chassis voltage

st-70 chassis bleed question. all my caps have been upgraded including the driver board,
also the selenium diode removed and  and diodes/caps changed to replace it.
but the question involves the fact that ive got 40vac if i read my chassis to a ground receptacle
in the wall. if i unplug and re-plug it the opposite way i get the same 40vac im guessing this is filter
bleed,
BUT - im curious if this indicates anything else. im wondering if this unit might benefit from some add on at this point.

NOTE, if it matters to anyone
plugged into a Gator GRR-8PL-US rack with a built in 5 plug 15a surge protector power strip.
the rack has a 3 prong power cable to the wall
the wall outlet is checked/correct orientation
bias is set to 1.48 on both sides
all OEM Dynaco stock healthy tubes

PS I CINCERLY hope everyone had a great Christmas, or whatever holiday you might celebrate, or none

D, what is your preamp? Some have a R/C configured across the incoming AC for filtering . As that ages it tends to bleed over to chassis. Just a thought.

AND; HAPPY NEW YEAR, Dale

preamps are
sometimes- preamp is a DH100, or
sometimes- creative labs soundblaster SBX studio pro
but this was measured with preamp disconnected,
and also i see its the same no matter what preamp i use
aPS happy new year to ya

MAYBE it's not just your chassis, MAYBE it's your AC outlet. Neutral SHOULD be 0vac compared to ground.

well. like i said in my post, the outlet was checked and is correct

It could be just potential with no drive behind it.
Measure the current with a 1kΩ resistor in series with one of the VOM leads.
Use clip leads. Don't hold the resistor.

Is there any difference between the Earth to chassis and Neutral to chassis?

Any amp that lacks ground connection will have it's chassie at a voltage level between the live
and return. It's normally a very high impedance thus not dangerous but still a nuisance.

Proper grounding ( such as a 3 wire wall connection ) will solve the issue.

peterh wrote:Proper grounding ( such as a 3 wire wall connection ) will solve the issue.

And depending on the rest of the system, possibly introduce a 'ground loop'

1.6 AC at the smaller blade terminal, 1.8 AC at the ground terminal, 45vAC at the larger blade terminal

incidentally to install the 3 prong cable was where i was going towards, but i don't want the ground to effect the circuit adversely. the install basically removes the death cap and allows ground to chassy why maintaining the tranny isolated correct?

dmagazz wrote:1.6 AC at the smaller blade terminal, 1.8 AC at the ground terminal, 45vAC at the larger blade terminal

Were the VOLTAGE measurements across the 1kΩ resistor?
You DO NOT want to be measuring anything relative to the line [narrow] terminal

dmagazz wrote:incidentally to install the 3 prong cable was where i was going towards, but i don't want the ground to effect the circuit adversely. the install basically removes the death cap and allows ground to chassy why maintaining the tranny isolated correct?

¿Que?

Death Cap?

No offence, but are you certain you should be messing around with line voltages and the inside of a tube amp?

YOU- Death Cap?

so your unfamiliar with the term "deathcap"

YOU- No offence, but are you certain you should be messing around with line voltages and the inside of a tube amp?

i shouldn't be in an amp because i am familiar with the term deathcap ?

no offence but if your gonna give advise, you should know- that capacitor pet name is given because it connects neutral to chassis for a ground and if the polarity is switched and it fails it could "SHOCK THE SHIT OUT OF YOU"!!
and when you hook up a 3 prong cord, that cap is usually removed or it may explode if a polarity switch is in use (if there is one existing) its no longer needed as an "AC ground" if your using a ground terminal 3 prong cord.

YOU- Were the VOLTAGE measurements across the 1kΩ resistor?

no they were not or i would have said so.

YOU- You DO NOT want to be measuring anything relative to the line [narrow] terminal

my fluke is not a wire. if i test line reference to the chassis all its gonna do is tell me if good continuity exists between the common and the chassis, its NOT going to explode

PS, im no engineer, but i am ABSOLUTLY capable.
at this point this has gone astray. i just want to know if this phantom voltage might be caused by the chassis ground reference cap(death cap) or if that voltage is from the circuits nature and is grounded off by hooking up a 3 prong cord might it change the behavior or sound of this amp in any way. no offence, i guess i was looking for someone more insightful, not a judge. lol, don't hold the resistor SMH i mean really. :/ just forget i asked

Sorry.

