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Help ID and schematic: Monacor STA-300X

Patrice B

Patrice B

AK Subscriber
Subscriber
Hi,

Looking for a schematic for a Monacor STA-300X tube receiver.

I understood by searching the AK forum that it could be similar to: Olson, Armaco, Calrad, Trio, Kenwwod, Allied, Lafayette, Radio Shack (Realistic), Martel/Roland and even Pioneer of the same era.

The nearest thing I could find is it looks similar to the Pioneer SX-34 (talking schematic here...) but it's not the same.

It's a PP 6BM8 with two decent-sized OPT's. The tuner/preamp section is built on PCB's. It's SS rectified (two diodes).

Inputs:

- phono mag
- phono ceramic
- aux
- tape mon

One headphone jack, loudness control, AFC switch, AM-FM and FM stereo.

The tube complement is:

- four 6BM8's
- three 12AX7's
- four 6BA6's
- one 6BE6
- three 6AQ8's
- one tuning eye tube...

The pics on Canuck Audio Mart are form the one I bought yesterday.

The seller said to me that if works for a while than makes an horrible hum. Not surprised as it's full of those Japanese gray caps... :) Will rework prior to switch it on again (filter caps, resistors out of spec, testing tubes, all gray caps, Deoxit job, yada yada...) but need a decent schematic.

Thanks for any hints.

Patrice


Pics: http://www.canuckaudiomart.com/details/165621-monacor_model_sta300_x_recepteur_a_tube_/

and

IMGP1283.jpg


IMGP1283.jpg
 
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Help... and bump again. No one recognize the faceplate and could be able to identify a similar model and point me to a reliable schematic?

I should be able to work on it without schematic but it sure help to have one.

Thanks.

Patrice
 
I just grabbed one of these from the local thrift for $5. They said "tested and working", but that could just mean they plugged it in and it lit up. It could also mean they cooked the OPTs. Keeping my fingers crossed and will report back.
 
It's alive!

Since they plugged it in at the store anyway, I decided to try it. It played well and sounded good. However, see the last pic, I think one of the tubes was redplating. I'm still kind of new to the world of tubes and haven't encountered this first hand before, though I have read about it.











 
How about a pic with the top off. To me, it does look like red plating through the slats but let's see it clearly.

It is definitely time for a recap. Everyone of those capacitors have gotta go! :yes:
 
Oh yeah, I plan to recap. The power cord is integrated into the cage. A safety feature, I presume? I know the picture is lacking.
 
If the writing on them hasn't melted off from the heat they generate, it should be printed right on them somewhere.

If no printing can be found, you can always disconnect one side and measure them with an ohm meter. I believe that those are 20 watt.
 
I don't see anything that looks like a bias pot. Am I correct in assuming there isn't a bias adjustment on this unit?
 
Great. Thanks. With no info on the unit it sure is handy to have folks around who know what they are looking at.
 
FYI, if you moved that red plating tube to another socket and it still redplates, it is probably bad. If you move it to another socket and it doesn't red plate, then it is most likely the coupling capacitor for that socket but all the capacitors should be replaced anyway. This would eliminate any red plating to any of the output tubes.
 
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