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 Post subject: Desperate For 70's Super Twin Help!
PostPosted: Thu Nov 22, 2012 7:56 pm 
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I just received a 70's Super Twin that didn't do too well in shipping. The Distortion on/off control pot snapped mid shaft. Anyone know where I can find a replacement? Anyone know what else might work say from Radio Shack, Ebay, wherever? It looks to be a 100k pot with on/off at the 7o'clock position but it also ties in to the distortion circuit somehow. I'd appreciate any/all comments or ideas. Been a Fender guy for over 40 years! Thanks!


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 Post subject: Re: Desperate For 70's Super Twin Help!
PostPosted: Fri Nov 23, 2012 3:19 am 
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I think that this is a special made pot. 100K-ohm Linear with special switch (if I remember correctly). Fender part number 012561.

May want to try email or call to WD Music Products:

http://www.wdmusic.com/fender_pages_pots.html

Schemo:

http://www.webphix.com/schematic%20heav ... _schem.pdf

Good luck!


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 Post subject: Re: Desperate For 70's Super Twin Help!
PostPosted: Fri Nov 23, 2012 4:17 pm 
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Thanks Beemer. You've been a great help. I've been looking at the schematic and I thought that was the switch I needed just wasn't 100% sure. No luck finding one yet. I'm thinking maybe the push/pull type might work if it's within spec with the proper lugs. Appreciate your time.


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 Post subject: Re: Desperate For 70's Super Twin Help!
PostPosted: Fri Nov 23, 2012 4:29 pm 
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Can someone tell me if this might work? Looks pretty much the same.

http://www.surplusgizmos.com/100k-OHM-P ... _2402.html

Thanks!


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 Post subject: Re: Desperate For 70's Super Twin Help!
PostPosted: Fri Nov 23, 2012 8:21 pm 
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If you see the back end of the pot in your and the two wires connected to the switch portion --- you can use this pot. I just recalled that some Fender amps had special switch-pots.

I can't find where that switch is in the schematic.


Good luck!


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 Post subject: Re: Desperate For 70's Super Twin Help!
PostPosted: Sat Nov 24, 2012 9:29 am 
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Thanks again. This switched pot looks exactly the same as the one I need. I'm also having a hard time with the schematic. I think I located the switch somewhere around the mid top of the drawing. I just followed the distortion circuit. I ordered the switch. My fingers are crossed! Appreciate your time!


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 Post subject: Re: Desperate For 70's Super Twin Help!
PostPosted: Sat Nov 24, 2012 4:33 pm 
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Pull-In Bright Switch

It's not this one. I believe that this is part of the Master Volume control pot. Look at the BOTTOM-MIDDLE of the schematic, near the Foot Pedal Jack. See S1 Switch On? I think this is it.

Yes, the linear 100-K pot you bought should work fine.

http://www.webphix.com/schematic%20heav ... _schem.pdf


BTW... this amp uses a 6CX8 (triode-pentode) and 6C10 (triple-triode) tubes. Boy, these are getting as rare to find as hen's teeth (esp the 6C10). There is no new production of these tubes. The Commies never used such beasts in their military equipment. I'd surf EBay and good NOS suppliers like Tube World to find GE, Sylvania, or RCA made NOS tubes, for future use. They are well-made tubes and should last a good 5-10 years in a gigged amp.

Good luck!


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 Post subject: Re: Desperate For 70's Super Twin Help!
PostPosted: Sun Nov 25, 2012 12:15 am 
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You're 100% correct. Somehow the distortion switch ties in to the output / master switch also. Weird circuit. Thanks for reminding me about the 6c. I was actually looking around every once in a while before I even bought the amp and had forgotten all about that. The ones that came with it have some life left and should serve me but some spares are definitely at the top my list. Commies....Funny!! Once again, thanks you've been a huge help! I'll post again after the switch repair.


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 Post subject: Re: Desperate For 70's Super Twin Help!
PostPosted: Sun Nov 25, 2012 1:55 am 
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Good luck with the pot/switch. BTW... my 1962 Ampeg Jet uses 6C10s. It took awhile to find some good NOS ones. There is a seller on EBay that posts USAF mil spec ones (VT-23 designation), every now and then. Keep an eye out for these. They are very hard to find Raytheon made puppies.


Image


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 Post subject: Re: Desperate For 70's Super Twin Help!
PostPosted: Tue Nov 27, 2012 4:20 pm 
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Or, get from Tube Depot, Tube Store, KCANOS, AES.

TubeDepot:
6C10
6CX8

TheTubeStore:
6C10
6CX8

KCANOS:
6C10

AES lists the 6C10, but in tube sets for various amps. They list the 6C10 by themselves as out of stock. The 6CX8 is listed.
6C10
6CX8

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


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 Post subject: Re: Desperate For 70's Super Twin Help!
PostPosted: Tue Nov 27, 2012 5:04 pm 
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Shimmy, in my experience those outlets are OOS of NOS 6C10 triple triodes. Unless they found another source. Best to call.

As for the 6CX8, a lot of Ham radios use this tube. So if you go to a Hamfest, you may find good NOS ones. I like RCA > GE > Sylvania. My personal preference.


