Pioneer SM-B200B Valve Receiver

[damiena]

I've tested all the capacitors now with an ESR meter. All the large caps have been replaced, and many of the smaller ones. The majority of them are testable in-circuit with the ESR, and are showing a good capacitance and ESR reading. A few however are not giving a reading in-circuit, however they are the same new ones as the ones that do test OK.

There are many original low capacitance ceramic caps, these won't test at all in-circuit, in fact they are lower capacitance than my ESR meter goes. Not sure what to do about these, I don't really want to unsolder them all.


And there are about 6 grey elna caps left. These won't test either. They are all located across the mode switch, bass, treble and volume potentiometers.


Then there are a bunch of Suzuki's which I have also read to be wary of. These are all inside this enclosure. I think this might be the phono stage, which is the only section that uses transistors.


I'm still working through the schematic. This is a bugger to decipher with the point to point wiring plus the resolution of the values on the circuit diagram.

The FM tuner is also working now. The guy I got it from told me it did not work at all. Possibly a bad valve connection in the FM section, however the volume level of the FM is much lower than either MW, Aux or phono so I suspect it's more than that.

[damiena]

Really need a user manual to work out how the mode and selectors work together. It's mad magic.

So far I'm cadging what I can from partial pictures from this sold manual listing! 

https://www.etsy.com/ca/listing/1219383651/original-pioneer-sm-b200a-instruction?show_sold_out_detail=1&ref=nla_listing_details

Why do you play the selector 1 MW on mono 1 but the SW, which is also on selector 1, on mono 2?

FM, which is on selector 2 plays on mono 2, but not on mono 1. This led me to believe that mono 1 is channel 1 and selector 1, and mono 2 is channel 2 and selector 2. But not according to that manual, unless it's a printing error. If anyone understands this please let me know!

[aboos]

Those small 'Suzuki' labeled capacitors are low value ceramics. These are used in the RF and IF sections - do not touch them as they most probably are parts of the RF and IF filters. If changed, all these filters need a retune which is almost impossible without the right measurement equipment. Furthermore, these are usually quite stable and do not change significantly over time. For the FM section, even unsoldering and resoldering them might detune RF circuits due to small differences in effective stray capacitances due to slightly changed positioning.

[damiena]

Those small 'Suzuki' labeled capacitors are low value ceramics. These are used in the RF and IF sections - do not touch them as they most probably are parts of the RF and IF filters. If changed, all these filters need a retune which is almost impossible without the right measurement equipment. Furthermore, these are usually quite stable and do not change significantly over time. For the FM section, even unsoldering and resoldering them might detune RF circuits due to small differences in effective stray capacitances due to slightly changed positioning.

Many thanks for the advice Andreas. That is really useful.

I don't want to unsolder anything unless it's clearly broken. I primarily want to ensure it's all safe, the fact that all the big caps have been replaced and read OK is increasing ,my confidence there. Although, I will need to measure some voltages next. My next focus is why the FM volume level is so low.

Aside from that it all sounds great and I don't think anything needs replacing to improve the sound quality. RF circuits are way beyond me and I don't want to touch 

[damiena]

I’ve been enjoying this especially today. Yesterday I gave the volume pots, the mode and channel selector switches a deep contact clean. I’d squirted a bit of contact cleaner on them when I got it and it was fine, but recently I’ve been getting noise on the volume change, and after moving into a new HiFi rack I thought I had blown an output transformer - after moving I fired it up not realising one speaker wasn’t connected  - one channel appeared dead, but it turned out it was a bad connection on the switches.

It’s working perfectly now. No bad connections, and no noise when I adjust the volume. Bliss.

I’m now more keen than ever to get this properly serviced. The two separate amp channels are not “in tune”. It’s very apparent listening to the two mono channels, they have a very different sound. One is higher volume, more punchy, better for rock and the like. The other is quieter, but more airy and spacious, it excels for vocal or acoustic recording however.

So when it comes to the mixed modes it’s unfathomable. Some records sound better set to “mix”, others on “individual”, others on “stereo R”, others on “stereo N”. I really want to find a User Manual to better understand what it’s doing on these different settings as currently I just have to ad-hoc find the best setting by ear, without fully understanding how it’s meant to be blending or separating the two channels.

[stevieg]

I assume El84 power valves? Very sweet.  Hope the tuner knob has satisfying flywheel effect when spun.
Cheers Steve

[analogadikt]

So when it comes to the mixed modes it’s unfathomable. Some records sound better set to “mix”, others on “individual”, others on “stereo R”, others on “stereo N”. I really want to find a User Manual to better understand what it’s doing on these different settings as currently I just have to ad-hoc find the best setting by ear, without fully understanding how it’s meant to be blending or separating the two channels.

Stereo R and N should be reverse and normal. In R mode the L input should output through the R speaker. You can confirm this by connecting a source to only one side and check the output.
The mix mode should allow you to mix the two channels using the balance or volume control(s).
Not sure about individual. It is likely to be some sort of mono. On some vintage amps , you can select which input channel is to be used to feed both outputs.

Regards,

Anwesh

[damiena]

Stereo R and N should be reverse and normal. In R mode the L input should output through the R speaker. You can confirm this by connecting a source to only one side and check the output.
The mix mode should allow you to mix the two channels using the balance or volume control(s).
Not sure about individual. It is likely to be some sort of mono. On some vintage amps , you can select which input channel is to be used to feed both outputs.

Regards,

Anwesh

Ahh, reverse and normal! Thank you Anwesh.

That makes sense now. What confused me was that R sounded louder than N, but I realise now when I’m adjusting the amp I am closer to one speaker - if I’m right next to the right speaker N and R will sound even more quiet/loud than they actually are do to where I’m standing. Since I moved things around the amp is positioned more centrally between the speakers, and the effect is less pronounced than before. I’ll confirm this later with a HiFi test record (not thought of doing that previously).

Mix, makes sense.

Individual - I presumed that’s just the right channel via the right speaker and left via left. But is that stereo or mono? If it was stereo, it would be no different from Stereo N, so it can’t be that. Same query regarding Mix, is it stereo or mono?

I’ll get the HiFi test record out, don’t know why I’ve not thought of that before.

[damiena]

I assume El84 power valves? Very sweet.  Hope the tuner knob has satisfying flywheel effect when spun.
Cheers Steve

The power tubes are 6BM8 (or ECL82), at least I think those are the power tubes (it has 15 tubes in total and I've yet to fully decipher the circuit diagram)

No flywheel action on the knob I'm afraid.

[stevieg]

A mighty 8 watts or so per channel.  I recently copped a pair of Aureavox arcana 82 that use the same valve. It is a triode/pentode; two valves in the same glass envelope. Have also a battleship grade Pioneer tuner. Wonderful if large and heavy. Have fun
Cheers Steve