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  #16  
Old 12-23-2014, 10:20 AM
VTVM VTVM is offline
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A sharp step bit does a great job on sheet metal if you keep it from walking around. I drill a 1/4" pilot hole with a regular bit, then clamp the work piece to a chunk of 2x4. Then I drill down through the metal and into the wood underneath. It helps keep the bit from wallowing around or snagging. A little de-burring, if needed, with sandpaper and I get a neat hole for tube sockets or whatever. I have been meaning to buy a set of Greenlee punches, but they are expensive...well so is a step bit, but I already have that.

Here are some final pictures:





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  #17  
Old 12-24-2014, 11:01 AM
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maxhifi maxhifi is offline
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Why a hot chassis?

I keep looking at this thread, and can't keep my mouth shut any longer

1. Beautiful job on the cabinet

2. Awesome metal work

3. Why did you use a hot chassis? This thing could kill someone, and an isolation transformer capable of powering it is cheap, i.e. $20 at digikey or mouser. It would also prevent ground loop/hum issues during use, and make it a more useful test instrument.
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  #18  
Old 12-24-2014, 06:56 PM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by maxhifi View Post
I keep looking at this thread, and can't keep my mouth shut any longer

1. Beautiful job on the cabinet

2. Awesome metal work

3. Why did you use a hot chassis? This thing could kill someone, and an isolation transformer capable of powering it is cheap, i.e. $20 at digikey or mouser. It would also prevent ground loop/hum issues during use, and make it a more useful test instrument.
It's kind of hard to tell if the chassis is the B-. It looks like the negative on the electrolytic is connected to a B- line of the terminal strip.
It's easy enough to use an isolated B- line, bypassed to the chassis by a .1 mfd cap to the chassis. Maybe, that's what was done.
As a retired electrician, I can't stress enough that your work bench has a GFCI receptacle.
I make portable GFCI's, by using a plastic single device box, a three wire power cord and a GFCI receptacle.
Even if your place, doesn't have grounding receptacles, using an adaptor will give you the same protection, using the portable GFCI.
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  #19  
Old 12-24-2014, 11:21 PM
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maxhifi maxhifi is offline
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If you click on the images it goes to his photos, and this one is also there



It confirms what I thought - hot chassis.

Merry Christmas all!
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  #20  
Old 12-25-2014, 07:46 AM
VTVM VTVM is offline
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Double post
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  #21  
Old 12-25-2014, 07:48 AM
VTVM VTVM is offline
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Thank you for the kind comments.

As I wrote in my very first post:
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Originally Posted by VTVM View Post
(Note: I do not claim that this tracer meets UL or any other safety standards, but it is only for my use, and I know where and how I'm using it.)
This is an experimental unit for my own use. The chassis is connected to the ground prong of the cord and is fused. It is still, in my opinion, safer than the hot chassis vintage radios that it is promarily intended for. An isolation transformer is a must.

This entire device is posted for, as they say, "entertainment purposes only."

cheers
Rob
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  #22  
Old 12-25-2014, 11:58 AM
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maxhifi maxhifi is offline
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Quote:
Originally Posted by VTVM View Post
Thank you for the kind comments.

As I wrote in my very first post:

This is an experimental unit for my own use. The chassis is connected to the ground prong of the cord and is fused. It is still, in my opinion, safer than the hot chassis vintage radios that it is promarily intended for. An isolation transformer is a must.

This entire device is posted for, as they say, "entertainment purposes only."

cheers
Rob
The wide blade is the "neutral", not the "ground"... There's a variety of scenarios which can result in the neutral becomin live, so a polarized cord with the neutral conductor bonded directly to the chassis isn't really enough to say the chassis is grounded.

