5E3 too clean, no distortion

[paulj]

Hello Everyone!

This is a new member Paul here. First of all I want to thank everyone posting on this forum. I have learned a lot from you all, while building my first amp, the 5E3 from a kit. Great thanks!

As in the title, I can't get much distortion from the amp. It is just very clean, unless at almost full power when the distortion is not that pleasant sounding and combined with vibration/speaker farting sort of sound.

What I have tried so far:

- Following the advice here I tried to address the high B+ voltage. Originally at 359 VDC, the plate dissipation at JJ 6V6S was around 14W.
So I used Zener to reduce by 30V. I am at 329 now. Dissipation around 11W, but still no distortion.

- Used another Zener which dropped my plate voltage to 301VDC. Dissipation at 9.5W but still no distortion. Went back to using only one Zener since that seemed to be the more correct set point.

- I was very surprised that originally the amp fired up very successfully. Then I had to go through the "de-humming" by isolating grounds etc. Moving cables around and shielding some allowed me to eliminate some parasitic oscillations that appeared. At the end the amp has very little hum and just plays nicely but no distortion or the characteristic "tweed" tone.

- Tried different speaker, guitar, no difference.

The amp is very loud when cranked so I think all the stages are working properly.
Also the inputs as well as Volume/Tone controls work as they should. I have checked voltages in multiple points (following fender 57 reissue diagram) and all seem OK.

I don't have other tubes to try, my preamp are EH 12AY7 and JJ 12AX7.

When using a tube screamer type of pedal, I get some overdrive but not as much as I would expect.

I am suspecting a bias problem but not sure where my distortion should come from.
Would it be the first or second half of V2 or rather the power tube?

Can you shed some light on me?

[loudthud]

Look at this thread and try the resistance checks in post 14. It will verify that the input jacks are wired correctly. http://music-electronics-forum.com/t12667/

[paulj]

loudthud,

It looks like I may have the numbering of channels reversed (ch. 1 switched with ch. 2 compared to the usual naming) but I took the following measurements:
In addition, I use the Switchcraft jacks.

Pins 2 and 7 show 32.8k to ground.

With cable in input 1, I read 66k on pin 2 and 33k on pin7
With cable in input 2, I read 1048k on pin 2 and 33k on pin7

With cable plugged in:

#1 input reads 132k
#2 input reads 1018k

Now between the tip of the cable and the grid pin on the tube socket:

Mic channel:
Input 1: 66k on pin2 and 33k on pin 7
Input 2: 33k on pin2 and 1048k on pin 7

Inst. channel:
Input 1: 164k pin 2, 66k pin 7
Input 2: 1048k pin 2, 33k pin 7

[paulj]

I posted too soon, let me just clarify (all measurements identical with the previous posting, just explaining what I am doing):

Pins 2 and 7 show 32.8k to ground. (this is with nothing plugged in)

(these will be with an open ended cable plugged in):
With cable in input 1, I read 66k on pin 2 and 33k on pin7
With cable in input 2, I read 1048k on pin 2 and 33k on pin7

With cable plugged in (and reading between tip on the guitar end and ground, guitar end unplugged of course):

#1 input reads 132k
#2 input reads 1018k


Now between the tip of the cable (on the guitar end with guitar unplugged) and the grid pin on the tube socket:

Mic channel:
Input 1: 66k on pin2 and 33k on pin 7
Input 2: 33k on pin2 and 1048k on pin 7

Inst. channel:
Input 1: 164k pin 2, 66k pin 7
Input 2: 1048k pin 2, 33k pin 7

[loudthud]

The input jacks look ok. Are you sure the volume controls are the correct value? Check this thread: http://music-electronics-forum.com/t18458/

[paulj]

thanks loudthud,

From reading that post, my tone/volume acts in a similar way. I get some attenuation and tone change from using the other channel's volume pot. To me it is all normal and matches your description of how they interact.

My tone pot just changes the tone and is very good at it.

But I still don't get any "dirt", no matter which combination of pots.
My pots are all 1MA from a kit, all identical and they measure the same.

My feeling it has to have something to do with the tubes' operating opoint as I can't really find any other fault with the amp.
If I wanted a clean amp, this would be perfect but I am after that blues crunch.
More ideas?

[MWJB]

"My feeling it has to have something to do with the tubes' operating opoint "

I doubt this, even a 5E3 with 400v+ on the 6V6 plates can give a dirty sound. Your amp was at ideal voltages before you added the zener diode, now you shouldn't be able to get virtually ANY clean tone!

First stop, if you want dirt, get rid of the 12AY7 in V1, use a 12AX7.

List all dc voltages. Specify which tube you have in V1 as 12AX7 & 12AY7 will return different plate & cathode voltages. It would actually be sensible to remove any zener diodes for this test so that your voltages are "ball park" & can be related to other 5E3s.

Plug in the Normal/Mic channel, turned up high, with the Bright/Instrument volume set halfway up - still no dirt?

"It is just very clean, unless at almost full power when the distortion is not that pleasant sounding and combined with vibration/speaker farting sort of sound." This makes no sense. The amp should remain fairly clean up to "full power", that's how power ratings are determined - max clean power. Do you mean that you only get distortion at high settings on the pots ?

Do you have pictures of the chassis, tube sockets & pot wiring?

