Advice needed...

[The4thWatcher13]

Update: The American Strat sounds fabulous, the bit of buzz that I assumed was attributable to my shop guitar is not so fabulous. To describe it I'd say it's a high'ish pitched buzz. Not like 60Hz ground "hum". I swapped outlets here in the shop and it didn't change. I'll have to address the buzz tomorrow. In regard to the pots the originals are not in the best condition, cleaned with DeOxit but still a little wonky.

[TriodeLuvr]

I'd complain to the manufacturer about those pots. They shouldn't be failing after only 55 years.

Does the amp buzz when nothing is plugged into the jack? The ground on the input is only connected to the preamp ground, right? That would be the bottom of the grid resistor and the cathode RC at V1. One of your pics looks like it's connected to a ground lug riveted to the chassis wall. That would be a big no-no.

Jack

[The4thWatcher13]

I'd complain to the manufacturer about those pots. They shouldn't be failing after only 55 years.
Does the amp buzz when nothing is plugged into the jack? The ground on the input is only connected to the preamp ground, right? That would be the bottom of the grid resistor and the cathode RC at V1. One of your pics looks like it's connected to a ground lug riveted to the chassis wall. That would be a big no-no. Jack

Yeah, I was also thinking 55 years a bit shy of my expectations.
The amp does not buzz at all when nothing is plugged in.
The input's ground, V1 cathode RC, V2 cathode RC, V2 grid stopper (R6) and filter cap C3-C are all soldered to a rail which connects to a ground lug which is bolted to the side of the chassis. Should each component have it's own lead to the ground lug or is the grounding spot itself a problem?

[The4thWatcher13]

Does the amp buzz when nothing is plugged into the jack? The ground on the input is only connected to the preamp ground, right? That would be the bottom of the grid resistor and the cathode RC at V1. Jack

Ah! So V1, by itself, is considered the "preamp", but V2 is not? V2 would be considered part of the power amp circuit and therefore both of it's grounds should go to the star ground?

[The4thWatcher13]

In regard to my statement above, V2 not being part of the preamp would make sense, as it applies to grounding, since it's filter cap is grounded with the pre. Duh..!
(..man, this star business is Sirius!)

[TriodeLuvr]

Rather than separate the V1 and V2 grounds, lift that lug off the chassis and ground it to the star. You might have to separate the preamp and PI grounds, but the small amount of current drawn across the common ground wire by the PI probably won't create an issue. It's too bad the lugs on the terminal strip are cut off in that location. They would make this work easier. I often assign more than one lug as signal ground, and more than one as B+, even when the same B+ feeds two stages. That provides the option of separating the circuits later if there's unwanted interaction.

Anyway, let's hope this quiets it down. If not, we'll have to look elsewhere.

Jack

[The4thWatcher13]

Rather than separate the V1 and V2 grounds, lift that lug off the chassis and ground it to the star. You might have to separate the preamp and PI grounds, but the small amount of current drawn across the common ground wire by the PI probably won't create an issue. I often assign more than one lug as signal ground, and more than one as B+, even when the same B+ feeds two stages. That provides the option of separating the circuits later if there's unwanted interaction. Anyway, let's hope this quiets it down. If not, we'll have to look elsewhere. Jack

I got rid of the (pre) lug on the side (assuming eliminating it is the same as isolating it) ...and I used the 3rd of the 4 terminal connections which has the input jack and pre grounds all going back to the star on their own lead. The PI grounds are connected together and go to the star on their own lead as well. I separated the PI grounds because it's the only configuration I believe that hasn't been tried yet. Tying the pre and PI grounds together and running them back to the star is exactly the way it was laid out at the beginning except for the pre-cap being grounded at the pre section instead of directly to the star.
But it is, of course, also now grounded to the star but still connected up by the input jack. As a side note; the closer I get the guitar to the amp the worse the noise gets. I tried using the tube shields on V1 & V2 but it didn't help at all. Also the blue wire connecting the input jack tip to the grid isn't shielded; it's only an inch at best but just another observation.

[The4thWatcher13]

Correction: in the "original" layout Pre, PI, jack and vol were grounded to their own point up front. Not all going to the star, as I stated above. Also, I tried re-connecting V1 & V2 grounds all of which now go to the star on one lead. Both of the ways Jack recommended trying previously. Still no real difference in the level of buzz.
So to recap, for my own sanity, I've tried:
All ps caps to star, Pre & PI, connected, grounded up front.
Pre filter cap was moved from star to ground up front.
Pre and PI separated, Pre grounded up front, PI grounded to star.
Pre and PI separated, grounded to star on separate leads.
Pre and PI reconnected and grounded to star on same lead.
No appreciable difference in the level of buzz.

