Princeton Treble noise

[CharacterZero]

Hi there,
I have a Weber 6a-14 Princeton clone that I built some time ago.  There has long been a certain amount of hiss that I have not been pleased with.  Below 5 or so on the volume it is not that significant.  Raising volume and raising the treble pot significantly increases hissing noise.  I often play in a quieter setting and it can get overwhelming.  I recently changed the plate resistors to higher watt versions and changed all of the pots to higher grade CTS pots.  This all seemed to help some.  However, when I cranked the treble pot, I got some significant clicking/oscillation/weird noise.  Not that I need the treble dimes, but I am wondering if this is a function of the new pot, or am I getting a clearer picture of some noise/oscillation that was always there?  I have chopsticked all over to no avail.  I changed out the caps between the V1 and the volume and treble.  Just not sure what to do. 
Also, (maybe separate topic) despite running a tube screamer and other pedals into this amp, I can not seem to get much of any overdrive.  It sustains, but nothing gritty can be achieved with this amp.  Is this typical?
Thanks,
Tyler

[pdf64]

For responses to be anything more than generic, links to the schematic, layout, details of any deviations from those, and some detailed, well lit photos of your amp’s internal chassis, are really needed.

[CharacterZero]

Yes, I should have known to have more info.  Sorry :)

I should say that the treble issue is the more significant.  Changing the pots and the higher watt plate resistors really did bring down the overall hiss.  Just wondering if there is a way to get it lower.  When I push it hard with pedals, it just stays loud and doesn't really get much breakup.  Not sure if that is just the nature of this design.  I know that it is supposed to be chimey and clean with lots of headroom.  Also, I put a Weber 12F150 50 watt speaker in it.  I am sure that I am not getting much breakup from that either.

V1   Voltages  EH 12AX7 Gold Pin
1   144.7
2   0
3   1.035
6   139.9
7   0
8   1.102
   
V2   JJ ECC82
1   323.9
2   0.011
3   15.27
6   323.2
7   0.011
8   15.27
   
V3   NOS Jan 12AX7WA
1   142.3
2   0
3   1.069
6   143.1
7   0.008
8   1.091
   
V4   Genalex Gold Lion Gold Pin 12AX7
1   280-140
2   0
3   0.001
6   166
7   12.91
8   49
   
V5   JJ 6v6S
3   343.3
4   332.9
5   -29.07
V6   JJ 6v6S
3   344.8
4   333.4
5   -29.69

Rectifier JJ 5U4GB   
4   277.5 AC
6   277.8 AC
8   345.6 DC

[pdf64]

Regarding the V4 trem oscillator voltages, the trem has to be switched on for the readings to bd meaningful.
The reverb driver swap to an ECC82 looks to drawing more current than an ECC81.
Is there any VDC at the hot end of the treble pot, red wire.

[CharacterZero]

The reverb driver swap to an ECC82 looks to drawing more current than an ECC81.

Here are the V2 voltages with the ECC81 in place:
V2   ECC81
1   332.6
2   0.006
3   5.63
6   332.2
7   0.006
8   5.62

Is there any VDC at the hot end of the treble pot, red wire.

As for the red wire on the Treble pot, there is no voltage DC measured there.  Just a lot of noise when probing there.

Regarding the V4 trem oscillator voltages, the trem has to be switched on for the readings to bd meaningful.

As for the V4 measurement, I should have known  My bad.

V4    At 6 on the Pot
   
1   276 to 134
2   -1.9 to 0.6
3   1.4 to 2.2
6   167.2
7   12.89
8   49.2

Thank you

[shooter]

Just wondering if there is a way to get it lower.

can you notice any change by rotating the reverb pot?


add some 1 ohm R's on the PA tube cathodes, those help lots when you're trying to get more roar

[pdf64]

Yes, how have you assessed the idle anode or cathode current of the output valves?
My point is, does it change in the fault mode, ie at high treble & vol settings (still with no signal)?

[CharacterZero]

can you notice any change by rotating the reverb pot?

