Fender Dual Showman....made in 1966

[bsco]

This one had a 2 prong plug with a ground select switch.....after sizing this up for awhile I decided to replace the power cord with the proper 3 prong one......I soldered the live and neutral wires, white and black, to their respective terminals on the accessory socket.....I crimped the ground wire to an eyelet connector, removed one of the nuts for the transformer mounting, cleaned the chassis, installed a new nut with lockwasher, installed the connector and then installed another nut and lockwasher.....

Then I clipped out that death cap.......changed the fuse wiring as the return lead from the power transformer was connected to the fuse holder terminal that was closest to the chassis and moved it to the end of the fuse holder...and the wire that was at the end of the fuse holder is now soldered to the terminal that is closest to the rear of the chassis.....I also heat shrinked both connections in order to insulate them..... Did a continunity check between chassis and both sides of the power cord with power and standby switches turned on and there is an open circuit.....

so my conclusion is that when replacing a two prong cord with the proper 3 prong cord, the only thing one has to do is to clip out the death cap,reverse the connections to the fuse holder and insulate them.....and attach the live and neutral wires to where the original ones were connected.......correct????

I also had to replace the elect caps. and there was a bunch of resistors that were way out of spec....100K was reading over 120K...... 220K was reading up to 250K, etc.....the plate resistors for the PI were also out of spec.....as were the screen and grid resistors for the output tubes.....all in all there must have been 15 or more resistors that had to be replaced.....plus all the electrolytics as well.....before I install tubes I will power it up and check voltages to all the sockets to make sure everything is normal.....if anybody else has anything to add I will be most interested in hearing about it.....Have a good one everybody.....
Cheers,
Bernie

[patlaw]

A light bulb limiter would be a good thing to use when powering it up the first time.

[bsco]

A light bulb limiter would be a good thing to use when powering it up the first time.

Right you are....Thank you......

[bsco]

Ok. Back again. One thing I did was to increase the wattage of the screen resistors on this amp from 2W to 5W.....The 2W ones were cooked......I haven't powered it up but will do so later this week and will use my Light Blub Dimmer unit for protection......I just wanted to check here about the new 470/5W I used...the originals were 470/2W and looked like they were original.....
Cheers

[52 Bill]

Ok. Back again. One thing I did was to increase the wattage of the screen resistors on this amp from 2W to 5W.....The 2W ones were cooked......I haven't powered it up but will do so later this week and will use my Light Blub Dimmer unit for protection......I just wanted to check here about the new 470/5W I used...the originals were 470/2W and looked like they were original.....
Cheers

The original screen resistors on these amps were carbon comp, 470 ohm, 1 watt. They can get warm and can burn open when a power tube fails. Some people believe that they are used as a fuse and should not be replaced with a higher wattage.

[bsco]

The original screen resistors on these amps were carbon comp, 470 ohm, 1 watt. They can get warm and can burn open when a power tube fails. Some people believe that they are used as a fuse and should not be replaced with a higher wattage.

I thought that they were two watt resistors.....they are awful big for a 1 watter......Maybe I can put 2 watters there instead....as I did read somewhere that they should be increased.....I was going by other older tube Fender amps which had 5 watters there with 4 output tubes.....thanks for the heads up.....
Cheers

[SoulFetish]

This one had a 2 prong plug with a ground select switch.....after sizing this up for awhile I decided to replace the power cord with the proper 3 prong one......I soldered the live and neutral wires, white and black, to their respective terminals on the accessory socket.....I crimped the ground wire to an eyelet connector, removed one of the nuts for the transformer mounting, cleaned the chassis, installed a new nut with lockwasher, installed the connector and then installed another nut and lockwasher.....

Then I clipped out that death cap.......changed the fuse wiring as the return lead from the power transformer was connected to the fuse holder terminal that was closest to the chassis and moved it to the end of the fuse holder...and the wire that was at the end of the fuse holder is now soldered to the terminal that is closest to the rear of the chassis.....I also heat shrinked both connections in order to insulate them..... Did a continunity check between chassis and both sides of the power cord with power and standby switches turned on and there is an open circuit.....

so my conclusion is that when replacing a two prong cord with the proper 3 prong cord, the only thing one has to do is to clip out the death cap,reverse the connections to the fuse holder and insulate them.....and attach the live and neutral wires to where the original ones were connected.......correct????

