Fitting Grounded Cords
Fitting Grounded Cords
From detritu–(at)–x.netcom.com Fri Jan 31 10:33:27 CST 1997
From: detritu–(at)–x.netcom.com(Lord Valve)
Newsgroups: alt.guitar.amps
Subject: Re: ’63 Princeton Questions
Date: 31 Jan 1997 07:52:17 GMT
X-NETCOM-Date: Fri Jan 31 1:52:17 AM CST 1997
In
Rodrick) writes:
>
>Anwari (anwar–(at)–net.net) wrote:
>: That’s not really true about a ’63 Princeton. Adding a 3 wire cord
>: :does: involve drilling out the hole, as the strain relief is not
big
>: enough to handle a 3 wire cord. It will cause permanent damage to
the
>: amp. While I’m a firm believer in safety, you must weigh the cost
with
>: the benefits. I’d probably go with the 3 wire cord.
>
>I’ve heard this said before and have never understood it – simply buy
a
>new strain relief, the largest size that fits in said hole, clip off
the
>”teeth” which normally crimp the cord, and, using a round file as
close
>in diameter to the 3-wire cord of your choice as possible, remove some
>(a great deal of) plastic from the inside of the strain relief,
shaping it
>until it crimps the cord but does allow the thing to be inserted with
a
>specialized tool made for this purpose (available from Mouser, among
other
>places). I’ve done this on two ’66 Princetons. No damage necessary.
>
>Bill R.
Lord Valve Speaketh:
If you want to cruise the surplus catalogs or the surplus stores, you
can find a 3-wire linecord that will fit into the existing strain
relief on many of the smaller amps. I found some a while back, and I
bought all the joint had (55 pieces). They were ‘power cords,’ the
kind that you see on most everything, including your puter…I just
snip the female part off and shove ‘em in. BTW, that Heyco
strain-relief insertion/removal plier is the TITS. One of my favorite
tools, but they cost almost SIXTY BUCKS!!! A real time-saver, though.
Lord Valve
detritu–(at)–x.netcom.com
(Fat Willie)
I’ve got two amps that use LOKTAL 7F7 tubes for preamp phase inversion, a Fidelity 3T (perhaps made by Valco, not sure) and a MASCO MAP 15. Both were DOA when I acquired them but revived with retube and new caps.
I attempted to go the extra mile and add 3 prong grounded cords to both of these amps as I’ve done in other amps before, but upon completion, both amps tripped my circuit breaker. I’ve been searching for answers to this and can’t find any guidance or instructions about replacing 2 prong with 3 prong cords when working on amps that have tubes that start with something other than a 6 or 12, i.e.. 6L6, 12AX7.
The LOKTAL tube which I’m just starting to learn about is supposed to be equivalent to the 6SL7, but the locks from the center pole piece that is grounded to chassis on both my amps. I never found a schematic for the Fidelity 3T, but found the schematic for the MASCO MAP 15 but it only shows the later 6SL7 version of the amp and has a sidenote, or 7F7.
I’d greatly appreciate your Most Omnipotent Lord Valve subject matter expertise on this or perhaps a referral to someone or reference that might help me safely ground these amps correctly. Both amps work great with 2 prong cords and I removed the “death cap” from both amps as well. My suspicion is these types of pre-octal tube amps used chassis for signal path and there is a low voltage on the chassis, i.e.. hot chassis. I think there should be a common procedure to lift a cap or resistor from these tubes when installing a 3 prong cord.
Thanks again!
SIG
The post you are responding to was written in 1997. You might ask again on
http://groups.google.com/group/alt.guitar.amps/topics
(Warning this group is very knowledgeable about amps, but spends much of its time bickering about politics.)