Hmm....the Reverb adds a moderate amount of hum into the output.  This is why I had originally used the lower powered tube in V2 in order to diminish that noise.
However, the strong hiss that I am getting is only impacted by the treble pot and the volume pot.  When Volume goes to zero, the hiss goes to zero.  Likewise, it is gone when I pull V1.  I have used several different tubes there as well and none have removed it.  If I keep the volume at about 5-6, I can play without too much distraction.  I play a fair amount of solo jazz, so, noise is kinda annoying. 

add some 1 ohm R's on the PA tube cathodes, those help lots when you're trying to get more roar

Do you mean PI (phase inverter)?  Just wondering.  How does this work?  1 ohm doesn’t seem like it would have much effect on biasing the tube.  I am still learning:)

Thank you for your help!

[CharacterZero]

Yes, how have you assessed the idle anode or cathode current of the output valves?
My point is, does it change in the fault mode, ie at high treble & vol settings (still with no signal)?

Hmm, not entirely sure how to do that.  Sorry.
I did test my test probes with 1 Ohm Rs on the cathodes.  They do not change at all when adjusting volume or treble.  They are biased at about 16 milliamps. 
How do you asses the current on the plates?

[mresistor]

PA = Power Amp  he's talking about the power tubes (6V6) .  With a one ohm resistor on the cathode you can check bias of the power tube really easy because the milivolts you read there directly convert to milliamps.  So you just have to check the plate voltage and multiply by the reading on the one ohm resistor. Of course this is total tube current and you would then subtract a couple ma for the screen.

[CharacterZero]

PA = Power Amp  he's talking about the power tubes (6V6) .  With a one ohm resistor on the cathode you can check bias of the power tube really easy because the milivolts you read there directly convert to milliamps.  So you just have to check the plate voltage and multiply by the reading on the one ohm resistor. Of course this is total tube current and you would then subtract a couple ma for the screen.

Yes, I have those.  And now realizing that my bias is pretty cold.  344.2 * .016 mA= 5.5 watts.  This is way under the 14 * .7 = 9.8 watts that I should/could be shooting for.  I will try and increase it tomorrow to see what effect that has on the situation.

[pdf64]

The photo is rather murky around the input jacks.
I can’t work out how the screened cable used there and at the vol control is wired.
What type of resistors have been used for the input jacks?
Metal film would be best there, and at the first anode load too.
Have they been wired up correctly / are the switching jacks working right, so as to put them in parallel when input 1 only is used?

[CharacterZero]

The photo is rather murky around the input jacks.
I can’t work out how the screened cable used there and at the vol control is wired.
What type of resistors have been used for the input jacks?
Metal film would be best there, and at the first anode load too.
Have they been wired up correctly / are the switching jacks working right, so as to put them in parallel when input 1 only is used?

Funny you should mention that.  I had fixed the way that I grounded the input jacks about a month ago.  I had both jacks with a 1 Meg R going to the ground bus.  Now they both are routed through the ground 1 Meg on the high input.  That helped a lot!  Now, I am wondering if that still could be better.  Also wondering if my V1 socket is in need of cleaning or replacement. 
Also, is there any consensus about the gauge of wire to be used on a ground bus wire?  I had used some 12 gauge wire and have always wondered if that was giving me problems.  All preamp is connected to bus wire that is bolted to chassis near input jacks.  Ground for coax is grounded on bus wire not directly to the bolt.  Does that matter?
Tyler

[acheld]

The gauge of the preamp ground buss does not matter.   12AWG is overkill electrically, though it has the advantage of being sturdy and will stay in place nicely.  A fat wire will not introduce noticeable noise (no comments about Johnson-Nyquist noise, please) into a guitar amp circuit, so no disadvantage there. 

Since the usual preamp current to ground is in the mA range, current requirements are practically irrelevant, any of the usual hookup wires we commonly use are (far) more than sufficient.

Grounding your coax shield to the buss wire is fine, assuming your buss grounding point is close to your input jacks. 

[CharacterZero]

Ok, so I had time to mess around with my amp some more.  The hiss that I am getting is measuring at a strong 119 Hz frequency.  When the amp is full volume and full treble, that frequency is around 49 db on the speaker.  The bass pot has no effect on that hiss.
When I increase the Reverb pot, the hiss changes to a 301 Hz frequency.  As I lower the volume to around 1/2 or below and the reverb is brought up slowly, the amp develops a strong 346 Hz tone/harmonic(?) that goes up to around 75 db on the speaker.  As I bring it back down it begins to slowly oscillate back and forth between 346 and 119 until it fades away as the reverb pot settles back down to zero.
Grounding the eyelet where the Reverb Mix is (where 3.3 meg resistor and 10 pF connect with wire to 0.022uF cap coming off of V2b pin 6. 

