Fender Twin 1977 ground switch repairs

[Ragnamoog]

Hello everyone!

I'm currently doing some maintenance on my 1977 Twin Reverb amp, and plan on doing the 1/2 blackface mod as soon as I get the parts.
But my current question is regarding the ground switch.
First of, the amp's power supply has 3 prongs and therefore the ground switch is used as a line filter.
I noticed that the .47 125V capacitor connected to the ground switch looked like it had water damage, so I would like to replace it. Not only does is seems pretty hard to find a .47 125V capacitor these days, but I also read on a specialized website (https://robrobinette.com/Death_Cap_a...witch.htm) that it was recommended to change the capacitor for a safety capacitor 400/250V 0.01uF Y5V 20% (https://www.mouser.com/ProductDetail...HYGThGSybaZQ==).
Now, I'm a real beginner at this, and I was wondering if that was indeed recommended for me since the two capacitors do not have the same capacitance or voltage.
Thank you for reading through and for your help.
Cheers

[The Dude]

That cap (in that circuit) is what's commonly known as a death cap. I'd just clip it out and leave it out. If your amp is grounded and using a grounded plug, you don't need it.

[Jon Snell]

Remove that death capacitor, it is dangerous and fit a three core mains lead with a bonded earth.
A bonded connection is a connector, similar to the one shown.
The earth cable is stripped and crimped into the connector, the connector is then bolted to a transformer or threaded bolt to the chassis.
Soldering the earth cable to a connector is not bonded and apparently can crack anf fail ... never seen one fall apart but the boffins who make the rules are either right or have shares in Spaffax, Lucas, SnapOn or another crimp manufacturer,/distributor I would say.

[Enzo]

Already has a three wire power cord, per first post.

[Jon Snell]

Already has a three wire power cord, per first post.

Whoops, missed that.
In that case, cut it out of circuit to avoid the danger.
A switch is not to be used as a mains filter for obvious reasons!

[pdf64]

Loose bolts on old Fender PTs seem fairly common in my experience, hence they seem a poor choice to double up for duty as the chassis safety ground.

...I'm currently doing some maintenance on my 1977 Twin Reverb amp, and plan on doing the 1/2 blackface mod as soon as I get the parts...

What's a 1/2 blackface mod, and what are you hoping to achieve with that?
You've got a really good, well designed amp there; pretty much any reversions to the AB763 circuit will make it less stable and liable to a flabby, farty bass end. The biggest weak point of the 70s amps were the basic stock speakers.

[Ragnamoog]

Thank you very much for your answers, gentlemen.
I will remove the death cap, and therefore always leave the ground switch in open position, right? (Although, now that I'm thinking about, removing the cap means that the switch doesn't do anything anyway?)

The 1/2 Blackface mod is something I found online, specifically meant for ultralinear (late 70s) fender amps in order to bring them slightly closer to a blackface. I believe it only consists in changing a few caps, but I haven't seen the schematics nor the parts yet, the order is still on its way. Here's where I bought the kit: https://vintagefenderamprepair.com/p...linear-fenders

You mentionned that the speakers in the 70s models are lacking, and I believe the speakers in my amp are original. From what I found online they are Pyle/Utah speakers (codes are 005379 C1098102). I might be interested in changing these, but again I don't really know my way around speakers. What should I be looking for in order to replace those speakers? Any speakers you would recommend?
Thanks. Best.

[The Dude]

......I will remove the death cap, and therefore always leave the ground switch in open position, right? (Although, now that I'm thinking about, removing the cap means that the switch doesn't do anything anyway?)......

Right. The switch no longer does anything with the cap removed. FWIW: You can remove the switch and use the hole for jacks, pots, or whatever- if you have any mods that require it. If not, the unused switch can stay.

[Enzo]

Or leave it there and put a small label over it saying something cryptic like "PHASE".

[pdf64]

Unfortunately the linked page provides no actual detail about the changes?
My view is that they’re excellent amps as is, the only change I suggest is a trimmer to facilitate bias adjustment, and the removal of the bright cap on the master volume.
Note that their many of their pot tapers differ to BF and RIs, so control settings can’t be directly compared. Set like for like, they’ll tend to sound bassier.
And the speaker jacks are wired in series, and include impedance switching.
Regarding speakers, it’s next to impossible to recommend anything without knowing your preferences; I guess that Jensen C12N would be a good all rounder? Maybe look into neos to keep the weight down? The Eminence Wheelhouse 150 seems well regarded.

[The Dude]

I have a friend who put a label "EJECT" on his.

[Enzo]

Or GLORY. As in separate power and glory switches.

[The Dude]

Ah,.... a nod to the Pseudoacoustic Infector. One of my favorite Rane data sheets.

https://www.ranecommercial.com/legacy/pdf/pi14data.pdf

[Leo_Gnardo]

What should I be looking for in order to replace those speakers? Any speakers you would recommend?

I've replaced Twin speakers with Eminence Texas Heat on several occasions. I like the sound quality & so do the amp owners. Rated at 150W so it takes a lot of effort to wreck them with a Twin. At a mere $95 I call it the "Poor Man's EVM12L."

[The Dude]

...... and about half the weight of an EVM12L.