Help with Stout Build - Low output

[Garrett335]

Howdy friends,

I wanted to see if you can help with my Stout build.
Got it all assembled fired up, no pops, hums, or hiss, but the output was very low. The voltages were also very low around 305 on the OPT and Plates of the el84. Impatient I cut out the 5y3 and popped in SS diodes. Voltages are better now on B+ however the output is still terribly low.
I subbed in a new OT because I had another brand new one, that did nothing, re-installed the old OT. Tried new output tubes and switched the pre tubes.

Only noted changes to the schem is R18 I used 33k (did not have 47k) and R19 used 4.5k (did not have 4.7k)

Hoffman has the voltages listed on the PI grids as 53 and 55 / I'm getting 267mV and 260mV

V1A P/255 C/2.2v
V1B P/252 C/2.22v

V2A P/340 C/5.1 G/267mV
V2B P/340 C/5.1v G/260mV

V3 P/349 SG/356v C/11.7v
V4 P/352 SG/357v C/11.7v

Thanks in advance!!! I'm hoping this is a simple error, I've gone over the schem and layout a dozen times for errors.

[sluckey]

Looks like the bias node on the PI is grounded, either accidentally or by wiring error. See pic.

[Garrett335]

I caught that one during the build seemed funny. No they are not grounded, just double checked.

[shooter]

I got 45mA for bias but I forgot what's normal 


jack a music source, with vol control, into the Lifted, Left side of C6, any louder?

[Garrett335]

@shooter, I'm not sure I understand what that means.
Sub in the wiper of the volume pot to the other side of c6?

[sluckey]

Concentrate on V2. Those voltages are totally wrong. Ain't gonna work until you fix that.

[sluckey]

Can you post some hi-rez pics of your amp guts?

[Garrett335]

@Slucky Here are some photos. (And thank you for always helping me out, I appreciate it)
Before I get heat, this was a test build with the intention of cleaning everything up, this is far from my final build. I flipped the layout because this is my proto chassis.
(I had to use two resistors in series for the 4.5k for R19, thats what that great mcdonalds arch is)
(There is a ground buss under the board)
(I detached the NFB, it's just hanging there)
(The 5y3 socket is not connected)
(The pots are wired L to R Bass Middle Treble Vol)

[sluckey]

I circled R16 in the pic. It should be 820Ω (gray,red,brown). Looks like 680K in the pic. Measure it. Can get an accurate reading in circuit.

[Garrett335]

THAT DID IT! What a big flub.
I don't have a 820 but I do have a 750, I popped that in there and boom she's alive.
I do have a mad hum going on even with the guitar unplugged, C5 seems to be microphonic when I tap it, and the 16ohm tap alters the hum.  I'll have to do some more tweaking to try and get that to quiet down.
Thank you for putting me on the right course Sluckey. Man this thing is a beast though, the tone is really cool

[Garrett335]

I have a 120hz hum I believe (Compared with my signal generator) this is a grounding issue then right?
I have two ground points in the chassis, the mains, transformers, and on the other side of chassis the preamp, input, pots etc.

When I pull V2 the hum goes away. Also I had hooked up the NFB, and got a loud motorboat sound after about 30seconds of running the amp, disconnecting NFB it made it stop.

Also the input shielded cable is super microphonic when the volume is turned up. Hoffman uses a few shielded cables in his build, looks like from both v1b grid to volume, and from the 500pf cap to the treble pot. I can try adding these.

[Garrett335]

I didn't want to start a new thread as this amp still has issues.

Loud 120hz hum / tapping everything in chassis, only V1 makes noise / also V1 .022uf coupling caps make noise when tapped.
When I remove the PI (V2) the 120 noise becomes very very faint
(Touching the grids of PI with my DCV meter kills the noise also)

I have two chassis grounds, one for the HT CT/AC /Output jack, and one for the preamp section.

Any suggestions on where to go from here? I've been messing with this for a couple weeks, I feel like it's going to be one wrong ground wire or something. Thanks again amp gods for your never ending wisdom :) always saving my butt.

[PRR]

> grounds, one for the HT CT/AC

I can't see where the Red/Yello wire goes. It gets lost in a snarl.

[Garrett335]

It goes to a HT .5A fuse, then to ground.
I left this in place from my Marshall 2022 build

[Willabe]

The B+ red/yellow CT wire from the PT should be twisted evenly and tightly with the 2 B+ red wires on the way to the B+ CT fuse holder.

[shooter]

the red B+ wire that feeds the early pre section is way to close to the wires running to the pots.  Make it go about 2" UP 1st then make the bends down to the turrets

[PRR]

It goes to a HT .5A fuse, then to ground. ...

What is "to ground"? Not all grounds are the same.

Specifically this wire should go DIRECTLY to the first filter cap "-" terminal. With no other "grounds" branching off along the way. This wire is "dirty" with buzz.

[Garrett335]

@willabe I'll try doing that, I've tried moving all loose wires around but hear no difference in tone or hum.

