Aaaaannd it's on... (amp build)
- Thread starter Surgeon
- Start date
Re: Aaaaannd it's on... (amp build)
Hmmm.
One more thing you can try.
Make sure/Re-solder your ground connection on the last can cap.
Do you have a couple of Elytics.?
They can be Radials or Axials. You can try replacing...is it C9 and C26...that last can on your B+ rail...Nodes C and D.
Does not even have to be the same value.
Is that schem right...are they really 50 Mics.?
Anyway...as long as they are 10-20 mics and 400 volts.....you can try pulling that last can, use another dropping resistor if you have one, if not pull it from that can. You can see where this is going...see if that can is the problem. You can also try grounding Node-C (the phase inverter) with the B+ for the power amp (A and B). And keep Node-D where it id with the Ground Buss wire.
Something in that area is giving you fits, and I am out of ideas.
While the amp is running, do you get a voltage drop across R15 on that can.?
Do you have a scope.?
Have you tried disconnecting your NFB.?
Just lifting it off the Impedance selector, or maybe connect it to a different tap.?
Hmmm.
One more thing you can try.
Make sure/Re-solder your ground connection on the last can cap.
Do you have a couple of Elytics.?
They can be Radials or Axials. You can try replacing...is it C9 and C26...that last can on your B+ rail...Nodes C and D.
Does not even have to be the same value.
Is that schem right...are they really 50 Mics.?
Anyway...as long as they are 10-20 mics and 400 volts.....you can try pulling that last can, use another dropping resistor if you have one, if not pull it from that can. You can see where this is going...see if that can is the problem. You can also try grounding Node-C (the phase inverter) with the B+ for the power amp (A and B). And keep Node-D where it id with the Ground Buss wire.
Something in that area is giving you fits, and I am out of ideas.
While the amp is running, do you get a voltage drop across R15 on that can.?
Do you have a scope.?
Have you tried disconnecting your NFB.?
Just lifting it off the Impedance selector, or maybe connect it to a different tap.?
Last edited:
Re: Aaaaannd it's on... (amp build)
Already done but I can redo them again, no harm in this...
I'm afraid I don't have any of this voltage on hand... I'Ll order if it gets to this though.
Nope
Yes, I've tried disconnecting it: no effect.
Thank you a lot for all the suggestions my friend.
Already done but I can redo them again, no harm in this...
I'm afraid I don't have any of this voltage on hand... I'Ll order if it gets to this though.
Will check
Nope
Yes, I've tried disconnecting it: no effect.
Thank you a lot for all the suggestions my friend.
Re: Aaaaannd it's on... (amp build)
Oh Man.....I know you have poured over this thing a hundred times by now.
I wish I were a Tech, and could tell you what is wrong.
I am thinking it must be parasitic. This layout has probably been used hundreds, or thousands of times by now. That can cap is probably fine...but since you still have a problem, I thought it would be worth a try.
Have you gone over your chassis....does it follow the Weber Layout pretty faithfully...again, I am assuming they have used it to success with many other customers.
Have you tried logging onto the Weber Forum...they have a lot of qualified people over there.
best
I cannot tell from your pics, but where does that last can ground to.?
Have you tried grounding that to your buss wire.? Is that where the PI grounds to...the buss wire.?
Oh Man.....I know you have poured over this thing a hundred times by now.
I wish I were a Tech, and could tell you what is wrong.
I am thinking it must be parasitic. This layout has probably been used hundreds, or thousands of times by now. That can cap is probably fine...but since you still have a problem, I thought it would be worth a try.
Have you gone over your chassis....does it follow the Weber Layout pretty faithfully...again, I am assuming they have used it to success with many other customers.
Have you tried logging onto the Weber Forum...they have a lot of qualified people over there.
best
I cannot tell from your pics, but where does that last can ground to.?
Have you tried grounding that to your buss wire.? Is that where the PI grounds to...the buss wire.?
Last edited:
Gone_Shootin
New member
Re: Aaaaannd it's on... (amp build)
Surgeon, here's a thread I found over at The Amp Garage that might help. http://ampgarage.com/forum/viewtopic.php?t=24424&highlight=jcm+800+hum
If it doesn't, it's free to sign up over there and the folks are pretty good at helping a guy out.
Surgeon, here's a thread I found over at The Amp Garage that might help. http://ampgarage.com/forum/viewtopic.php?t=24424&highlight=jcm+800+hum
If it doesn't, it's free to sign up over there and the folks are pretty good at helping a guy out.
GoldenVulture
Braindeadologist
Re: Aaaaannd it's on... (amp build)
Is D5[IN4007] hiding under the 100 mfd cap next to R32[39k] ? maybe swap it out for another one.
Is D5[IN4007] hiding under the 100 mfd cap next to R32[39k] ? maybe swap it out for another one.
this suggests it's something in that area of the circuit.
Last edited:
crusty philtrum
Vintageologist
Re: Aaaaannd it's on... (amp build)
Yup, the cap numbers are from the schematic you linked to.
Yup, the cap numbers are from the schematic you linked to.
crusty philtrum
Vintageologist
Re: Aaaaannd it's on... (amp build)
Don't forget the electro cap that is the filter for the bias supply, C21. It often gets overlooked at times like these.
How did you first power the amp up ? Slowly, using a variac, or just hard turn on, 0 Volts to 110 Volts straight up with a flick of the power switch ?
Don't forget the electro cap that is the filter for the bias supply, C21. It often gets overlooked at times like these.
How did you first power the amp up ? Slowly, using a variac, or just hard turn on, 0 Volts to 110 Volts straight up with a flick of the power switch ?
crusty philtrum
Vintageologist
Re: Aaaaannd it's on... (amp build)
I'm not sure this would cure the issue, but the choke coil should be rotated 90 degrees on the surface of the chasis.
