Ohm out

a DIY, modified Mullard 5-20 monoblock design

Ohm out

Postby Marshman » Tue Sep 13, 2005 8:08 am

Hey guys,

I have my first ike built and ready to fire up, but I have some questions.

1. Everything ohms out EXCEPT pin 7 of V1 (12ax7) I am getting 480k instead of the 23k in the chart AND J4-6 & 7 says 40 ohms and I am getting closer to 800 or 900k.

These are with tubes in and trannys hooked up.

2. The switch wiring in schematic does not seem to match up with the note. There are 3 pins on the switch, but only two are shown in the schem?

could anyone shed some light on this?

Thanks so much!

Marshall
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Re: Ohm out

Postby Shannon Parks » Wed Sep 14, 2005 5:59 am

Marshman wrote:Hey guys,

I have my first ike built and ready to fire up, but I have some questions.

1. Everything ohms out EXCEPT pin 7 of V1 (12ax7) I am getting 480k instead of the 23k in the chart AND J4-6 & 7 says 40 ohms and I am getting closer to 800 or 900k.

These are with tubes in and trannys hooked up.


Hi Marshman,

1) Your V1-7 checks out fine, as that is the resistance from the grid, through the grid stopper and then to ground through the grid resistor. I must've had a load attached when I took this measurement and I should make a correction.

With your center tap grounded, resistance checks at J4-6,7 are basically measuring the secondary taps resistance. If you are using a standby, I would jumper it or remove it as the center tap should be grounded at all times. If you center tap is grounded to the chassis, rather connect it straight to J4-5. You can have a short jumper from J4-4 back to the chassis.

Marshman wrote:2. The switch wiring in schematic does not seem to match up with the note. There are 3 pins on the switch, but only two are shown in the schem?

could anyone shed some light on this?

Thanks so much!

Marshall


2) I omitted the neon indicator part of the schematic as it seemed confusing to me, and decided to just leave a note below the switch on the schematic:
SW1: Connect pin 1 to the fuse, pin 2 to the primary and pin 3 to J4-1, as the neon bulb is in parallel to the primary winding.


Also be sure to move your RCA input ground to J4-3 for best noise performance. Good luck!

Shannon
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Postby Marshman » Wed Sep 14, 2005 6:56 am

OK, Thanks Shannon!

So just to be clear on this, I would have a line from pin 3 of the switch AND the other side of the primary both at J4-1?

Thanks again, can't wait to get these fired up.

marshall
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Posts: 34
Joined: Mon Jul 18, 2005 12:43 pm

neon, neon

Postby Shannon Parks » Wed Sep 14, 2005 8:24 am

Marshman wrote:OK, Thanks Shannon!

So just to be clear on this, I would have a line from pin 3 of the switch AND the other side of the primary both at J4-1?

Thanks again, can't wait to get these fired up.

marshall


Yes - the neon light is strapped across the mains voltage. Probably a current limit resistor in series with it internally, too.

Shannon
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