Sansui G7500

[Super Noob]

Tone Control Boards:

Old Parts:

 

[Super Noob]

Selector Board:

Before:

After:

 

[kevzep]

I see you're using the Nichi KT series, I used those for Audio Path and low voltage PSU.....

Would not hurt to check for any VD1212 or MV12 diodes in there too...it would not surprise me if there were a few...

 

[Super Noob]

I see you're using the Nichi KT series, I used those for Audio Path and low voltage PSU.....

Would not hurt to check for any VD1212 or MV12 diodes in there too...it would not surprise me if there were a few...

Doing these picks on the phone in the airport is not ideal.

KA where possible... I did miss three caps. Two BP 220uf on the selector and one 470uf low voltage on the tuner board. Think I did see some double diode packages in there. Few more parts are coming and I will replace those double diodes.

 

[kevzep]

Doing these picks on the phone in the airport is not ideal.

KA where possible... I did miss three caps. Two BP 220uf on the selector and one 470uf low voltage on the tuner board. Think I did see some double diode packages in there. Few more parts are coming and I will replace those double diodes.

Ah, KA.....Nichi have a never ending series of great caps, as soon as I think I have my formula nailed, then someone else is using something I never knew about!!

Yeah, phones are fiddly for doing that sort of thing...

 

[Super Noob]

Before -Filter Caps:

Soldered on Some Ring Terminals.

After:

 

[Super Noob]

Repasting Outputs:

 

[Super Noob]

Offset:

Bias - Each Channel:

 

[kevzep]

Repasting Outputs:

Like my grandfather used to say, "a little dab will do ya"........

 

[Super Noob]

Like my grandfather used to say, "a little dab will do ya"........

Paste is a little heavier than I normally go... but I was finessing a bit more than typical to get the outputs back into place.

 

[ghazzer]

Nice work!

I like the fact that the G7500 mounts the emitter resistors on the F-2980 bd rather than on the smaller card with the OP TRs as Sansui did with the G-5/6/7700. Since the wiring is the same, is there any reason that those emitter resistors cannot be re-located to the F-2980 bd?

 

[Super Noob]

I bought some .33 ohm resistors:
Dale 5 Watt 5% .33 ohm Wire Wound

Was going to replace the sand block resistors... but I wanted to check the tolerance of existing emitter resistors.

 

[ghazzer]

I think that the OEM ones are 5%. 0.33Ω X 0.05 = 0.0165Ω.
The SM lists the tolerance for "bias voltage" as 5mv±1mv, or ±20%.
The more critical thing is to get a good reading on the resistance of each emitter resistor so that you can correctly compute the bias current, spec'd at 5mv/0.33Ω=15.15mA. If your emitter resistors are other than 0.33Ω you will need to recompute what your "bias voltage" should be.

I don't know how critical this value is, but I always try to meet the mfg spec.

 

[Super Noob]

I think that the OEM ones are 5%. 0.33Ω X 0.05 = 0.0165Ω.
The SM lists the tolerance for "bias voltage" as 5mv±1mv, or ±20%.
The more critical thing is to get a good reading on the resistance of each emitter resistor so that you can correctly compute the bias current, spec'd at 5mv/0.33Ω=15.15mA. If your emitter resistors are other than 0.33Ω you will need to recompute what your "bias voltage" should be.

I don't know how critical this value is, but I always try to meet the mfg spec.

Bias is +\- 10mV
FYI

 

[kevzep]

I think that the OEM ones are 5%. 0.33Ω X 0.05 = 0.0165Ω.
The SM lists the tolerance for "bias voltage" as 5mv±1mv, or ±20%.
The more critical thing is to get a good reading on the resistance of each emitter resistor so that you can correctly compute the bias current, spec'd at 5mv/0.33Ω=15.15mA. If your emitter resistors are other than 0.33Ω you will need to recompute what your "bias voltage" should be.

I don't know how critical this value is, but I always try to meet the mfg spec.

There really isn't a need to be this precise with the bias, you just want to start some idle current flowing, there's no magic to it.
However, if you do want to be "that precise" you can always look at one of the first gain stages in the pre-driver section, and observe the crossover distortion, then wind in some bias until the crossover distortion disappears....job done, but the window for that is fairly large so not too difficult to achieve the optimum without having to go down that road...I admit though, if I don't know or can't find an amplifiers spec, I'll do this method to find that ballpark zone....

 

[ghazzer]

Bias is +\- 10mV
FYI

My bad - I was looking at the G-6700 SM.

 

[Super Noob]

Here is the verified list for anyone's use.
https://drive.google.com/open?id=1j_WBNq3qldudEGYMVne9oyl-AdDu8EwV

Changed a few more parts:

New LEDs

 

[Super Noob]

Change Out the Speaking Spring Clips:

Added Ring Terminal to the Internal Wires

Was Happy with the Results

 

[Super Noob]

Call it Done.

Listening to It Now = Nice.

Time to Find the Next Project.

Thanks for Viewing.

 

[Hipocrates]

Nicely done!, kudos!