Shocking bit of information about old Silverfaces

[Securb]

Apparently if you dont play them for 7 years they throw 110w through the chassis and the guitar cable to punish you. I first got shocked when I was rolling the volume. My hand hit the front panel. Then when I went to move the guitar it was ALIVE! Not quite 110w but enough for you to take notice.

 

[Surgeon]

Re: Shocking bit of information about old Silverfaces

2 prong power cord?

 

[Securb]

Re: Shocking bit of information about old Silverfaces

Yep, the amp is going to the tech. I am dropping it off when I pick up my Marshall. I am going to have him go through it and put on a 3 prong.

 

[Surgeon]

Re: Shocking bit of information about old Silverfaces

Wise. The problem also lies in the fact that, on top of using 2 prong cords, lots of old amp builders used the chassis as a multiple-grounding point.

Theoretically, you want to reference your ground to the chassis only in two points: 1- for your cord center pin; 2- as a reference for all your grounds (meaning you bring all your grounds to a single point [ie star-ground] and tie that to one point on the chassi.

Otherwise, you end-up having current flowing through the chassis between the different ground points, which is a bad idea even if it's not that much in theory.

 

[Rand-O-Monium]

Re: Shocking bit of information about old Silverfaces

Things get mad when you don't use them for a long time...

 

[SlyFoxx]

Re: Shocking bit of information about old Silverfaces

Ouch!

I live in a 90 year old house. About ten years ago I made the mistake of assuming a 3 hole outlet was grounded. My lip was bitten quite badly by my microphone. Grabbed a meter and found 70V flowing between my guitar and the mic! I've never failed to confirm ground since.

Checked the outlet and the wire just had hot and cold...there wasn't a ground wire available. Now I have a few non grounded outlets about the house and I run lamps and the like off them no problem. But a special kick in the head is deserved to the idiot who put a three hole outlet there with no ground available. :smash:

 

[treyhaislip]

Re: Shocking bit of information about old Silverfaces

Apparently if you dont play them for 7 years they throw 110w through the chassis and the guitar cable to punish you. I first got shocked when I was rolling the volume. My hand hit the front panel. Then when I went to move the guitar it was ALIVE! Not quite 110w but enough for you to take notice.

Whoa! I bet that was a bit of a shock you weren't expecting! (pun fully intended) Wasn't Leo Fender Shocked by one of his amps? I thought I remember reading something about it...

Sorry about that, glad you are getting it serviced and grounded correctly...those are awesome sounding amps and would be a pity to not be able to play it!

Ouch!

I live in a 90 year old house. About ten years ago I made the mistake of assuming a 3 hole outlet was grounded. My lip was bitten quite badly by my microphone. Grabbed a meter and found 70V flowing between my guitar and the mic! I've never failed to confirm ground since.

That is a great habit to have...I should do that as I frequently play in a lot of old buildings and homes.

 

[Gearjoneser]

Re: Shocking bit of information about old Silverfaces

Find a tech that knows Fender well enough to convert it to 65 blackface specs.

 

[Myaccount876]

Re: Shocking bit of information about old Silverfaces

2 prong power cord is all that you needed to say. Which model is it? A few of the old silverface schematics I've looked at had the old capacitor to ground connected to a switch that goes to either the hot or neutral wire of the power cord. That can possibly drain voltage to the chassis. Does your amp have such a switch? If it is a three way usually the center position takes the capacitor out of the circuit.

Anyways, I'd always recommend just converting every 2-prong cord to a 3-prong cord. It makes the amp less of a hazard, and possibly reduces noise. I'm actually surprised you didn't already change it. Also, check the outlet to ensure the polarity is correct and there's a good ground. You can get a tester from nearly any hardware store worth it's name for cheap.

And to be *that guy*, you didn't get 110 watts through the chassis, you got 110 volts AC through the chassis.

 

[Securb]

Re: Shocking bit of information about old Silverfaces

2 prong power cord is all that you needed to say. Which model is it?

It is a 72 Quad Reverb, no three way switch. It has needed some work for a while. This is the first year of that model and at that point CBS had not drifted that far off from the Fender design. The amp sounds killer for that reason I have never felt the need to mod it, too much. I did upgrade the speakers to Celestions but I still have the original speakers in a the old Celestion boxes. So when Tom gets done with the Fender I will have two shinny new amps to play with.

I will say after I changed the tubes I was so looking forward to cranking that beast.

