Everything was going ok when hiss appears in AB763 build.

[SourCream23]

Ok, I will change all anode resistors one more time.

[SourCream23]

Well, no change as expected. If a grounding the grid the hiss goes away, which leads me to believe that noise goes into the tube by grid and is amplified.

I installed a 200K pot between grid and ground to test. Any resistence between grid and ground produces white noise.

I installed a 12at7 in v3 to see the issue is the factor of amplification but with 12at7 I have white noise too. Lower, but still there.
I run out ideas again.

[tubeswell]

I installed a 200K pot between grid and ground to test. Any resistence between grid and ground produces white noise. I installed a 12at7 in v3 to see the issue is the factor of amplification but with 12at7 I have white noise too. Lower, but still there. I run out ideas again.

Then it must be coming from either previous stage (or one of the load resistors going to the grid of V3a). V3a is the mixing stage for dry-wet, so you need to check the resistors around the reverb level circuit.

[pdf64]

Have you verified that the issue isn’t related to the ecaps decoupling the anode supply and cathode? eg tack a cap across them, of similar spec to the current cap.

[shooter]

If you want to go wild;
remove the reverb section by disconnecting the "input to V3" You WILL need the 220k to ground for V3 grid
Take the plate output of the 1st stage (V1A?) tack a .02uF cap to the plate and run it as the input to V3
bypassing the TS circuit


If you go down that rabbit hole, use a test signal as your input, verify it's good at the input then chase it to the speaker, screenshot each stage, EXCEPT the PA tubes output, and OT, skip over to the speaker

[SourCream23]

Then it must be coming from either previous stage (or one of the load resistors going to the grid of V3a). V3a is the mixing stage for dry-wet, so you need to check the resistors around the reverb level circuit.

Hey tubeswell! I think is not the issue because I disconnected all previous stages. Just v3 connected with a 220K on the grid gives me the hiss.

Have you verified that the issue isn’t related to the ecaps decoupling the anode supply and cathode? eg tack a cap across them, of similar spec to the current cap.

Hi pdf64, I installed the 15nF across 820ohm/25uf. No change.

If you want to go wild;
remove the reverb section by disconnecting the "input to V3" You WILL need the 220k to ground for V3 grid
Take the plate output of the 1st stage (V1A?) tack a .02uF cap to the plate and run it as the input to V3
bypassing the TS circuit


If you go down that rabbit hole, use a test signal as your input, verify it's good at the input then chase it to the speaker, screenshot each stage, EXCEPT the PA tubes output, and OT, skip over to the speaker

Hey shooter. I did right now.
I connected the v1b directly (through .022 and the 220K) to v3a pin. The hiss is there! And when I increase the volume everything gets worse.

I start to think that problem is not a white  noise produced by components, but some type of EMI interference in whole circuit.

I will move the preamp ground to a belt next to input jack and see what happens.

[tubeswell]

Then it must be coming from either previous stage (or one of the load resistors going to the grid of V3a). V3a is the mixing stage for dry-wet, so you need to check the resistors around the reverb level circuit.

Hey tubeswell! I think is not the issue because I disconnected all previous stages. Just v3 connected with a 220K on the grid gives me the hiss.

When you say 'all the previous stages' are you including the reverb recovery stage? (Because that's also a 'previous stage' in the case of V3a)

[shooter]

think that problem is not a white  noise produced by components, but some type of EMI interference in whole circuit.

 

[SourCream23]

When you say 'all the previous stages' are you including the reverb recovery stage? (Because that's also a 'previous stage' in the case of V3a)

Yes, I disconnected the v3b totally (removed the wires of pins 6, 7 and 8).

Well, Im going to be very practical now. I will change the big blocks of the amplifier. It is a wild solution but here we go.
Starting by the main board. I will change it with ALL components. See what happens.
Let´s go guys.

[tubeswell]

Hang on, before you do that, what about the 3M3||10pF?

[shooter]

^^ what he said


also;
have you changed you Environment? taken the amp to the neighbor's house, the garage
do you have access to an aluminum or steel plate to set the amp on, "shielding the open bottom"

[SourCream23]

Hang on, before you do that, what about the 3M3||10pF?

Hey tubeswell, I just removed anything before the v3a, please take a look on picture to see the details. With that configuration I hear the hiss on speaker. If I ground the pin 2 everything becomes died quiet. I have no master volume and I put a 47K resistor to replace it.

^^ what he said


also;
have you changed you Environment? taken the amp to the neighbor's house, the garage
do you have access to an aluminum or steel plate to set the amp on, "shielding the open bottom"

Hey shooter, good guess! I did not move the amplifier to another place.
I fixed two fender twins few days ago and I put the chassis side to side to my amp. The twins are died quiet even though chassis is opened. Same thing to a swart, chassis opened side to side with my amp, died quiet. So I thought at moment the issue was not related with external interferences. Should I move the amp to another place? I can do that.

[tubeswell]

Hang on, before you do that, what about the 3M3||10pF?

Hey tubeswell, I just removed anything before the v3a, please take a look on picture to see the details. With that configuration I hear the hiss on speaker. If I ground the pin 2 everything becomes died quiet. I have no master volume and I put a 47K resistor to replace it.

So if you keep the reverb recovery stage hooked up to V3a but remove the connection to the pre-amp by lifting the 3M3||10pF off the board, does the hiss go away? Or not?

[SourCream23]

So if you keep the reverb recovery stage hooked up to V3a but remove the connection to the pre-amp by lifting the 3M3||10pF off the board, does the hiss go away? Or not?

