Help! please… The good news is it works.

[Jlanguirand]

So I just got the amp working! However, when I turn the volume past 10, it starts making a loud oscillating noise.

Also, this may be normal, but I expected the amp to be louder. My 5e3 deluxe is twice as loud.

Thanks very much in advance!

Justin

[Robin]

Sounds like parasitic oscillation, be sure the wires to the grids as short as possible. Use a chop stick to push the leads around and see if the problem can be made better (or worse). Depending on what power tube you are using and how efficient your speaker(s) is/are, the volume range can be pretty broad. The 6V6 is only about 4 watts while the EL34 could be more like 10-11 watts. Funny that you mention the 5E3, my first motivation to build a 2Stroke was because my 5E3 amps (when adjusted to their sweet spot) were too loud for my application. That’s before I knew what a great amp the 2Stroke is. BTW. my 2strokes are both pretty loud. I use them full up (they sound great that way) all the time and adjust the volume and distortion with the guitar volume control. If shortening the grid wires doesn’t fix the issue, post a gut photo or two and we’ll see if we can spot a problem area.

[Jlanguirand]

Thanks for the reply Robin!

I’ll check it out and send an update. i have a 6L6 in there right now. Once I can turn it up all the way, it should be loud enough

[Jlanguirand]

On second thought, I have every ground from preamp and power section terminating at one star ground. I should probably set up two star grounds, one for each section.

[Robin]

Indeed, that will help make for a quiet amp, but probably not resolve the oscillation issue.

[Jlanguirand]

Okay, I’ll try to post a picture soon. My wires aren’t too long.
i guess this is where I’m confused because i didn’t use shielded wire on my 5e3.

At first I didn’t use any shielded wire in my two-stroke and then I heard the oscilation. I put shielded wire in but it looks like it should be grounded somehow??

Thanks so much!

[Robin]

Using the shielded wire from the 68k resistor on the input jack to V1 will reduce the possibility of interference (noise) but you are correct, Fender has gotten away without it (mostly) forever. But they also had issues with oscillation when they “improved” on Leo Fender’s original lead dress in the CBS days. Some of the black face ’60 amps will do it if you dime all the controls (like a Super Reverb for example). Does the oscillation change when you adjust the tone control? As in, roll off the treble?

Ground only one end of the shielding on the shielded cable, it doesn’t matter at which end. On my 2Strokes, I grounded it to the chassis by putting a ground lug on one of the V1 socket screws and soldering it there. Putting a little heat-shrink tubing on the ungrounded end will keep the end of the shielding from touching anything at that end. If you ground both ends of the shielding you will create a ground loop in induce noise rather that prevent it.

[wesolowski]

Here are some pics, i switched the ground to the V1 screw. This helped a little i can now get to eleven without interference.

[wesolowski]

two

[wesolowski]

three

[wesolowski]

four
thank you

[Robin]

And the other end of the shielding is not connected to anything, correct?
Using a chop stick, move the leads around a little and see if you can hear a difference.

[Robin]

What is the value of the cap next to the large 40uf/500v? It should be 16uf/450-500v. This is the cap connected between to the junction of the 10k/5w and 68k/1w resistors and the lead going to pin 4 of the power tube, the other end to ground.

What did you use as ground for the control pots? I don’t see a buss wire or a copper plate, is it hidden under the chassis edge?

[wesolowski]

I have moved it around without a change. a friend and i built the same amp, and the are both doing the same thing. i am thinking it is on the lines of a ommitence of something or a connection problem, and not a loose wire or random wire touching something it shouldn’t be.

[wesolowski]

The way i have the cap positioned i can not read what voltage it is but Jlanguirand will respond later he has the piece list and scamadic. all the grounds are to a screw on the left side of the chasis, and conected with and unshielded wire.

[Author]

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