 

[Myaccount876]

Re: Shocking bit of information about old Silverfaces

I don't think the schematic I was looking at was your exact amp, because there's a 3-prong power cord with a 3 way ground switch. Here's the schematic I'm looking at (I googled "72 Quad Reverb schematic" and this came up): https://irationaudio.files.wordpress.com/2015/03/fender-twin_reverb_sf_100_schem.jpg

However, in the up and down positions of the ground lift switch, a .047 uF capacitor is introduced into the circuit, one capacitor lead connected to either the neutral or hot wire, the other end of the capacitor is connected to ground. Having the ground switch in the center position removes the capacitor from the circuit, and leaves the green wire (third prong) grounded. But you said your amp is two pronged, and doesn't have a switch. This leaves me to believe that there is a capacitor hard wired to either the neutral or hot wire and ground, and excess voltage was bled to the chassis, making you feel the power of Thor.

Now, were you playing Ride The Lightning? That might've also been the cause.

 

[hydro]

Re: Shocking bit of information about old Silverfaces

What doesn't kill you, makes you stronger.

 

[Securb]

Re: Shocking bit of information about old Silverfaces

I don't think the schematic I was looking at was your exact amp, because there's a 3-prong power cord with a 3 way ground switch. Here's the schematic I'm looking at (I googled "72 Quad Reverb schematic" and this came up): https://irationaudio.files.wordpress.com/2015/03/fender-twin_reverb_sf_100_schem.jpg

I have seen that schematic it is not my amp. If you look it was drawn in 1971 but looks like it wasn't put into production until 1976. My amp doesn't have the ground option, three prong or the push/pull master volume.

What doesn't kill you, makes you stronger.

I will get stronger carrying that heavy beast to the tech shop.

 

[the toad]

Re: Shocking bit of information about old Silverfaces

That's what you get for not playing a Plexi! jk

 

[Securb]

Re: Shocking bit of information about old Silverfaces

That's what you get for not playing a Plexi! jk

Not a Plexi, but my Marshall is in the shop too. Right now I am down to the 80's Fender halfstack which is good for cleans and metal not much else and the Excelsior. I am out of gigging commision.

 

[DrNewcenstein]

Re: Shocking bit of information about old Silverfaces

"Good for Cleans and Metal but not much else!?"

What else is there? If it can do Metal it can do Blues and Rock. If it can do Clean it can do Jazz and C&W. If it turns on it can do R&B.

 

[Myaccount876]

Re: Shocking bit of information about old Silverfaces

I've actually wondered about the Excelsior. Are they discontinued now? I've never had the chance to try one and I'm curious now.

 

[Securb]

Re: Shocking bit of information about old Silverfaces

I've actually wondered about the Excelsior. Are they discontinued now? I've never had the chance to try one and I'm curious now.

Nope they are still in production, check one out they are a fun amp.

"Good for Cleans and Metal but not much else!?"

What else is there? If it can do Metal it can do Blues and Rock. If it can do Clean it can do Jazz and C&W. If it turns on it can do R&B.

No it is not a great blues and rock amp. It does high gain very well, it also sounds great with scooped mids. If you are looking for any kind of slight break up or brown tone this is not your amp. Even with a decent pedal giving you gain it just doesn't sound right. It sounds thin and anemic with little sustain or girth to the tone. Sure I could use the cleans for Jazz and C&W, unfortunately I dont have and Jazz and C&W gigs coming up.

 

[Securb]

Re: Shocking bit of information about old Silverfaces

Myaccount my apologies you were right on two counts. It has been so long since I played this amp and so long since it has been moved off the wall. I thought you were talking about a three way on switch. Yes there is a separate ground three way switch on the other side of the chassis. The plug is also a three prong but someone (probably me as a teenager) ripped the ground off the plug to get it into a two prong outlet. The date on it is August 72 The date stamp is Sept 1971, with the name J. Castillo so happy birthday to my amp. This amp is in desperate need of some TLC it was gigged with hard and heavy.

 

[Artie]

Re: Shocking bit of information about old Silverfaces

I don't think this has anything to do with the third prong. It, (the "third" prong), goes back to your breaker box and ties to the same ground bus as the "ground" prong. When the EE council debated whether or not to incorporate that third prong, it wasn't exactly a consensus. The vote was split approximately 50.1 vs 49.9 %.

I don't think your problem is the "ground". I think it's a malfunction in the amp. Check that before you plug in again.

Just my 2-cents worth.

Artie