Page 19

[Karl5150]

The instructions on the bottom of page 19 of my 12-17-13 CrackManual have a revision 5-6-10 that says changing the lead that connects terminal 4 on the transformer from 22L to 14U may make for quieter operation. It does say 14U instead of 22L.
I attached the lead to 14U and finished the build. All the resistance # checked out except 22 which did not give a 0 OHM reading. It freaked me out a little as both 11 and 17 show 0 and they are also directly connected to the transformer and have nothing else attached.
Power up resulted in no tube glow or LED light. Powered down to find a blown fuse. I went through a complete visual, checking orientation of critical components and another resistance check. All the same. Not wanting to run the risk of another blown fuse, let alone damage I hooked a jumper from T4 to 22 L resulting in tube glow and LED light. I will run the voltage checks next.
Can someone please help me understand? Thanks in advance.

 

[Adrian]

I installed the same wire to 14U and this leaves NOTHING attached to terminal 22.
Terminal 22 is a hard ground to the chassis plate via the strip hold down screw and nut.  22U has to be zero ohms when checked from another ground point, such as 12U as suggested for the resistance checks.
14U is also a ground connection as well as 20U and 12U and jumpered to the ground at the phone jack sleeve, the volume pot ground and the ground at the input jacks.
Placing the red heater wire at power transformer terminal 4 to ground at 14U eliminates one of the ground connection points - the ground connection at 22 that is not needed.
I'm not positive of the reasoning here but I think it may have something to do with the elimination of ground points and possible ground loop problems.
If you did not get zero ohms at 22 you might recheck all of the connections to ground and their solder joints.
It's unfortunate that the simplified schematic does not have terminal points numbered for transformer, strips, and tube socket pins.  This makes it so much easier to double check and troubleshoot.

 

[Karl5150]

Thanks for the post Adrian.
I went through the voltage check with the jumper from T4 to 22 in place and all the #s are good.
I re checked 22 this morning and with the jumper removed I get 0 on 11 and 17 but open on 22. I visually checked for the star washer between the transformer and bell and it is there.
I even checked with a second volt meter. Same results. I checked the 4 bolt heads: 11, 16 & 17 all 0, 22 open.
The only thing I can think of is the paint is keeping the bolt head from grounding to the bell, the varnish build-up on top of the transformer is thick enough that the star washer hasn't made contact, and the bolt is centered and not making contact with the washer.
Unlikely, but it's all I got.
I'm  still puzzled.

 

[Paul Birkeland]

If nothing is being connected to 22, then you don't need to worry about it exhibiting an abnormal resistance.

 

[Karl5150]

Thanks Paul.
I'll give it another try w/o the jumper to 22. Maybe a weak fuse the first time.

 

[Grainger49]

Terminal 22 is screwed to the top plate.  When reading resistances to ground you should have under an Ohm resistance to terminal 22.  This is regardless of whether the heater ground goes to terminal 22 or to terminal 14.

Terminal 17 is grounded to the chassis ground and the IEC connector with a bare wire.  This should ground the whole transformer (including terminal 22) to the chassis and the incoming safety ground on the IEC connector.

So... something screwy is happening.  Does terminal 22 read under an ohm to the nut that is holding the transformer to terminal 22?

I think the fiber washer might have been inserted improperly.

 

[Adrian]

Terminal 22 is directly screwed to the top plate but it is possible that because of the nylon shoulder washer on the transformer and the fiber shoulder washer at the terminal 22, the ground established there is weak at best (maybe even lucky if you get one).
This might explain why you don't meter out 0 ohms at 22 - the nylon and fiber shoulder washers are not allowing a solid ground to the plate.
If BH wanted 22 to be a solid ground to use for the heater power supply, then a real ground wire should have been connected to the safety ground, like what is done for terminal 16 to ensure the bell housing cover is grounded (protecting you on the topside).
By suggesting the heater power supply be rewired to 14 does establish a solid ground via the following path:
Terminal 20 to 14 to 12 to phone jack sleeve (this is connected to terminal 3 which is a solid ground connection to the plate) through the volume pot to the input jack ground lugs.
Basically, there are two good grounds at the plate: the safety ground lug and terminal 3.
You should be able to read 0 ohms from 20 to terminal 3 or the safety ground lug or any of the grounded points listed above.

