Pioneer SM-B201 tube receiver rebuild project

Fongolio

I aquired a vintage Pioneer tube receiver from a flea market the other day. The model # is SM-B201. It's a dual tuner type (two tuners for both AM and FM..one for each channel). It's almost all there. All tubes are present and appear to be working but the GZ34/5AR4 rectifier is not original and I don't think working to spec. It plays in stereo when hooked up to a cd player but is very distorted. I suspect electrolytic caps and some resistors are out of spec. I've finally found a tube tester in my area and will be testing all the tubes. I was drawn to this piece by its good looks and the fact that it's the earliest Pioneer I've ever seen. Manuals, schematics and parts will be very hard to find I'm sure but I really want to see this unit run like new. After the success of my Eico ST-70 rebuild I feeel confident I can reserect this beast from the ashes. I paid $100 for this unit and 5 really good records so my initial investment is very small.

I've attached pics for your viewing pleasure.

Joe08867

I was looking this up on the internet yesterday. Two Tunas to get you your music Soona. Very unique piece you got there.

I look forward to seeing your progress.

mhardy6647

As you probably know, the dual AM and FM tuners are from the pre-MPX days of AM-FM simulcast stereo. One channel on AM, the other on FM. One of the side benefits is that the AM sections in the simulcast tuners and receivers were of about the highest performance ever made.

You also probably know that all of those grey caps will need to be replaced; especially the coupling caps. The distortion is likely due to bad coupling caps, which also put the output tubes at risk. What kind of outputs does this receiver use?

I'd suggest resisting the temptation to change tubes willy-nilly in the tuner sections (even if they test "bad", which they likely won't); the tuned circuits in the tuner are matched to the relevant, specific tubes in those circuits. Changing tubes in the tuned circuits will likely require realignment.

Note that this receiver covers both the US and Japanese FM bands; interesting.

Fongolio

Thanks for the input. The output tubes are 6BM8's (ECL82). I've found a schematic for it!! That will help a lot in trying to match caps that might have faded or worn lettering. I figured I'd do a full re-cap just like on my Eico and very likely resistors as well. I'll try posting the schematic here for you to look at.

Kelvin