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Vintage threads from the first ten years

Sunn Sceptre Guitar Amp head

11/9/1999 6:37 PM
JD Sleep	Sunn Sceptre Guitar Amp head Anyone know anything about the subject amp? I found one this morning, sitting by the side of the road with the rest of someone's trash. Of course I'm not above dumpster diving, so I slammed on the brakes and threw it in the car. The thing looks to be fully intact except the power tubes and the power cable. The transformers are pretty rusty. I'd like to know: 1 - Does this thing have any vintage value? If not I'll probably turn it into something custom. It's got a good chasis and the cabinet is in very good condition. 2 - Schematic anywhere? 3 - What kind of power tubes (they are missing)? 4 - How can I tell if the (huge) transformers are any good? Thanks, JD

11/9/1999 6:37 PM

JD Sleep

Sunn Sceptre Guitar Amp head

Anyone know anything about the subject amp? I found one this morning, sitting by the side of the road with the rest of someone's trash. Of course I'm not above dumpster diving, so I slammed on the brakes and threw it in the car.
The thing looks to be fully intact except the power tubes and the power cable. The transformers are pretty rusty.
I'd like to know:
1 - Does this thing have any vintage value? If not I'll probably turn it into something custom. It's got a good chasis and the cabinet is in very good condition.
2 - Schematic anywhere?
3 - What kind of power tubes (they are missing)?
4 - How can I tell if the (huge) transformers are any good?

Thanks,
JD

11/9/1999 10:33 PM
John Stokes	Wow, what a find. Hopefully, it isn't too far gone and you can restore it. I think you can get a schematic from Pittman's book. I believe these, like most Sunns, used 6550 output tubes. A replacement power cord should not be a problem. Re the rusty transformers, that may be a problem. If the laminations are too far gone, the transformers are paper weights. Get a sacrificial cloth rag and spray something like WD40 on it. Rub down the transformers and see how they clean up. Do not, under any circumstances, use anything abrasive to try to remove the rust. Let us know how far you get and we'll take it from there. Best luck.

11/9/1999 10:33 PM

John Stokes

Wow, what a find. Hopefully, it isn't too far gone and you can restore it. I *think* you can get a schematic from Pittman's book. I believe these, like most Sunns, used 6550 output tubes. A replacement power cord should not be a problem. Re the rusty transformers, that may be a problem. If the laminations are too far gone, the transformers are paper weights. Get a sacrificial cloth rag and spray something like WD40 on it. Rub down the transformers and see how they clean up. Do not, under any circumstances, use anything abrasive to try to remove the rust. Let us know how far you get and we'll take it from there. Best luck.

11/10/1999 2:03 AM
WRL	According to the 1969 catalog the Sceptre was designed to push 4-12". Tubes 1- 12AX7, 1-12AU7,1-6AN8,1-GZ-34, 2-6650. 60wRMS, 140w peak. It oughta be a gas. Congrats.

11/10/1999 3:07 AM
JD Sleep	Thanks for the information, that's great. I don't have a 4x12 cab, so I'm in trouble! I may have a newer model, the GZ-34 is not on this amp...diode rectifier. Quick survey of the layout, it looks like the reverb and tremolo are solid state, and the tremolo rate pot looks like a triple-gang pot! I've never seen that before, hope I don't need to replace that one. It looks like the tubes and caps are all still original (power tubes were gone though). The rust on the PT may be more than just surface rust. Not sure what I'll do with it if the transformers are bad. JD

11/10/1999 3:07 AM

JD Sleep

Thanks for the information, that's great. I don't have a 4x12 cab, so I'm in trouble! I may have a newer model, the GZ-34 is not on this amp...diode rectifier. Quick survey of the layout, it looks like the reverb and tremolo are solid state, and the tremolo rate pot looks like a triple-gang pot! I've never seen that before, hope I don't need to replace that one. It looks like the tubes and caps are all still original (power tubes were gone though). The rust on the PT may be more than just surface rust. Not sure what I'll do with it if the transformers are bad.

JD

11/10/1999 4:21 AM
Farrow	The triple-gang pot is just a fancy trick.. If it is bad, you can slightly change the cct. to use a single 3M pot. I have a schem if you want it. Please email me. BTW see the thread above this one "Sunn Amps," John has some useful stuff to say. I have a Sceptre also, got it used for $100 and it's the best amp I ever heard for Farfisa organ. Don't laugh. Most guitar amps won't kick out the low end like these old Sunns, and the continuous tones of organs tend to overheat al but the stoutest amps. Farrow http://surf.to/pharaohamps

11/10/1999 4:21 AM

Farrow

The triple-gang pot is just a fancy trick.. If it is bad, you can slightly change the cct. to use a single 3M pot. I have a schem if you want it. Please email me. BTW see the thread above this one "Sunn Amps," John has some useful stuff to say. I have a Sceptre also, got it used for $100 and it's the best amp I ever heard for Farfisa organ. Don't laugh. Most guitar amps won't kick out the low end like these old Sunns, and the continuous tones of organs tend to overheat al but the stoutest amps.