I think I tried that but I will do again to confirm. I will let you know. Thanks tubeswell!

[SourCream23]

So if you keep the reverb recovery stage hooked up to V3a but remove the connection to the pre-amp by lifting the 3M3||10pF off the board, does the hiss go away? Or not?

I installed the recovery triode again. Removed 3m3/10pf. No change at all.

[tubeswell]

Okay lets keep focusing around V3 to eliminate some other stuff. Have you tried re-tensioning the socket pin clamps?

[sluckey]

Hmm, what's missing from this thread? Oh yeah. There's not a single pic of the amp! Surprised no one has even asked.

[shooter]

been assuming it looks like an antenna farm, tried to "show" the noise is the same throughout, I failed 

[PRR]

> Surprised no one has even asked.

I'm tired of asking.

[SourCream23]

Hmm, what's missing from this thread? Oh yeah. There's not a single pic of the amp! Surprised no one has even asked.

I can provide photos with no problem. I did not provide because anyone asked, so I believied is not important. But ok, tomorrow I will send.

Okay lets keep focusing around V3 to eliminate some other stuff. Have you tried re-tensioning the socket pin clamps?

Actually, I changed the socket to another new one. Same thing.

been assuming it looks like an antenna farm, tried to "show" the noise is the same throughout, I failed 

I did not understand that sentence. Anyways, I will try total shield that week.

> Surprised no one has even asked.

I'm tired of asking.

Again, I did not understand that sentence.

[Bieworm]

PRR means he does not want to ask for pictures anymore, because nobody does that spontaneously.. while they should. The poster has to provide us with as much information as possible,  and photos are a valuable resource.

Why don't you try removing both cathode bypass caps of V3 and see how that affects the noise. The reverb will be much less, but the noise should be less too. Then start tweaking with lower value bypass caps, on one cathode at a time. On my recent Princeton Reverb build i landed on removing both 22uf caps and substituted one cap with a 10uf on V3b. Plenty of reverb still, but wayyy less noise.

Also, I seem to conclude the 220k grid reference resistor to ground on V3b has always been left in the circuit. Did you replace that one too? I know I am always very careful when I solder that one in. I always heat sink it with alligator clips when soldering  and I always use 2W metal film resistors there. That's a notorious resistor for allowing noise to the reverb recovery.

[SourCream23]

Removing bypass caps of v3 decrease de noises, but not so much.

Pics for you

https://imgur.com/a/xWp58TM

[tubeswell]

At least one of your polystyrene caps looks like it was melted by the soldering iron


Did you initially say (or imply?) that the amp worked fine without this hiss when you first made it? (and if so, did you do anything to the amp between that point in time, and the time when the hiss started?

[sluckey]

There has been some recent discussion about the merits of not sharing cathode resistor and cap on V3. Probably won't fix your hiss, but just may help. Anyhow, easy to do since you have some extra turrets right next to the 820Ω/cap. Just use a separate 1.5K/22µF for pin 3 and another for pin 8. Remove any jumper between pin 3 and pin 8. Worth a try.

[SourCream23]

At least one of your polystyrene caps looks like it was melted by the soldering iron

Did you initially say (or imply?) that the amp worked fine without this hiss when you first made it? (and if so, did you do anything to the amp between that point in time, and the time when the hiss started?

Absolutely, the amp works fine at beginning but the Reverb was too hum! So I opened to try to fix (put isolated jacks and grounding at input jack). I just remember that I put the amp on wrong voltage too (the fuse not blow up, incorrect value, my bad). So, I lost two filter caps. I replaced all caps (5 caps and resistors) on dog house.
I turn on the amplifier and it stays quiets by two days. Everything ok, no hum, no white noise... After some days, (maybe 3 or 4) the hiss appears.

There has been some recent discussion about the merits of not sharing cathode resistor and cap on V3. Probably won't fix your hiss, but just may help. Anyhow, easy to do since you have some extra turrets right next to the 820Ω/cap. Just use a separate 1.5K/22µF for pin 3 and another for pin 8. Remove any jumper between pin 3 and pin 8. Worth a try.

Yes, I tried separate the cap/resistor of cathode bypass v3, no change too.

[SourCream23]

Ok, no change isolating total amp with a sheet of copper.
Im going to wild solutions, starting to change ENTIRE preamp board.
Wish me luck.

[tubeswell]

At least one of your polystyrene caps looks like it was melted by the soldering iron

Did you initially say (or imply?) that the amp worked fine without this hiss when you first made it? (and if so, did you do anything to the amp between that point in time, and the time when the hiss started?

Absolutely, the amp works fine at beginning but the Reverb was too hum! So I opened to try to fix (put isolated jacks and grounding at input jack). I just remember that I put the amp on wrong voltage too (the fuse not blow up, incorrect value, my bad). So, I lost two filter caps. I replaced all caps (5 caps and resistors) on dog house.
I turn on the amplifier and it stays quiets by two days. Everything ok, no hum, no white noise... After some days, (maybe 3 or 4) the hiss appears.

Thank you for this explanation.


Then the hiss was something that ‘appeared’ after you ‘fixed’ the reverb and ran the amp overvoltage. Grounding the grid of V3a kills the hiss. All the plate resistors have been changed out, and the tube sockets, and the tubes. Anything else you’ve done?

[SourCream23]

Quick update.
I removed the ENTIRE preamp board and installed a new one. All new components too.
The hiss goes away!!!! So, probably was a faulty component on it.
But, I still get some hiss when treble goes up. I think its normal, but I guess I can decrease a little.
So, Im going to reinstall 10K on grids. See what happens.
Thank you guys!