Please help!
I've managed to get my mind in a knot regarding this, and need some pointers.
The valves are 12AX7, so triodes.
There are 4 of them in my phono pre-amp.
I know one can supply the heaters either in series (12.6v) or in parallel (6.3v).
AFAIK the 12.6v series feed goes to pins 4 and 5, and the 6.3v feed goes to pins 4and9 and pins 5and9, for each half of the valve.
But that's all with respect to the heaters, inside the glass tube.
Now what about how the 4 by 12AX7 valves are supplied from the transformer?
Can they again be supplied either in series, or in parallel?
Can 4 valves whose heaters are supplied in parallel be, individually, supplied in parallel?
Let's say my heaters are wired in series and not in parallel.
Then, if my 4 by valves are supplied in SERIES, the transformer needs to supply 50.4v.
Is it possible that they are supplied in parallel, and the transformer only has to supply 12.6v?
How do I check this / test my PCB for this?
(printed on the PCB at the valve power input connector block it says 12.6v).
If I need a 50.4v transformer, what must the VA be? (or how many amps must it be able to supply?)
If I need a 12.6v transformer, what must the VA be? (or how many amps must it be able to supply?)
More info:
I have connected a 12.6v transformer, and with the valves fitted the heaters do not glow, and I
measure 3.4v at the "input connector" on the PCB.
I have connected a 54v transformer, and the heaters came on immediately but appeared so bright
orange in clear daylight that I switched it off immediately, worried that I may damage the valves.
Interestingly, at the time of switch-on/switch-off, the DMM measured just over 30V, and not 54v.
I assume that this was the initial current draw, and as that stabilised, the voltage would go up?
(if I had waited and watched, but I did not want to risk it).
PS. IT is a 4-valve John Topham valve MM/MC phono pre-amp board.
Looking forward to any and all answers and directions.
Cheers,
Johan
I've managed to get my mind in a knot regarding this, and need some pointers.
The valves are 12AX7, so triodes.
There are 4 of them in my phono pre-amp.
I know one can supply the heaters either in series (12.6v) or in parallel (6.3v).
AFAIK the 12.6v series feed goes to pins 4 and 5, and the 6.3v feed goes to pins 4and9 and pins 5and9, for each half of the valve.
But that's all with respect to the heaters, inside the glass tube.
Now what about how the 4 by 12AX7 valves are supplied from the transformer?
Can they again be supplied either in series, or in parallel?
Can 4 valves whose heaters are supplied in parallel be, individually, supplied in parallel?
Let's say my heaters are wired in series and not in parallel.
Then, if my 4 by valves are supplied in SERIES, the transformer needs to supply 50.4v.
Is it possible that they are supplied in parallel, and the transformer only has to supply 12.6v?
How do I check this / test my PCB for this?
(printed on the PCB at the valve power input connector block it says 12.6v).
If I need a 50.4v transformer, what must the VA be? (or how many amps must it be able to supply?)
If I need a 12.6v transformer, what must the VA be? (or how many amps must it be able to supply?)
More info:
I have connected a 12.6v transformer, and with the valves fitted the heaters do not glow, and I
measure 3.4v at the "input connector" on the PCB.
I have connected a 54v transformer, and the heaters came on immediately but appeared so bright
orange in clear daylight that I switched it off immediately, worried that I may damage the valves.
Interestingly, at the time of switch-on/switch-off, the DMM measured just over 30V, and not 54v.
I assume that this was the initial current draw, and as that stabilised, the voltage would go up?
(if I had waited and watched, but I did not want to risk it).
PS. IT is a 4-valve John Topham valve MM/MC phono pre-amp board.
Looking forward to any and all answers and directions.
Cheers,
Johan
