12xxx Larry Ground

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clusterstudios
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Re: 12xxx Larry Ground

Post by clusterstudios » Mon Nov 12, 2012 7:26 am

does anybody off hand know the drill bit size of the power tube screw holes??
Joseph

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Re: 12xxx Larry Ground

Post by vanhalen5150 » Mon Nov 12, 2012 11:06 am

clusterstudios wrote:does anybody off hand know the drill bit size of the power tube screw holes??
5/32"
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Re: 12xxx Larry Ground

Post by BoogieEngineer » Mon Nov 12, 2012 1:15 pm

vanhalen5150 wrote:If your using a PT bracket, your probably an 1" away already.
You are right. I initially had #5 close to the PT but when I mounted it with brackets the hole got in the way so I re-drilled a new one. Thank God I made it more than 1" away :).

I didn't have 5/32 so I used 3/16. A little loose but still fits nicely

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Re: 12xxx Larry Ground

Post by Twistingcrow » Sun Jun 23, 2013 4:56 pm

Hi.
Do you guys ground the 1ohm resistors to the ground lug on each power tube (regular method) or do you send them to ground to another spot as per the JTM45 or JMP50 Larry's grounding scheme???
Thanks!

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Re: 12xxx Larry Ground

Post by Strat78 » Sun Jun 23, 2013 8:58 pm

Yep, right to the socket bolt lug, just be extra careful that you are getting good metal contact with the lug for a secure ground. You can also just use a buss wire to ground and bias a different way, but the 1ohm resistor is the safest. I've seen dedicated ground bolts for the power sockets, which makes sense because there would be less chance of the lug coming loose from changing tubes over the years. Check out John Suhr's approach to this, pretty cool:
https://www.dropbox.com/s/5og36yddsy63bsi/SL68.jpg" onclick="window.open(this.href);return false;

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Re: 12xxx Larry Ground

Post by vanhalen5150 » Mon Jun 24, 2013 7:17 am

I could never make out what exactly those things are he has in there? Anybody know?
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Re: 12xxx Larry Ground

Post by rgorke » Mon Jun 24, 2013 11:38 am

They sort of look like the same "posts" or micro boards that the 68k input resistors are wired to by V1. You can see them a bit better at V4.
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Re: 12xxx Larry Ground

Post by Twistingcrow » Tue Sep 24, 2013 9:53 am

Hi there!
I've got a screen wire on my mains transformer (green/yellow). I know it needs to be grounded and have grounded it at spot #4. Is that right or does it need to be somewhere else? Her's the transformer data sheet:

http://www.ig-transformatoren.com/catal ... m100rs.pdf

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Re: 12xxx Larry Ground

Post by Strat78 » Tue Sep 24, 2013 12:28 pm

Yes, #4. Just a reminder: use medium bolts, a star washer against the inside of the chassis and at least two lugs per ground except #5. Allow a good length of wire so you can lift the board for access and future tinkering. Robert has a chassis shot somewhere here showing all the correct ground locations.

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Re: 12xxx Larry Ground

Post by vanhalen5150 » Wed Sep 25, 2013 7:12 am

I could be wrong but I think that yellow/green usually has to be extended and go all the way to #1. The screens/mains ground comes off the small cap board. Some trannys its 2 different colors. The new Merc I have is green/blue.
The yellow/green(edit: "on your diagram") is a tranny ground correct?
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Re: 12xxx Larry Ground

Post by vh junkie » Wed Sep 25, 2013 7:24 am

Whoa! The screen wire he is talking about is a shield for the tranny itself. I would post this question in the Transformer forum before connecting it.
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Re: 12xxx Larry Ground

Post by vanhalen5150 » Wed Sep 25, 2013 8:09 am

Yeah, from the diagram its from the tranny itself. So it would be #5?
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Re: 12xxx Larry Ground

Post by Strat78 » Wed Sep 25, 2013 10:33 am

OK, the number 16wire is odd, it's all kind of odd. What are the two brown wires (6 and 7)? Is wire #1 the common? wire 11 to ground #4 and wire 14 (Heater CT) to ground #1 Is wire 16 redundant (just ground it close to the PT)? I want to try a set of Ingo's tranny's now that he is back in business.

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Re: 12xxx Larry Ground

Post by vanhalen5150 » Wed Sep 25, 2013 10:55 am

Odd. 6 and 7 are listed(blue) as though they should be on the secondary side. 15V @1amp?

The way the two 120v and 240v scenarios are drawn out, #4 is the common ground on the primary for both voltages.

Is 16 just grounding the entire tranny?
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Re: 12xxx Larry Ground

Post by Strat78 » Wed Sep 25, 2013 11:15 am

I wonder if it just insures a solid ground given that the lacquered laminates might prevent contact with the chassis in some cases, those Germans are pretty thorough, good beer too.

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