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I'm not sure if there's something going on with my '68 Sunn Sorado, but I can't seem to get a good response (playing guitar) with any pedal I'm putting in front of it. Pedals that normally sound excellent through all my other amps. I've tried different cabs, different guitars, different pedals, with mostly the same result. The only thing I can pin point that's different about this amp compared to my other amps is that it has a tube rectifier. I'm not sure if this is what people call "sag" but every pedal I throw in front of the amp cuts the volume, sounds slughish and squishy, and has zero to low bass response. Almost like the pedal seems to "sound" out of phase. I've also tried using a Bigshot to swap phase with no luck. Here's the thing, the amp sounds EXCELLENT with a direct signal, no pedals. Just as all other of my amps do. Thick and beefy, loud, good cleans, etc. A bit of sag when cranked and volume drop from being fuzzed out, but still sounds great at its volume/headroom peak, which is volume around 6-7. The only two pedals I've gotten to not cut volume or low end have been my Pharaoh and my TAFM, and it's only at certain settings. The amp has been re-capped, stock circuit, Winged =C= 6550 tubes, Mullard rectifier, basically in great shape. And I'm mainly only having this issue with guitar. It seems to sound and perform well with pedals on bass. Some pedals I've tried with it on guitar with the issue I'm explaining have been: Elements, Mini, Fuck, MKII, Bluebeard, Rat Tail, Rat King, and the two I previously mentioned.

So, I'm curious to hear from anyone else playing tube rectified Sunn amps:
A) have you ran into a similar issues?
B) what pedals are you using with which model head?
C) what's the rest of your set up (cab, speakers, etc)?


Any feedback or opinion on what the issue on my particular head has (if it's only me having this issue? Maybe I just need a new rectifier tube?) is appreciated.
Thanks, friends!

Pre amp tubes?
Do you have like a 12au/at in there that just can't handle getting smashed by that much pedal generated awesome?
I dunno dude, I'm at a loss.
I would think tube rectifiers shouldn't effect what is essentially a front end issue.

Iommic Pope wrote:Pre amp tubes?
Do you have like a 12au/at in there that just can't handle getting smashed by that much pedal generated awesome?
I dunno dude, I'm at a loss.
I would think tube rectifiers shouldn't effect what is essentially a front end issue.

Yeah, man. I'm puzzled as fuck and I've been pretty knowledgable as far as all my other amps, which are all vintage tube amps. The pre is a Mullard 12AX7 and the PI is a Sylvania 6AN8. I just put in a pair of GE 6550's I had laying around, and I'll try a different preamp tube just in case.

i bought a sunn 200s many years ago and felt more or less the same. Im pretty sure the 200s and sorado have the same design with different part values to voice for guitar and bass.

i was using it mostly for bass but really love high gain synthy esque fuzzes which sounded not as great on this as my other amps. I recapped the power section and replaced the tube rectifier with diodes. Rebiased it a bit and then it sounded amazing clean and with pedals. I really recomend changing to diode rectification.

edit: you just have to rebias it because the B+ supply voltage will increase a bit when you go to diode vegas. Its not like biasing it is what changed the sound imho.

Just play bass, it's better anyways.

multi_s wrote:i bought a sunn 200s many years ago and felt more or less the same. Im pretty sure the 200s and sorado have the same design with different part values to voice for guitar and bass.

i was using it mostly for bass but really love high gain synthy esque fuzzes which sounded not as great on this as my other amps. I recapped the power section and replaced the tube rectifier with diodes. Rebiased it a bit and then it sounded amazing clean and with pedals. I really recomend changing to diode rectification.

edit: you just have to rebias it because the B+ supply voltage will increase a bit when you go to diode vegas. Its not like biasing it is what changed the sound imho.

Thanks. This is what I've been planning on doing. The 200s and Sorado are identical minus the cab they came with. And I was definitely aware of rebiasing post rectifier sub. I know regardless of playing bass or guitar, this should tighten up the low end, which would be nice considering our tuning (which really isn't too far down) and volume we play at. Just seems like the only logical reason why this is happening since, again, non of my other amps are tube rectified.

Hope more players/owners chime in.

I have a 200s and have no issues like what you mention

Jero wrote:I have a 200s and have no issues like what you mention

Tube rectified? Guitar? Particular pedals and/or speakers you use?
Thanks.

I had a Sceptre and I didn't think it took pedals as well as my non tube rectified amps. Not sure if it was my particular Sunn, but I did notice the same sort of sag that I didn't personally care for. Don't they make Solid State rectifier drop in 'tubes' now? Maybe give that a go?

skullservant wrote:I had a Sceptre and I didn't think it took pedals as well as my non tube rectified amps. Not sure if it was my particular Sunn, but I did notice the same sort of sag that I didn't personally care for. Don't they make Solid State rectifier drop in 'tubes' now? Maybe give that a go?

Thanks, Skully. They do made SS rectifier replacements. It's just kind of a pain in the ass, I would have to re-bias the amp and that means taking it in because I don't have a bias meter/tool. But it seems this will be the best solution for this sag issue.

Jero wrote:I have a 200s and have no issues like what you mention

I had a 200s and I never had any issues like that.

Thanks.
Again, I'd love to know which pedals were used to sound good. And not all of the old Sunn amps were tube rectified. They converted to SS/Diode around '70-'71. Just wanna be sure we're all on the same page a far as talking about only the tube rectified models

I used to own a tube rectified Sunn Sorado from the same time frame and never had any noticeable problems with it taking pedals.
I used it for guitar with a 412 loaded with G12H30s and a 215 with Legend 1518s.
The only difference in mine and yours is that I was using JJ KT88s and the preamp and rectifier were JJ's as well.
The PI was Amperex or something similar.

Pedals Used:
Pharoah
Supercollider
Centurion
Megalith
Heavy Machine
Hoof
PPB
Doomidrive
OX Fuzz
I'm sure there's more.

Have you checked the Bias? I usually ran mine on the colder side.
I did notice that if I cranked the volume, the amp sounded weaker so I kept the volume around 4 and
slammed the front end with volume from the pedals.
I don't think I had a single coil guitar at the time so it was always humbuckers.

Insuborination bought it from me so maybe he'll chime in too.

chillerthanmost wrote:

skullservant wrote:I had a Sceptre and I didn't think it took pedals as well as my non tube rectified amps. Not sure if it was my particular Sunn, but I did notice the same sort of sag that I didn't personally care for. Don't they make Solid State rectifier drop in 'tubes' now? Maybe give that a go?

Thanks, Skully. They do made SS rectifier replacements. It's just kind of a pain in the ass, I would have to re-bias the amp and that means taking it in because I don't have a bias meter/tool. But it seems this will be the best solution for this sag issue.

The Sorado is SUPER easy to bias. You can probably do it by ear even.
If not, you can get a bias probe for around $20 and you are good to go as long as you have a multimeter.

Thanks MEC. And thanks for the info from your rig. I don't have a multimeter nor a bias probe, but I'll definitely look into it. I know the bias pot is right in between the two power tubes. I might try some KT88's when I replace the rectifier.

Thanks for the replies. Still interested in hearing from other owners, preferably with detailed info.