@Shooter do you mean float the B+ wires 2" above the board?

@PRR The CT for B+ goes to the .5a fuse, then the fuse is grounded to the star ground under the filter cap. Also on this ground is the Filter cap - terminal, the heater CT, the mains ground. Should I ditch the HT fuse?

The only other ground point I have is near the input jack below on the chassis, this is where the grounds on the board, pots, and input go to. I have the board grounds attached under the board with jumpers, I've double checked that they are correctly connected and not touching anything else.

Hoffman has a big ground bus line on the back of the pots, I don't have that, maybe that would make a difference?

[Willabe]

@willabe I'll try doing that, I've tried moving all loose wires around but hear no difference in tone or hum.

What I'm talking about you won't hear by just moving the wires around.

Twisting wires that are out of phase with each other or are +/- to each other will cause cancellation of noise and/or the wires from radiating noise/magnetic field into close circuitry and other wires.

Those 3 wires are the start/finish/CT of the B+ secondary. They should be twisted   -tightly and evenly-  together.     

[Willabe]

A lot of the answers your looking for on grounding are in here;

http://www.valvewizard.co.uk/Grounding.pdf

[Willabe]

@PRR The CT for B+ goes to the .5a fuse, then the fuse is grounded to the star ground under the filter cap. Also on this ground is the Filter cap - terminal, the heater CT, the mains ground. Should I ditch the HT fuse?

No. He's saying that the PT B+ CT should go directly to the 1st filter caps negative lead. Then run a wire from there to the ground star.
 

The only other ground point I have is near the input jack below on the chassis, this is where the grounds on the board, pots, and input go to. I have the board grounds attached under the board with jumpers, I've double checked that they are correctly connected and not touching anything else.

This sounds ok.

Hoffman has a big ground bus line on the back of the pots, I don't have that, maybe that would make a difference?

No, there's a few ways to do this. You don't have to have a ground buss on the pot backs.

Read this, reply #17;

https://el34world.com/Forum/index.php?topic=28022.msg308463#msg308463

[Willabe]

On the B+ CT ground connection;

https://el34world.com/Forum/index.php?topic=27769.msg306843#msg306843

And this;

https://el34world.com/Forum/index.php?topic=27769.msg306950#msg306950

And;

https://el34world.com/Forum/index.php?topic=27769.msg306982#msg306982

And;

https://el34world.com/Forum/index.php?topic=27769.msg306990#msg306990

And here he got it;

https://el34world.com/Forum/index.php?topic=27769.msg307005#msg307005
And from that same thread towards the end, on twisting wire pairs and in 3's and the 1st B+ filter cap location;

There's rules of thumb for lead dress. One of them is to use twisted pairs of wire when/where you can. It's just good practice when doing a build. We know that 2 wires of opposite polarity or opposite phase if -tightly and evenly-   twisted together will greatly help cancel any noise and/or magnetic fields from being radiated/induced into other wires and other adjacent circuitry. That's why you see PT and OT wires twisted together.

There's reasons why the power ac cord, PT, and heaviest current is on 1 end of the chassis far away from the sensitive low signal input/preamp side of the chassis. Part of good layout and good lead dress.   

You had the amp gutted, you should have moved the stacked B+ filter caps for node A, OT CT. They have the most current going through them and their +/- leads. They could have gone right in between the PT and the eyelet board, inside the chassis. Would have been pretty easy. You could have left the B node, screens and C node, PI in the dog house.

[Garrett335]

@Willabe Thank you for all of these links and information!
I know what I'll be reading tonight when I get home from work. I appreciate you taking the time. I'll go through all of these and make adjustments and report back.

[shooter]

Ya, make it 2" AWAY from any signal wire in the pre, especially the 1st tube
they should cancel since it's at 90 degrees, but......worth eliminating one more thing that could be

[sluckey]

Do this...

[Garrett335]

@Willabe okay I twisted the HT CT and connected directly to the can cap (-) post, then ran a ground wire to the mains star ground from there.
(I also removed the Diode rectifier and re-installed the 5y3)

@Slucky I removed the green ground wire you suggested, confirmed that those 4 turrets were all connected, and ran a jumper ground wire from the C10 (V4Cathode cap)

I also changed the output jack from cliff (with an original ground wire running to star), to a Switchcraft using chassis as ground removing the ground jumper to mains.

Hum is still there, amp tone sounds really cool with guitar, turning volume past 6 with chord being strummed causes a high frequency oscillation electric sound. I'm wondering if this is from V1 being so microphonic/vibration? I'm worried about that, do you think it's directly related to this grounding issue sound? Are other V1a/b grids so sensitive? I've tried switching between shielded and regular wire which is not making a difference.

[Willabe]

@Willabe okay I twisted the HT CT and connected directly to the can cap (-) post, then ran a ground wire to the mains star ground from there.

Got a new picture?

.....I'm wondering if this is from V1 being so microphonic/vibration?

