Is an empty sour cream container dangerous for cap tool?

[Mike_J]

I was looking for a box that had some terrible components in it. Couldn't find it but what should pop out of the dishwasher but this sour cream container. What I want to use it for is some 250VDC caps which will be either across the presence pot, a coupling cap or tone cap and maybe something else that I haven't thought of. It is obviously made of plastic which I tested and unsurprisingly is not at all conductive. Does anyone see any danger in using this for the purposes mentioned? Would not use it above the rated voltages of the components. The switch is also rated for 250VDC.


Thanks
Mike

[tubeswell]

No EM shielding

[Latole]

This type of container can disintegrate or crack over time. I wouldn't use it.

[Mike_J]

No EM shielding

It will have. My 5f6a chassis has gone from a steel chassis to one made out of aluminum tapes. This thing is going to be wrapped with aluminum tape. Thanks for notifying me of the need for this.

[Mike_J]

This type of container can disintegrate or crack over time. I wouldn't use it.

No chance. The aluminum tape has held my 5f6a Bassman chassis together for 22 years. Sure it will do the same for this. Plan on getting a more dignified chassis if I can find one at the Dollar Store.


Good news. The roofers have started over at the neighbors house. Will have all the metal I need shortly.


Thanks
Mike

[Latole]

You can find small piece of light metal at any hardware store.

[Mike_J]

You can find small piece of light metal at any hardware store.

Even better next door. Have to wait for them to start cutting the metal. Bought some flashing at Ace Hardware. Nothing more than thick aluminum foil. This roofing will be much better.


Another thing, you need a metal bender and I don't have one. Need a box that I can cover with metal. That is how I did the last tool I made. Used the plastic box and put a new metal faceplate in it. Need to find more plastic boxes I can do that with.


Thanks
Mike

[Mike_J]

No EM shielding

I am sure this is what you had in mind. Fear it lost some of its panache because I had to cover the taco.


Thanks
Mike

[Mike_J]

Picture of the sides and bottom. Everything is well covered. From my experience with this stuff this will probably last into the next millennia. Will be looking for new reasonably priced plastic containers to be used to house my contraptions and use the sheet metal from the house next door for the faceplate. This one will be retired when I do.

An advantage of this one over the metal boxes is it is plastic on the inside. There will be close to 230VDC going on inside that container and no ground to earth whatsoever. Seems to me plastic is the way to go for the box. The faceplate can be metal because the switch is plastic and will isolate the voltage from me.

Thanks
Mike

[PharmRock]

How about a metal junction box from Lowe's? They're less than $2.  grab a scrap piece of sheet metal and just cut a rectangle to size for the lid.  Drill a few holes and you're done.

[Mike_J]

How about a metal junction box from Lowe's? They're less than $2.  grab a scrap piece of sheet metal and just cut a rectangle to size for the lid.  Drill a few holes and you're done.

Very good suggestion. Could have a third wire with an alligator clip on it to tie the metal box to earth through the chassis that is being tested. Do you think that would be a good idea?


Thanks
Mike

[Mike_J]

Got my first two pieces of scrap metal from next store. It is a nice turquoise on one side and white on the other. Should make fine faceplates. Plus it isn't so thick that my tin snips won't be able to cut it.

[Latole]

How about a metal junction box from Lowe's? They're less than $2.  grab a scrap piece of sheet metal and just cut a rectangle to size for the lid.  Drill a few holes and you're done.

You got it !

[Mike_J]

How about a metal junction box from Lowe's? They're less than $2.  grab a scrap piece of sheet metal and just cut a rectangle to size for the lid.  Drill a few holes and you're done.

You got it !

The deeper one will do the job.


Thanks
Mike

[tubeswell]

No EM shielding

It will have. My 5f6a chassis has gone from a steel chassis to one made out of aluminum tapes. This thing is going to be wrapped with aluminum tape. Thanks for notifying me of the need for this.

It’s not critical for a multi test tool- it just means that it will be noisy if connected to the signal path.


I doubt simply wrapping it in foil will achieve anything. Shielding needs a ground connection to be effective. The connection wires would also pick up noise if they aren’t shielded.


But if a bit of noise doesn’t bother you it’s probably fine in the plastic container, as long as you aren’t relying on it to protect you from high DC voltages. (The insulation rating of plastics is variable and polymers ‘designed’ for food packaging probably aren’t required to be of any standard rated for High VDC, so anybody’s guess as to whether 250v would punch through the plastic. But ok if you are connecting to the ‘AC side’ of any coupling caps in the amp and not using it in the PS rail or on any plates or screens. YMMV)

[acheld]

You know, this is designed to be a short term substitution box.  None of the ones I have are shielded -- they're all bakelite.  And they work just fine. 

Given the long leads from the circuit to the box and back, there will always be noise -- it's just part of the deal.

If the plastic container is suitable for you -- go for it. 

