Help me with this guitar tube amp!

[DrFireBottle]

Hi all, hope you are doing well, so... i have a few questions about a tube amp that i recently built... The following problem is i looked thru the schematic and everything was fine, then i carefully built an amp, plugged it into the wall and the filaments heated up, everything seemed okay and it still seems okay, then i plugged the guitar and i barley heard it at maximum volume, it produced strange hum and hiss, the hiss was getting stronger when i turned the 1MOhm pot around... So... what could it be... bad grid resistor? Coupling cap? or something else... (I tested everything with the multimeter and everything seemed fine.) Here's the schematic...




Thanks for replying in forward!

 

[DF96]

Try the Instruments and Amps forum. Anyway, it sounds like you have oscillation. Poor layout is one possible cause.

 

[Sorento]

probably parasitic oscillations;
the grid stoppers (resistors on pin 2 of both tubes and the resistor on pin 9) must be soldered directly to the socket, no wire whatsoever between socket pin and these resistors;
I'm not shure about the 100ohms from heaters to pin 3, try ground.

 

[Ketje]

The elevated heater on the cathode EL84 can cause trouble if the decoupling isn't good indeed.
But a bad potmeter is also possible ,try like this.
Mona

 

[DrFireBottle]

Hey, thanks for sorting that one out... But, sadly it did not solve the problem...

It started to hum, noise, and motorboat(on a very high speed).
Before it just made some weird sounds, but as i plug it in to the power it gets louder and louder, after 5 minutes of working it starts to "shake" walls...

Here i will post a sound sample on vocaroo:

Vocaroo | Voice message

 

[mjf]

why is the 47uF elcap (between 2k and 10k) in the psu drawn reverted in the schematic?

 

[DrFireBottle]

It is a mistake that I corrected... the schematic is from some online source, I don't remember which one...