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Thread: Fender Dual Showman....made in 1966

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    Supporting Member bsco's Avatar
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    Fender Dual Showman....made in 1966

    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

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    Member patlaw's Avatar
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    A light bulb limiter would be a good thing to use when powering it up the first time.

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    Supporting Member bsco's Avatar
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    Quote Originally Posted by patlaw View Post
    A light bulb limiter would be a good thing to use when powering it up the first time.
    Right you are....Thank you......

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    Supporting Member bsco's Avatar
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    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

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    Quote Originally Posted by bsco View Post
    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.

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    Supporting Member bsco's Avatar
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    Quote Originally Posted by 52 Bill View Post
    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

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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by bsco View Post
    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.

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by SoulFetish View Post
    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.

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    Enjoy. Every. Sandwich.

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    Quote Originally Posted by SoulFetish View Post
    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.

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    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

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    Quote Originally Posted by g1 View Post
    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

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    Supporting Member Randall's Avatar
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    Let us know if that weller gun does the job.

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    It's weird, because it WAS working fine.....

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    Supporting Member bsco's Avatar
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    Quote Originally Posted by Randall View Post
    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

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by Randall View Post
    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

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    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.

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    Quote Originally Posted by bsco View Post
    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
    I will often solder the earth wire to chassis in Vintage Fenders in the same way as Leo describes as well. I'm not sure how much contact area the Weller gun can get on the chassis, but 240W should be plenty of heat. I find that going over the area you're planning to soldering with a cheap emery board (or scoring up the chassis with a tool), and using liquid flux really help getting a nice strong solder connection.

    edit:
    Quote Originally Posted by bsco View Post
    I sure will.......Can't see why it would not work.........I'll give the chassis a very good scraping and cleaning first.....
    Cheers
    I just read down and saw this. Looks like you are a step ahead of me. Good luck

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    Quote Originally Posted by 52 Bill View Post
    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.
    Think I will switch them back to the 1W and will use FP resistors......

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    Supporting Member bsco's Avatar
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    Quote Originally Posted by SoulFetish View Post
    I will often solder the earth wire to chassis in Vintage Fenders in the same way as Leo describes as well. I'm not sure how much contact area the Weller gun can get on the chassis, but 240W should be plenty of heat. I find that going over the area you're planning to soldering with a cheap emery board (or scoring up the chassis with a tool), and using liquid flux really help getting a nice strong solder connection.

    edit:

    I just read down and saw this. Looks like you are a step ahead of me. Good luck
    Yes sir. That 240W weller monster worked great......

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    Supporting Member bsco's Avatar
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    Quote Originally Posted by Randall View Post
    Let us know if that weller gun does the job.
    Yes sir...That worked excellent....

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    Quote Originally Posted by SoulFetish View Post
    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.
    I had another look at that accessory socket...it is polarized......correct me if I am wrong but isn't the wider prong used for the neutral return wire....aka white wire, and the live or black wire is connected to the smaller prong?? this socket has the brass screw on the wide connection and the smaller prong has the silver or tin type screw on it.....with that being the case, the black wire is connected to the smaller prong and the white wire is connected to the larger prong.....from the factory........

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    Yes, the wider prong is normally the neutral. This is also the 'identified wire;' on flat zip cord it will be the ribbed or striped wire.

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    I don't think the color of the screw is significant since they had to be removed in order to get the eyelet on and the underpaid, disgruntled employee of the month didn't care which screw went where he/she put them back in. Which wire going to which side is significant, however.

    I pulled an early '70's chassis with a three-pronger and it has the screws in their proper configuration, but the wires are on the wrong sides. The tin screw is on the wide side, but the black wire is connected to it. An interesting thing is that the wires were cut to lengths that would have allowed the proper connections.

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    Don't forget the joker g1's Avatar
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    Quote Originally Posted by bsco View Post
    I had another look at that accessory socket...it is polarized......correct me if I am wrong but isn't the wider prong used for the neutral return wire....aka white wire, and the live or black wire is connected to the smaller prong?? this socket has the brass screw on the wide connection and the smaller prong has the silver or tin type screw on it.....with that being the case, the black wire is connected to the smaller prong and the white wire is connected to the larger prong.....from the factory........
    This is what I was talking about. There was something very deceptive about how it looked and which screw terminal actually connects to which blade.
    Can you do a resistance check with one probe in the actual smaller prong and see which lug & screw it connects to?

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    Supporting Member bsco's Avatar
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    Quote Originally Posted by g1 View Post
    This is what I was talking about. There was something very deceptive about how it looked and which screw terminal actually connects to which blade.
    Can you do a resistance check with one probe in the actual smaller prong and see which lug & screw it connects to?
    Yes sir...I'll be downstairs after supper and I will check it out for you and let you know......
    Cheers

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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by Bloomfield View Post
    Yes, the wider prong is normally the neutral. This is also the 'identified wire;' on flat zip cord it will be the ribbed or striped wire.
    Check it again it if you follow the brass terminal, It will go to the thinner prong. But it looks like it’s right behind the neutral one. This confused the shit out of me when I first noticed it. But I’ve never seen The socket terminated incorrectly.

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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by 66 Kicks View Post
    I don't think the color of the screw is significant since they had to be removed in order to get the eyelet on and the underpaid, disgruntled employee of the month didn't care which screw went where he/she put them back in. Which wire going to which side is significant, however.