[JMPGuitars]

Correction: in the "original" layout Pre, PI, jack and vol were grounded to their own point up front. Not all going to the star, as I stated above. Also, I tried re-connecting V1 & V2 grounds all of which now go to the star on one lead. Both of the ways Jack recommended trying previously. Still no real difference in the level of buzz.
So to recap, for my own sanity, I've tried:
All ps caps to star, Pre & PI, connected, grounded up front.
Pre filter cap was moved from star to ground up front.
Pre and PI separated, Pre grounded up front, PI grounded to star.
Pre and PI separated, grounded to star on separate leads.
Pre and PI reconnected and grounded to star on same lead.
No appreciable difference in the level of buzz.

Match my ground scheme, then try the Paul Ruby mod. Both can be seen here: files/JMPGuitars_18_Watt_Superlite_TMB_Layout.pdf

You'll note on my ground schemes the PI goes to the power amp star ground.

If that has no effect, post a demo of what the amp sounds like. Turn it up to a moderate volume level, plug a guitar in, wait 10 seconds or so, then also play the guitar a little.

Thanks,
Josh

[TriodeLuvr]

As a side note; the closer I get the guitar to the amp the worse the noise gets.

I would have replied sooner, but our power is out due to a storm.

Josh, have you ever seen a ground loop act like that?

I know this is a long shot, but is there any chance the input jack is wired wrong?

Jack

[The4thWatcher13]

Match my ground scheme, then try the Paul Ruby mod. Both can be seen here: files/JMPGuitars_18_Watt_Superlite_TMB_Layout.pdf
You'll note on my ground schemes the PI goes to the power amp star ground. If that has no effect, post a demo of what the amp sounds like. Turn it up to a moderate volume level, plug a guitar in, wait 10 seconds or so, then also play the guitar a little. Thanks, Josh

I'll give it a look and give it a try, Josh, thanks. One thing I've been dealing with is trying to determine exactly how much amp "noise" inevitable or acceptable. The noise isn't bad until you get up to 3/4 or so. I didn't know I could post an audio file here. That'll help too.
Also do you think with my 1"in lead from the jack "tip" to the grid should be shielded? And is the shielded lead in your diagram grounded on one end (at the jack)

[The4thWatcher13]

As a side note; the closer I get the guitar to the amp the worse the noise gets.

I would have replied sooner, but our power is out due to a storm.
Josh, have you ever seen a ground loop act like that?
I know this is a long shot, but is there any chance the input jack is wired wrong? Jack

No worries here, Jack. As long as you and yours are OK. I've got a "shorted" or "switched" input the tip goes directly to the grid of V1 and a 1M R goes to the ground tab that lifts when you plug in a plug, and then to the ground tab. The grounding input jack isn't shown on my schematic, apologies. I've got new Cliff jacks coming soon.

[JMPGuitars]

As a side note; the closer I get the guitar to the amp the worse the noise gets.

I would have replied sooner, but our power is out due to a storm.

Josh, have you ever seen a ground loop act like that?

I don't think so, but guitars getting closer to an amp will increase feedback (if there is any), so this may be along those lines. I think we need to hear what the noise actually sounds like.

[The4thWatcher13]

Well, I'm attempting to upload a sound sample of the amp and the noise it's making. Something odd happened today as well. The amp started an oscillation, something which hasn't happened to date and I've been standing in the same spot every time I've tested the amp. It also kind of sounds like the buzz may actually be getting worse.
On the recording the amp was set at 50% and tone at about 75%. Forgive my lack of guitar skills, I'm actually a drummer! (..I bet that clears up a lot! ) Last night I moved the 1M/R on the input jack which previously went from the tip tab to the ground lift tab to the ground tab. Now it goes from the tip tab to the ground tab to the ground lift tab. This enabled me to move the resistor further away from the V1 cathode CR and also seemed a more correct per Josh's layout.

[TriodeLuvr]

When routing wires, it helps to consider the various connection points in terms of the impedance to ground. For example, the highest impedance - and therefore the most susceptible to picking up stray signals - would be grids. OTOH, a bypassed cathode of a common-cathode stage is very low impedance. It will have almost no AC voltage on it. As a result, it's not possible for a wire connected to such a cathode to radiate into (or be affected by) a grid circuit. The two can be right next to each other without issues.

Maybe the amp is oscillating all the time. That sometimes sounds like a buzz. It might also explain why the location of the guitar changes the symptom. Like Josh said, it would help to hear it.

