Monacor STA-150x.. Any good?

Mr Creosote

Super Member
Hi
My brother called me today and said he picked this Monacor STA-150x at a garage sale. Googling it turned up very little. Can anyone here give me any info on it? He hasn't plugged it in yet. He's 300 miles from me so I can't run over to his house to see it. Is it any good? Aprox age and output?

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Not sure of the age, but what type of output tubes it uses would give a clue about the power (wattage) output.
 
Some info from Worthpoint (sorry about the caps copied from original post):
THIS IS THE FIRST ONE OF THESE MONACOR BY MONARCH ELECTRONICS CALIF MADE IN JAPAN I HAVE SEEN, LOOKS AND IS CONSTRUCTED VERY MUCH LIKE A SANSUI 1000 AND PIONEER EARLY TUBE RECEIVERS
TUBE LINE UP IS 2 6BQ5. 4 6BA6, 6CA4, 2 6U8, 2 6AQ8, 12AX7, 6BE6, 6R-E13 INDICATOR MOST TUBES APPEAR TO ORIGINAL MATSUSHITA OR FIJITSU JAPAN ONE WESTINGHOUSE 6BQ5

In the pics there is a tube layout diagram showing a stereo single ended power amp, with one 6BQ5 per channel: http://www.worthpoint.com/worthopedia/monarch-monacor-sta-150x-am-fm-stereo-197391193
 
Thanks. I sent him the info about bringing up old tube gear with a variac. I know he doesn't have access to one so we'll see. He said he was going to hook it up today. I'll let you know what happened.
 
Just a big caution: those Japanese made amps/receivers almost always have grey caps that are all dried out now, especially the smaller paper in oil ones that sounded great when new, but are now dried up.

Advise your bro to replace all the grey caps, including the big electrolytics, before running this regularly. It is quite likely that it won't function now, even when brought up with a variac. He should make and use a dim bulb tester to use in circuit for first power up. If it glows brightly and stays that way then he should shut off immediately and get on with ordering replacement caps!

If you search the threads here on Pioneer or Kenwood tube receivers you'll see this, but this is my personal experience too.
 
Thanks everyone
I'm making a dim-bulb tester to fire it up. From what I understand a bulb close to the same wattage as the receiver should be used. Or as a rule of thumb, 100 watt for solid state and 200 watt for tube. Most the stuff I've read about using a dim-bulb tester shows using incandescent bulbs. Now that incandescent bulbs are non existent what do you use? CFL? LED? I was going to use a halogen bulb as the are dimmable. Any advice on how to proceed?
Thanks....

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Check out the watts/volts/amps/ohms calculator at rapidtables.com. Try different wattages and the same wall voltage to see that lower wattage bulbs have a higher resistance and draw less current. So, they show up the problem faster if there is one. They might even burn out quickly with a dead short but will also glow brightly if there are less dramatic issues.

At the other end of the scale a high wattage bulb may not show up the problem. I would use a 60w bulb in the U.K.'s 240v supply which suggests 120w for the US's 117v, given the same current draw. I hope I've got this right and am happy to be corrected. Experiment with the 100w first. The 200w might not offer enough resistance to glow brightly if there is a problem.

You have to use an Incandescent bulb. These are still available here for 'rough use' at hardware stores. With the ideal wattage bulb, it should glow brightly when first switched on and quickly get much dimmer as the unit under test warms up. Usually a fault shows immediately with a very bright bulb.

Also, for safety, I prefer to locate the unit well away from where I'm standing beside the wall on/off switch. I once accidentally put an unmarked but very low watt night light bulb in the tester by mistake and it burst. As this is a visual test and you do need to be near the off switch, use the wall outlet.
 
The wiring in those units is the opposite of neat and tidy. It is a wonder that the assembly line people even knew what went where. At the time that those units were made was nearly the end of commercially made mass produced tube audio and the profit margins must have been very small. Therefore the manufacturer tried to save on every little bit. Therefore, you need to be very careful of how much you torque on the solder lugs on tube sockets and other joints or they will break. good luck
 
I have a Monacor STA 300 X with PP 6BM8's and it sounds shockingly good. However, it was a pain to work on as there are old PCB's in the tuner section.

I have some more work to do also to resurrect the MPX stereo stereo section not working at the moment. Good luck to find a schematic.
 
