Peavey JSX amp

[bsco]

Good morning...well it is morning here...I have a question...This amp has a grounded ac power coed...with the three prongs....It also has a ground switch with this so called death cap there as well.....correct me if I am wrong, but if there is a three wire power cord used(which is from the factory), is there still a need for this ground selector switch? I am just curious about it....and being told in previous posts to remove the death cap when installing a 3 prong power cord...Also this amp had one of the power tubes forced into the socket in the wrong position.....and also had a 20 amp fuse installed in the rear of the chassis....The primary winding is blue and black???? if it is it is burned up and one of the protection diodes on the output board is also burned up...totally.....output transformer checked ok as far as resistance measurements go....any thoughts on the power cord thing???

[Chuck H]

Look at the schematic and duplicate it. Peavey gets tricky with their grounding schemes (to good effect usually) and it could be that the polarity switch difference is only operating above a certain frequency relative to some grounds that are joined by caps between boards. If the "death cap" actually goes from the AC leads to the chassis that would be odd.

It sounds like the protection diode did what it was supposed to and protected the OT in the event of a power tube failure. The "forced" socket thing sounds funny. Is it clearly the work of a bad tech? I can't imagine it left Peavey like that.

[bsco]

The amp was purchased at a pawn shop some time ago....so it wasn't a factory mistake by any means...I just emailed Peavey to see if a transformer was available and the cost associated with it...the tube that was inserted wrong wasn't all the way down in the socket,but was far enough so that the pins of the tube could make contact with the socket pins.....the diode was the only component with physical damage that was visable.....I'll double check on that polarity cap and let you know.....I was just curious to see one there with a properly grounded 3 prong power cord....Thanks for the reply.
Cheers,
Bernie

[Jazz P Bass]

As to the polarity capacitor, from what I understand, Peavey uses a rated capacitor for this application.
In the event of the capacitor going bad, it will go open, not shorted.
I am also led to believe that Peavey feels there is a need for the cap in certain instances.

[bsco]

Thank you Jazz P...

[52 Bill]

Both Fender and Peavey at one time installed 3-wire ac cords and polarity switches in their amps.

I don't know if they still have them posted, but Peavey used to have a number of white paper reports on their website, one of which discussed the polarity switch and 3-wire ac cord. As Jazz said, they do not or at least did not agree that the polarity switch was a bad thing.

Maybe somebody here has a copy of that report.

[bsco]

Thanks 52 Bill...I'll see if i can find it from Peavey....I was just talking to their service manager...I'll check it out with him.....
Cheers,
Bernie

[g1]

The only problem with the so called "death caps" was that they could short when they failed, which would put AC line voltage on the chassis.
There are now class X and Y capacitors that can not fail in this manner.
Since they have been available, many manufacturers have returned to putting caps across the AC line, or from line to chassis.
So the critical issue is the type of caps in use. With modern amps, like this Peavey, they will be the correct (UL and CSA approved) type of cap.
In older amps, they should be removed, or can be replaced with the correct classX or classY type as applicable, whichever type is required for the particular circuit. Class X for across the line, Class Y for line to ground.

[bsco]

Thanks g-one....I didn't know that......I always learn something every time I come here. You guys are a great help...like Enzo said to me before. I have a panel on international experts backing me up....and I am very grateful for that.....
Cheers,
Bernie

[g1]

I didn't know it either. I saw it on some Yorkville schematics and looked into it. Now that I know they are in use, I look for them on modern schematics and notice them quite often.
Not so much with the typical "ground switches", but just in supply primary circuits in general.

[Enzo]

SOMETIMES the cap to chassis from either side of the mains will quiet some noise, so there is the switch. As I recall, are the little ground rockers a center off type anyway? The JSX schematic shows it as does the 5150. How many you need to see? I am not concerned over a potentially hot chassis, the thing is wired to earth.

[bsco]

g-one...I noticed these x and y caps in the primary side of power supplies....No ground toggle switch...that was why I had asked....No problem Enzo....I don't have the experience you guys have so this is why I ask questions....sometimes they might sound dumb....hope not....I was told that the only dumb question is the one that is not asked....anyway, thanks for the help guys.....