Try different known good 12AX7 tubes. Sounds like a bad microphonic tube.

[Garrett335]

[Auke Jolman]

Hi,

I'm not seeing it clearly in the picture, but it looks like your gridstopper on V1 and the attached shielded wire touches the chassis. Maybe you better put some heatshrink there or add a post for the connection between the resistor and the shielded cable.

[Garrett335]

@Auke Jolman
Thank you, it is floating, the pictures are deceiving.
I will certainly clean that up, just connected real quick. I re-installed shielded cable on both of V1 grids, it helped by reducing some of the microphonics.
The hum is still present though. This is so frustrating.

I put back both shielded cables to grids of V1. Grounded the shields to input jack, and to the volume pot ground lug which has a jumper going to jack ground.
I also connected the pre board grounds with the green jumper wire to the ground lug of the jack, this way everything attaches to the jack, and one jumper from jack to chassis ground

*Side note, maybe has nothing to do with this, I was checking the plates of the Output tubes V3 was causing my multimeter to freak out causing all lights to flash, V4 plate was fine giving normal readings dc. I disconnected OT primary wires and flipped them, V3 now giving normal readings. IDK if it was a bad connection, the problem is gone now. Hum is still there so I don't think it's related idk.

[sluckey]

May be time to revisit Hoffman's Stout build pages. Look for differences in his build and your build.

[shooter]

causing all lights to flash

House lights?? 


have you pulled the preamp tubes to see if hum goes away?

[Garrett335]

@slucky
I think you are right....
I have the printouts of the schem and layout but maybe I'm missing something. The layout is already different due to the placement of the transformers etc.

@shooter
My Multimeter screen flashing
When I pull the PI V2 the hum is almost inaudible

[Willabe]

.....I'm wondering if this is from V1 being so microphonic/vibration?

Try different known good 12AX7 tubes. Sounds like a bad microphonic tube.

Did you try different tubes for V1 and V2 yet?

[Willabe]

May be time to revisit Hoffman's Stout build pages. Look for differences in his build and your build.

Doug's got the tubes in the front of the chassis under the pots.

Garrett's has the normal layout, tubes along the back of the chassis.   

[sluckey]

May be time to revisit Hoffman's Stout build pages. Look for differences in his build and your build.

Doug's got the tubes in the front of the chassis under the pots.

Garrett's has the normal layout, tubes along the back of the chassis. 

Might be a good place to start. I bet Doug's amp works.   

[Willabe]

Might be a good place to start. I bet Doug's amp works.   

I'm sure it does, but it's laid out differently.

I was looking at the 2 and Garretts doesn't look that different to me, other than the 2 layout's.  Doug does have a ground wire running from the output jacks to the power ground. Garrett did have that groung wire but when he changed the output jack to a switchcraft he took it out.   

I'm waiting to hear if anything changes when he try's different 12AX7's.

[Garrett335]

@Slucky Steve you have me in stitches HAHAHA. You are right I bet his does work.

@Willabe, I popped in 2 new pres and output tubes (Entire new set) no difference.
With no guitar plugged in and I turn the volume all the way up V1 is super sensitive, just tapping it with a chop stick I can hear everything. (The shielded cables did help reduce the grid wire sensitivity) The hum seems to go away with the volume all the way up, like an out of phase sound. With vol off the hum is constant.

When I put the multimeter probe on the grid to the PI all signal cuts out and a loud pop, hum disappears but so does the signal I think. Voltages read close to Hoffmans.

Wires going to tone control are loud, maybe I'll add a shielded cable there too. Seems like V1 sensitivity is going to cause issues with the amp turned up rattling inside the head.

Anyways I owe you guys a beer or three for sticking this out with me. You are really so helpful and I appreciate it.

[Garrett335]

Just reporting back.
I had previously removed the negative feedback resistor during all of this.
Adding it back in the circuit reduced that hum by I would say 70%.

It might come down to lead dress in the end. Going to probably rewire the whole thing, change the layout a bit.
Thank you for all of your help.

[Willabe]

That's great news! 

As long as your going to you re-wire the whole amp, you could try a little experiment. 

You need 1 ~20uF (even a 10uF) @ 500v or 450v will work. 

Disconnect the last 20uF from your cap can that feeds the 1st preamp tube and take out that wire that goes from the cap can to the eyelet/turret board.

Now put the new cap on the eyelet/turret board right at the B+ the old cap was feeding. Run the ground end of the new cap to the ground buss right there.

Now that 1st preamp tubes grounds including the B+ filter cap will be separated from the power ground. 

That might help a lot.

[Willabe]

Try this 1st;

Take a gator clip test cable and hook 1 end to the speaker jack ground and the other to the chassis power ground, not the cap can, the chassis power ground.

Any better?

If not remove the gator cable and use it to ground V1b grid to the preamp ground.

Any better?

If not now try grounding the PI, V2a input to the chassis, anywhere.

Any better?   

[sluckey]

This is just a suggestion and it will not change your issue...