I also had to replace the elect caps. and there was a bunch of resistors that were way out of spec....100K was reading over 120K...... 220K was reading up to 250K, etc.....the plate resistors for the PI were also out of spec.....as were the screen and grid resistors for the output tubes.....all in all there must have been 15 or more resistors that had to be replaced.....plus all the electrolytics as well.....before I install tubes I will power it up and check voltages to all the sockets to make sure everything is normal.....if anybody else has anything to add I will be most interested in hearing about it.....Have a good one everybody.....
Cheers,
Bernie

Here are a couple of important safety points I would make. First, I've often seen the accessory outlet wired incorrectly in vintage Fenders. If you wish to connect the mains live/neutral wires to the accessory outlet, the Live (black) wire MUST be connected to the internal Brass terminal and the neutral to the standard tinned color terminal. These outlets are often polarized two prong AC outlets, and the incorrect polarity could lead to a hazard for people and equipment without the protection of an earthed outlet. This is a matter of electrical code and needs to be wired correctly regardless of the original wiring. Some technicians elect to remove all connections to the accessory outlet, and disengage the receptacle altogether.

Second, a transformer lug is probably the worst place to make the earth bond connection. Transformers (EI lamination transformers in particular) vibrate mechanically when subjected to an intense magnetic. This is called magnetostriction. The vibration can (and does) cause the nuts to loosen, causing the earth/chassis bond to open. I've seen this on several occasions.
The earth wire should have it's own designated terminal connection and dedicated fasteners.

[Leo_Gnardo]

The earth wire should have it's own designated terminal connection and dedicated fasteners.

To keep the scanny eyed collector "experts" satisfied, I don't drill an extra hole in the chassis for a separate ground terminal, but solder the AC line ground wire to the chassis. A little scraping, dab 'o' flux, 80 watt Weller "pencil", a couple inches of Kester 60/40 and it's all done in less than 5 minutes. Keeps the "oh my god don't drill any holes in my chassis!" crowd from flipping out. Typically the landing zone for this connection is between the power transformer and the side gusset of the chassis box.

If you must use a chassis bolt, it's a good idea first to wire brush crud off the chassis metal where your spade or ring terminal is going to land, then apply a small dot of Loc-tite or other glue/goo to the threads so the nut won't walk up the bolt over the course of time & vibration.

[g1]

I've often seen the accessory outlet wired incorrectly in vintage Fenders. If you wish to connect the mains live/neutral wires to the accessory outlet, the Live (black) wire MUST be connected to the internal Brass terminal and the neutral to the standard tinned color terminal.

I've found the same, and I think some of them are not colour coded. Going by what 'appears' correct ends up reversed, and I think that is why so many are wrong from the factory. Best to always do resistance checks that the hot is going to the proper hot lug.
If memory serves, this issue was for the 2 prong type accessory sockets.

[bsco]

Thanks SoulFetish.....I'll double check that acc outlet.....I do not think that ground is going to come loose.....as I have coated the threads after securing the ground connection....but I might take it off and just solder the wire right to the chassis like Leo had suggested below your post as I have just picked up a Weller 240W soldering gun....that should have plenty of heat for that job.....
Cheers

[bsco]

I've found the same, and I think some of them are not colour coded. Going by what 'appears' correct ends up reversed, and I think that is why so many are wrong from the factory. Best to always do resistance checks that the hot is going to the proper hot lug.
If memory serves, this issue was for the 2 prong type accessory sockets.

Yes, this acc plug is 2 prong and I do believe it is NOT polarized so I will double check that.....I will let you know......
Cheers

[Randall]

Let us know if that weller gun does the job.

[bsco]

Let us know if that weller gun does the job.

I sure will.......Can't see why it would not work.........I'll give the chassis a very good scraping and cleaning first.....
Cheers

[nosaj]

Let us know if that weller gun does the job.

I have one of the 120 watt ones. I replaced the element with a short piece of number 12 solid wire, tinned it( I could not do this with the supplied weller tips though., I have no problem making chassis connections with it. It's pretty fast too. I forget where I got that tip. I have also used a long piece of wire to cut styrofoam like a knife.

nosaj

[Enzo]

The power cords on the old two-wire Fenders were not polarized anyway. After basic set-up, the first thing we did on stage was get all the ground switches set for best, and turned plugs over in the outlets as needed.