anyone seen this OPS before?

[gain]

i apologize for the crudity of this schematic, i drew it in ms paint as i dont have any good drawing tools.

some quick background info, i am relatively new to stereo repair although i have successfully repaired amps with EF and CFB OPS's. However i have never seen anything like this before.

i have no schematic for this amp, so this is a basic sketch i made of the main OPS components from tracing the circuit visually on the PC board.

here is what i know so far:

- Make/Model: RCA - VS 4000W. I have no schematic or service manual, i have searched extensively on the web to no avail. If anyone knows where i may find any literature on this unit, your help would be vastly appreciated.

- Left channel is blown. Both of the 2SC830's on that channel are showing low resistance (~0.6 Ohm) between collector and emitter. The two 0.5 ohm resisters are cooked.

- The predrivers (2SC984 and 2SA565) both test OK. (Diode tester shows B-E junction is good, no shorts between leads).

- All rectifier diodes on power supply are shorted, but not cooked.

- Amp does not have +/- rails. Rather, it has one +60 V rail and one ground rail. There is no negative rail. Ground rail serves as speaker negative terminal. This is an unusual configuration for me.

- There are two trimpots near the VA stage for each channels (four trimpots total). Not sure if they are both for bias adjust or one is bias and the other is for dc offset?

As of now I am planning to replace the two shorted 2SC830's and the cooked resistors and shorted diodes on the power supply, feed it a 1kHz sine wave while slowly increasing rail voltage and watching the output with a scope.

Any advice / explanation / sources of information will be greatly appreciated. I can post photos of the unit if needed.

Many Thanks,
-John

[latala]

This is as basic as an amplifier can almost be its a quasi complimentary output stage, that will be capcitor coupled to the spk ! You must check the bias network that will be connected between the bases of the drivers .
These type of output stages were all the rage in the late 60,s and 70,s
Some people like them
Naim still manufacture this type of output stage and with suitable design they can produce very low distortion
Regards Trev