TR-707a Recap

dpcornell

Member
Hello all!

One of my many projects is a lovely TR-707a I purchased some time ago. It has sat until now, since I have been learning how to read schematics and successfully recap receivers.

Has anyone else recapped one of these before? I'd appreciate the insight on the equivalents for the various black diodes (Sony B378A, B381, and the SW-05, 15).

I've got my parts list mostly lined up with the exception of two 3uF 10v caps. I've found this cap: https://www.mouser.com/ProductDetai...GAEpiMZZMsh%2b1woXyUXj9WY2Sz0t6jR9mabXrOSsgg=
But it really seems like overkill. Any suggestions?

Is there a general consensus on keeping the incandescent lamps or switching to LEDs?
 
I am watching this thread like a hawk. Actually am listening to my TR-707A right now since my Sansui 210 is awaiting new output transistors. Can I tap your brain just a bit on your TR-707A? Would love to compare notes with another owner/fan of this receiver. I don't want to hijack your thread so here just want to say I am watching and very interested to see what you do. I have not recapped mine but did replace the outputs which were blown when I got it. The fixed bias design makes this receiver interesting to work on. But man it sounds sweeeeeeeeet. In terms of bulbs, there are the fuse style bulbs which I personally prefer using incandescent bulbs for. They need to shine through the side of the glass display and I never could get LEDs to shine enough of their light into the glass since they are so directional. Your luck may vary with a different LED. I know some LEDs are more directional than others. There is also the matter of the bulbs with the screw on base such as the VU meter illumination and the FM stereo indicator. My stereo indicator went out and for that I just got a generic white LED and soldered it onto the original bulb socket and then pressed it right up against the red plastic lens for the indicator. It works like a champ and looks good. For the VU meter, I found some NOS of those bulbs when radio shack had them but unfortunately I am out now and haven't had luck finding the right bulb with that threaded base. You might try an LED for the VU meter or getting another style bulb base and bulb and replacing the screw base which seems to be hard to source for.
 
I have just started on mine and the schematic I have printed shows 3UF 25WVDC caps on the pre amp board, but mine has 10UF 12WVDC caps on the board. The schematic on the lid of mine shows 10UF not 3UF. Also mine used 2SD46 outputs and 2SC115 drivers. This is what the schematic on mine shows, but that does not match the one I downloaded from the internet.
 
I have just started on mine and the schematic I have printed shows 3UF 25WVDC caps on the pre amp board, but mine has 10UF 12WVDC caps on the board. The schematic on the lid of mine shows 10UF not 3UF. Also mine used 2SD46 outputs and 2SC115 drivers. This is what the schematic on mine shows, but that does not match the one I downloaded from the internet.

Interesting. I found some differences between schematic and the as-built in mine too. The original drivers are 2SC696 and 2SC245 outputs in mine. Two outputs were bad on one channel when I got mine so I have replaced all 4 with 2N5885 motorola. 2N3055 also worked for a time but have since changed to the 2N5885. Once I'm done repairing my Sansui 210 I look forward to turning attention to the TR707a again.
 
I was concerned about the transistors as well, but they are correct according to the schematic on the top cover. I did notice that mine has 4 caps on the driver board by the driver transistors where some have only 2. There must have been some run changes on this model. I have both channels working now, but it really doesn't sound good and doesn't have the output it should. I have checked the transistors and they check ok. I think a good recap will help.
 
It looks like the voltage across C180 and C183 which are 2000uf coupling caps should measure 27V. Maybe take a measurement there and see if it is off. If so I'd start with just recapping the power supply and then see how she performs.
 
Is everyone happy with their schematic? I have the factory one if needed.
And could use a final updated cap list.
Mine is running good with hums and hisses.
 

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Is everyone happy with their schematic? I have the factory one if needed.
And could use a final updated cap list.
Mine is running good with hums and hisses.

That's where I'm at as well Brutha. Nice sounding receiver but just a bit more hiss than I'm comfortable with. I have always felt if I could fix the hiss, this would hands down be the best sounding receiver I own.
 
Well then the question I would ask is,,,,
Does anyone have one of these up and going 100% yet?
And if they do what does it sound like?
What else do you have as a reference for us?
 
I've honestly never heard another receiver quite like it. It sounds powerful, really drives the speakers. It also is very detailed, bringing out all kinds of nuances in the music. Lots of presence. Tight bass. Downsides have been the hiss. Not so much hum for me but hiss. The volume seems touchy like it only needs to be turned a little to get to listening volume.
 
Alright everyone, since I'm trapped inside during this northeastern snow storm (what a way to spend spring break) I have *almost* finished putting together a list of capacitors.
I'm doing this on a more budget conscious level, so some of the higher working voltage capacitors could be replaced with different ones if you don't feel they are appropriate.

