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  #1  
Old 12-26-2008, 07:37 AM
korby korby is offline
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1960's Harmony H400A

I want to put a three prong cord on this but read somewhere that if you ground this it will short out . What do you think ?
This is what I read .

"Ooops! I just looked at that schematic. It's set up almost like an AC/DC amp, with one conductor of the mains line hooked to the chassis. You CAN'T ground that. You'd get an intense blue flash and pop when you plugged it in, then your circuit breaker would trip and your lights would go out. The only way to run that completely without risk of shock is to plug it into an isolation transformer. However, you can make it a lot safer by replacing the cord with a polarized two-prong one arranged so that the neutral wire of the socket is always connected to the chassis. As long as somebody didn't wire a socket backwards, you're OK with that.





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  #2  
Old 12-26-2008, 07:50 AM
jawjatek jawjatek is offline
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You need an isolation transformer. Something like this one.
http://www.bkprecision.com/products/...s/?model=1604A

It is not safe to operate this amp without one.
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Old 12-26-2008, 07:54 AM
korby korby is offline
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Quote:
Originally Posted by jawjatek View Post
You need an isolation transformer. Something like this one.
http://www.bkprecision.com/products/...s/?model=1604A

It is not safe to operate this amp without one.
What are the risks ?
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  #4  
Old 12-26-2008, 09:51 AM
jawjatek jawjatek is offline
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Electrocution. Duh!

Sorry, look at the schemo - see the lower AC plug blade goes thru switch "SW" and straight to the earth symbol on the guitar inputs? Plug in a guitar and the strings are connected to the same blade. If the plug is rotated in the socket, or is wired incorrectly, that same side of the plug (and your guitar) gets connected to the hot AC wire. If you touch a ground while holding the guitar, like a PA mic, other piece of grounded equipment, water pipe, building metal, etc, etc., you will get the shit, and possibly the LIFE, shocked out of you.

If you want to use this amp get an isolation transformer. That is what they are for. A harp-player buddy bought an amp like yours on Ebay (Danelectro Cadet), but he got a isotap on Ebay like the BK for around $60. Cheap insurance, IMO, and worth every penny.
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Old 12-26-2008, 09:58 AM
korby korby is offline
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Ok I got ya' . My cheap amp is getting less cheap . Will a Ebtech Humx fix the shock problem or just the hum ? I paid $150 for the amp I'm looking for the cheapest way to make it safe . Or should I sell it and let it be someone elses problem ? It does sound great . Has a Stones vibe . I'll check into the isotap .
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Old 12-26-2008, 11:16 AM
hasserl hasserl is offline
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Install an isolation transformer, for an example go to tubesandmore.com and do a search for P-TN-51X That will provide isolation from the mains. Then you can connect a three wire cord with the safety connected to the chassis, just as you would with any other amp using a power transformer. Mount the trans in the cabinet and connect the hot lead to the switch to the primary side of the trans.
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Old 12-26-2008, 11:41 AM
Structo Structo is offline
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Yes the isolation xfmr is the way to go.

It has a 1:1 ratio so it doesn't change the voltage, it just provides a barrier to the voltage on the secondary so you don't end up with a hot chassis.

Install the three prong cord so the black goes to the switch then to fuse, then to the primary of the xfmr.
The white (neutral) wire so connect to the other primary lead to the xfmr.

On the secondary side of the xfmr connect the 100R/plate wire of the rectifier and the other wire to wire the switch was before.
Ground the green wire to a transformer bolt.

Search for P-T169SS http://www.tubesandmore.com/ $32.72
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  #8  
Old 12-26-2008, 12:20 PM
korby korby is offline
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I've got a 12.6 volt AC 3 - amp power transformer sitting around , could I use that ? I have a friend who could do all the connections I'll let him see this thread and let him have at it .
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  #9  
Old 12-26-2008, 12:45 PM
Trout Trout is offline
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Quote:
Originally Posted by korby View Post
I've got a 12.6 volt AC 3 - amp power transformer sitting around , could I use that ? I have a friend who could do all the connections I'll let him see this thread and let him have at it .

Nope, you need one of the ones listed above.

115-125 Primary, 115-125 secondary.
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  #10  
Old 12-26-2008, 09:16 PM
korby korby is offline
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Ok , it's in my amp tech's hands now and I took a shot of the guts before leaving .
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  #11  
Old 12-27-2008, 11:02 AM
Jaybird03 Jaybird03 is offline
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Nice pics. You will be glad you put in the isolation tran . Show us a pic of the finished job when you get it back from your tech.
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  #12  
Old 12-27-2008, 11:07 AM
hasserl hasserl is offline
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I've got one of these, it's on my "to do" list.
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Originally Posted by GearHeadFred
...Can we coin a new TGP acronym here? TIDOAAD (though I'm dubious of any audible difference) ;)

Just think of all the typing (and server storage) this will save!
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  #13  
Old 12-27-2008, 12:12 PM
korby korby is offline
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I got the pricier one .
Click on underlined Part # for more information P-T169VS
2007 Catalog
page 34


TRANSFORMER - LINE ISOLATION, HAMMOND, 175 VA


Hammond 169 Series Line Isolation Transformer
  • 175 VA capacity, 1300 secondary current ma.
  • Primary 115 VAC, 60 Hz.
  • Secondary 115 VAC
  • Electrostatic shield between primary & secondary
  • Connection by flexible leads, 8" minimum length
  • Perfect for circuit isolation or "Classic" bias power supply
  • CSA certified (# LR3902)

RoHS Compliant
41.70
$37.53
Qty
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  #14  
Old 12-29-2008, 09:46 PM
JJman JJman is offline
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Anyone know anything about those brown couplers? I've got a bunch I pulled from my old Harmony.
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  #15  
Old 01-09-2009, 08:45 PM
korby korby is offline
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Gotter' done .
Caps changed killed the hum , new old tubes made it twice as loud ,installed a fuse ,isolation transformer and grounded cord keeping us from getting killed and replaced puke green ,water stained grill cloth .


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