Can you all please help me understand something, I'm using Heyboer/Mojotone Hiwatt 50w PT for DR504 clone.
I'm following Mark Huss (Hiwatt.org) schematic for the most part and layout but obviously my PT only has 120V on the primaries so no voltage switch.
Is it possible to wire this PT up for a DR504 using SPST switches for both Mains and Standby (just like, say, a Marshall JMP50)?
Dunno for your country but the norm in France, maybe Europe, seems to be switching both poles (DPxT) if the device is connected through a permanent cord, one which is not removable from the device.
If the cord is connected to the device through a plug - something like that
3455_0.jpg
then you're only required to switch one pole (SPxT)...
Still that involes only single throw (xPST).
You may use the other "throw" side (xPDT) for standby purposes but not "as is".
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I'm in the U.S.
I understand electrical code varies by region so that might explain the use of DPDT being the norm in France.
But Marshall uses SPST for both Mains and Standby (?). I suppose one could "get away" with using SPST switches for both Mains and Standby in a Hiwatt circuit but I have concerns that there might be compelling reason to use DPDT.
sluckey wrote: ↑Mon Jun 29, 2020 4:04 pm
There are plenty of double pole switches in Marshall amps. Used for power as well as standby switches. Just browse through the schematics.
Thanks for correcting me, Sluckey!! I need to be more careful.
Ok, so is there some "advantage" to using DPDT in the mains? Maybe advantage is not the right term, but from cost perspective one would think the the cost is higher for DPDT switches (since more parts?).
mrfreddieboy wrote: ↑Mon Jun 29, 2020 4:28 pm
Ok, so is there some "advantage" to using DPDT in the mains?
Well, no advantage using a DPDT, but plenty of advantage in using a DPST in an amp fed by 240VAC where both lines are hot. I think this is the case in England so it makes sense for Marshall to use a DPST switch. And since Marshall probably was buying DPST switches by the barrel it would probably be cheaper to use the same DPST switches even on their USA 120V models.
But here in the USA, on a 120VAC amp, there is no need to break the hot and the neutral lines. In fact NEC says thou shall not break the neutral conductor in residential or commercial wiring. NEC has no say in what goes on inside an amp though.
Well, the advantage of DP__ switches is you're certain the live has been disconnected even if the mains was reversely wired. For example I have a cord whose connection (live-neutral) are interchanged from one end to the other ...
sluckey wrote: ↑Mon Jun 29, 2020 5:44 pm240VAC where both lines are hot. I think this is the case in England
Nope. UK domestic mains supply is single phase 230V and neutral is tied to earth. The UK (and EU) regulations are that if a device has a fixed mains cable then both live and neutral must be switched, if it has a removable (IEC) mains cable then switching just the live would be acceptable however many manufacturers will still switch both even with a removable cable.
The Hiwatt DPDT switch dates from the early days (60s-70s), before widespread code enforcement and during the era where handwired Bulgin plugs were in common use. At that time a reversed hot/neutral was a non-trivial risk. In the Hiwatts they also used a DPDT switch for standby, but used an unused terminal as a tie point for the indicator (pilot) connection. I imagine they just never thought about changing that configuration later on - this was before the era of MBA penny-pinchers.
mhuss wrote: ↑Fri Sep 04, 2020 3:16 pm
The Hiwatt DPDT switch dates from the early days (60s-70s), before widespread code enforcement and during the era where handwired Bulgin plugs were in common use. At that time a reversed hot/neutral was a non-trivial risk. In the Hiwatts they also used a DPDT switch for standby, but used an unused terminal as a tie point for the indicator (pilot) connection. I imagine they just never thought about changing that configuration later on - this was before the era of MBA penny-pinchers.
(resurrecting an old thread)
Thank you, Mark.
I, for one, certainly appreciate the history lesson.
For my build, we have 120 V wall so I just decided to go with the SPDT switches I had on hand. Works like charm!