[pdf64]

Paul, are you hoping to get blues crunch / tweed tone at domestic sound pressure levels? If so you may have the wrong amp, or at least will need something additional to achieve overdrive at reasonable domestic friendly sound levels.
A 5E3 with a single 12" speaker may struggle to keep up with a full band, but overdrive won't happen until it's kicking out >105dB.
Additionally, 5E3 overdrive can be rather 'farty', and if the cab isn't very solid, rattles will occur.
Pete.

[Steve Conner]

As in the title, I can't get much distortion from the amp. It is just very clean, unless at almost full power when the distortion is not that pleasant sounding and combined with vibration/speaker farting sort of sound.

That seems like a fair description of what a 5E3 does, if you're used to a modern high-gain amp.

[Jazz P Bass]

It sounds like you need more gain.
A 12AX7 will help.
On amps such as this, you need to get past the 'farting' to get good breakup.

[paulj]

"My feeling it has to have something to do with the tubes' operating opoint "

I doubt this, even a 5E3 with 400v+ on the 6V6 plates can give a dirty sound. Your amp was at ideal voltages before you added the zener diode, now you shouldn't be able to get virtually ANY clean tone!

First stop, if you want dirt, get rid of the 12AY7 in V1, use a 12AX7.

List all dc voltages. Specify which tube you have in V1 as 12AX7 & 12AY7 will return different plate & cathode voltages. It would actually be sensible to remove any zener diodes for this test so that your voltages are "ball park" & can be related to other 5E3s.

Plug in the Normal/Mic channel, turned up high, with the Bright/Instrument volume set halfway up - still no dirt?

"It is just very clean, unless at almost full power when the distortion is not that pleasant sounding and combined with vibration/speaker farting sort of sound." This makes no sense. The amp should remain fairly clean up to "full power", that's how power ratings are determined - max clean power. Do you mean that you only get distortion at high settings on the pots ?

Do you have pictures of the chassis, tube sockets & pot wiring?

Thank you guys,
All the suggestions are very helpful.

I will remove Zeners to bring it to the starting point. I also have a higher voltage tap on the transformer available to try but that would give me around 385V on the plates. Since with 359V, power tube idle wattage is already at maximum 14Watt, I am struggling with the thought of even trying that.

I have EX12AY7 in V1 and JJ12AX7 in V2. I could buy a 12AX7 tube for V1 but I still would like to achieve good crunch and keep the tone of 12AY7.

I don't get the expected dirt with the amp set as you described.
If you look at this video, the lowest setting that he is demonstrating, I can not get that crunch even at full power:

Thom Hoglen Tweed Deluxe 5E3 Jensen P12R - YouTube

And yes, I only get distortion at full power settings and, my gut feeling is that it is the power tube distortion and I am missing all the distortion from the preamp. Again, just a gut feeling as I have little experience with amps.

I will post some photos soon. The problem is, my board is upside down, you can not see elements but everything else is quite easy to figure out.

[paulj]

Paul, are you hoping to get blues crunch / tweed tone at domestic sound pressure levels? If so you may have the wrong amp, or at least will need something additional to achieve overdrive at reasonable domestic friendly sound levels.
A 5E3 with a single 12" speaker may struggle to keep up with a full band, but overdrive won't happen until it's kicking out >105dB.
Additionally, 5E3 overdrive can be rather 'farty', and if the cab isn't very solid, rattles will occur.
Pete.

Pete,
Thanks , I get what you are saying. I am not sure if I should push the power tubes even more or address the problem in the preamp. See my previous response and video link. I would like at least that. I know that I have to crank it to get breakup. I am expecting that but I am testing at full power and still no crunch (preamp crunch I think, because the power section does indeed get crazy at full power that is why I am more suspicious about the preamp section). I just don't get that "creamy" overdrive at any setting.

[paulj]

That seems like a fair description of what a 5E3 does, if you're used to a modern high-gain amp.

Yes, I am not expecting that at all. I have gone through many videos and sound clips where the 5E3 has this perfect crunch (not screaming, just a little "raspy" at moderate setting). That is all I want.

[paulj]

It sounds like you need more gain.
A 12AX7 will help.
On amps such as this, you need to get past the 'farting' to get good breakup.

Thanks,
As I wrote earlier, to even try that, I would need even higher plate voltages and then it would exceed the max 14W power point of the JJ 6V6 tubes.
As most people agree that my plate voltage seems perfect, I am hesitant to try that.

But I may if I we run out of ideas. I am lost in the wood right now.

[paulj]

Guys,

I took the voltage measurements. I removed the Zener trick so all is in the original state.
All voltages DC. Omitted the filament voltages as that is checked OK already. Let me know if something is missing:

Voltages for both output tubes on pins (both the same or very similar)

3 _____359
4 _____325
5 _____0
8 _____21

Voltages for V1 (12AY7) Pins

1 _____114
2 _____0
3 _____1.9
6 _____115.5
7 _____0
8 _____1.9

List your voltages for V2 (12AX7) Pins

1 _____146.8
2 _____0
3 _____1.2
6 _____182.7
7 _____2.9
8 _____44.2


Power supply voltages starting at the rectifier tube

1st node ______366
2nd Node _____323
3rd Node _____234