Re: Sunn Sceptre
- From: John King <kingsx@xxxxxxxxxx>
- Date: Wed, 05 Jul 2006 06:29:55 GMT
Steve Luckey wrote:
"John King" <kingsx@xxxxxxxxxx> wrote in message news:KH0og.29187$VE1.22333@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxSteve Luckey wrote:I'm looking for a schematic for a 1970 Sunn Sceptre. I've checked all the obvious sources and although there are plenty of Sceptre schematics out there, they are all the same.... and all of the late '60s model, which is slightly different.
The most notable visual difference in the 1970 model is the addition of a mid boost switch on the front panel. Schematic-wise, the power supply, power amp, and 1st input stage are identical, but the tone stack is different and the solidstate reverb/tremolo board is different.
The differences are not so drastic as to make restoration impossible, but is does add a layer of frustration. The physical layout, point to point terminal strip to tube socket and neatly laced wiring harness will make drawing this circuit difficult.
Any info on this amp would be much appreciated. BTW, the amp works but I just want a valid schematic to check everything in detail.
....Thanks, Steve
Have you tried checking for Solaris schematics? They had a similar
or same separate reverb/trem board. Tone stack might be the same too,
I don't remember for sure.
Hi John. Yes, I've checked all the different models. No help. I finally gave up looking and just drew it out. Here's a copy. And I've also sent a copy to Larry's schematic heaven. Take a look....
http://home.comcast.net/~seluckey/sceptre.pdf
Here's an obscure tip for you, if you check the layout of those amps,
*all* of the preamp signal is forced through that SS verb/trem board,
and it sucks gain and tone.
Yes, the signal does pass thru the R/T board...., but only thru the LDR in the tremolo 'roach'. Sure, that knocks the signal down, but it's simply a series variable resistor that cannot suck tone. Unlike the Fender shunt type roach, Sunn choose to use a series application, hence the 'pass thru'. However, the signal loss is very well compensated in other ares of the amp. I've never heard anyone say my 'old' Sunn is not loud enough! Unless it was broken.
I once bought a Solaris that was modified with a mini switch in one
input jack hole; to bypass that whole board. The result was an amazing
boost in gain and tone. Of course, while in that mode the "effects"
didn't work. I may still have drawings and pictures of the circuit
around here if you're interested.
Yes, it would be very easy to bypass the tremolo circuit. A 1/2' jumper on a terminal strip in the preamp is all it would take. Or you could run shielded cables to a switch to do this. I don't doubt that the tone changed when you bypassed your trem, but I suspect it was due to the huge signal level (gain) increase that in turn just over drove the already high gain 6AN8 amp following the tone stack. The Sunn amps were built to be clean, warm, but powerful sounding amps. Anyone who wanted distortion just put a pedal in front of it.
One more obscure point... The reverb recovery amp is a single transistor. I'm not too keen on the Sunn reverb anyway. That single transistor is the only silicon in the reverb path and the main signal path is pure tube.
Thanks for your interest....Steve
Regards,
John King
Steve,
Sorry it has taken so long to respond. I forgot to mark
this thread. Thanks for the nice drawing.
The few of Sunn Heads I've had were Sonoro, Sorado and
a Solaris. I got the 6550 powered Sonoro first, and though
it was killer, but it didn't have reverb... So I sold it
to Walter Campbell. Bought the Solaris with the bypass
switch for reverb & tremolo. It had EL-34s and only sounded
ok to me at best; but the bypass mod really was a significant
boost in tone and gain, almost into the range of a "high gain"
amp.
Simple, and certainly worthwhile for anyone into such
tone, but as you said, the warm clean was what I appreciated
about them. The last one I had was a Sorado that had KT-88s in
it, though probably came from the factory with 6550s. At any
rate, it sounded great.
I'll have another one of these days if the right deal comes
along on a keeper. I should have kept the KT-88 equipped one.
Oh, and the guy that did the "mod" on the Solaris... didn't
use properly terminated (grounded) shielded wire in the circuit,
so it was a little more noisy that it might otherwise have been.
Like I said though, worth the trouble for anyone that wants
to be able to get a "high gain" sound our of one of the effects
equipped Sunns without having to resort to a pedal.
Regards,
John King
.
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