Farrow
http://surf.to/pharaohamps

11/10/1999 3:22 PM
John Martin	The Sunn heads have 4,8,and 16 ohm taps on the output. Only two are brought out to the back panel depending on the model. The Sceptre has 4 and 8 brought out with the 16 tied to a lug strip on the inside. When you plug in to the jack marked 4 ohm, it switches both jacks to the 4 ohm tap so that you can use either two 8 ohm cabinets or one 4 ohm cab. I wire my home built amps the same way. I own about 10 tube Sunn amps and one hybrid they called the "Solos" JM

11/10/1999 3:22 PM

John Martin

The Sunn heads have 4,8,and 16 ohm taps on the output. Only two are brought out to the back panel depending on the model. The Sceptre has 4 and 8 brought out with the 16 tied to a lug strip on the inside. When you plug in to the jack marked 4 ohm, it switches both jacks to the 4 ohm tap so that you can use either two 8 ohm cabinets or one 4 ohm cab. I wire my home built amps the same way. I own about 10 tube Sunn amps and one hybrid they called the "Solos"

JM

11/10/1999 3:26 AM
John Nickerson	Sunn amps JD, Clean off the rust with a Scotchbrite pad. Don't use any gunk (like WD-40). Keep it dry! If you can, undo the bolts and end bells and you will have a better idea of the extent of the rust. I am guessing (from past experience) that it goes down through the laminations. Gerald Weber (of Kendrick amp fame) insists that rust is magnetically conductive and will alow eddy currents. The laminations are normally insulated from one another and are there to direct the field so the transformer operates efficiently. In his theory? the rust conducts so the energy can jump from one lamination to the others, so some of the energy can run around in circles and is wasted causing the tranny to over heat and not work properly. Now are you thoroughly confused? I have mentioned this to a number of "transformer people" and none of them had an answer! So, I did a quick and dirty experiment: my friend has a Dynaco MKIII, which by the way is probably the same ckt as your amp! I am guessing looks like your rig. I plugged it in (without any tubes in it) and measured the current draw from the AC line (which was, I think, about .15 amps or so). Then I went home and measured my squeeky clean pair of MKIII's and found that they had the same excitation current! So much for that. By the way Sunn used actual Dynaco amps at first - then Dynaco iron and ckts on their own chassis! Later, they went to Schumacher - like Fender (and many others). The trannies will have an EIA code on the end bell. I don't have the book of codes here for whatever dynaco used, but Schumacher's is 606. The dyna iron was primo stuff ( very HiFi) and, I assume Schumacher was given the same specs for their trannies. Good luck

11/10/1999 3:26 AM

John Nickerson

Sunn amps

JD,
Clean off the rust with a Scotchbrite pad. Don't use any gunk (like WD-40). Keep it dry! If you can, undo the bolts and end bells and you will have a better idea of the extent of the rust. I am guessing (from past experience) that it goes down through the laminations. Gerald Weber (of Kendrick amp fame) insists that rust is magnetically conductive and will alow eddy currents. The laminations are normally insulated from one another and are there to direct the field so the transformer operates efficiently. In his theory? the rust conducts so the energy can jump from one lamination to the others, so some of the energy can run around in circles and is wasted causing the tranny to over heat and not work properly. Now are you thoroughly confused? I have mentioned this to a number of "transformer people" and none of them had an answer! So, I did a quick and dirty experiment: my friend has a Dynaco MKIII, which by the way is probably the same ckt as your amp! I am guessing looks like your rig. I plugged it in (without any tubes in it) and measured the current draw from the AC line (which was, I think, about .15 amps or so). Then I went home and measured my squeeky clean pair of MKIII's and found that they had the same excitation current! So much for that. By the way Sunn used actual Dynaco amps at first - then Dynaco iron and ckts on their own chassis! Later, they went to Schumacher - like Fender (and many others). The trannies will have an EIA code on the end bell. I don't have the book of codes here for whatever dynaco used, but Schumacher's is 606. The dyna iron was primo stuff ( very HiFi) and, I assume Schumacher was given the same specs for their trannies. Good luck

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