Actually... where to tie the heater and how are tricky issues. It is a very simple thing to do however.
We need to see a schematic of your amp... the schem doesn't have to show the changes you made... really, it just needs to show how the heater circuit WAS wired.
But, we need tie the heater circuit to something. Otherwise, your tubes are trying to talk to each other... and the transformer is trying to talk to the tubes etc... the circuit should not be left floating.
How is the issue of DC voltage going?
We need to see a schematic of your amp... the schem doesn't have to show the changes you made... really, it just needs to show how the heater circuit WAS wired.
But, we need tie the heater circuit to something. Otherwise, your tubes are trying to talk to each other... and the transformer is trying to talk to the tubes etc... the circuit should not be left floating.
How is the issue of DC voltage going?
Hmm...that makes sense conceptually, if not practically. But I'm all ears!
The schematic is:
http://thegoldenbears.net/images/Ampex.jpg
Thanks for enquiring as to the DC side of things; I'm going to have to order the 3,300 mfd caps before anything else happens. But I'm confident this will finally nail things down. The REAL challenge, as I wrote earlier, is understanding WHY to take these steps, rather just knowing to do them!
Thanks again,
Seth
The schematic is:
http://thegoldenbears.net/images/Ampex.jpg
Thanks for enquiring as to the DC side of things; I'm going to have to order the 3,300 mfd caps before anything else happens. But I'm confident this will finally nail things down. The REAL challenge, as I wrote earlier, is understanding WHY to take these steps, rather just knowing to do them!
Thanks again,
Seth
If you look at the old schematic, you'll see that old 6.3 VAC supply was essentially connected to ground through the "hum balance" pot.
We need the keep the potential on the new DC circuit about the same. So it would be appropriate to connect the negative side of the DC heater supply to ground... the same ground that big caps in the high voltage connect to.
Why make a connection? The 6.3 volt winding has a capacitive coupling to all kinds of junk in the transformen. and therefore so does your DC supply. There is also capacitance between the cathodes on the tubes and the heater filament inside. All these can "talk to each other"... not a good thing. Energy can travel through these hidden capacitors... in BOTH ways.
Now, you can't do much about the energy... it will flow regardless. But, instead of having the transformer talking to the tubes, how about making both the transformer and the tubes talk to ground? This will isolate one from the other.
You may wish to wait and see what the cat has to say... he will probably know the ideal point at which to ground the new DC supply. Not usually... but sometimes, a few inches (the attachment point) can make a difference even though you are connecting to the same "electrical" point.
We need the keep the potential on the new DC circuit about the same. So it would be appropriate to connect the negative side of the DC heater supply to ground... the same ground that big caps in the high voltage connect to.
Why make a connection? The 6.3 volt winding has a capacitive coupling to all kinds of junk in the transformen. and therefore so does your DC supply. There is also capacitance between the cathodes on the tubes and the heater filament inside. All these can "talk to each other"... not a good thing. Energy can travel through these hidden capacitors... in BOTH ways.
Now, you can't do much about the energy... it will flow regardless. But, instead of having the transformer talking to the tubes, how about making both the transformer and the tubes talk to ground? This will isolate one from the other.
You may wish to wait and see what the cat has to say... he will probably know the ideal point at which to ground the new DC supply. Not usually... but sometimes, a few inches (the attachment point) can make a difference even though you are connecting to the same "electrical" point.
I don't think it will make very much difference where on the chassis you connect the new DC supply to the chassis, but it does make a difference how you do it. You need a low resistance connection, so that means a serrated washer between the solder tag and chassis. It also means doing the screw up tight - use a spanner on the nut. Use a short wire to the solder tag. Then, using wires as short as possible (1mm extra is 1mm too much) connect each heater pin on each valve to chassis via a 10nF capacitor.
Hmm....
Again, verrrry interesting. And verrry confusing. To wit:
-Currently, the filaments are connected to the filament power supply in the "usual" way; in other words, through two wires going to each tube socket. I'm aware that this is redundant, now that filament ground is chassis ground, but I didn't see any reason to change this, as the connections were already made. (Plus, I didn't know which tube pins are supposed to represent "+" and "-," if it matters, so long as they're consistent).
So there's a real benefit to connecting the "-" tube pins directly to the chassis? Or am I reading that wrong, that the "+" and "-" pins should still receive their power through the two wires?
-Secondly, I'm a little confused by the advice to connect each pin to chassis through a cap. Or is the idea that the caps are not "-" returns to chassis, rather they isolate the pins from ground (because caps don't pass DC)?
Thanks, confusedly,
Seth
Again, verrrry interesting. And verrry confusing. To wit:
-Currently, the filaments are connected to the filament power supply in the "usual" way; in other words, through two wires going to each tube socket. I'm aware that this is redundant, now that filament ground is chassis ground, but I didn't see any reason to change this, as the connections were already made. (Plus, I didn't know which tube pins are supposed to represent "+" and "-," if it matters, so long as they're consistent).
