Kenwood Trio stereo receiver KW20

[ghzi]

Recently I have obtained a Kenwood Trio KW-20 stereo receiver. Each channel has one EL84 single ended, not a push-pull. I looked for schematics of this receiver through Google and turns out nothing. All I found are either KW-33 and KW-220 and some others. The configuration are completely different.

Does anyone have a copy of the schematics?

 

[arts]

Are you certain that it is not a KW-22?

 

[Tom Bavis]

Perhaps the same as Lafayette LA-215?

 

[ghzi]

Are you certain that it is not a KW-22?

You are right. It is KW-22, my mistake. But still, I don't find any information on KW-22 either except a few pictures of the unit, no schematics.

 

[ghzi]

Perhaps the same as Lafayette LA-215?

Tom, thank you very much. It looks very similar to the circuit I see. Probably it was the same design. I have verified a few details that matches the circuit I see in the unit. Thanks again.

 

[BinaryMike]

There are some interesting features in that schematic, and at least one error: The 210V screen voltage given for the 6BA6 driver tubes has to be wrong.

 

[Tom Bavis]

The Lafayettes of that period were made by Trio/Kenwood, may be the same unit. I have a pair of output transformers that I think came from one of these.

 

[Dandy]

There are some interesting features in that schematic, and at least one error: The 210V screen voltage given for the 6BA6 driver tubes has to be wrong.

It's interesting to wonder how an illogical error like that gets through. What other features of the circuit interest you?

 

[BinaryMike]

What other features of the circuit interest you?

The way DC power for the preamp heaters is derived, and then used for 'fixed bias' which is itself unusual in this class of equipment. I say 'fixed bias' in quotes because I believe it actually operates somewhere in between classical auto-bias and fixed bias. Output tube current probably accounts for something over half of the total current flowing in the negative heater/bias side of the power supply.

 

[Dandy]

I believe Trio does a similar thing with DC heater power for the phono stage tubes in their other tube receivers; at least they do in my W38.