12002: 2" OT

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Strat78
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Re: 12002: 2" OT

Post by Strat78 » Wed Oct 05, 2011 9:59 pm

Did you resolder that 100k V3B plate resistor, it looks like it might not be making a connection at the turret with the 82k.

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Re: 12002: 2" OT

Post by vh junkie » Wed Oct 05, 2011 10:28 pm

Check your HT fuse. Post your power tube socket voltages. Also voltages at the 2w 10k resistors.

Basic power flow:
Diodes, Fuse, Choke, Screens, (2) 10k res, PI, through sleeved wires on board to next 10k, etc.
From memory... think this is right... find out where the power is interrupted on its way to pin 1 on the preamp tubes.
When checking for heater glow, look thru the holes in the sockets...
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Re: 12002: 2" OT

Post by vanhalen5150 » Thu Oct 06, 2011 6:41 am

Strat78 wrote:Did you resolder that 100k V3B plate resistor, it looks like it might not be making a connection at the turret with the 82k.
Yeah did that. No change.
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Re: 12002: 2" OT

Post by vanhalen5150 » Thu Oct 06, 2011 6:52 am

vh junkie wrote:Check your HT fuse. Post your power tube socket voltages. Also voltages at the 2w 10k resistors.

Basic power flow:
Diodes, Fuse, Choke, Screens, (2) 10k res, PI, through sleeved wires on board to next 10k, etc.
From memory... think this is right... find out where the power is interrupted on its way to pin 1 on the preamp tubes.
When checking for heater glow, look thru the holes in the sockets...
With no power tubes in I dont have any voltage on the power tubes. The HT fuse looks fine, but Ill have to get another to try. Nothing at the 10k's.

Changed testers and put new batteries in both.

Do I need to lift things from the board to test for continuity? Start at secondaries from PT? I may need to lift the power board as well to check the wires on the bottom. Should have put those on top as well.
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Re: 12002: 2" OT

Post by vanhalen5150 » Thu Oct 06, 2011 7:31 am

Odd because I was getting really high voltages on 2 days ago. Didnt leave it running for long that way, just a minute. Could the caps be smoked?
Only thing I changed was the 470K to a 470ohm resistor last night. Then nothing.

Booked the weekend for "amp recone diagnosis".
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Re: 12002: 2" OT

Post by vanhalen5150 » Thu Oct 06, 2011 8:46 am

The only voltage on the power tubes sockets is the DC voltage bias at -42. Bias resistor/diode is about 100 AC.
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Re: 12002: 2" OT

Post by vanhalen5150 » Sat Oct 08, 2011 7:38 am

With lights out looking into top holes of preamps, only the v3 is glowing. Shouldn't all 3 be if the heater wires are at 3.0 vac?
On v1 pin 1 there is still nothing. If I flip on the standby, voltage starts to climb quickly, from 0 to over 200. Didn't wait to see if it levels out somewhere. :?
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Re: 12002: 2" OT

Post by vh junkie » Sat Oct 08, 2011 4:49 pm

Who made your OT? The wiring looks correct for a Marstran, wrong for a ******. Should not have done any damage, unless you had the power tubes in... :roll: You can check you HT fuse with an ohmeter... SB 0 ohms
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Re: 12002: 2" OT

Post by vanhalen5150 » Sat Oct 08, 2011 4:51 pm

It's a ****** OT. It's wrong?
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Re: 12002: 2" OT

Post by vh junkie » Sat Oct 08, 2011 5:13 pm

Scratch my previous thought about the Marstran.
My 12xxx is a ****** 1.5" with the red/white going to the tubes.
Strat78 12xxx is a ****** 2" with the red/brown going to the tubes.
So yeah, its probably wrong.
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Re: 12002: 2" OT

Post by vanhalen5150 » Sat Oct 08, 2011 5:44 pm

Really? I'll check that out Junk. I thought I had that correct.

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Re: 12002: 2" OT

Post by Strat78 » Sat Oct 08, 2011 8:14 pm

Hold on, isn't that Chris's 2" OT? The wire codes I posted were for Chris's OT. :shock:

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Re: 12002: 2" OT

Post by vh junkie » Sat Oct 08, 2011 8:39 pm

Yep, Chris' 2"... I think the OT wires should look like your pics... not mine cause mine's a 1.5"...

I did not see your posting for the OT, just the PT.

Might be able to check with a an ohmmeter... the "power tube wire" to "power tube wire" reading should be twice that of either "power tube wire" to the "center tap"(B+ wire)... power tubes must be out to check this...
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Re: 12002: 2" OT

Post by vanhalen5150 » Sun Oct 09, 2011 10:13 am

I don't think I understand what you mean.
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Re: 12002: 2" OT

Post by vh junkie » Sun Oct 09, 2011 11:33 am

Which part?

If you have a two inch ******, it should be wired like strat78s:
Red/Brown going to the power tubes, white to the HI-V.

These wires form the center tappped primary of the OT.
SHould be:
Brown(tubes)->White(CT, HI-v)->Red(tubes)
As such the resistance from Brown to Red should be twice as much as from Brown to White, or White to Red.
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