For most of these I took the highest voltage and used that. It isn't much cheaper to buy a 10v capacitor over a 25v or 50v capacitor and it should not make much of a difference anyway.
Some uf were unavailable or expensive, so they were substituted within 20%.

uf wv
0.001 400 axial (6 total) [Mouser Part Number 505-MKP10-10006305P7]
0.005 400 (1 total) [Mouser Part Number 667-ECW-H8512JV]
0.01 600 axial (1 total) [Mouser Part Number 598-103MMR630K]
0.47 25 (3 total) [Mouser Part Number 505-MKS2C034701C00MS]
3 10 axial (2 total) [Mouser Part Number 598-335CKE050M]
10 12 (16 total) [Mouser Part Number 598-106RSS016M]
25 25 axial (1 total) [Mouser Part Number 75-TVA1306]
30 25 (25 total) [Mouser Part Number 710-860240472002]
100 15 (1 total) [Mouser Part Number 140-TEA101M1HBK1017P]
200 50 axial (1 total) [Newark Part Number 65K2227]
200 25 axial (3 total) [Newark Part Number 97M3994]
200 25 (6 total) [Mouser Part Number 661-EGXF161ELL201ML2]
500 6 (4 total) [Mouser Part Number 667-EEU-TP1E511]
500 25 axial (2 total) [Newark Part Number 97M5050]
1000 60 (1 total) [Mouser Part Number 647-UVR1J102MHD]
2000 60 (3 total) [Mouser Part Number 871-B41231A8228M000]

The total for these is about $35 so far.

The last capacitors I need are one 400uf 40wv safety capacitor and one 5uf 10v.

I will also be adding some LEDs. I think if properly positioned some of the directional LEDs will light the glass dial quite nicely. I'll add those once I get the receiver up and running correctly.

Finally, does anyone have experience substituting radial capacitors for axial? Radials are significantly cheaper and if possible, I'd like to use them.

I've read that it is possible to bend the negative lead over the capacitor and insulate it, keeping the positive end short. Thoughts?

Edit: I've also noticed that the service manual was different that what was in my unit. I would recommend taking an inventory of what you need specifically, before ordering anything.
 
Alright everyone, since I'm trapped inside during this northeastern snow storm (what a way to spend spring break) I have *almost* finished putting together a list of capacitors.
I'm doing this on a more budget conscious level, so some of the higher working voltage capacitors could be replaced with different ones if you don't feel they are appropriate.

For most of these I took the highest voltage and used that. It isn't much cheaper to buy a 10v capacitor over a 25v or 50v capacitor and it should not make much of a difference anyway.
Some uf were unavailable or expensive, so they were substituted within 20%.

uf wv
0.001 400 axial (6 total) [Mouser Part Number 505-MKP10-10006305P7]
0.005 400 (1 total) [Mouser Part Number 667-ECW-H8512JV]
0.01 600 axial (1 total) [Mouser Part Number 598-103MMR630K]
0.47 25 (3 total) [Mouser Part Number 505-MKS2C034701C00MS]
3 10 axial (2 total) [Mouser Part Number 598-335CKE050M]
10 12 (16 total) [Mouser Part Number 598-106RSS016M]
25 25 axial (1 total) [Mouser Part Number 75-TVA1306]
30 25 (25 total) [Mouser Part Number 710-860240472002]
100 15 (1 total) [Mouser Part Number 140-TEA101M1HBK1017P]
200 50 axial (1 total) [Newark Part Number 65K2227]
200 25 axial (3 total) [Newark Part Number 97M3994]
200 25 (6 total) [Mouser Part Number 661-EGXF161ELL201ML2]
500 6 (4 total) [Mouser Part Number 667-EEU-TP1E511]
500 25 axial (2 total) [Newark Part Number 97M5050]
1000 60 (1 total) [Mouser Part Number 647-UVR1J102MHD]
2000 60 (3 total) [Mouser Part Number 871-B41231A8228M000]

The total for these is about $35 so far.

The last capacitors I need are one 400uf 40wv safety capacitor and one 5uf 10v.

I will also be adding some LEDs. I think if properly positioned some of the directional LEDs will light the glass dial quite nicely. I'll add those once I get the receiver up and running correctly.

Finally, does anyone have experience substituting radial capacitors for axial? Radials are significantly cheaper and if possible, I'd like to use them.

I've read that it is possible to bend the negative lead over the capacitor and insulate it, keeping the positive end short. Thoughts?

Edit: I've also noticed that the service manual was different that what was in my unit. I would recommend taking an inventory of what you need specifically, before ordering anything.
I don't have any experience with caps at all.
I will probably order your list and reorder at the end as needed.
Can't wait to get you opinion of the finished unit.
Thank you for the list.
 
Is everyone happy with their schematic? I have the factory one if needed.
And could use a final updated cap list.
Mine is running good with hums and hisses.
I would like to see the factory schematic. I have 2 different ones. is it small enough to be emailed?
 
Last edited:
That looks like one I have a pdf of. if it shows 2sc245 outputs it does not match my actual receiver. I would still like to compare the schematic.
 
That is the manual I have. My receiver has a schematic pasted on the lid, but it is kinda small. My receiver matches the one on the lid, but not the one in the service manual. I will try to make a picture of it tomorrow. It uses 2sd45 output transistors, and different drivers.
 
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