Flea market find

[Chuck H]

Interesting. Also just thinking out loud now, but wouldn't 60Hz be a low enough frequency to be included in the mono portion of the amplification with almost none getting past the 200Hz filter? More lily gilding?

[gui_tarzan]

Notice full power reaches a woofer boc, with an added low pass filter. I wonder why you crossed it out because itīs *essential* for this system.

As I said, the top schematic is not this amp, but it was the closest schematic I could find after searching for three hours. That's why I crossed it off, this amp does not have those components.

Sorry for the confusion, that's why I am drawing my own based on the actual amp.

In any case, the amp looks more like a "proof of concept" job than anuthing else.
Maybe it was designed by an Engineer experienced in disc cutting Electronics and he applied his specialized knowledge here..

Could be, however the only connectors on this were normal power in, power out through a harness, audio in and audio out. The best I can come up with is it's a CBS/Columbia stereo unit, possibly out of a phonograph console. The tubes have CBS printed on them along with "made in Great Britain" on the rectifier and the 12AX7/ECC83, and "made in Germany" on the one 6BQ5/EL84. I wish the other 6BQ5 was there but it was gone when I got it.

[gui_tarzan]

I'm not the circuit guru around here really. I have no issue with the thing as drawn. It simply has an extra stage of filtration before it starts using it. Less ripple hits things. Might be gilding the lily, since push pull stages tend to cancel B+ ripple. But it costs a few volts to get smoother DC.

The more I think about this, the more I'm thinking you're probably right about extra filtration. That's the only thing I can come up with since there are no other parts hooked up to it.

[Enzo]

I still believe that, same reason those Champ models added the stage. But Juan appears to be right as well, I was ignoring the preamp, so this is essentially a pair of single ended amps sharing a transformer. On the other hand, the two sides don't know their grid signals come from different sources, so they still ought to cancel B+ ripple in the power tube stage.

[gui_tarzan]

Here we go. I will double check this again after I get some sleep but I am pretty confident it's exactly the way the amp is set up. I just need to identify the combo resistor/cap parts and the pot values. I have to believe the plates on the 12AX7 are getting B+ through that combo part since lead four goes to B+.

I haven't checked voltages since all I've done is map out the circuit.

[Enzo]

So get out the ohm meter.

B+ goes into D and I expect a resistor (100k?) from D to A and F.

From A and F I expect a coupling cap to B and E.

B and E ought to also have a resistor each to C. (220k-470k?)

What's that, six parts? Likesiwe the other one is tone stack parts.

[gui_tarzan]

Oh yeah, that's the next step.

[jagora]

Hey Enzo,
How can I start a new thread ?

[Jazz P Bass]

http://music-electronics-forum.com/n...newthread&f=48

Up top: click on 'Forum'
Then pick which forum you want.

[Enzo]

New thread? Look at the main menu, pick a topic (music electronics, or schematic request, or whatever). Open the topic. Upper left or the topic menu, is a start new thread button. CLick it.

[jagora]

Thanks Mr. Jazz P Bass,
My first guitar was a Schecter C4 Custom Bass, Love it, But never really understood how to play it as a solo instrument
Thanks for the help regarding the forum

Joe

[jagora]

Mr.Enzo,
That's great information and I thank you for acknowledging my question. I really like this type of forum because I actually went through an Aviation Communication and Navigation system electronic course 10 years ago. The bench tests and basic principles of resistors, diodes, transformers never really sunk in. Especially how to test using an oscilliscope and reading the sine wave. Now I have a greater appreciation for the Art of repairing micro circuits and semi conductors.

Thanks for the assistance
Joe

[jagora]

Wow, I am very impressed with the depth of knowledge you have Mr. Fahey,

I've also traveled extensively through the Country and have even lived their temporarily. Always considered relocating there.

Joe

[jagora]

Thanks, I'll try participating

Joe