you want is a 5e3 sound at lower volume then an attenuator isn't a bad choice. Sometimes we need to make concessions. It's an "if... then..." scenario.

[olddawg]

The easy fix for your problem is to simply get the right pedal or a smaller amp. I constantly see people trying to mod a great amp for an application for which they are simply not suited. Get a $100 five watt head, set it on top or behind it, and plug in the speaker. Use a 50 watt Weber Mini Mass attenuator if needed. Case and point. I was playing some small venues a while back. I got lots of compliments on the sound of my ratty old 1960 Ampeg Rocket amp. It wasn't even switched on. I had an Epiphone VJ head behind it plugged into the speaker. AND the speaker was an Eminence ceramic magnet replacement, lol. But it sure looked like I was getting the vintage mojo from a ratty old vintage amp!

[jack briggs]

I just added this master volume mod to my newly built 5e3
https://robrobinette.com/5e3_Modific..._Master_Volume
using a 1 meg audio pot I've installed it on the back where the ext speaker jack use to be ,I'm not really impressed ,it goes from hardly any sound to about 1/2 volume right away turning the rest of the way increases slightly .also it sounds kind of anemic untill it gets up to almost full volume .
I think i will reverse this mod . I really like this amp cranked with a Boss SD 1 boosting it .

I added this same master volume and removed it after a few minutes as I found exactly what you described here for its performance. My aim was to lower the phase inverter distortion, which RobRob stated a pre-PI master would handle nicely. It didn't. I used the 470K grid stop resistor instead to accomplish that - much better to my ears.


cheers,

[Helmholtz]

My aim was to lower the phase inverter distortion, which RobRob stated a pre-PI master would handle nicely. It didn't.

If the pre PI MV did not lower distortion, you probably had no significant PI distortion. The MV also provides some grid stopper effect when not fully up.

[mozz]

Put the pot so it jumpers the channels.

[Helmholtz]

Put the pot so it jumpers the channels.

What channels?

[Enzo]

I suspect he means the positive and negative sides of the phase inverter. Or upper and lower sides if you prefer.

[mozz]

The picture is not of a 5E3. That being said, on a 5E3, there are 4 inputs, a very common mod is to jumper the channels so you are using both halves of the input tube. I'm sure you can make it variable.