For your dim bulb, CFL or LED wont work, but if you go to your local big box hardware store you can get halogens in what look like a standard bulb in 38, 95 etc watt sizes, they work just fine for your dim bulb. If it were me I would as a matter of fact replace the coupling caps before doing anything. I tried to warm up an old Sansui 1000a with the original caps on a dim bulb...it didn't go well. After coupling caps were replaced it worked pretty well, but I went ahead and did a wholesale replacement of the caps.
 
I put together a DBT and am going to visit my brother next week. He hasn't plugged it in yet, I think I talked him out of doing that with out the DBT.

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And the results are in.... We fired it up with the DBT. I started it with the 60w bulb. The bulb came on and stayed on and nothing came from the unit. Next with the 100w bulb. The bulb came on, went dim and slowly brightened up. Still nothing from the unit. Then the 150w bulb. Same thing, bulb came on, went dim and brightened. This time a bit quicker then the 100w. But this time it was able to pull in a couple of am radio stations. When we plugged in directly. It was pulling in am and fm stations. we where able to tune in KPIG, which is a weak signal where he lives. We listened to KPIG for a couple of hours to let it burn in. In the end it got pretty warm but no funny or burnt smells. Just that tube smell. Like our old TV from when I was a little kid. Really cool. I'm not sure what he is going to do with it. He asked if it was worth restoring. I couldn't answer that. Like how much would it cost to recap it? It sounded nice but we didn't have a turntable or CD player to really gave a listen to. So what next? Should we just play it? Is it worth restoring? In that I mean is it worth putting money into? The end result being worth what he'd put into it? It looked like we where the first to look inside. All the tubes look original. Not a tremendous amount of dust. unmolested. What happens if a cap fails? How should we proceed from here? Anyway, It was exciting to see the tubes glowing and music flowing from the speakers. Thanks for all your comments and interest. Here are a few pictures...

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It's a tuner combined with an integrated amp, with single ended output. Not a lot of power, but a sweet sound; see post 6 above. Would make a great bedroom or office system. I suggest he tries it with a CD player or similar input to assess whether it is useful to him in the real world. It's in great cosmetic condition and clearly in working order. If it were mine, I'd definitely restore and use it.

If you/he are willing to replace the capacitors, it could be put into daily use. If not, those old grey caps will fail sooner or later, maybe causing long term damage. You don't say whether you heard any hum, but that is an indicator that the power supply caps are not filtering and smoothing the rectified AC adequately. The replacement cost of the caps is not great, I'm guessing less than $50 in total. If you want to recap, there is help here. The printed circuit boards will make some of the work easier, but also require you to be careful with them.
 
Thanks Dandy. Cosmetically it gorgeous, not a scratch, dent or rust. The lettering is perfect. I didn't mention any hum because there was non. well, when I had switched to phono or tape and turned it nearly full blast I could hear a very faint hum if I put my ear next to the speaker. It sounded nice, equal out both channels. I'm imagining recapping can be done in stages. Like first tackle the power supply caps. Thoughs are the big ones right? The one standing up next to the power supply and at least the three big ones off the terminal strip underneath? I can tackle at least that much. The smaller ones mounted directly to the printed circuit boards look like a bit of a challenge. Too bad he's a three hour drive. I'll have to get him to bring it here, my bench, tools and soldering station are all set up here.
 
As it sounds like it's working really well, your bro could use it for a while, but just be sure to stay in the room when it's on.

Looking ahead, as well as the power supply caps, replace the coupling caps to the 6BQ5 output tubes (pin 2, I think). A schematic would be really useful, but I can't find one.
 
Okay, I can identify the coupling caps in the photos I took. They run between the output tubes and the 12AX7. .05uf 400wv. it looks like. I think we need to get a parts list going.
 
According to this site http://www.radiomuseum.org/dsp_hersteller_detail.cfm?company_id=9143 Monacor was a trademark of Monarch electronics, as was Concertone. You might try looking for a schematic under those names.

If you (or he) wants to do the work yourselves, it would not be hard or expensive (at least the amplifier section; tuners can be tricky but it sounds like this one basically works). The cash value of the receiver is probably not high, so do it for fun or pass it on to someone who wants to & use your money for something you like. I'm playing with a small amp of similar power & it sounds quite nice. I won't replace my main systems with it, but it is definitely worth having.
 
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