Fender Super Twin.

[DrNomis_44]

Hi Everyone,

One of the students doing a different music course than the one I'm doing, has offered to sell me a Fender Super Twin amp chassis for $300.00, it looks in reasonable condition, except for a missing control knob, and apparently it does work.

I'm going to organize paying him the money for it over the next couple of fortnights, it looks like it could be a good amp restoration project, I'll post a pic of it once I get it home so you can check it out, it is an all valve amp that is apparently capable of putting out 180 watts of audio power

Stay tuned for more updates.

[wazkelly]

Bargain price if not too much wrong with it. You mention amp chassis which implies no speakers and possibly no longer contained with original amp/combo setup?

[DrNomis_44]

Bargain price if not too much wrong with it. You mention amp chassis which implies no speakers and possibly no longer contained with original amp/combo setup?

Yep, the chassis itself is housed in an old Fender Bassman head cabinet that has the front missing, the front panel of the chassis is still good though, what I can do tomorrow is take my Samsung Galaxy Y phone into uni and use it to take a pic of the amp chassis and post it in this thread so you can see exactly what it looks like, it's a Fender Blackface Super Twin with the EQ and Distortion control next to the Master Volume control.

And I'm guessing that it's probably an early 70's model.


Apparently, this is what they looked like brand new:

[DrNomis_44]

Update,

I've been having some trouble getting my laptop to connect to the Uni's Student WiFi network in order to get online, and seeing as the guy who's selling the amp chassis to me said I could take it home with me today, I'm going to see if I can get a couple of pics of the amp chassis "as is" sorted for you guys to check out shortly, will post them in this thread, stay tuned.


I've got the amp chassis at home now, it's in my loungeroom.

[Simon Barden]

It's going to be very loud. They were known for regularly burning out the 2 x 100W JBL speakers that were fitted as standard in the combo when the amp was pushed. Probably not surprising as the wattage rating is normally given with the signal to the speakers at 3%THD, so still very clean, whilst when pushed into heavy overdrive you might get another 50%-80% more power from the amp. But those JBL speakers were also a few dBs more efficient than the normal Jensen or Eminence speakers Fender normally used at the time, so it was an even bigger volume jump over their standard models (though in the 70s you could also get the Twins fitted with the JBLs).

It was obviously designed to be a very loud clean amp, but it did make a very good even louder distorted amp (replacement speakers at the ready) when used by people like Ted Nugent, who used six of them on stage!

[DrNomis_44]

I just took a couple of pics of the amp chassis with my Galaxy Y phone, just waiting for Windows Update to finish updating Windows 10 on my laptop, after that I'll get the pics sorted out so that I can post them in this thread.


While waiting for Windows to finish updating, I thought I would see what valves were installed in the chassis, here's what I found:


Three 12AX7 valves, one 7025 (basically a lower-noise version of the 12AX7), one 12AU7A, and six 6L6 power valves!!


Here we go, as promised, the pics of the amp chassis "as is":







Should make a pretty good amp restoration project.


So, it's looking like I'll have to build myself a 400 Watt Dummy Load for testing the amp's performance once I get round to doing whatever restoration work on it that it needs to get it up and running again, I wonder where I could source a new combo cabinet for it from?, or, should I just keep it as an amp head and invest in a new 4 X 12 Speaker box?

It'll probably be good for annoying my noisy neighbors....heehee.....180 Watts of audio power.

[Simon Barden]

While waiting for Windows to finish updating, I thought I would see what valves were installed in the chassis, here's what I found:


Three 12AX7 valves, one 7025 (basically a lower-noise version of the 12AX7), one 12AU7A, and six 6L6 power valves!!

OK, bad news. Looking on the web for a schematic of the amp, one thing is certain - it shouldn't have three 12AX7s in it! http://acruhl.freeshell.org/mga/sche.../supertwin.jpg

The valves should be:

V1 = 7052
V2 = 6CX8
V3 = 6C10
V4 = 12AX7A
V5 = 12AT7

The 6C10 is a triple triode valve, so certainly can't be replaced with a 12AX7 unless the amp has been seriously modified. Maybe by omitting the reverb unit they've been able to do this, but the amp certainly isn't standard, and you don't know how well any modifications have been made.

