Wonderland/JM100 build

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pompeiisneaks
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Re: Wonderland/JM100 build

Post by pompeiisneaks »

if you are getting 6 and 0, does the transformer have a center tap for the heaters? If so it sounds like you've got the center tap connected to one end of the heater line and the other end to one of the 6v rails? Pictures of the guts would help I wager.

Nevermind on the pics, I've been following the thread, and remembered seeing them in the past, I definitely don't see anything wrong there, they look fine from what I can tell.

I didn't see any 100ohm to ground for the artificial center tap, but did just see a comment about them. I once had to get a humdinger installed or the hum just wouldn't mellow out.

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martin manning
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Re: Wonderland/JM100 build

Post by martin manning »

Hmm... 100R to ground from each side with the PT filament leads disconnected and no valves installed, and 6V across the PT filament leads, then when you reconnect the PT filament leads you get 6V on one side and 0V on the other?
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Re: Wonderland/JM100 build

Post by norburybrook »

it has no center tap I'm using 100r to ground on each side of the filament.

it was working perfectly until I inadvertently shorted pin 2 and 3 while probing for plate voltage.

it blew the 100r and caused a huge hum.

I replaced the 100r and the hum was quieter but not as it was. I then noticed that the filament voltages had gone weird form 3 per side to 6 and 0.


M
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Re: Wonderland/JM100 build

Post by martin manning »

Did you replace both 100R?
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Re: Wonderland/JM100 build

Post by dhudson »

I would double check the 1 ohm and 100 ohms as they are there together per the layout , may have confused which one connected where?
because a 1 ohm where a 100 suppose to be would do exactly what your describing.

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Re: Wonderland/JM100 build

Post by pompeiisneaks »

I would try temporarily desoldering them from the pilot light and just ensrue that you're getting the expected across the two there, to remove the PT as the problem (it probably isn't) and I'm going to guess that maybe the other resistor to ground is having issues? Did you measure it and make sure it's not significantly lower in some way?

I once blew the ass out of all of my heaters because I got a defective EL34 from tube depot that was shorted from pin 2 to 3 and sent HT through the heaters.

you may have also damaged one or more of the tubes in doing so, if that voltage was on long enough to the heaters. Most heaters can only have 50 to 100 max volts.

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Re: Wonderland/JM100 build

Post by norburybrook »

guys I didn't replace both as one was measuring 100r.

perhaps I should do that.

I'll re check the 1r and the 100r , but I'm sure I did check that when I replaced it.


One thing, when checking the resistance from each side, I also checked across the pins and expected to get 200R, instead I got 0R , all with no valves in.

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Re: Wonderland/JM100 build

Post by dhudson »

remember your also reading the low resistance of the transformer winding.
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Re: Wonderland/JM100 build

Post by pompeiisneaks »

dhudson beat me to it, the dmm signal goes through the path of least resistance, which is the transformer winding back to the other side. You may need to lift a leg of the resistors to get a good measurement.
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Re: Wonderland/JM100 build

Post by martin manning »

Should have read 50R to ground then.
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Re: Wonderland/JM100 build

Post by dhudson »

be best at this point to disconnect the transformer wires and do a good check of all pin 2 pin 7 at each socket.
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Re: Wonderland/JM100 build

Post by norburybrook »

pompeiisneaks wrote: Fri Apr 21, 2017 4:10 pm dhudson beat me to it, the dmm signal goes through the path of least resistance, which is the transformer winding back to the other side. You may need to lift a leg of the resistors to get a good measurement.
Are talking voltage or resistance now with the resistor legs lifted?

M
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Re: Wonderland/JM100 build

Post by dhudson »

resistance of pins to ground.
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Re: Wonderland/JM100 build

Post by pompeiisneaks »

just resistance to ensure you're getting a good reading. I'd also desolder the heaters to ensure they're still reading the right amount on their own. As I mentioned, it's unlikely the transformer got bit, but it can't hurt to double check Then you also have an open ended circuit and you can double check continuity across the string etc.

Take it back to basics and ensure the entire line isn't grounding out somewhere etc.
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Re: Wonderland/JM100 build

Post by martin manning »

This was done above.
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