There is no 'death cap' in a Dynaco ST-70

Hello, I'm new to the Dynaco forum. For some personal history, I have a good electrical understanding due I was raised on TV repair during the 60's and on. I've been involved with electrical component repair for many years. I'm not a master, but I have a lot of time spent dealing with TV, audio and amp repairs; among other things.

I purchased a VTA ST-120 off of E-Bay a few years ago. Upon its initial usage, within about 10 minutes, one output tube began to red plate. I took a look inside the amp and someone did a very poor job of replacing the grid resistors so I fixed that up. The volume knob retaining nut was also off of the threads so I fixed that too. I also tensioned the tube socket terminals. They looked pretty abused. Too many tube swaps maybe?

The amp build looked very well done except the output tube socket connections didn't look very healthy. It looked like someone without electrical knowledge did a number on them with the solder iron. The grid resistors had cold solder joints too.

Anyway, after installing a new set of Gold Lion tubes, and several grid resistors due to a continuing of grid resistor popping, the amp was working OK though I always suspected there was still issues. I set the amp aside for a couple years and recently, I hooked it up again just to see what might happen.

It played well for several days of short term use, but then, one output went into red plating. I opened it up to find that the grid resistor didn't open. I took that as a sign that the tube socket was probably the culprit so I replaced all four output tube sockets.

The amp has been running very well since.

This brings me to the reason for this posting. I noticed how I could feel voltage on the chassis and also on my preamp and turntable. None of the units have a safety ground but they use polarized plugs. My digital meter was reading 136 volts AC from the chassis to earth ground. Yes, an odd voltage reading.

I opened up the amp, looked at the schematic, but the only circuit that appears to touch the chassis ground are the output transformer negative side windings.

I can't see how any part of the actual AC line voltage can be present on the chassis, besides those winding ground points. Line voltage hits the power transformer which in turn gets rectified, so I can't see where the voltage is being injected.

I added an AC cord with a safety ground circuit and the issue is resolved, but I don't think that should have been needed.

I saw a post by Bob Latino stating there isn't any voltage on the chassis so a ground shouldn't be required. But why does my amp have AC voltage present on the chassis?

Might someone have a suggestion? Thank you.

Grizz wrote:Hello, I'm new to the Dynaco forum. For some personal history, I have a good electrical understanding due I was raised on TV repair during the 60's and on. I've been involved with electrical component repair for many years. I'm not a master, but I have a lot of time spent dealing with TV, audio and amp repairs; among other things.

I purchased a VTA ST-120 off of E-Bay a few years ago. Upon its initial usage, within about 10 minutes, one output tube began to red plate. I took a look inside the amp and someone did a very poor job of replacing the grid resistors so I fixed that up. The volume knob retaining nut was also off of the threads so I fixed that too. I also tensioned the tube socket terminals. They looked pretty abused. Too many tube swaps maybe?

The amp build looked very well done except the output tube socket connections didn't look very healthy. It looked like someone without electrical knowledge did a number on them with the solder iron. The grid resistors had cold solder joints too.

Anyway, after installing a new set of Gold Lion tubes, and several grid resistors due to a continuing of grid resistor popping, the amp was working OK though I always suspected there was still issues. I set the amp aside for a couple years and recently, I hooked it up again just to see what might happen.

It played well for several days of short term use, but then, one output went into red plating. I opened it up to find that the grid resistor didn't open. I took that as a sign that the tube socket was probably the culprit so I replaced all four output tube sockets.

The amp has been running very well since.

This brings me to the reason for this posting. I noticed how I could feel voltage on the chassis and also on my preamp and turntable. None of the units have a safety ground but they use polarized plugs. My digital meter was reading 136 volts AC from the chassis to earth ground. Yes, an odd voltage reading.

I opened up the amp, looked at the schematic, but the only circuit that appears to touch the chassis ground are the output transformer negative side windings.