I'm not sure this would cure the issue, but the choke coil should be rotated 90 degrees on the surface of the chasis.
Re: Aaaaannd it's on... (amp build)
As best as I can... I'm a first-time builder but a pretty analytic person and a meticulous one at that. I can't swear on my life that it's faithful but I'm pretty darned sure...
Yep, started asking questions before I started the build. They are on the case too and helping me. Still no one found the answer though.
All three cap cans are linked through a bus bar (only these three though) and the bar is then linked to the star-ground you see just on the right, where all the power-stage grounds are grounded.
Thanks for the link. The hum described in this thread is different as it's independent from the volume pot. Still lots of great info!
Yes, it's hidden there. I'll check if I have another one around. Last time I tested it it was good but it's worth a try.
Thanks, I'll check it too.
Light-bulb limiter.
Theoretically, what would the effect of this be? (or why is this important?)... just curious. I'll have to drill new holes before I can rotate it, no big deal.
As best as I can... I'm a first-time builder but a pretty analytic person and a meticulous one at that. I can't swear on my life that it's faithful but I'm pretty darned sure...
Yep, started asking questions before I started the build. They are on the case too and helping me. Still no one found the answer though.
All three cap cans are linked through a bus bar (only these three though) and the bar is then linked to the star-ground you see just on the right, where all the power-stage grounds are grounded.
Thanks for the link. The hum described in this thread is different as it's independent from the volume pot. Still lots of great info!
Is D5[IN4007] hiding under the 100 mfd cap next to R32[39k] ? maybe swap it out for another one.
this suggests it's something in that area of the circuit.
Yes, it's hidden there. I'll check if I have another one around. Last time I tested it it was good but it's worth a try.
Thanks, I'll check it too.
Light-bulb limiter.
Theoretically, what would the effect of this be? (or why is this important?)... just curious. I'll have to drill new holes before I can rotate it, no big deal.
Re: Aaaaannd it's on... (amp build)
You do not need to drill any holes...you just try turning it (if there is slack) and see if there is any effect.
The magnetic coupling is usually a problem between the lams of the PT and OT...but at this point, Crusty has an option that would be easy to try...it might be the answer.
Does not need to be at 90 degrees, You will frequently see a choke in all kinds of offset angles...the OT as well.
(sorry for butting in)
You do not need to drill any holes...you just try turning it (if there is slack) and see if there is any effect.
The magnetic coupling is usually a problem between the lams of the PT and OT...but at this point, Crusty has an option that would be easy to try...it might be the answer.
Does not need to be at 90 degrees, You will frequently see a choke in all kinds of offset angles...the OT as well.
(sorry for butting in)
crusty philtrum
Vintageologist
Re: Aaaaannd it's on... (amp build)
So did the voltage readings on the low side of the coupling caps read zero on a low-volt scale on your meter, or 1 Volt, or 2 volts ... any small readings at all on the low scale ?
Have you tried different brands/ models of tube for V2 ?
So did the voltage readings on the low side of the coupling caps read zero on a low-volt scale on your meter, or 1 Volt, or 2 volts ... any small readings at all on the low scale ?
Have you tried different brands/ models of tube for V2 ?
crusty philtrum
Vintageologist
Re: Aaaaannd it's on... (amp build)
Are the components in an actual JCM this close together ?
^ What is that curled brown wire to the left of what i assume is the impedance selector switch? Why is it coiled and not cut to length ? Is it one of the o/t primary wires to the power tube plates that has since been cut to length once the phase was worked out ?
Are the components in an actual JCM this close together ?
Last edited:
Re: Aaaaannd it's on... (amp build)
Good point, I only used the higher scale... will recheck tonight if/when I get a chance.
Used the stock Shugs, TS and EH in v2 with no better results.
I'm guessing that the layout would be different (actually is... based on the pics I've seen) but as others have used that same layout successfully I'm guessing that this is not the issue.
Good point, I only used the higher scale... will recheck tonight if/when I get a chance.
Used the stock Shugs, TS and EH in v2 with no better results.
I'm guessing that the layout would be different (actually is... based on the pics I've seen) but as others have used that same layout successfully I'm guessing that this is not the issue.
crusty philtrum
Vintageologist
Re: Aaaaannd it's on... (amp build)
Yes, you must use a low-voltage scale on the meter. Start on a higher scale and then dial it down for a more accurate reading. Sometimes it doesn't take many volts to leak through a coupling cap for a hum to be created in the next stage.
Yes, you must use a low-voltage scale on the meter. Start on a higher scale and then dial it down for a more accurate reading. Sometimes it doesn't take many volts to leak through a coupling cap for a hum to be created in the next stage.
Re: Aaaaannd it's on... (amp build)
Good point... I wish I had thought of it myself but it's getting a bit crowded up here at the moment with all the debugging that's been going on for a week with no resolution.
Good point... I wish I had thought of it myself but it's getting a bit crowded up here at the moment with all the debugging that's been going on for a week with no resolution.
Re: Aaaaannd it's on... (amp build)
Ok, for once I have something interesting to report.
C17: I have 28 mv on the side which should be zero
C18: I have a reading that fluctuates between 0.2 and 1.6
C2: Approx same as C18
Now, I don't know if the numbers for C18 and C2 are high enough to be considered leaky but would C17 (28mv) be considered bad enough to cause the humming I hear?
Ok, for once I have something interesting to report.
C17: I have 28 mv on the side which should be zero
C18: I have a reading that fluctuates between 0.2 and 1.6
C2: Approx same as C18
Now, I don't know if the numbers for C18 and C2 are high enough to be considered leaky but would C17 (28mv) be considered bad enough to cause the humming I hear?
Similar threads
