Seeking circuit for Sony TR-6400 - UK Vintage Radio Repair and Restoration Discussion Forum

Wenlock · 27th Oct 2018, 10:13 am

Hi,

Wondering if anyone can help with a circuit for Sony TR-6400 please. I have moderate distortion and have tracked it down to the first AF transistor. I'm getting base-emitter bias i.e. 0.6V and 1.3V but nothing on the collector. Probably an open resistor?

Thanks

Wenlock

julie_m · 27th Oct 2018, 7:33 pm

An open-circuit or high-resistance collector resistor, bad solder joint or faulty PCB trace certainly could account for those readings; although I wouldn't expect any signal to reach the next stage under those conditions

Can you trace out the relevant part of the circuit from the PCB, or perhaps an enlarged close-up photograph of it? (Select the "flower" icon for "macro" mode, if available, and support the camera / phone steady for the clearest results.) If you can follow the copper traces from the collector of the transistor, you should be able to find the suspect resistor that way. If in doubt, check the continuity of the trace with your multimeter.

If you connect the base of the transistor to an external audio amplifier via a 10nF capacitor, do you get a clear signal? What about at the collector of the same transistor?

Wenlock · 28th Oct 2018, 2:16 am

Confused by the flower icon, macro isn't available on iPhone 5s unless I missed something. I'll have a bit more of look at it shortly.

I looked up the specs for the 2SC1384 transistor in question and see I had the leads confused. The voltages I have are:

C 1.3V
B 0.6V
E 0V

Doesn't look good for the transistor, I did check with an ohmmeter and get good results for b-e and b-c but there appears to be a c-e leak one way and open the other.

Wenlock · 28th Oct 2018, 9:41 am

I did try an external amplifier, but I think it somewhat inconclusive as the amplifier has far less bass and appears to sound much clearer because of that.

orbanp1 · 28th Oct 2018, 11:54 am

Hi Wenlock,

That Sony TR-6400 looks "suspiciously" close to the Sony 6R-33 radio:
https://www.radiomuseum.org/r/sony_s...6_r_336r3.html

Same number of transistors, same description, same time of production, same number of batteries for power source.
It is possible that the circuits are the same, just in a different case.
It would be worthwhile to check this out.

Here are some pictures of the TR-6400:
https://www.radiomuseum.org/r/sony_s...e_tr_6400.html
https://radioattic.com/item.htm?radio=1340021

Regards, Peter

Wenlock · 28th Oct 2018, 11:38 pm

Thanks Peter.

The transistors are different types to the TR-6400 but it does look like the circuit is similar. I’m looking at two AF transistors of the same type (both NPN rather than NPN/PNP) but likely they are DC coupled as in the 6-R33. Might try a new tone cap as I’ve got too much bass, sounds ‘woofy’ and lacks treble.

27th Oct 2018, 10:13 am	#1
Wenlock Retired Dormant Member Join Date: Oct 2018 Location: Darley, Victoria, Australia Posts: 4	Seeking circuit for Sony TR-6400 Hi, Wondering if anyone can help with a circuit for Sony TR-6400 please. I have moderate distortion and have tracked it down to the first AF transistor. I'm getting base-emitter bias i.e. 0.6V and 1.3V but nothing on the collector. Probably an open resistor? Thanks Wenlock

27th Oct 2018, 7:33 pm	#2
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Seeking circuit for Sony TR-6400 An open-circuit or high-resistance collector resistor, bad solder joint or faulty PCB trace certainly could account for those readings; although I wouldn't expect any signal to reach the next stage under those conditions Can you trace out the relevant part of the circuit from the PCB, or perhaps an enlarged close-up photograph of it? (Select the "flower" icon for "macro" mode, if available, and support the camera / phone steady for the clearest results.) If you can follow the copper traces from the collector of the transistor, you should be able to find the suspect resistor that way. If in doubt, check the continuity of the trace with your multimeter. If you connect the base of the transistor to an external audio amplifier via a 10nF capacitor, do you get a clear signal? What about at the collector of the same transistor? __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

28th Oct 2018, 9:41 am	#4
Wenlock Retired Dormant Member Join Date: Oct 2018 Location: Darley, Victoria, Australia Posts: 4	Re: Seeking circuit for Sony TR-6400 I did try an external amplifier, but I think it somewhat inconclusive as the amplifier has far less bass and appears to sound much clearer because of that.

28th Oct 2018, 11:54 am	#5
orbanp1 Heptode Join Date: Nov 2009 Location: London, Ontario, Canada Posts: 675	Re: Seeking circuit for Sony TR-6400 Hi Wenlock, That Sony TR-6400 looks "suspiciously" close to the Sony 6R-33 radio: https://www.radiomuseum.org/r/sony_s...6_r_336r3.html Same number of transistors, same description, same time of production, same number of batteries for power source. It is possible that the circuits are the same, just in a different case. It would be worthwhile to check this out. Here are some pictures of the TR-6400: https://www.radiomuseum.org/r/sony_s...e_tr_6400.html https://radioattic.com/item.htm?radio=1340021 Regards, Peter

28th Oct 2018, 11:38 pm	#6
Wenlock Retired Dormant Member Join Date: Oct 2018 Location: Darley, Victoria, Australia Posts: 4	Re: Seeking circuit for Sony TR-6400 Thanks Peter. The transistors are different types to the TR-6400 but it does look like the circuit is similar. I’m looking at two AF transistors of the same type (both NPN rather than NPN/PNP) but likely they are DC coupled as in the 6-R33. Might try a new tone cap as I’ve got too much bass, sounds ‘woofy’ and lacks treble.

28th Oct 2018, 2:16 am	#3
Wenlock Retired Dormant Member Join Date: Oct 2018 Location: Darley, Victoria, Australia Posts: 4	Confused by the flower icon, macro isn't available on iPhone 5s unless I missed something. I'll have a bit more of look at it shortly. I looked up the specs for the 2SC1384 transistor in question and see I had the leads confused. The voltages I have are: C 1.3V B 0.6V E 0V Doesn't look good for the transistor, I did check with an ohmmeter and get good results for b-e and b-c but there appears to be a c-e leak one way and open the other.