Mojotone 5E3 With No Gain

[Chodrick1]

I have a stock Mojotone 5E3 kit that I've assembled. It plays fine, but it's very, very clean. All headroom and no distortion. I can turn volumes and tone to 12 but I cannot get the amp to breakup. The rectifier and power tubes begin to run hotter than normal with only being on for 2 minutes. I mean really radiating some heat.

I began troubleshooting the amp at the inputs, everything Ohm'd out properly, so I am not losing any output there. Move on down to the power supply and I begin to notice some major differences in my B+ Voltage. I look up some standard voltages for my tubes and I notice that V1, V3 and V4 have some issues.
I believe my problem is with my rectifier having too high of a VDC output, but I need a second opinion from someone with more experince than I have.

Don't get me wrong, I love this clean tone, but that's not the reason I chose this amplifier. I wanted a lower outup than my 68' Custom Deluxe Reverb so that I can drive it a bit harder. I play with a standard Stratocaster with Alnico single coil pickups. I've tried using a 12AX7 in the preamp socket, but it did not fix the issue, just made the amp brighter. The speaker is an 8 Ohm Jensen C12Q.

Here is the readings on the tubes, along with what manufacturer.

Pin# Measured V/Standard V

V1: EH 12AY7
Pin 1 116V/164V
Pin 2 ___
Pin 3 2.06V/1.35V
Pin 4 Fil
Pin 5 Fil
Pin 6 124V/160V
Pin 7 ___
Pin 8 2.06V/1.35V

V2: JJ Ecc83s (12AX7)
Pin 1 157V/164V
Pin 2 ___
Pin 3 1.33V/1.2V
Pin 4 Fil
Pin 5 Fil
Pin 6 197V/200V
Pin 7 19V/17V
Pin 8 45V/50V

V3: JJ 6V6S
Pin 1 ___
Pin 2 Fil
Pin 3 380V/362V
Pin 4 342V/317V
Pin 5 ___
Pin 6 ___
Pin 7 Fil
Pin 8 22V/20V

V4: JJ 6V6S
Pin 1 ___
Pin 2 Fil
Pin 3 380V/362V
Pin 4 342V/317V
Pin 5 ___
Pin 6 ___
Pin 7 Fil
Pin 8 22V/20V

V5: JJ 5Y3S

B+1 = 390V/370V
4.7K 2W Resistor
B+2 = 342V/318V
22K 2W Resistor
B+3 = 247V/248V

Wall voltage = 121VAC
Power Transformer Mojo756
Output Transformer Mojo768sp

Also, my bias is set to about 38mA which I have read is right for a 5E3.

Standard DC Voltages from Rob Robinette.

[mozz]

What's the filament 6.3 or higher? Your voltages are not really out of line at all. A old 5y3 may drop it some. It should break up before 6. Sounds like you have a resistor misplaced. Have you measured power out?

[Chodrick1]

Thanks for getting back to me so soon.
I am getting 6.69VAC across the filaments on all tube sockets and pilot light. And I checked the resistors with my multimeter and everything checks out fine. Nothing deviates from it's 5% tolerance. I guess I'm not 100% sure on how to measure my power out.

[mozz]

6 percent high on filament, 6% high on HV, its normal. Maybe the transformer is meant for 117v or 115v. I don't mean test resistors with a meter, look for a resistor in the wrong location.

[Chodrick1]

I checked the resistor values with the layout I have. It looks like everything is within tolerance in its designated area. The documentation I have on the power transformer shows it is a 120v primary with a 5v, 6.3v and 768v taps on the secondary. But that could be untrue of this exact transformer that I have here. This is my first time building an amplifier, but I have dug through my Deluxe Reverb quite a few times. If Leo wanted an amp to stay clean at higher volumes, he could have done whatever it is that I did here haha. I don't know if it helps any, but the response to touch while playing is very extreme. It doesnt sound quite right to me. I always thought that higher voltage meant less gain in guitar amplifiers, but I have only been studying them independently for a little over a year now.

[Jazz P Bass]

Certain 5E3 amps simply don't break up.

It seems that it depends entirely on the guitar pickups.

If there is a bypass capacitor on the output cathode resistor, try removing it.

[pdf64]

It might help if you uploaded some detailed photos of the chassis.
It seems very strange that swapping from a 12AY7 to 12AX7 didn't yield a noticeable increase in gain, so that may indicate there's a build error / component fault.

[Chodrick1]

So Jazz, are you thinking that I may have an open bypass cap. The bypass cap is what creates the gain, is this correct? I suppose that would make sense, since my v1 has very low voltages and trying out a 12AX7 didnt increase the gain by any amount, I think my issue may be with my preamp tube. Ill have to investigate further. It will take me some time, I wrapped the leads from the resistor around the cap leads in parallel fashion and soldered them together.

[mozz]

12ay7 is always going to have lower voltages than a 12ax7 in the 5e3 circuit. Does rob's site specify which tube he used? Post the schematic you used, maybe there is a error. Check bypass cap polarity, audio taper pots? High plate voltages will make it cleaner. High efficiency speaker? You know about the interactive controls?

[loudthud]

Check that the wires to pins 7 and 8 of V2 are not reversed between the board and tube socket. This is a common mistake.

[Chodrick1]

Here is the readings I get from Rob's site. It shows a 12AY7 in the preamp socket, which is what I used for my voltage readings.

The electrolytic caps are set in just right, and when I did a capacitance test, my meter showed the correct values.

The speaker is a Jensen C12Q, which I have read is a common 5E3 speaker, its only 35 watts which may be a little higher for the 5E3s output, but it should start to break up.

When I set my bright volume to 12, and my normal at 6, its starts to have a little crunch. Its very mild though, I wouldnt even call it crunch, it is more of a nibble.

[Jazz P Bass]

Which guitar are you using?

It's all about the pickups. (whether they are 'hot' enough)

[Chodrick1]

I have a set of '69 Clone single coils from Mojotone. But I have tried the amp with a les paul studio through it and the gain didnt really improve. The Deluxe just sounded really bloated. I know that the amp is supposed to be boomy with higher output pickups, which sounds about right, but the gain doesn't get any more noticeable

[Dave H]

I have tried the amp with a les paul studio through it and the gain didnt really improve. The Deluxe just sounded really bloated. I know that the amp is supposed to be boomy with higher output pickups, which sounds about right, but the gain doesn't get any more noticeable

Is there a different 5E3 type amp you could compare it with? It could be that it's working correctly. By today's standards the 5E3 is a low gain amp. It just gives the illusion of being high gain because of the funky quick start volume controls. The vol pot is after the first stage so there's no pre-amp distortion without a boost pedal. There's no low volume distortion. It will only distort at full power output and it will sound bloated because it passes too much bass for a good distorted tone.

[copperheadroads]

A strat wont break up like a tele or p-90 guitar or humbucker equipped guitar . use the bright channel & turn the normal channel all the way down .tone on 6 or more & the louder you turn up the bright vol you may turn up the tone as well theirs you breakup ...it's not a JCM .... .pushing it with a boss SD-1 works great as it takes off some of the bass .
it's not a JCM ..but you can easily do some modding toit to give it more gain .