I can't see how any part of the actual AC line voltage can be present on the chassis, besides those winding ground points. Line voltage hits the power transformer which in turn gets rectified, so I can't see where the voltage is being injected.

I added an AC cord with a safety ground circuit and the issue is resolved, but I don't think that should have been needed.

I saw a post by Bob Latino stating there isn't any voltage on the chassis so a ground shouldn't be required. But why does my amp have AC voltage present on the chassis?

Might someone have a suggestion? Thank you.

any device connected to an asymmetrical mains connection ( one connector is live the
other at about zero) small creeping currents will get the chassies somewhere between
live and zero. Creeping is due to capacitive coupling, (hopefully not)resistive coupling and
on some mislead device the so called death caps that actually forces the chassies to be
half-way.

The currents are often very small, it won't kill you but can be felt with a fingertip.
Solution is to use 3-prong outlets and interconnects that implemets an real ground
connecton to chassies parts.

peterh wrote:

Grizz wrote:Hello, I'm new to the Dynaco forum. For some personal history, I have a good electrical understanding due I was raised on TV repair during the 60's and on. I've been involved with electrical component repair for many years. I'm not a master, but I have a lot of time spent dealing with TV, audio and amp repairs; among other things.

I purchased a VTA ST-120 off of E-Bay a few years ago. Upon its initial usage, within about 10 minutes, one output tube began to red plate. I took a look inside the amp and someone did a very poor job of replacing the grid resistors so I fixed that up. The volume knob retaining nut was also off of the threads so I fixed that too. I also tensioned the tube socket terminals. They looked pretty abused. Too many tube swaps maybe?

The amp build looked very well done except the output tube socket connections didn't look very healthy. It looked like someone without electrical knowledge did a number on them with the solder iron. The grid resistors had cold solder joints too.

Anyway, after installing a new set of Gold Lion tubes, and several grid resistors due to a continuing of grid resistor popping, the amp was working OK though I always suspected there was still issues. I set the amp aside for a couple years and recently, I hooked it up again just to see what might happen.

It played well for several days of short term use, but then, one output went into red plating. I opened it up to find that the grid resistor didn't open. I took that as a sign that the tube socket was probably the culprit so I replaced all four output tube sockets.

The amp has been running very well since.

This brings me to the reason for this posting. I noticed how I could feel voltage on the chassis and also on my preamp and turntable. None of the units have a safety ground but they use polarized plugs. My digital meter was reading 136 volts AC from the chassis to earth ground. Yes, an odd voltage reading.

I opened up the amp, looked at the schematic, but the only circuit that appears to touch the chassis ground are the output transformer negative side windings.

I can't see how any part of the actual AC line voltage can be present on the chassis, besides those winding ground points. Line voltage hits the power transformer which in turn gets rectified, so I can't see where the voltage is being injected.

I added an AC cord with a safety ground circuit and the issue is resolved, but I don't think that should have been needed.

I saw a post by Bob Latino stating there isn't any voltage on the chassis so a ground shouldn't be required. But why does my amp have AC voltage present on the chassis?

Might someone have a suggestion? Thank you.

any device connected to an asymmetrical mains connection ( one connector is live the
other at about zero) small creeping currents will get the chassies somewhere between
live and zero. Creeping is due to capacitive coupling, (hopefully not)resistive coupling and
on some mislead device the so called death caps that actually forces the chassies to be
half-way.

The currents are often very small, it won't kill you but can be felt with a fingertip.
Solution is to use 3-prong outlets and interconnects that implemets an real ground
connecton to chassies parts.

I just found your reply. Thank you for that.

Yeah, the leakage current may be low but the voltage present on the chassis, which affect all other components via the RCA ground on line level connections, made for an unpleasant listening environment. It also injected some hum as well.

I have a three prong AC plug on the amp currently. I think it's better all the way around having an earth ground, but too, I would think it shouldn't be a necessity either. But, as you describe, if these small leakages are just bound to happen, I guess I won't worry too much about it. It is a great sounding amp and it's been running very well for a solid year now.

Take care.