voltage on 6v6 GT

[sluckey]

OK that's good. Now put V3 back in the socket and use a gator clip test lead to ground pin 7 of V3. Does this kill the oscillation?

YES!

That means the oscillation is coming from the preamp or the reverb circuit. Remove V1 and remove the ground clip from V3 pin 7. This removes the pream from V3. Does this kill the oscillation?

[rafaelctt]

OK that's good. Now put V3 back in the socket and use a gator clip test lead to ground pin 7 of V3. Does this kill the oscillation?

YES!

That means the oscillation is coming from the preamp or the reverb circuit. Remove V1 and remove the ground clip from V3 pin 7. This removes the pream from V3. Does this kill the oscillation?

With V1 removed there is oscillation.
With V1 and V2 removed: there is oscillation

[sluckey]

So, the oscillation is coming from the reverb recovery circuit.

Turn the reverb pot to zero. Does this kill the oscillation?

Use a gator clip test lead to ground pin 2 of V3. Does this kill the oscillation?

[rafaelctt]

So, the oscillation is coming from the reverb recovery circuit.

Turn the reverb pot to zero. Does this kill the oscillation?

Use a gator clip test lead to ground pin 2 of V3. Does this kill the oscillation?

I'll try it as soon as I get home. Thank you!!

[Williamblake]

And by the way, please: How do you call your terminal boards? They look like fun but i don`t know how to google them.

[rafaelctt]

And by the way, please: How do you call your terminal boards? They look like fun but i don`t know how to google them.

https://www.tube-town.net/ttstore/tube-town-ez-board-60-x-300-mm-fr4-2-mm-schwarz.html

[rafaelctt]

And by the way, please: How do you call your terminal boards? They look like fun but i don`t know how to google them.

I have tried grounding points A,B,C individually and in all cases there is still oscillation. Only when I connect pin 7 of V3 to ground does the oscillation disappear.


NOTE: I have not connected the speaker to ground, nor the feedback

[rafaelctt]

I just verified that by injecting the signal from my guitar (passive pickups) into pin 7 of V3 I already have a fairly high signal. If I feed it into the V1 preamp, there's a lot of distortion and I have to turn the signal all the way down.

[sluckey]

Measure resistance from V3 pin 7 (probe directly on socket) to chassis. What do you have?

[rafaelctt]

Measure resistance from V3 pin 7 (probe directly on socket) to chassis. What do you have?

471K
Measured with revervb pot to ground

[sluckey]

Resolder that red wire on the wiper of the reverb pot. Looks suspicious to me.

Can you post a better high-resolution pic of your amp? I would like to be able to clearly see the color bands on your resistors.

[rafaelctt]

Resolder that red wire on the wiper of the reverb pot. Looks suspicious to me.

Can you post a better high-resolution pic of your amp? I would like to be able to clearly see the color bands on your resistors.

[rafaelctt]

[rafaelctt]

I also send you the draft that I made at the beginning

[sluckey]

That's a much better pic, but now I can't see the front panel pots.

Did you check the wire on the reverb pot?

[rafaelctt]

[sluckey]

Use some gator clip test leads to connect a 470k resistor directly to V3 pin 7 and chassis. Does this kill the oscillation?

[rafaelctt]

Use some gator clip test leads to connect a 470k resistor directly to V3 pin 7 and chassis. Does this kill the oscillation?

Sorry, I'll have to do it later, I'm already working. To do that test, I disconnect everything that is connected to pin 7 of V3? Or do I connect the resistor without disconnecting anything?
Thanks

[sluckey]

Just connect the resistor without disconnecting anything.

[rafaelctt]

Just connect the resistor without disconnecting anything.

ok, when i do i tell him

[rafaelctt]

Just connect the resistor without disconnecting anything.

When putting the resistance, very annoying noise is produced and the oscillation continues. With or without the resistor, when I vary the value of the reverb potentiometer (100k) the oscillation goes from 16Khz to about 60KHz

[sluckey]

When putting the resistance, very annoying noise is produced and the oscillation continues. With or without the resistor, when I vary the value of the reverb potentiometer (100k) the oscillation goes from 16Khz to about 60KHz

OK. Now remove the wire from V3 socket pin 7 and connect a 470k resistor directly to V3 pin 7 and chassis. Does this kill the oscillation?

[rafaelctt]

When putting the resistance, very annoying noise is produced and the oscillation continues. With or without the resistor, when I vary the value of the reverb potentiometer (100k) the oscillation goes from 16Khz to about 60KHz

OK. Now remove the wire from V3 socket pin 7 and connect a 470k resistor directly to V3 pin 7 and chassis. Does this kill the oscillation?

if there is oscillation

[sluckey]

if there is oscillation

Not sure what you mean???

[rafaelctt]

Connecting pin 7 of V3 to the chassis through a 470K resistor, there is still oscillation.

