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Old 30th January 2009, 01:30 AM   #11
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Keith-
That .01 uF cap is there to filter out/bleed off to ground high frequency noise ( like radio stations, and line noise from dimmer switches, etc).

If I'm going to use them at all, I generally put in two caps, one from each AC leg (black,white) to a solder lug at the chassis ground point where the green (or grn/yell) wire attaches.

On a newer (or newly-built) amp with an IEC (computer-style) receptacle for the line cord, the caps can be soldered right on the chassis connector. On a vintage amp, you may have to 'look around' a bit to find secure soldering points. Though you see a lot of 'hanging connections' (solder joints in mid-air) in diy pics, it's not a good idea. Even if you have to put in a short lug strip (on one of the power transformer bolts?), it's wise to find secure anchoring points for all connections.

Cheers
John
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Old 30th January 2009, 02:16 AM   #12
KP11520 is offline KP11520  United States
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Hi John,

I have seen the two caps from each leg to chassis ground before and That is what I think is appropriate but after reading about the Safety Caps, that looks like a better idea. I guess designers have learned a thing or two over the past 44 years!

I don't want my friend to have too many beers while playing his electric guitar outside and have a bathroom accident just as something shorts out in the amp!

He couldn't live with himself after that! LOL

Thank you for the refinement kelp of bringing this amp "up to date" safely while respecting its vintage status!

Cheers to you too!

Regards//Keith

BTW, attached is a photo of the undersideof the chassis
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File Type: jpg supro chassis bottom w.jpg (39.6 KB, 66 views)
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Old 30th January 2009, 04:35 AM   #13
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Keith-
It looks like one of the PT bolts would be a good spot for a terminal (solder lug) strip if you have one handy. Then you could terminate the line cord there, solder in your caps, and carry the wiring along to the fuse/switch, etc. And no visible alteration to the chassis.
A 15 cent terminal strip is always a good excuse for another electronics order! ;-). (Steve at apexjr had some the last time I looked. Otherwise, the usual (tube) suspects will surely fix you up....)

Sometimes the hole in the lug strip needs to be drilled/reamed out a bit to fit the #10? PT bolt. Be sure to use a good star washer and extra nut.

John
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Old 30th January 2009, 05:59 PM   #14
KP11520 is offline KP11520  United States
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Hi John,

With the new cord entering the chassis right there, that is a great idea... No added hole drilling to mount a strip! I am sure I can find something like you have pictured. I have to order the Pot, Power Cord (16/3) and some sort of chassis clamp (is that what they call them?) for the cord, two Safety caps and a small terminal strip anyway, so why not make it one big order. That is if I can find a similar pot to the original. That is a 500K Rotary Linear Taper Pot with a rotary SPST switch (not push/pull or push button) and 1/4" threaded sleeve by 3/8" split nylon shaft, at the same place that has the rest!

Wish me luck!

Thanks again!

Regards//Keith
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Old 19th February 2009, 10:15 PM   #15
KP11520 is offline KP11520  United States
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Hi John,

I have 2 questions if you are still watching.

I did all that was suggested.

I used two Y2 safety Caps as Just Radios suggested for line to ground connections. I also used the same value of the Ceramic Disk Cap I removed, .01uf. Hopefully that is OK or was I supposed to divide that to .005uf X 2?

BTW, what happens as you change these values?

Also when adding a ground to chassis, did it matter which side I chose to become Hot or Neutral? (I removed the old 2 wire cord and non polarized plug and replaced it with a 16/3 with a ground) I used the side with the switch (see schematic) to be Hot and moved the fuse to before the switch and put the caps at the points (and to ground) where the power cord wires are first soldered to anything in the amp.

Here is the schematic: http://www.schematicheaven.com/barga...upro_s6616.pdf

It's done and everything works as it should but I just appreciate a more experienced set of eyes checking my work!

Thanks Again!!!

Regards//Keith
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Old 21st February 2009, 01:48 AM   #16
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Hi, Keith-
Sounds like you 'did the right thing' with your amp project.

Those caps on the AC lines are just for filtering out high frequency junk/static/local radio station that can be on AC lines from dimmer switches and such. The caps look like a direct short to high frequency signals, but keep the 60Hz chugging along the rails.

Putting the fuse and switch on the hot line is considered best these days, though I've seen quite a few older amps with 'one on each'- mostly for convenience in finding solder points, I think.

You've done a good thing for the amp and now can feel better about some kid plugging in to it- it's a lot safer than it was.

Cheers
John
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Old 21st February 2009, 01:59 AM   #17
KP11520 is offline KP11520  United States
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Thank you John!

I really appreciate you looking over my shoulder!!!!

I owe you a beer or two!

Next time you come to NYC let me know!

Regards//Keith
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Old 21st February 2009, 03:05 AM   #18
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Keith-
Thanks for the kind words.
Just part of the 'pass it on' principle that keeps this hobby going.

Keep rocking!

John
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