WTB Laydown jmp/jtm 50w transformer

  • Thread starter Thread starter Exo-metal
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Can't really spec a DC voltage on a PT. The secondaries put out AC and it's up to the rest of the amp design to dictate the DC voltage on the plates/B+. But for 470v DC at 120v mains, you're probably looking at a PT with 350-0-350 secondaries or higher. Hard to find anything higher than that in typical Marshall spec unless you order custom from someone like Merren or Heyboer/Marstran. Maybe Mercurcy Mag would do it too. Merren is gonna be a long wait. Not sure about Marstran/Heyboer. But give 'em a call.

Your best bet is a 1202-55 PT but there's no guarantee you'll get 470v on the plates. It really depends on the amp.
 
I was laughing when I realized my mistake. Glad u pointed that out. I changed it so it makes sense now brother lol.
 
Exo-metal said:
I was laughing when I realized my mistake. Glad u pointed that out. I changed it so it makes sense now brother lol.
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lol no worries dude.

But wait... you're trying to get a PT that gives you 470v DC on the power tube plates, right? If so, you probably want a PT with 350-0-350 secondaries (700v AC). That will typically translate to 450-480v DC on the plates depending on the actual amp circuit and rectifier type.
 
FourT6and2 said:
lol no worries dude.

But wait... you're trying to get a PT that gives you 470v DC on the power tube plates, right? If so, you probably want a PT with 350-0-350 secondaries (700v AC). That will typically translate to 450-480v DC on the plates depending on the actual amp circuit and rectifier type.
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I think he means 470V DC unloaded, which puts it at roughly 440V DC loaded or so which is fairly common.

I had MM spec me a transformer for 480V loaded at 0.5A multi-tap primary capable which put it at 520V unloaded or 520V*1.414 at 735VAC on the secondary which is close to 365-0-365. It’s loosely based on a 67 plexi 100W that was made for only a year or two. I haven’t installed it yet but plan to - I needed more beef for a quad of 6550s.
 
glpg80 said:
I think he means 470V DC unloaded, which puts it at roughly 440V DC loaded or so which is fairly common.

I had MM spec me a transformer for 480V loaded at 0.5A multi-tap primary capable which put it at 520V unloaded or 520V*1.414 at 735VAC on the secondary which is close to 365-0-365. It’s loosely based on a 67 plexi 100W that was made for only a year or two. I haven’t installed it yet but plan to - I needed more beef for a quad of 6550s.
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Well 470v is no problem, even loaded. Either way, 1202-55 PT would be quickest to find. 1202-118 is too weak. Other than that, maybe order a custom one. But it's gonna take months and months to arrive.
 
Yeah 470vac unloaded but dropped to 440/450 approx on the plates under load.
What about the 8089-H
 
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Exo-metal said:
Yeah 470vac unloaded but dropped to 440/450 approx on the plates under load.
What about the 8089-H
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That one appears to be a 1202-118 clone? It's spec'd for 650v secondaries I think. Not high enough. You'll want at least 700v (350v on each tap).

Mercury Magnetics has a bunch of option that would work.
 
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Just curious but what is good approximation for the load?

The Mercury P4550JT-G1 is supposedly ~448vdc loaded and they state 200mA as the load. But the spec sheet says it is 380-0-380 vdc which seems like it would yield a much higher B+. Wouldn't be the first time Mercury wasn't exactly as advertised.

FWIW @Exo-metal, I have a P4550JT-G2 in a homebrew Jose and it is just below 430vdc loaded. That one is advertised as 323-0-323 and 420vdc loaded. They have that same PT with several different voltages. They all have the 5v tap for Tube Rectifiers but I didn't use it.
 
FourT6and2 said:
That one appears to be a 1202-118 clone? It's spec'd for 650v secondaries I think. Not high enough. You'll want at least 700v (350v on each tap).

Mercury Magnetics has a bunch of option that would work.
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I disagree - 650VAC would put him in 440VDC loaded range. 350VAC center tapped would put him in my range of 480 loaded.
 
Any transformer can be a laydown, just take one of the bells off and cut off any stray mounting tab on the other bell
 
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