    I pulled an early '70's chassis with a three-pronger and it has the screws in their proper configuration, but the wires are on the wrong sides. The tin screw is on the wide side, but the black wire is connected to it. An interesting thing is that the wires were cut to lengths that would have allowed the proper connections.
    No it doesn’t matter about the screws it’s the actual terminal that’s a significant

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    Quote Originally Posted by SoulFetish View Post
    Check it again it if you follow the brass terminal, It will go to the thinner prong. But it looks like it’s right behind the neutral one.
    Aren't the screws offset 45 degrees from the slots so that either one has an equal distance to both slots? Maybe there are different models?

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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by 66 Kicks View Post
    Aren't the screws offset 45 degrees from the slots so that either one has an equal distance to both slots? Maybe there are different models?
    I apologize, I meant to say beside the neutral one (or "next to" would have probably been clearer). What I mean by that is, The tab you actually solder to is directly adjacent to the opposite input. So, it's incredibly easy to misidentify which connector goes to what terminal. After a little searching, I was able find a clear photo showing this.



    This photo is well lit and taken from a clear angle. But the practical reality is that those terminals are recessed in the back of the receptacle, and almost always suffering years of oxide build up. This, coupled with the reality of working over the a receptacle (tucked under the lip of the chassis) is what leads to so much confusion for the technician.

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    Supporting Member bsco's Avatar
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    I think the best way to do this is to remove the mounting screws so it can be pulled out from the chassis, install the wiring the proper way and then re-install it...That way you will have a very clear view of the rear of the terminals in question, and if the wiring is not long enough to do that, then it is just a matter of installing a couple of pieces of wire that would be long enough to be able to work comfortable...as it stands now with the unit I have, it s wired correctly.....but in the future I might just pull the outlet from the rear of the chassis.....as it is a bit of a pain to work at that while it is installed.....

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    Supporting Member bsco's Avatar
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    Quote Originally Posted by g1 View Post
    This is what I was talking about. There was something very deceptive about how it looked and which screw terminal actually connects to which blade.
    Can you do a resistance check with one probe in the actual smaller prong and see which lug & screw it connects to?
    Just getting back at this.....had to do a few personal things over the last few days and Had to take care of some stuff for my mom as she has been diagnosed with a form of Alzimers....we now have some appointments set up and have to get some forms filled out by the doctors, etc, etc......ANYWAY.......Hey g1...you are right...Me stupid.....well maybe not totally stupid.....That confused the hell out of me...now that I have this figured out and I have removed that death cap, and installed a new 3 prong cord and have soldered the ground directly to the chassis, there are two small yellow colored wires also connected to the accessory plug.....were they also wired wrong at the factory, or was it just the power cord wires.......if it was only the power cord wiring, then I have it done......
    Cheers

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    Senior Member SoulFetish's Avatar
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    Just so happens i just haf a drip edge silverface princeton on my bench on Friday which looks to be in factory condition. It was build in the exact way we are discussing in this thread so I snapped some pics to clear up some confusion. (Im doing this on my phone so lets see how it turns out)
    The first couple of pics show the original wiring and then rewiring the line chord with proper earth connection (via soldering in this case, but i prefer crimped terminals). The neutral and live wires have been rewired so the live is in series with the fuse and switch.

    Click image for larger version. 

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    FYI- i used a washer magnet to hold the wire flush and still for soldering and secured the wire with its own designated strain relief to protect it.

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    If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

  32. #32
    Supporting Member bsco's Avatar
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    OK. Back at this again....powered it up and the voltages check ok....will install the output tubes later next week and give it a good check out...however, I do have a problem.......I think.........I seemed to have misplaced the back panel....I have searched down in the basement and even upstairs here in the house but can't find it so far......anybody here on this site have a Fender back panel which would fit the dual showman cabinet?? Doesn't matter if it is from another Fender head as long as it will physically fit......I would be very willing to buy it no problem.....I am hoping that over the weekend I will find it but it does have me worried just in case I do not.....
    Cheers

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  33. #33
    Supporting Member The Dude's Avatar
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    Was it there to start with? I often get amps in without those back panels.

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  34. #34
    Supporting Member bsco's Avatar
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    Quote Originally Posted by The Dude View Post
    Was it there to start with? I often get amps in without those back panels.
    I just talked to the owner.......He has the back panel.....Boy and I ever happy about that.......when he had originally dropped it off I didn't make note that the back cover was not there......what a relief......I can sleep stress free tonight...from now on I am going to make a note of anything that is missing when something is dropped off to me.....and...while I had him on the phone, I asked him about the pots.....as some of them had been replaced......

    There is a mixture of white splined plastic shafts, regular metal shafts and a couple of brass shafts...I don't think that it came from the factory like that and the owner said he had bought that brand new and it was never repaired....he did however inform me that he had it on consignment at a local music store for sale but after a year, he decided to take it back.....so I figure the pots were replaced there....

    The head was bought back without the tubes installed...the tech said he didn't want to transport the head with the tubes installed because he was afraid they might fall out......the owner picked up the tubes a few days later(which was strange) and when he got home he opened the package up to find what he thinks was a different set of tubes....but he couldn't say for sure.....so I better stick them on a tube tester to at least check to see if they have good emission and no shorts or leakage before I install them.....and use a variac......only goes to show that there are a few shady people out there that make it bad for us honest folks...I'll fire the amp up later this week and let you know how it works out.......
    Cheers

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  35. #35
    Don't forget the joker g1's Avatar
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    If they are solid smooth metal & brass shaft pots (not split knurled) I think they may be factory. I don't think they could get all the values needed with just one type of shaft so I think you end up with a mix, at least in some era/models.

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