Resistance checks issues - first time build

[Motordiesel]

Good evening,
I’m new to building amps and just completed my first Bottlehead Crack OTL. I got to the resistance checks a week ago and on some if the terminals with asterisks I got OL on my Klein MM600. Being that they were not 0 as stated they shouldn't be in the manual, I thought this was ok. when I fired up my amp to do the the voltage checks, the fuse blew. I traced back thru my connections and found the 2-3/4" red wire between the middle terminal on the lower deck of the volume pot and A7 had melted onto A9 right through the casing on the wire. this is what I assume caused the fuse to blow. what did you guys get for ohm ranges for the terminals with asterisks beside them? :
1
2
4
5
13

 

[Paul Birkeland]

Can you post some build photos? I wouldn't expect the problem you found to blow the fuse.

The Klein meter is about the worst meter you can get for the most amount of money. You'll get better results with this meter.

1, 2, 4, 5, and 13 need to read a high resistance, so several hundred thousand ohms, or OL on your meter.

A fuse that blows immediately typically means you have a diode or a cap in backwards.

 

[Motordiesel]

Can you post some build photos? I wouldn't expect the problem you found to blow the fuse.

The Klein meter is about the worst meter you can get for the most amount of money. You'll get better results with this meter.

1, 2, 4, 5, and 13 need to read a high resistance, so several hundred thousand ohms, or OL on your meter.

A fuse that blows immediately typically means you have a diode or a cap in backwards.

Man, that’s good to know about the meter. The Klein was incredibly expensive from Home Depot and doesn’t really seem to work good in this use. Here’s some pics of my build:

 

[Motordiesel]

I’ve got those two caps by the power supply angled towards the cabinet right now to facilitate connecting the negative clip of the meter to the 12 terminal. Had to bend those so many times to retest I’m afraid of breaking the leads off those caps. I’ll need to apply some fresh solder from all the movement to those when I’m getting good resistance readings.

 

[Paul Birkeland]

One of your 220uF/250V power supply capacitors is not landing on the correct terminals.

 

[Motordiesel]

One of your 220uF/250V power supply capacitors is not landing on the correct termin

One of your 220uF/250V power supply capacitors is not landing on the correct terminals.

Oh man! Can you see that in my pictures? Which one is it?

 

[Jameson]

Oh man! Can you see that in my pictures? Which one is it?

Check the cap by the RCA jacks.

 

[Motordiesel]

Alright, fixed the cap, also fixed the red wires on the rca jack side of the transformer. They were connected to 18 and 15, got them on 17 and 14 now. Still blowing the fuse. What could be the issue now?

 

[Jameson]

How were the resistance tests?

 

[Motordiesel]

How were the resistance tests?

On the money! The first asterisk was like 74-80k and then the rest of the asterisks were all in the K ohms range. Got the new Amazon meter recommended on here. Works super. The transformer wouldn’t be fried right? That wouldn’t be the reason the fuse keeps blowing? When I originally built this the transformer tested out great during it’s voltage test. Also looking at each solder point and connection. I can’t really see things shorting out so I’m wondering about down inside of the tube sockets if solder melted into those and is causing a short.

 

[Motordiesel]

I’ve never seen the LEDs come on underneath so however, far the circuit flow gets it either happens really fast or it cuts out before it could get to the LEDs

 

[Paul Birkeland]

Try removing the red wire from power transformer terminal 11 and let it poke up into the air, then see if the amp still blows fuses.

The LEDs will not come on until the 12AU7 has warmed up, so definitely don't pay any attention to that until the fuse blowing problem is sorted out.

Depending on how many fuses you blew with that cap connected improperly and what amperage rating they may have been, it is certainly possible to damage a power transformer. Doing the test above will tell us whether the PT needs to come out or whether there's some other fault that needs to be fixed to get your amp running.

 

[Motordiesel]

Try removing the red wire from power transformer terminal 11 and let it poke up into the air, then see if the amp still blows fuses.

The LEDs will not come on until the 12AU7 has warmed up, so definitely don't pay any attention to that until the fuse blowing problem is sorted out.

Depending on how many fuses you blew with that cap connected improperly and what amperage rating they may have been, it is certainly possible to damage a power transformer. Doing the test above will tell us whether the PT needs to come out or whether there's some other fault that needs to be fixed to get your amp running.

Excellent! That’s what I’m gonna try next. Thank you for that information. I was wondering how I could test the transformer again after having everything wired up.

 

[Motordiesel]

Excellent! That’s what I’m gonna try next. Thank you for that information. I was wondering how I could test the transformer again after having everything wired up.

Can I leave the tubes in when I test that or take them out?

 

[Paul Birkeland]

Yes.

 

[Motordiesel]

Alright, just fired it up. Didn’t blow the fuse and the tubes warmed up nicely.