So there's a real benefit to connecting the "-" tube pins directly to the chassis? Or am I reading that wrong, that the "+" and "-" pins should still receive their power through the two wires?
-Secondly, I'm a little confused by the advice to connect each pin to chassis through a cap. Or is the idea that the caps are not "-" returns to chassis, rather they isolate the pins from ground (because caps don't pass DC)?
Thanks, confusedly,
Seth
OooooooooooooooooooooooooK...
The heaters within the tube don't have a negative or positve. They will wind up that way after the DC supply is working...
You WILL run wires from each heater to the next in parallel... they are like this already!
Forget about caps for now... we'll get back to that. They are called "bypass" caps. Their purpose is to divert noise and garbage on EITHER heater supply to ground.
We grounded your DC supply because a floating circuit is bad news here.
What is a floating circuit? Your car is a good example. Let call earth zero volts. Relative to earth... what is the voltage on either of your battery terminals? Who knows? Depends what mood your tires are in... seriously. Your car has a floating system.
Now clamp a wire with 100 Volts (relative to earth) to the chassis.
What is the voltage at the negative battery terminal? !00 Volts... RELATIVE to earth. What is the voltage at the positve terminal? 112 Volts... What is the voltage on the positive terminal relative the the negative? 12 Volts.
Voltage is a relative measurement. When you hang a meter on a circuit... and it says 20 Volts... it means that THIS point is 20 Volts greater than THAT point.
Think about tire pressure... fill your tire to 35 PSI... how much pressure is in it? About 49.7 PSI... 35 + 14.7 PSI, our normal air pressure around us. What does the 35 mean? It means THAT pressure inside the tire is 35 PSI greater than THIS pressure around us.
Just connect the negative lead from your new circuit to ground as EC explained... and feed the positive and negative leads of the new circuit the old heater circuit... as you have I believe!
When all that is working... and the DC voltage... then we'll deal with bypass caps...
This place needs a chalkboard... and a paddle...
The heaters within the tube don't have a negative or positve. They will wind up that way after the DC supply is working...
You WILL run wires from each heater to the next in parallel... they are like this already!
Forget about caps for now... we'll get back to that. They are called "bypass" caps. Their purpose is to divert noise and garbage on EITHER heater supply to ground.
We grounded your DC supply because a floating circuit is bad news here.
What is a floating circuit? Your car is a good example. Let call earth zero volts. Relative to earth... what is the voltage on either of your battery terminals? Who knows? Depends what mood your tires are in... seriously. Your car has a floating system.
Now clamp a wire with 100 Volts (relative to earth) to the chassis.
What is the voltage at the negative battery terminal? !00 Volts... RELATIVE to earth. What is the voltage at the positve terminal? 112 Volts... What is the voltage on the positive terminal relative the the negative? 12 Volts.
Voltage is a relative measurement. When you hang a meter on a circuit... and it says 20 Volts... it means that THIS point is 20 Volts greater than THAT point.
Think about tire pressure... fill your tire to 35 PSI... how much pressure is in it? About 49.7 PSI... 35 + 14.7 PSI, our normal air pressure around us. What does the 35 mean? It means THAT pressure inside the tire is 35 PSI greater than THIS pressure around us.
Just connect the negative lead from your new circuit to ground as EC explained... and feed the positive and negative leads of the new circuit the old heater circuit... as you have I believe!
When all that is working... and the DC voltage... then we'll deal with bypass caps...
This place needs a chalkboard... and a paddle...
I will rework my heater DC board with the LM350 and have another crack at it. 
RE: Dead PC Power Supplies
Yes, the kind fellow who initially turned me on to this PS mod suggested I check dead computers for the parts; as it turned out, new heat sinks and accessories are so cheap I just ordered them online.
In any event, the new value (3300 mfd) caps arrived today, and the PS is happily putting out 6.3V! Now, about those bypass caps....
Best,
Seth
Yes, the kind fellow who initially turned me on to this PS mod suggested I check dead computers for the parts; as it turned out, new heat sinks and accessories are so cheap I just ordered them online.
In any event, the new value (3300 mfd) caps arrived today, and the PS is happily putting out 6.3V! Now, about those bypass caps....
Best,
Seth
OK then...
The cat says 10 nf. So... I would get some 10 nF (100 nF would be fine too... don't DARE ask which is better) monolythic ceramic axial leaded caps... X7R rating should be fine. You will need 2 per heater (tube). A 50 Volt rating should be fine... IN THIS CASE.
Solder one end of each cap onto the heater tabs of the tube socket. Solder the other ends of both to a tab on the chassis.
These caps will divert high frequency energy (trash) toward ground and away from your heaters.
The cat says 10 nf. So... I would get some 10 nF (100 nF would be fine too... don't DARE ask which is better) monolythic ceramic axial leaded caps... X7R rating should be fine. You will need 2 per heater (tube). A 50 Volt rating should be fine... IN THIS CASE.
Solder one end of each cap onto the heater tabs of the tube socket. Solder the other ends of both to a tab on the chassis.
These caps will divert high frequency energy (trash) toward ground and away from your heaters.
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