In the context of using it only at home and only with a known safe outlet I agree risk is minimal, I just had to bring it up plus you never know, some day this may pass from your hands into those of some wide eyed kid who has never heard of a live chassis.
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  #23  
Old 12-25-2014, 06:57 PM
VTVM VTVM is offline
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I understand, but the wide blade doesn't go to the chassis. Can you see the legend on the left there where the chassis ground symbol is different than the B- ? The center prong on the plug...the widest and longest center one in the picture...does not represent the prong in the grounded circuit conductor (often technically incorrectly referred to as "neutral" in a 120V single phase circuit). The prong to the chassis is the system ground. The metal chassis is at the same potential as the earthed grounding conductor of the building wiring.

Scroll down and see the right hand column: http://www.electronic-symbols.com/el...rs-symbols.htm

Last edited by VTVM; 12-25-2014 at 07:01 PM.
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  #24  
Old 12-26-2014, 12:06 AM
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maxhifi maxhifi is offline
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Yes, on the schematic, but the photos in post #1 show very clearly a two prong ungrounded cord, with one of the conductors attached to the chassis, and not a three prong grounded power cord. Also, the schematic also shows signal ground to the probe connected directly to the neutral wide blade, rather than to the third prong. If there was a three prong cord, and the safety grounded third prong was also connected to the probe, of course this would be an entirely different matter, I am only making a comment on what I see.
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  #25  
Old 12-26-2014, 06:21 AM
VTVM VTVM is offline
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Ah yes, the three pronged cord was not installed yet. The schematic reflects the construction plan, the photos are only of the construction in progress. It had a two prong cord for testing and adjustment. I did not have a good computer type cord on hand during construction. There are also part missing in the photos. I thought it obvious that the schematic would be referred to, and not the under constuction photos--missing parts and all--as to how I was building my tracer. The signal ground is through a capacitor to allow the chassis to act as a shield against feedback or external noise. The chassis itself is in fact hard wired to the earth prong and the power conductor is fused. The fuse should blow if the chassis is cross connected to any "hot" lead.

I don't understand why you posted the schematic above, and stated that it (the schematic) confirms it to be a hot chassis, but now are referring to the under constuction photos to state that it is a hot chassis?

Last edited by VTVM; 12-26-2014 at 06:28 AM.
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  #26  
Old 12-26-2014, 06:31 AM
VTVM VTVM is offline
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This is where I get lost in your comments:


Quote:
Originally Posted by maxhifi View Post
If you click on the images it goes to his photos, and this one is also there



It confirms what I thought - hot chassis.

Merry Christmas all!
Quote:
Originally Posted by maxhifi View Post
Yes, on the schematic, but the photos in post #1 show very clearly a two prong ungrounded cord, with one of the conductors attached to the chassis, and not a three prong grounded power cord. Also, the schematic also shows signal ground to the probe connected directly to the neutral wide blade, rather than to the third prong. If there was a three prong cord, and the safety grounded third prong was also connected to the probe, of course this would be an entirely different matter, I am only making a comment on what I see.

Last edited by VTVM; 12-26-2014 at 03:15 PM.
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  #27  
Old 12-26-2014, 11:00 AM
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maxhifi maxhifi is offline
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If you look at the GND alligator clip going out to the probe, and the shield for the audio in and the scope out, all those on the schematic connect back to the signal ground/ AC line neutral and not The chassis ground. Since you didn't actually use a grounded power cord and went to the trouble of using a heyco strain relief clip it looked permanent to me. If the GND clip was capacitor isolated like in the vintage designs this would obviously not be a point for discussion.

I never intended to sound argumentive and I apologize if this has gone in that sort of a direction. The only reason I even brought it up, is I once decided to use a polarized cord and not bother with isolating the chassis on a phono amp to get rid of hum, and ended up giving myself a huge shock with a miswired extension cord.
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  #28  
Old 12-26-2014, 03:09 PM
VTVM VTVM is offline
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Quote:
Originally Posted by maxhifi View Post
I never intended to sound argumentive and I apologize if this has gone in that sort of a direction. The only reason I even brought it up, is I once decided to use a polarized cord and not bother with isolating the chassis on a phono amp to get rid of hum, and ended up giving myself a huge shock with a miswired extension cord.
I didn't take it that way, and I'm sorry if I sounded that way.

I will delete reference to the schematic so that there will be no more confusion.
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