The 6CX8 and the 6C10 aren't made any more, so you have to rely on a dwindling supply of NOS valves (which aren't cheap if you can get them), so I can see why someone made some changes. However, it isn't a proper Super Twin amp any more, so is worth what someone is willing to pay for what it is now. The big question is, were the changes made by someone who knew what they were doing and all the supporting resistors for the valves were changed to the right values so they work properly? You can't simply change valve types and expect them to do the same job without changing the supporting circuitry. Even the 12A_7 range (12AX7, 12AT7 etc.) aren't 100% compatible and the bias resistors for them need to be tweaked to get the best from them.

In the light of this, I wouldn't advise even powering it up, but it needs to go straight to an amp specialist who should be able to tell if it's safe to use and whether the modifications have been done correctly. If not, it could be lethal.

Also note that it needs a 4 ohm load (no alternate tappings are available), so a standard 4x12" cab will need to be modified so that all four 16 ohm speakers are wired in parallel.

[DrNomis_44]

OK, bad news. Looking on the web for a schematic of the amp, one thing is certain - it shouldn't have three 12AX7s in it! http://acruhl.freeshell.org/mga/sche.../supertwin.jpg

The valves should be:

V1 = 7052
V2 = 6CX8
V3 = 6C10
V4 = 12AX7A
V5 = 12AT7

The 6C10 is a triple triode valve, so certainly can't be replaced with a 12AX7 unless the amp has been seriously modified. Maybe by omitting the reverb unit they've been able to do this, but the amp certainly isn't standard, and you don't know how well any modifications have been made.

The 6CX8 and the 6C10 aren't made any more, so you have to rely on a dwindling supply of NOS valves (which aren't cheap if you can get them), so I can see why someone made some changes. However, it isn't a proper Super Twin amp any more, so is worth what someone is willing to pay for what it is now. The big question is, were the changes made by someone who knew what they were doing and all the supporting resistors for the valves were changed to the right values so they work properly? You can't simply change valve types and expect them to do the same job without changing the supporting circuitry. Even the 12A_7 range (12AX7, 12AT7 etc.) aren't 100% compatible and the bias resistors for them need to be tweaked to get the best from them.

In the light of this, I wouldn't advise even powering it up, but it needs to go straight to an amp specialist who should be able to tell if it's safe to use and whether the modifications have been done correctly. If not, it could be lethal.

Also note that it needs a 4 ohm load (no alternate tappings are available), so a standard 4x12" cab will need to be modified so that all four 16 ohm speakers are wired in parallel.

The wood cabinet that the amp chassis is in needs replacing with a new one because I noticed that the corner-joints are starting to come apart, good call about the 6CX8 and 6C10 valves, I didn't notice that, I'm going to wait till I've paid the guy the money I owe him for the amp before I go and do anything with it, I'm familiar enough with the safety procedures for working on valve amplifiers so I'll see if I can do the work myself, I'll certainly give it a good check out electrically to make sure it's electrically safe beforehand, that's for sure, I don't think I will sell the amp once it's all sorted out, I think I will keep it.

One thing I have noticed is that the standby switch definitely needs replacing because it appears to be stuck in the on position, the power switch seems good though, but I might just replace both as a matter of course, I think I can get a new knob for it from Evatco.


On the back panel of the amp chassis, near the speaker output socket, it says that the minimum load impedance is 4 Ohms.

[Marcel]

So, it's looking like I'll have to build myself a 400 Watt Dummy Load for testing the amp's performance once I get round to doing whatever restoration work on it that it needs to get it up and running again, I wonder where I could source a new combo cabinet for it from?, or, should I just keep it as an amp head and invest in a new 4 X 12 Speaker box?

It'll probably be good for annoying my noisy neighbors....heehee.....180 Watts of audio power.

I've built a few 'dummy loads' out of old style jug elements.... the ones which have coils of resistance wire wrapped around a porcelain block and has two brass rods holding the block suspended in the water. In their original form they are good for 1500W with 240VAC going in, but cut back down and rewound to 8 ohms and suspended in water they easily handle 800W RMS...

It was actually quite funny way back when to demo two of these loads to my electrician friends ... push 1kHz into an Jands 920 stereo amp, wind up to 450W RMS per channel (just short of clipping) and listen to the 2 cups of water squeal their way to boiling...

[dave.king1]

It ain't 180w of audio power it's 180w RMS which is significantly more, there was a bass equivalent that one of my mates owned back in the day.

Heavy as hell and even louder, excellent if you are planning a Ted Nugent tribute show