Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jjasilli on September 05, 2011, 10:05:37 pm
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Got a Fisher 400 hi-fi stereo receiver on the bench. I don't know the working condition of the amp; it was in storage by the customer for many years. So far I pulled the tubes and gave it a badly needed cleaning. My next step was to replace the power chord, but I ran into this conundrum. If I go to a 3-prong power chord, do I need to ditch the resistor & cap? Use a polarized 2-prong plug & modernize the cap + resistor? The existing 2-prong power chord is wired as follows:
* One side goes > Fuse > PT primary. This side also goes to ground through an 820K 1/2W CC resistor (actually reads 891K) IN PARALLEL with a .01 600v black beauty type cap. My research shows that this was done for hum & noise suppression.
* The other side of the power chord goes to a DPDT SW > PT primary; and 2X 2-prong courtesy outlets.
Got some insights, plus some confusion here: http://www.justradios.com/safetytips.html (http://www.justradios.com/safetytips.html) file:///C:/Documents%20and%20Settings/John%20Jasilli/My%20Documents/HiFi/Fisher/Fisher.400.Rebuild/Can%20someone%20tell%20me%20what%20this%20resistor%20does%20%20[Archive]%20-%20AudioKarma.org%20Home%20Audio%20Stereo%20Discussion%20Forums.htm
Any suggestions are appreciated. Thanks!
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Hi-Fi systems are often UN-grounded.
Hi-Fi systems are not often played on concrete or in a splash of beer.
The user is not holding onto a hi-fi ALL the time, like a guitarist holds the end of a guitar cord.
Personally, for living-rrom hi-fi, I'd replace the probably age-cracked cord with fresh 2-wire and cut-out the chassis cap. For garage disco, I'd probably 3-wire instead.
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Thanks for all the info in this thread. :worthy1: I scoured the web before posting and good info was not forthcoming.
Actually the power chord on this amp is in excellent condition. Perhaps the thick coating of grease & tobacco residue protected it from oxidation. :icon_biggrin: I removed it; soaked in cleanser; scrubbed it clean; then treated it with rubber conditioner. And, the plug proudly displays the Fisher logo. So I guess I'll re-install it for old time's sake.
I'm definitely intrigued by the in line power conditioner modules. Will consider them on future builds (and maybe this Fisher re-build, if necessary). On another note, those modules may be just the ticket for another project -- in conjunction with a big iso tranny I've had laying around.