I am not sure if this is a normal amount of hiss... Kinda seems like it is more than it used to be.  Also, 120Hz seems like a power filter cap somewhere.  Not totally sure where to check.  Is my Weber CapCan starting to bite it?  It is definitely over 12 years old.  Is the loud reverb tone a concern?  What is the best way to identify the cause there?  I banged on the V2 and V3 tubes quite a bit to try and induce similar sounds, but no dice.  Any thoughts on where to track this down would be much appreciated.
Tyler 

[shooter]

Also, 120Hz seems like a power filter cap somewhere

the more likely would induced noise into the sensitive signal wires.
is you rev drive and recovery stages grounded at the same point?
If so, put the recovery ground with pre signal ground and the drive ground either by itself or maybe where the PI is grounded

[CharacterZero]

So I just thought that I would share.  I have been busy trying to eliminate this damn hum/shhh sound for quite some time.  I took many of your suggestions and reworked the grounding of the whole amp.  Improved modified star grounding scheme.  That brought down the noise a touch, but nothing like a magical moment.  I kept reading about people with their silent amps and getting more and more determined.  As all of this was happening, a weird thing happened to my pilot assembly, the hook up tabs seemed to be shorting out occasionally and my lightbulb limiter would go bright and then the soldier there would start to sizzle.  So I quickly went through the freak out about having a bad PT heater winding.  But many tests later and changing various things etc. etc. and I could not figure it out.
I happened to be watching an episode of the D-Lab on the U-tube and he mentioned that he hooks the green heater wires from the PT directly to the first power tube and then back to the lamp.  So I thought, the heck with this lamp, I’ll buy a new one and in the mean time, hook the green wires directly to my output tube.  I turned on the amp and Voila!  It was quieter than I have ever heard it.  So that was exciting!  And now, I am wondering about the lamp.  It seemed like the old one (Fender style) was not right.  Like all of it was grounding to the chassis when the lightbulb was in it, but not when the lightbulb was out of it????  Anyway, I am wondering if I end up wiring from V6 heaters back to the lamp, will my hum come back?  I really don’t want that.  Do all lamps make noise?  Should I use a 120 vac lamp wired to the IEC?  Will that be noisy?  I am open for any advice:).
Thanks,
Tyler

[PRR]

> Do all lamps make noise?

No.

Running 120VAC around the chassis *may* be more hum than 6VAC.

Why don't you just fix the wiring but leave out the lampholder for now? (You probably know when the amplifier is ON.) Make sure that WAS the problem.

Incandescent screw lamps are so 19th century. Do you still play Polonaises? Quadrilles? (Yes, you do still play waltzes, even if you don't admit it.) LEDs live nearly forever so do not need sockets. The last amp-lamp job I did, I cobbled the LED into a (well aged) #47 lampholder, but it could easily (with resistors) be on perf or P-2-P inside the jewel, or just an LED-size hole.

[CharacterZero]

> Do all lamps make noise?

Do you still play Polonaises? Quadrilles? (Yes, you do still play waltzes, even if you don't admit it.)

Of course I do 
Thanks, I will get an LED.
Tyler

[sluckey]

It seemed like the old one (Fender style) was not right.  Like all of it was grounding to the chassis when the lightbulb was in it, but not when the lightbulb was out of it????

Another forum member just ran into a similar issue. The actual bulb socket was bent slightly so that when the bulb was inserted the shell of the bulb would touch the frame of the lamp holder and short out the bulb thus also shorting the filament winding. Easy to spot the problem with your eyes and also easy to fix if this is your case.

No reason not to use a #47 incandescent bulb once you fix the problem with the lamp holder. But, there is a LED replacement for the #47 lamp that fits the Fender lamp holder. Still best to run the PT filament wires straight to the first 6V6 socket. Then run small wires from that socket to the lamp holder. Avoid that kludge of big wires on the lamp holder.

     https://www.tubesandmore.com/products/dial-lamp-led-version-47-or-44-t-3-63v-bayonet-base