Tube Depot 5E3 kit feedback loop question.

[Mungo Park]

Hello All, first post, wonderfull forum you all have here.
I have bought an alredy assembled tube depot 5e3 kit. It was a good price I could not resist. And figured it would be good to learn more about the 5e3 and the many mods.
In reading up on the kit it has a jumper on the board that when in place gives a feeback loop. I was of the understanding it can be removed to give more of the original 5e3 sound. I figured I would try it without the feedback loop and see if I wanted to put in a switch to have both as a option.
So I took it out, the amp gave a extreme distortion sound with my guitar and some poping and clicking for maybe 20-30 seconds. It then produced a normal rather sweet sound with maybe a slight reduced volume, but a ckick with the string attack. I shut it down and put the jumper back, figuring I was lucky I did not fry the amp.
Any ideas why this would act this way and not function well.


Maybe this is the wrong section I will post it in the kit section.
Cheers Ron.

[pdf64]

Maybe the amp was oscillating when the NFB loop was opened.
The wiring layout https://d1sjrnpi226dnf.cloudfront.ne...pdf?1400188816 shows the V2 common cathode grid wire running close to and alongside the wire from the speaker output socket.
Such an arrangement is an example of bad lead dress, prone to problems.
The board layout looks ill considered in that regard.
Try to get as much distance between that grid wire (from the volume controls) and that speaker signal wire and jumper area of the board as possible (at least an inch) and try again.
It may be that a grid stopper is needed at V2 pin2, eg 22k with one leg directly to the socket terminal, or that the yellow wire be disconnected from the speaker output socket, in order for the amp to operate without NFB.

[Jazz P Bass]

Reposted here: http://music-electronics-forum.com/t39568/

The incorrect (bias) jumper had been removed.

[Mungo Park]

Still good advice about the wire locations.
Cheers Ron