Issues with 5E3amp

[guile]

I built a 5E3 amp a while back and I just recently had the chance to try it out live. Unfortunately it has this nasty distortion/clipping at higher volumes.. I'm quite sure it's not part of the amps design.
I can't reproduce it easily at home because of the neighbours..
I also think it hums and hisses a lot.

Where to start? Could it be the power tube cathode? Mine is 220 ohm..
It further has a humdinger and a master-volume.

[Ten Over]

Valve Wizard recommends a large grid stopper on the cathodyne phase inverter to prevent nasty distortion. Like 470K.

[guile]

Thanks
Already did that. The master volume I installed is in fact a PRE Phase Inverter Master Volume (RobRobinette).

[Phil_S]

I suggest posting gut shots of the build. One overview shot of the whole thing as a consolidated reference and some close ups in two or three sections so we can get a better look at the details of the build. If you have a lot going on with the front or rear panel, get straight ahead shots of those, too. What you are describing could be any of a list of common problems. It could be a wrong part (like 100K resistor where you should have 1K), or lead dress, or bad solder, or something more complicated. Let the experienced builders have a look.

[Colossal]

Also, please post your power supply, plate, and cathode voltages. High voltages in a 5E3, in my experience, can lead to a harsh, edgy amp.

[guile]

I suggest posting gut shots of the build. One overview shot of the whole thing as a consolidated reference and some close ups in two or three sections so we can get a better look at the details of the build. If you have a lot going on with the front or rear panel, get straight ahead shots of those, too. What you are describing could be any of a list of common problems. It could be a wrong part (like 100K resistor where you should have 1K), or lead dress, or bad solder, or something more complicated. Let the experienced builders have a look.

https://www.flickr.com/photos/115176149 ... 1061564087

Hope these are helpful!

[joeboo88]

Hi...from the pictures it looks like V1 bypass cap is backwards?

[pompeiisneaks]

Hi...from the pictures it looks like V1 bypass cap is backwards?

Good catch! That would make that stage unbypassed and a bit gainier, possibly causing the issues you've mentioned.

~Phil

[guile]

Thanks. Well spotted, I will correct that.
I'll report back!

[sluckey]

The bypass cap on the output tubes is also connected backwards.

[pompeiisneaks]

Yup, confirmed, was hard to see but I realized when you said that the arrows on the - band point the wrong direction, even though the 'dimple' isn't as visible.

~Phil

[guile]

That fixed a lot! I need to get glasses (seriously, I'm of that age).
Thanks very much everyone.

Amp is much quieter and no more strange clipping (tested it loudly, sorry neighbours..).
Out of standby mode it still hums. Is that normal for a 5E3?

[joeboo88]

good to know you found the trouble - did you see sluckeys comment about the cathode bias resistor was also backwards?

by sluckey » Wed Sep 25, 2019 9:06 pm
The bypass cap on the output tubes is also connected backwards.

[guile]

good to know you found the trouble - did you see sluckeys comment about the cathode bias resistor was also backwards?

by sluckey » Wed Sep 25, 2019 9:06 pm
The bypass cap on the output tubes is also connected backwards.

Sure did (don't rub it in

[pompeiisneaks]

That fixed a lot! I need to get glasses (seriously, I'm of that age).
Thanks very much everyone.

Amp is much quieter and no more strange clipping (tested it loudly, sorry neighbours..).
Out of standby mode it still hums. Is that normal for a 5E3?

Hum is normal in most amps, does it go down with volume, change with specific pots etc? sometimes it's lead dress, sometimes it's a heater imbalance, sometimes it's just the normal hum for an amp at full volume (If that was how you were playing it). Were you using single coil pickups? Does the hum exist w/ nothing in the input? That could just be the guitar.

You can try replacing the 100 ohm resistors to ground on the heater circuit with a hum balance pot and see if you can dial it away. That's usually a subtle change though.
Some of your leads are a bit long and hanging around loose in the amp, this gives room for hum and noise transfer between wires. you can get a wooden chopstick and try moving the leads around and see if the hum dissipates.

Hum is a nefarious enemy

~Phil