 

[Karl5150]

Thanks all for the help. The amp works, is quiet, but it and the phones do need to break-in. Vocals and mids were good from the start, but the bass morphed in 20 minutes from an almost non existant whooshing to something quietly reminiscent of bass and back to somewhere in between.
I get the less ground points idea for reducing the chance of loops, I am just still twisted how 11 and 17 can be dead ground (actually read lower than touching the probes together on one of my DMMs) and 22 can be open. They are the 3 non-ground-buss corners of the transformer and, as wired, none are connected to anything else. My pea-brain says they should all be the same.
But I digress; THANK YOU Bottlehead for yet another fun project that I trust will, after cooking, sound as brilliant as the other BH kits here.
One other side note: During the build I was able to hide the included fuse from myself and following the parts list installed a 0.5A fuse which promptly blew. I used a 1A fuse to run the voltage checks. Prior to testing with the Crackphones I replaced it with another 0.5A which also blew. I put the 1A back in and all is well. While finishing up I found the baggie with the feet and original fuse, it is a 1A.

 

[Adrian]

Karl5150:  See my comment about terminal 22 - the same applies to 11 and 17.  These connection points all have the nylon and fiber shoulder washers that can potentially prevent a good ground to the plate.  I think BH should not use these connections as a ground unless they are specifically wired to ground.
Glad it worked out and don't stress over 11, 17, and 22 - you DIYed it and it works.

 

[Paul Birkeland]

Terminal 22 is directly screwed to the top plate but it is possible that because of the nylon shoulder washer on the transformer and the fiber shoulder washer at the terminal 22, the ground established there is weak at best (maybe even lucky if you get one).

This is actually the point of the nylon shoulder washer and black fiber washer.

If 22 isn't reading good continuity to ground, often times all one needs to do is to tighten down that particular screw until the reading stabilizes. 

 

[Grainger49]

I sent this at~ 8:00 this morning:

Page 17 in your manual goes through running a bare wire from the safety ground (incoming from the wall) to the chassis lug to Terminal 16.  This gives the whole transformer a good solid ground and helps reduce noise as it is internally shielded.

Terminal 22 should be grounded through the transformer.  If not take the nut off and verify that the screw and washers are right.  Then look at the star washer under the transformer end bell is touching the metal.  Terminal 22 should share ground through the end bell to the screw that goes to Terminal 16.

Give this some thought.  From the safety ground, to terminal 16, to the screw on terminal 16, through the end bell, to the screw on terminal 22 is the circuit.  Something went screwy in that circuit.

 

[Karl5150]

Thanks again all, I will try a little added torque. Again,  the thing is really quiet, looking fwd to when it calms down.

 

[Adrian]

OP said in an earlier post:

"The only thing I can think of is the paint is keeping the bolt head from grounding to the bell, the varnish build-up on top of the transformer is thick enough that the star washer hasn't made contact, and the bolt is centered and not making contact with the washer."

This is why I said the potential ground at 22 is weak at best.  Anytime the bell is painted the possibility exists for the bolt to not have good metal-to-metal contact with the bell leading to poor grounding.  Also, if the insulating varnish is not cleaned off the transformer iron then the iron may not be properly grounded - especially when you are depending only the star washer to cut through any varnish.
None of this is addressed in the manuals and can lead to potential safety concerns when the transformer is not properly grounded.
When I assembled my Crack and S.E.X amps I went through the manual step-by-step and numbered the schematic with the terminal and transformer connection numbers.  I also painted the bell housings and other parts.  I scraped paint from where the bolts would contact the bell and I took a wire wheel and cleaned the transformer iron in the area of the bolt holes and star washers.  I have previous experience with motor and generator insulation varnish, paints, and coatings that helped me identify potential areas where I had to take positive action to ensure good, solid electrical connections.
Now, if I could only learn how to solder better...and use solder wick...I still haven't developed the skill to "wick" up excess solder and such.

 

[Grainger49]

This is a good use for a Dremel tool with a wire brush on it.  Or just some sand paper, but the tool is cooler.