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 Post subject: Re: Desperate For 70's Super Twin Help!
PostPosted: Tue Nov 27, 2012 6:23 pm 
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Yes, probably best to call and make sure. I thought that they all listed OOS when none were available.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


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 Post subject: Re: Desperate For 70's Super Twin Help!
PostPosted: Sat Dec 01, 2012 5:06 am 
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I think only the super twin with reverb uses the triple-triodes. The standard super twin WITHOUT reverb uses only common dual triodes in the preamp and pi. It seems the reverb needed two more stages, so I guess using triple triodes allowed them to use the same chassis by converitng two dual triodes into triples. The good news is that you can use a chassis punch to put in another tube socket without making metal chips and convert the others, and change over to all common dual-triodes if necessary. One thing this amp definitely has going for it is that it's old enough to use point to point terminals on a strip instead of a printed circuit, so modification like this are usually straight-forward and nearly trivial if the heaters are in parallel; yet it's new enough to have decent modern capacitors.

If finding the correct switched pot is difficult, you might be able to substitute a push/pull switch pot or drill a hole and mount a toggle switch in desperation (put the switch in the back if necessary). I have, on occasion, managed to transplant a switch from one pot to another, so note the brand of the broken pot and if you can't get one with a swtich get one without and see whether you can transplant the switch or reverse transplant the shaft. Note that the rear footswitch jack is also involved in the circuit. BTW nobody likes that distortion 'feature' anyway. Nobody likes the distortion mode of the ultralinear output section either. So if you need dirty, use the master volume to get some preamp distortion...if necessary add an FET gain stomp box.

The stock super twin and super twin with reverb as well as the closely related sister amp the studio bass amp were all very top-heavy. When the wheel caster bases rotated toward the back the support wheelbase was very unstable with front weight. It is very common to find the super twins fell over on their faces. It would be nice if the cabinet ends protected recessed knobs, but no, the knobs protrude. The super twin I bought had many broken knobs, and that's typical. Even loaded in a truck with the cover on the amp and facing a flat wall the knobs get broken. Perhaps you were just unfortunate to have the pot break before the knob.

The stock super twin combo is a really heavy chassis with huge power transformers. THe chassis is held in by the hanger bolts threaded into spring-clips. Unfortunately the spring clips are on the sear side of the chassis instead of going thru the chassis to the far side. So the heavy super twin chassis tends to bend and twist an pop corner welds too. You might consider longer bolts, drill the other side of the chassis, and install nuts there too.

I don't usually condone changing nice classic amps, but IMHO the best thing you can do with a super twin is to install the chassis into a head cabinet. The super twin combo is just too heavy to move with the big trannys and incredibly heavy square ceramic magnet speakers in one package. If you leave it a combo, remove the wheels and put it on a slightly larger wheeled base instead, so that it doesn't fall over on its face anymore. If you leave it a combo, consider installing some of the excellent lightweight Eminence 12" speakers with modern neodymium magnets, or some good lighter alnico magnet speakers and eliminate more than half the speaker weight. As a seperate head and seperate 4X12 cab you won't ever worry about blowing your speakers. Or breaking your back; worth taking two trips to avoid. And with the right speaker cabinet the super twin chassis also makes one of the best single-output tube bass amps ever created (outside of a few wonderful new Fenders and the SVT). OK it doesn't have channel-switching etc. but it will hold its own against the really big tube bass amps for one third of their price.

If you convert it into a head, it needs a LOT of cooling. The combo has a lot of air inside. The head doesn't. I made my head cabinet a bit taller, and also deeper so air could get out past the chassis, then cut back the top of the cabinet to allow access to the jacks in the back. I also added vents in the bottom of the cabinet, taller rubber feet, bigger oval air inlet cutout in the rear panel, and the littel grille cloth panel in mine isn't solid, it actually passes air. I don't like fan noise, but consider a really quiet one.

If it's a super twin without reverb, there's a guy on ebay now with the very last OEM NOS super twin faceplate in known existence. I bought the next-to-last one, and they clean up to look perfect.

The EQ knobs are numbered with 0 in the middle so they are not standard Fender knobs, and they break. So if you leave it a combo see it you can pick up a few spares from Fender or on ebay before they disappear. Of course, you can always change to chicken head knobs for the EQ and get an even better visual indication of settings from a distance.

The single-impedance output transformer is sometimes a problem. For one thing, you can't as easily disable 4 output tubes and correct some of the output transformer input impedance mismatch by changing the output tap being used. So a 1/3 power switch might not be trivial. But the standard output sounds pretty bad in distortion unless you put in switches for the ultralinear tap and alter the feedback loop. You're probably better to leave it alone or go all the way.

The fact it has a black face makes some people expect it to sound like a blackface, which it doesn't. But cosmetically you have a lot of options. The white trim around the speaker grille was supposed to distinguish it as something special. It looks much better without it. For that matter, it looks good as a blonde with oxblood tolex; you can get away with more cosmetic options because to the black faceplate.


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 Post subject: Re: Desperate For 70's Super Twin Help!
PostPosted: Thu Dec 06, 2012 8:36 pm 
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Hi Everyone.
Just wanted to thank you all for your input, thoughts and assistance. The pot came and it looks like I'm good to go. I'll be installing it over the holidays and I'll be sure to post back with the outcome. I gave alot of thought to other options ala Cyclecamper but always wanted just a stock, correct combo unit. I had NO intentions of lugging this around anyway. I didn't mention that besides the damaged pot this thing literally fell out of the box in pieces on the floor so I had my work cut out for me. It took a few shots during shipping. Ironically the grill / dripedge, speakers and faceplate survived and the tubes were shipped seperately so it was just a matter of soting it all out, rebuilding the cab and repairing the switch. Thanks again everyone!
Joe NY


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