5C1 New Build Start Up Problem At Rectifier

[rp]

Got got something bad going on right at the beginning in the rectifier section.

Transformer is a Hammond 370DX with world taps. I'm pretty sure I got the primary jumpered right. (Note: I also buried two unused primary taps and the 50V bias tap into the bells nicely cut back and shrink-wrapped the tips, all carefully done but I messed around inside the bells.) But, I'm pretty sure the AC primary side is all ok as I get correct voltages without the rectifier and DBL doesn't light at all.

So, unloaded without the rectifier I have: 600VAC across pins 6 & 4, 300VAC to ground. 5.6VAC across 2 & 8, 2.5WAV to ground. 7.1VAC across 2 & 7 on the 6V6 & 6SJ7 sockets, 3.5VAC to ground. The power switch works correctly, light and all.

Therefore, my AC Mains and PT primary must be wired correctly, no? And, no harm done when I took the bells off - it's not caused by the buried bias or primary taps? A short from that would show up here?

Next I tried two 5Y3s, both are known good. So, with the DBL, rectifier and no other tubes I get: DBL w/ 100W bulb is medium low bright and appears to brighten slowly with time. I get no DC reading at pin 2 and no B+ further down at C1, C2, C3. When I try to get a DC reading without the DBL the Main AC fuse blows after 5 seconds.

Also tried testing w/o the B+ fuse in place so it can't be further down the line as the HT fuse is before C1.

I've checked the AC wiring 6 ways to Sunday. Did I screw something up in the PT taking the bells off? Is my Euro Tap wiring screwed up? I don't know what else to look for.

BTW the CTs for the 5V (yel/blk) & the 6.3V (green/yel) are grounded at the last terminal that holds the cap string, seen best in pict 3.

[rp]

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[selloutrr]

I don't think it's your Transformer if you are getting correct voltages.

With your Rectifier out the circuit is ok with it in - Which passes voltage on to the rest of the circuit you blow fuses.... Something else in the circuit is not grounded or a polarity is not correct. Faulty filter cap.. something is shorted that shouldn't be... etc.

If your
PT is giving the correct voltage
You are using known good Rectifier tubes

Assuming the octal socket is good and the PT leads are not cold soldered. (you can have issues getting a solid solder point if you have cut the leads.) It's time to look at the next stage.

[xtian]

I see your problem--wiring is too damn pretty, and your hubris has angered the gods.

[rp]

Assuming the octal socket is good and the PT leads are not cold soldered. (you can have issues getting a solid solder point if you have cut the leads.) It's time to look at the next stage.

The odd thing is the short shows up with the internal HT fuse pulled. This fuse is before everything on the B+.

[selloutrr]

Do you have a bench power supply?
You can unsolder your PT and hook up the bench supply to weed out any doubt.

[rp]

What happens to the Mains AC and the PT prim and sec when you add the rectifier and nothing else?

[rp]

Do you have a bench power supply?
You can unsolder your PT and hook up the bench supply to weed out any doubt.

Like a big DC supply? No. Good God, I don't want to unsolder the PT. Don't even go there... No...NO!

-rp

[selloutrr]

as long as the leads are not shorted together and you don't run the PT in extreme heat or covered under a pillow or blanket it should be fine.

[rp]

I see your problem--wiring is too damn pretty, and your hubris has angered the gods.

It was an offering - they are wanton and fickle!

[selloutrr]

Do you have a bench power supply?
You can unsolder your PT and hook up the bench supply to weed out any doubt.

Like a big DC supply? No. Good God, I don't want to unsolder the PT. Don't even go there... No...NO!

-rp

Yes it's the easiest test. If it still blows fuses with the Bench supply then it's not the PT. if the amp works with the bench supply it's a bad PT.

[rp]

This is looking like a bad PT. Maybe I screwed it up when I took the bells off to paint them, or buried the wires. But why does it work fine without the rectifier?

I'm might be out of luck too w/ Hammond. I painted the bells - it's obvious they came off. I'm going to eat this one I think. And there goes my nice wiring.

Maybe someone will spot something.

[rdjones]

Do Not ! ground the center tap for the rectifier filament. Doing so shorts the B+ to ground through the filament winding.
Also, the B+ should be taken from pin 8, not pin 2.
This is a fine point, but pin 8 allows a 5AR4 or other indirectly heated cathode rectifier to be used.

[rp]

That's it

Do Not ! ground the center tap for the rectifier filament. Doing so shorts the B+ to ground through the filament winding.

It never occurred to me to do or not do this, this is the first PT I've ever seen with a 5V CT, so I grounded it - Now why the hell does this OT have a CT that's shorts the HT?!?! You'd think a tech footnote in the wiring diagram would be in order? I always have a hard time with Hammonds.

Also, the B+ should be taken from pin 8, not pin 2.
This is a fine point, but pin 8 allows a 5AR4 or other indirectly heated cathode rectifier to be used.

I was going to ask about that, I just figured a diodes a diode. The schematic has it this way and 2 was closer to my fuse holder for a cleaner run. I will change it.

20 years ago before the internet and forums, I would have put this on a shelf and forgot about it - or gutted it into something else.

Brother RDJones if you're ever my way look me up I owe you few pints.

[rp]

Voltages are fantastic, so quiet you don't know it's on. Not even trace of octal hum with 10". A minute of risky 2AM NYC apartment guitar shows it works. Let it rip it tomorrow, unveil it soon. Thanks for the help all.