Jack

[The4thWatcher13]

When routing wires, it helps to consider the various connection points in terms of the impedance to ground. For example, the highest impedance - and therefore the most susceptible to picking up stray signals - would be grids. OTOH, a bypassed cathode of a common-cathode stage is very low impedance. It will have almost no AC voltage on it. As a result, it's not possible for a wire connected to such a cathode to radiate into (or be affected by) a grid circuit. The two can be right next to each other without issues. Maybe the amp is oscillating all the time. That sometimes sounds like a buzz. It might also explain why the location of the guitar changes the symptom. Like Josh said, it would help to hear it. Jack

Thanks Jack, every time you comment I look at this amp with different eyes. I appreciate it. I posted an audio file, above, earlier of the buzz sound etc. I also re-routed my heater wiring away from V3/V4's grid where previously they were kind of bunched up in close proximity and also ran under the grid circuitry. It didn't have much if any affect but a lesson still learned. I'm anxious to learn what you think of the buzz sound. The first leg of the heater run to V1 goes under both pots as well. I've been wondering about that also since I'm not definite about where and where not to run it. I think I can move it from that location if it's OK to run it over the "red/black/red" plate supplys & ground wire in forground of the picture below. I also re-added a 47uF/63V bypass cap to the OPT cathode ground resistor. It had been suggested somewhere earlier in the thread and it was there during the proto build but was so hidden I had forgotten about it. Again no affect on the buzz. (I didn't forget anything else! ) I've also added yet another current version of the schematic. Which is constantly updated for, at the very least, my own sake.

[TriodeLuvr]

Well, it sounds like the first stage grid might be picking up heater hum. Can you clip your scope across the speaker and see what the buzz looks like? I just want to rule out a high frequency oscillation. If it just looks like buzz, you might need to rotate the V1 socket so heater wiring isn't crossing the grid circuit. You could also heat V1 with a battery or DC bench supply temporarily to see if the buzz goes away. I'm thinking the grid circuit is picking it up, and it's riding into the guitar - and the wiper of the guitar's volume control - through the input jack. The wiper grounds the buzz when the guitar is turned down, and that's why it gets quiet. Just a theory...

That low frequency oscillation could be several things. Did you replace all the parts in the old amp, including coupling caps and tube sockets?

Jack

[JMPGuitars]

That buzz is not fantastically significant. It couuuuuuuuuld be the things we're talking about, or it could simply be a need for some chopsticking. Or made worse by the guitar pickups.

Regarding the oscillation, you need to determine if it's being caused by the amp, or being picked up by the amp. I spent a year chasing an oscillation once that was caused by a power supply in another room.

Chopsticking might help determine both, but if you have anything new plugged in, or power supplies (wall warts, laptop style bricks etc...) that you can unplug and see if the oscillation goes away, that may help determine the source. I use filtered inlets nowadays to reduce this issue.

Thanks,
Josh

[The4thWatcher13]

Well, it sounds like the first stage grid might be picking up heater hum. Can you clip your scope across the speaker and see what the buzz looks like?

Here are pics of the buzz at the output jack and the vol-pot wiper. Full amp vol, full guitar vol. No oscillations today so far.

I just want to rule out a high frequency oscillation. If it just looks like buzz, you might need to rotate the V1 socket so heater wiring isn't crossing the grid circuit. You could also heat V1 with a battery or DC bench supply temporarily to see if the buzz goes away. I'm thinking the grid circuit is picking it up, and it's riding into the guitar - and the wiper of the guitar's volume control - through the input jack. The wiper grounds the buzz when the guitar is turned down, and that's why it gets quiet. Just a theory...Did you replace all the parts in the old amp, including coupling caps and tube sockets? Jack

Yes, all components of this amp are new accept the Vol, Tone pots and the jacks. All of which will be replaced by new parts arriving tomorrow. Side Note: I've been thinking about not having a grid stopper resistor on this amp and was reading the Valve Wizard page about it (Miller Effect). I then put the scope meter on Hz, probes on output, and started the buzz. The meter measured it at +20MHz. When trouble shooting I know it's good to deal with and rule out one aspect at a time but the thought crossed my mind and I took a quick measurement.
[Top pic: output] [Bottom pic: vol wiper]

[The4thWatcher13]

That buzz is not fantastically significant. It couuuuuuuuuld be the things we're talking about, or it could simply be a need for some chopsticking. Or made worse by the guitar pickups.
Regarding the oscillation, you need to determine if it's being caused by the amp, or being picked up by the amp. I spent a year chasing an oscillation once that was caused by a power supply in another room.
Chopsticking might help determine both, but if you have anything new plugged in, or power supplies (wall warts, laptop style bricks etc...) that you can unplug and see if the oscillation goes away, that may help determine the source. I use filtered inlets nowadays to reduce this issue. Thanks, Josh

Thanks Josh, I'm heading for my Chop-sticks now. More to follow..