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-   -   TO-3 SYMASYM (https://www.diyaudio.com/forums/group-buys/187592-3-symasym.html)

evette 21st October 2012 01:43 PM

Mr. CJKPKG I have a suggestion send me your bad board and I,ll send you a blank board you can re-built another board and I,ll fix the one you send me. Regards Evette

joshvi 21st October 2012 02:31 PM

Carl,
Do what Andrew T. told.on post 554. Or measure the collector,emitter,base voltages of all transistors with reference to ground (0v)and post it.This information will help us to diagnosis the problem

joshvi

Rudi_Ratlos 21st October 2012 03:00 PM

1 Attachment(s)
Carl, do not yet give up! We (!) will do our best to enable you to fix the error.
Find attached a picture with the currents flowing, when you do the adjustment of the SYMASYM. But I wonder, if the image will help you.

Please tell me, what you did wrong.
I know from your post that you forget to isolate the back of the BD139 TEMPCO transistor. But his cannot be the only error.
Did you also forget to put "shoulder washers" beneath the screws of the drivers (MJE15030/MJE15031)?

Best regards - Rudi

AndrewT 21st October 2012 03:30 PM

BTW,
that marked up diagram shows two very useful bits of info.

1.) 1.225uA flowing into the bases of both input transistors. That combined with the 22k resistors gives identical voltage drops across these resistors. If the other ends of these resistors are at Zero Volts, then the bases of the input transistors MUST be at the same voltage.

2.) The currents in the input collectors and in the input emitters and in the input bases are all identical to their partners. This is the ideal you want when setting up your amplifier. If you have selected your 680r and your two input transistors well, then the Zero Volts from 1.) must ensure you have virtually 0.0mVdc of output offset.

A small error in Vbe between the two input transistors will result in a small error in output offset, if you have ensured that all the currents are equal as shown in the schematic.

cjkpkg 21st October 2012 03:39 PM

1 Attachment(s)
Shoulder washers installed...everything isolated....Here are the voltages.

First thing that comes to mind is why are the 0302s running at -125mV?

AndrewT 21st October 2012 03:42 PM

Please, voltages on the schematic as done for currents in post565.

Don't let the probes slip. That may/will blow up the amplifier.
Are your probes insulated? Right down to 1mm from the tips?

!!!
that PCB is not a To3 Symasym !!!

cjkpkg 21st October 2012 03:50 PM

And could someone please clarify how to hook up the A/C to the speaker protection circuit?

The text, diagrams, and instructions all seem to say something different.

Do I hook up one of the complete secondary windings to the A/C input or just one leg of A/C and one to earth ground?

AndrewT 21st October 2012 03:53 PM

don't connect any speakers until you have proved that the amplifier is working properly for at least a few switch on/offs and for a lengthy warm up.

cjkpkg 21st October 2012 04:00 PM

understood...I just want the small victory of hearing a "click" so that I know I can do SOMETHING right...

AndrewT 21st October 2012 04:15 PM

if DC is higher than threshold of the "trigger" then the relay will not pull over.


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