Schem. for a Sunn SA21

[Don]

I am desperately trying to salvage this amp, It just does not seem to give me the output it should. Thanks Don T. for the email on the wattage issue. But, it seems that when I bridge this amp and run to the 1/4 bridged outs the power  out suffers. The voltage should be okay, so I am not anticipating that to be the prob.
Is there any other way to bridge this amp (other than the back panel bridge switch) or is there anyway that I can test to see if its actually doing the bridge as it should?
I have a guy that will look at it but does not have the schem. I think that would be a big plus lol....

The amp just seem to act  like it is just running off one channel and then divide the power to the load... I have 2 8ohms cabs and in bridge should give me the 4 ohm load. If this amp is 600 watts and 4 ohms bridged then it SHOULD , Rock the cabs a bit, but instead I almost have to put my ear in front of the speakers to hear them.... Something is just not right.... Any Ideas...

Thanks
Don

[Don T]

Hello:
  Flip the bridge switch on the back panel and then plug a cab into the std outputs. Have signal sent to the "A" input only. In stereo mode only the "A side will have output. When switched into bridge mode both A & B should have output. A side will be normal and B will be inverted out of phase. The display should also reflect one or both channels driven when switched from stereo to bridge. The bridged outputs should now have A side connected to "tip" and the B side connected to "sleave". When in bridge mode, if the B side does not operate then open it up and look to see if the bridge switch is ok and then check to see if the "bridge input" (labeled on the board) has a wire hooked to it. The B side is the lower board as viewed with components up. Does your amp have 20-0166  or 20-0135 power boards? I have the schematic and bias adjust drawings that I can scan in. The Beta series amps used the 20-0135 board and there are drawings for it in the Beta service manual. Mailing it would be the best option if you want a real nice copy. It sounds to me like there is some sort of snafu in the connections or the 1/4" mono plugs or cable. If the B side is not inverting then it would act as you describe. could be just as simple as broken solder joints at the jack on the output board.
Don T.

[Don]

Don,
Thanks you so very much for all your help in this matter.
I am going to unrack this amp today and check out what board it has.But let me ask you this. WHen I had this thing hooked up the other night, I was running into the ch. A input which is the bridge input, I had the bridge switch set to bridge and I came out of the bridge outputs and went to the speakers. This all should be correct. I do remeber tho that the meters were only reading a very strong signal on A and just about 10% on the B meter. Should I only get signal to A (on the meter) or should both meters be working on the front equally?
 
Thanks again,
Don

[Don T.]

Hello:
 Just as an update to the ongoing repairs. We determined that the B side amp was not funtioning. My guess is that the output transistors are popped. I scanned in the schematic for the SA20-21 which can also be used for the SA10-11 with substitutions for power supply filter caps. In 82 we came up with a better bias adjust procedure which I also scanned in. This site got a copy as well.
Don T.