It is the so-called Carling progressive switch, marked Carling Mexico, there is no part # on it. For some reason they don't usually put part #s on their switches.
It has four contacts on the back, the vertical pair to the right (looking at the back) is for the AC connection from the PT primary and the left vertical pair for the B+ connection. Ideally I need that layout with an extra pair of isolated contacts to the left, but I bet it doesn't exist.
Zener Diode Question
Moderators: pompeiisneaks, Colossal
Re: Zener Diode Question
Like I said, with the existing switch, you can leave the AC primary pair where they are, and use the other switch section to switch between the CT and ground. That would apply and remove both plate and screen voltage in unison.
There's a reason why this isn't the preferred method - I believe to do with the fact that the voltages are still there, just without a return path to ground. Perhaps someone else can take it from here...
W
There's a reason why this isn't the preferred method - I believe to do with the fact that the voltages are still there, just without a return path to ground. Perhaps someone else can take it from here...
W
-
David Root
- Posts: 3540
- Joined: Fri Aug 04, 2006 3:00 pm
- Location: Chilliwack BC
Re: Zener Diode Question
You can do that with a reference voltage on the CT to ground thru say a 500K 2W resistor across the switch, but you're right it sort of leaves it hanging to some extent.
Re: Zener Diode Question
I hoped someone would chime in by now - I'm a little beyond my "comfort zone" in some respects 
Think about what would happen if something in either the plate circuit or the screen circuit shorted to ground while the amp was on standby.
W
Think about what would happen if something in either the plate circuit or the screen circuit shorted to ground while the amp was on standby.
W
-
David Root
- Posts: 3540
- Joined: Fri Aug 04, 2006 3:00 pm
- Location: Chilliwack BC
Zeners
tubeswell, assuming I can juggle the zeners to get about 470 Vp and 300 Vs, max current draw at 80W power is 292 plates, 36 screens, 11 PI/preamp, and 21 reverb tubes = 360mA. This is the rated output of the winding.
If I settle for say 30 V zener drop on the CT that is 2x30x0.36 = 21.6W, so either a 25W 30V zener or cobble up five or more of the 5W zeners in series that I have in stock, should work.
I still have this switch problem and it looks like a 3 pole is needed. Maybe I can add a SPST switch next to the progressive for the screen supply and somehow physically link the toggles so that the switch to HT is simultaneous on plate and screen? I think Wayne is right about these "hanging" voltages, it has serious risks of damage from arcing.
If I settle for say 30 V zener drop on the CT that is 2x30x0.36 = 21.6W, so either a 25W 30V zener or cobble up five or more of the 5W zeners in series that I have in stock, should work.
I still have this switch problem and it looks like a 3 pole is needed. Maybe I can add a SPST switch next to the progressive for the screen supply and somehow physically link the toggles so that the switch to HT is simultaneous on plate and screen? I think Wayne is right about these "hanging" voltages, it has serious risks of damage from arcing.