Hello Tube Amp community,
I am working on a Sunn 1200S from 1969 and I am looking for the the proper schematic. I found a schematic off of EL34 world for a later 1200S but it shows a Diode rectifier, the amp I am working has a tube rectifier.
The issue here is that the amp is motorboating. There was some work done to the amp recently, a new three prong power cord and new filter capacitors from the looks of it. The power cord was installed incorrectly causing the fuse to blow which I was able to fix. I would like to know the the correct value of the filter capacitors to see if the correct ones were installed. That's really what I am looking for off of the schematic.
Any help would be greatly appreciated.
Dan
Sunn 1200S Schematic
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Stevem
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Re: Sunn 1200S Schematic
This is a 2000S which is likely what your power supply is .
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When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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Stevem
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Re: Sunn 1200S Schematic
That’s a 1971. He’s got a 69.
With todays average wall voltage the first two filter nodes really need to be made up of stacked 300 volt filters with balance resistors.
With todays average wall voltage the first two filter nodes really need to be made up of stacked 300 volt filters with balance resistors.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Sunn 1200S Schematic
frag jan zuerst sells 550v caps that are speced for 600v surges
Re: Sunn 1200S Schematic
Does the 1200S have the Tremolo and Reverb board ? The earliest amps did not have this PCB and only had four knobs. Later amps added a small circuit board with solid state circuitry for Reverb recovery and an optical Tremolo oscillator. The Reverb drive was a tube with a matching transformer. These amps had seven knobs.
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Kagliostro
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1 others liked this
Re: Sunn 1200S Schematic
I suppose that as the Solid State Rectifier version also your 1969 amp has 4 Power Tubes
You don't specific which is the Tube Rectifier on your amp and say
Assuming it is a GZ34 like in the Sunn Sceptre of 1969 (but will it be able to feed enough current for 4 Power Tubes ?)
you can see that the first cap is a 30uF rated 525V
on datasheet the GZ34 first e-cap max value is stated at 60uF
so 30uF to 60uF is the range in wich you can put the first e-cap value
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Is the Tube Rectifier really one and is it a GZ34 ?
Franco
You don't specific which is the Tube Rectifier on your amp and say
has a tube rectifier (no more I suppose).... the amp I am working has a tube rectifier ....
Assuming it is a GZ34 like in the Sunn Sceptre of 1969 (but will it be able to feed enough current for 4 Power Tubes ?)
you can see that the first cap is a 30uF rated 525V
on datasheet the GZ34 first e-cap max value is stated at 60uF
so 30uF to 60uF is the range in wich you can put the first e-cap value
---
Is the Tube Rectifier really one and is it a GZ34 ?
Franco
Re: Sunn 1200S Schematic
Thank you all for the replies.
The tube rectifier is two GZ34 tubes. There are two 3-10C chokes, the first two installed Caps measure at 100uF.
This Amp has 7 knobs and a PCB. Knobs are labeled Reverb, Depth, Rate, Contour, Bass, Tremolo, Volume, and a Midboost Switch. It has a 12Au7 tube and a small transformer. The only reason I said it was a 69 is because there is a date marked on the inside of the chassis coupled with the fact that it is a tube rectifier, I could be mistaken on this model year though.
So far it looks like the schematic of the 2000s posted by SteveM is the closest.
The tube rectifier is two GZ34 tubes. There are two 3-10C chokes, the first two installed Caps measure at 100uF.
LOUDthud wrote: ↑Wed Oct 29, 2025 8:57 am Does the 1200S have the Tremolo and Reverb board ? The earliest amps did not have this PCB and only had four knobs. Later amps added a small circuit board with solid state circuitry for Reverb recovery and an optical Tremolo oscillator. The Reverb drive was a tube with a matching transformer. These amps had seven knobs.
This Amp has 7 knobs and a PCB. Knobs are labeled Reverb, Depth, Rate, Contour, Bass, Tremolo, Volume, and a Midboost Switch. It has a 12Au7 tube and a small transformer. The only reason I said it was a 69 is because there is a date marked on the inside of the chassis coupled with the fact that it is a tube rectifier, I could be mistaken on this model year though.
So far it looks like the schematic of the 2000s posted by SteveM is the closest.
Re: Sunn 1200S Schematic
Correction, the Chokes are not labeled 3-10C. The number on the two chokes is 27-3100 -- 606927
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martin manning
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