[sluckey]

We're dancing all around the problem but can't see the elephant in the room. The elephant is most likely that crazy layout. Sorry, but I'm out of ideas.

[rafaelctt]

I'm going to build on a separate chassis, just the part that's on that schematic. In this way I think we can have a clearer idea of ​​the problem since it will not depend on the design. do you think it will be a good idea?

[shooter]

a well-designed circuit with an il-designed layout will result in a poor outcome.


you have High voltage DC running parallel to sensitive, low voltage AC, a perfect environment for cross-coupling signals.  Signals that will meander throw-out your amp, causing all manner of chaos.

[rafaelctt]

ok, I'll touch up the whole design and I'll give you results. For now I'm going to do just that part on a separate chassis.

Thank you!!

[rafaelctt]

I have simulated the schematic circuit on a separate chassis and the result is the same.( there is still oscillation)
connecting pin 7 of V3 to ground, I measured pin 3 of V4 (anode): 381 V and pin 4 of V4 (screen): 388 V. Is it normal for a higher voltage on the screen than on the anode?
I'm thinking that the fault could be in the 6V6, can it be?

[rafaelctt]

Would it be possible to replace the 6V6 with an EL84 (polarizing it correctly)? I say this because I have an EL84

[shooter]

screens draw less current so there's less drag on the voltage.


the tube could be bad, did you swap it with another one?
you are most likely picking up something in the environment and coupling it into your circuit.  LED lights, routers, wall-warts for charging...


try putting a resistor with a value of 5K to 10K from pin 5 of the 6V6 to the junction of R22 and C8.


how are you viewing the oscillation?

[HotBluePlates]

... I'm thinking that the fault could be in the 6V6, can it be?

Would it be possible to replace the 6V6 with an EL84 ...

The 6V6 is not causing your trouble.  The layout of your circuit is causing your trouble, and it cannot be fixed without building the amp with a entirely different layout.  Sluckey proved this by stepping you through tests to kill the oscillation.

It might be wise to pick a ready-made kit that is a Fender amp with reverb, and build it.  Then you will have a known-working layout.

After building such an am with a known-working layout, compare it to your present layout.  You will see that what Fender lays out in a straight line, you have bent into a U-shape, putting output next to input and crossing over itself.  This fact plus long grid wire length is why your present layout is suffering problems.

I'm sorry this is true, because you obviously put a lot of time and care into your amp build.  But it is like a finely-crafted building on a foundation of sand: it will fail unless the core problem of the layout is fixed.

[rafaelctt]

... I'm thinking that the fault could be in the 6V6, can it be?

Would it be possible to replace the 6V6 with an EL84 ...

The 6V6 is not causing your trouble.  The layout of your circuit is causing your trouble, and it cannot be fixed without building the amp with a entirely different layout.  Sluckey proved this by stepping you through tests to kill the oscillation.

It might be wise to pick a ready-made kit that is a Fender amp with reverb, and build it.  Then you will have a known-working layout.

After building such an am with a known-working layout, compare it to your present layout.  You will see that what Fender lays out in a straight line, you have bent into a U-shape, putting output next to input and crossing over itself.  This fact plus long grid wire length is why your present layout is suffering problems.

I'm sorry this is true, because you obviously put a lot of time and care into your amp build.  But it is like a finely-crafted building on a foundation of sand: it will fail unless the core problem of the layout is fixed.

Sorry, I don't think I have explained myself. I have made a very simple design from scratch where there are hardly any threads or crosses. Only two 6V6 and Ecc83 valves connected and the power comes directly from the transformer and diodes. It can no longer influence that design that I made at the beginning. And still there is oscillation.

[sluckey]

Would it be possible to replace the 6V6 with an EL84 (polarizing it correctly)? I say this because I have an EL84

You can do that. But if you suspect the 6V6 why not just replace with another 6V6?

Show us a hi-rez pic of the test circuit on a separate chassis.

[rafaelctt]

[rafaelctt]

screens draw less current so there's less drag on the voltage.


the tube could be bad, did you swap it with another one?
you are most likely picking up something in the environment and coupling it into your circuit.  LED lights, routers, wall-warts for charging...


try putting a resistor with a value of 5K to 10K from pin 5 of the 6V6 to the junction of R22 and C8.


how are you viewing the oscillation?

I have put a 4k7 resistor as you have told me and this is the result in the speaker output:

[shooter]

what's it read for frequency?  I think it's 100Khz but I might have slipped a decimal.

[rafaelctt]

what's it read for frequency?  I think it's 100Khz but I might have slipped a decimal.

Yes, 100Khz
Very weird

[shooter]

it's there when you un-ground pin 7, or always?


did you remove all external noise sources from the room you're working in, or move the amp to a "quite room"?


If the 100khz is always there, ground the neg speaker lead to chassis with a gator-clip, any change?