I personally like more substantive boxes, but that is my problem  . . .

[HotBluePlates]

You know, this is designed to be a short term substitution box.  None of the ones I have are shielded -- they're all bakelite.  And they work just fine. ...

There were nice, expensive options as well as cheap & dirty options in the old days just as today.

General Radio's old old decade cap and resistor boxes appeared to be unshielded wood boxes.  But when you open them up you find a copper-lining that contacts the aluminum top plate for full shielding.

Later versions had metal boxes, so didn't need the extra step of copper-lining.

[Mike_J]

Thanks to all for your good suggestions and advice. I will be staying away from the power rail side of the voltage and only getting voltage after it has run through the plate load resistor. I like more substantial boxes as well but when I couldn't find the more substantial box and nearly at the same time this sour cream container that was destined to hold bacon grease shows up to potentially became a useful tool. Sad to learn I covered up the attractive taco on the container when it may make no difference to have the aluminum tape wrapped around the thing. Probably need to make a design that minimizes noise and maximizes the safety factor for the one using it. Probably an all metal enclosure with a designated wire to attach to the chassis so the box has a safety ground to earth. Also sounds like a good idea to use shielded wire, especially for testing tone caps, grounded at one end which is probably the metal box so the wire going to amp chassis is the only grounding point.


Thanks
Mike

[Mike_J]

Thought of something else regarding shielded wire. The significant wire in the 18 to 20 gauge stranded that is shielded all comes in multi-conductor (wire) packages. The single wires that are shielded seem somewhat puny. Okay I am sure for sending a low power guitar signal to the grid of a preamp tube but seeming somewhat inadequate for higher power applications. I may be wrong in my thinking but would like any suggestions you have for solving this. Could be a two conductor cable with somewhat substantial wire size that has four to six inches of wire showing on the amp side where the testing would be done. Alligator clips would be attached to those conductors.


Thanks
Mike

[Mike_J]

Have a picture of upgraded components for testing different valued components after the amp is proven sound.


The electrical supply store here has double gang metal electrical boxes. They all seem to be about 2-1/8" high so I purchased box extenders as well. Whole thing cost about $3.00. The green wire with the alligator clips on it will be the new ground wire to wire the electrical box to earth. The white cable has two shielded 22awg conductors (wires). I will ground the shield in the box. It will then be grounded to the chassis through the green wire. Will still have a little unshielded wire where the two conductors come out but they won't be very long. Should be as good as I can make it. May need to use some of the aluminum tape to cover up any holes in the electrical boxes and because it wouldn't be one of my projects without it.


The favorite element of this whole creation is the faceplate made from scraps from the neighbors new roof. It isn't finished yet but will take pictures to see how it ends up. By the way, my wife is pretty happy because she has some bacon grease to get rid of and needs the sour cream container to accomplish the task.


Thanks
Mike                                                                                                                                                                           

[Mike_J]

Have wired the switch for the cap selector. Picture is attached. Just need to put it in the electrical box, connect the wires and then I am ready to finish the 5f6a startup and tweaks.


Thanks
Mike

[Mike_J]

PharmRock and Latole had good suggestions about using junction boxes. Bought the one for this contraption to measure from 47 to 120pF for less than $2.00 from the local electrical supply store. Pretty good quality.


Decided to go all out and use my two conductor (wire) cable as well to shield the wires going from the box to near the alligator clips. Regretfully, I forgot the time I spent measuring shielded cable or I wouldn't have made this one so I could measure an amp at my neighbors house from my house. (May be a slight exaggeration in that last statement.) Using my Elike capacitor meter earlier a 100pF cap measured as 100pF across the cap meters  alligator clips. Put over a foot of cable on it and not any more. Now it is something like 132.9pF which isn't bad when it is carrying over a foot of shielded cable. Says something for the cable. However, it doesn't say much for my memory. Should have picked the caps measuring from the end of the alligator clips. A cable like this wouldn't be significant if I was measuring tone or coupling caps but definitely matters in the low pF range.


Thanks
Mike

[acheld]

So measure each position from cable in to cable out,  label your box;  you are now ready for an afternoon beer! 

Given the variability in capacitor values, plus cable capacitance, you'll now have a good idea of what each substitution really is. 

Well done!

[Mike_J]

So measure each position from cable in to cable out,  label your box;  you are now ready for an afternoon beer! 

Given the variability in capacitor values, plus cable capacitance, you'll now have a good idea of what each substitution really is. 

Well done!

Didn't send the picture of the box connected to the cap meter. The 100pF cap did measure 100pF when connected to the cap meter's alligator clips. Was a bit frustrated so found some 10 and 22pF caps to add to the box. Will measure and label them as you suggested. Didn't really need caps that were only a few pF away from each other anyway. Had another idea while I got away from this that I will address under another thread.


Thanks
Mike

[acheld]

Great!  Now it's time for a beer.  Preferably an American IPA.