[rafaelctt]

I think we are on the right track! I have changed location, I have removed resistance between pin 5 of V4-C8/R22. I have connected new chassis to ground. And in loudspeaker I get 20mV at a frequency around 50Hz(oscillating). What I notice is a lot of sensitivity since as soon as I get close to pin 2 of V3 with my finger, the signal goes up a lot. I have connected pin 2 of V3 to ground and there is still 50 Hz noise (oscillating) and the signal goes up to 400mV.

I think there is too much equipment in my shop that was affecting

[tubeswell]

It’s not only the ‘U’ shape of the layout with input close to output that’s problematic for unwanted cross-coupling, it’s also the long leads from the board to the sockets, where you’ve got grid and plate (and cathode) leads all running parallel closely bundled, and long leads everywhere threaded through the board passing closely to other components, (and, although it’s not evident from the pictures, I’m guessing they’re similarly routed higgledy-pigeldy with regard to signal voltage strength and phase, behind the board). The higher voltage wires will be making stronger EM fields that get inducted into the lower voltage signal wires, with signal phasing all over the place. = Recipe for oscillation.

[rafaelctt]

It’s not only the ‘U’ shape of the layout with input close to output that’s problematic for unwanted cross-coupling, it’s also the long leads from the board to the sockets, where you’ve got grid and plate (and cathode) leads all running parallel closely bundled, and long leads everywhere threaded through the board passing closely to other components, (and, although it’s not evident from the pictures, I’m guessing they’re similarly routed higgledy-pigeldy with regard to signal voltage strength and phase, behind the board). The higher voltage wires will be making stronger EM fields that get inducted into the lower voltage signal wires, with signal phasing all over the place. = Recipe for oscillation.

Please read the Reply #83
Thank you

[tubeswell]

It’s not only the ‘U’ shape of the layout with input close to output that’s problematic for unwanted cross-coupling, it’s also the long leads from the board to the sockets, where you’ve got grid and plate (and cathode) leads all running parallel closely bundled, and long leads everywhere threaded through the board passing closely to other components, (and, although it’s not evident from the pictures, I’m guessing they’re similarly routed higgledy-pigeldy with regard to signal voltage strength and phase, behind the board). The higher voltage wires will be making stronger EM fields that get inducted into the lower voltage signal wires, with signal phasing all over the place. = Recipe for oscillation.

Please read the Reply #83
Thank you

I have made a very simple design from scratch where there are hardly any threads or crosses. Only two 6V6 and Ecc83 valves connected and the power comes directly from the transformer and diodes.

The photo in your revised preamp driver and output tube layout is still getting its input signal from the preamp in the original layout is it not?

[rafaelctt]

No, there are only two valves (V3 and V4)

[tubeswell]

No, there are only two valves (V3 and V4)

It’s not clear from the photo what is happening at the input. Where is the input?

[rafaelctt]

No, there are only two valves (V3 and V4)

It’s not clear from the photo what is happening at the input. Where is the input?

No input connected yet. We are looking at output oscillation or noise in the absence of a preamp signal. It's like testing the circuit in phases from the end to the beginning

[sluckey]

No, there are only two valves (V3 and V4)

It’s not clear from the photo what is happening at the input. Where is the input?

There is no input in this partial circuit. Refer to the schematic in Reply #79. The problem is a 100KHz oscillation on the speaker. Pulling V3 will kill the oscillation. Put a ground on V3 pin 7 will kill the oscillation. Put a ground anywhere else in the V3A circuit will NOT kill the oscillation. What is the solution?

[rafaelctt]

No, there are only two valves (V3 and V4)

It’s not clear from the photo what is happening at the input. Where is the input?

There is no input in this partial circuit. Refer to the schematic in Reply #79. The problem is a 100KHz oscillation on the speaker. Pulling V3 will kill the oscillation. Put a ground on V3 pin 7 will kill the oscillation. Put a ground anywhere else in the V3A circuit will NOT kill the oscillation. What is the solution?

I think that the oscillation was caused by some external equipment that was interfering. I took the equipment to the terrace and the only thing there is now is the 50Hz of the network. I imagine that the circuit is open at the input.Reply #90

[tubeswell]

No, there are only two valves (V3 and V4)

It’s not clear from the photo what is happening at the input. Where is the input?

There is no input in this partial circuit. Refer to the schematic in Reply #79. The problem is a 100KHz oscillation on the speaker. Pulling V3 will kill the oscillation. Put a ground on V3 pin 7 will kill the oscillation. Put a ground anywhere else in the V3A circuit will NOT kill the oscillation. What is the solution?

There must be some positive feedback going on somewhere, or the 1st stage is acting like a radio antenna. What about grounding Pin 2 of v3? (A normal guitar amp has a ground tip switch on the input Jack, or an instrument plugged in.) Or running a meter over the PS rail to check the filter caps are properly decoupled?