Hello!
New to the forum and, of course, I have a question. Recently acquired the above mentioned amp and I do love it! But, I recently gigged with it and, wouldn't you know it, it died right in the middle of the set! Has power and a fairly substantial hum. And that's about it. Nothing comes through!
Power transistor perhaps?
Any help would be greatly appreciated.
Mutt
QuotePower transistor perhaps?
Perhaps. Trying to guess what's wrong is pretty futile. Just open it up, do a visual inspection and start probing.
QuoteAny help would be greatly appreciated.
Besides fixing the obvious fault, an amp as old as that will require a thorough overhaul and renewal of dried electrolytic caps, drifted components, worn potentiometers and switches etc. If you don't have them yet, you can find very poor schematics from the Tel-Ray page http://www.geocities.com/tel_ray/supernova.html. I don't know how accurate they are and they definitely seem to have some inconsistensies and missing parts. Those are still likely the best ones you'll find from Internet. You may have better chances trying to scetch one out by yourself.
It's an interesting amplifier and an item with historical value. Hopefully you'll get it fixed.
Opened it up and there doesn't seem to be any obvious smoked or melted components. I used to work on Airport Radars of the same era technology so the insides aren't completely foreign to me.
There's a daughter board that holds the power transistors and a few other components( you're right that schematic leaves a lot to be desired). There is a molex connector that passes the input and the output to their respective areas. Disconnect it and there is zero hum, so I at least know that the transformer is good to go. I think I'll start at the power transistors and work my way back from there.
I was just hoping that maybe someone here had dealt with one in the past, since they are rather rare birds and so little info is available.
I love the old ss amps. I also have a '71 Kustom 150 head and matching cabinet.
Anyone have any leads for a modern equivelant to an MMPS U57 transistor? Can't find anything anywhere!
Google MPSU57, or visit www.datasheet4u.com and search for the datasheet.
Well, it ain't the power section. Replaced the power transistors, and no change. Taped off the input from the signal section to the power section and quiet as could be. Now I guess we'll try the ol' half split method!
Broke one of MPSU57s moving the amp around... those things are damn hard to find and expensive! Fortunately I found a few at a local surplus shop!
Gonna keep plugging away at the old thing.
P.S. Just noticed that the boards all say "Sano". This amp appears to be the same thing as the Sano 1000R Combo Amp. No schematics for that guy either.
Correction... it ain't the signal section... Gotta be in the power section somewhere. Without signal to the power section it managed to smoke the speaker. Good thing it was one I didn't use anymore. Electrons are fun!
Finally found my multimeter. Looks like I'm reading 43VDC at the speaker connection! That ain't right...
Finally got around to poking around in this thing again. I was looking at the schematic...not that it helps much... and thought that maybe one of the transistors in the power section is bridging some of the existing voltages together incorrectly. So, I started pulling transistors until the 43VDC went away. Wound up being a 2n3645 that I pulled that got rid of the nasty DC voltage. Percieved output volume was way under half the normal volume of this amp. Not convinced that the transistor is actually bad. Doesn't read a short anywhere with the MM. There are a couple diodes on the board that appear to be the same but measure quite differently. One measures like a complete open in one direction(good!). The other... not so much...
Dear Muttomatic: ¿+43VDC on the speaker output? = 99%: Q4, 5, or 6 shorted. 5 %:R16 open. You can replace your expensive MPSU57 by a cheap Tip30 or BD140 depending on where you live.
I believe the 2n3645 is one of those transistors you mentioned... hard to tell... the board and the schematic don't really seem to correlate most of the time. Looking for a 2n3645 replacement now.
Looks like a 2905a is a replacement. Going to pick some up today.
Popped in the 2n2905a and the voltage dropped to just under 42V...then something popped and the voltage jumped up to 48V and settled back to 43V. I assume the new transistor popped. Everything else reads normal. Can't find any shorted resistors on the power board.... back to the drawing board...
Do you limit the circuit's current when you test the performed repairs? If not then you need to do that.
What would be your suggestion on limitting the current? I always test it with a speaker connected and the volumes turned all the way down. Should I put in a shunt or something somewhere?
Thanks
I always use a light bulb wired in series (in the mains line) with the tested equipment. If the device introduces a high current draw (e.g. as happens during short circuits) the high current flowing through the light bulb will warm up its filament, which then causes the filament resistance to increase. This effectively limits the current and in most cases saves stuff from blowing up in the tested device. Also, if the bulb is lit up it is a nice indication of a fault somewhere in the tested device. In normal operating condition the bulb should not light up or should only have a dim glow. In amplifiers the lightness will "pulsate" according to driving signal (hence the amount of loading). This pulsating can nicely reveal oscillation.
http://www.vintage-radio.com/projects/lamp-limiter.html
Great suggestion! Forgotten all about using lightbulbs as a load. I'll try it in the next day or so.
The bulb has a steady glow and there's still the audible hum coming from the speaker. But there doesn't appear to be any oscillation. The glow is fairly dim. About that of a night light so it's pulling current somewhere. I'm really getting frustrated with this thing. It sounded so good too.
And we're seeing around 20V at the speaker output. At least that's cut in half :p
Here is a pic of the power board.
(http://i45.photobucket.com/albums/f97/muttomatic/SupernovaPowerBoard.jpg)
Check the transistors support components and check you suppy current to them, I never limit current while testing an amp, if it won't hang when you turn it on under normal condition , then it's not right you still have a problem to solve and limiting current just would make it harder to do so. Good Luck, Bro
Dear Muttomatic: build the excellent lamp limiter suggested by Teemuk, and plug your amp into it *without* hooking the speaker, no signal, all pots on "0", etc.
Measure the voltage at the "hot" speaker out, probably you will read around +B (close to +40V) as you did earlier. Then measure the voltage across the power transistors (collector to emitter) , (probably either very low *or* close to 80V) and across base-emitter (around 500mV). Write a table such as , let´s say as an example:
"Q 4 - 2Nxxxx - VCE:80V - VBE:760mV" and so on. This particular measurement would indicate an open transistor.
Measure on the transistor pins themselves, you might have a worn or corroded socket, you might also have a cracked mica or some other unseen short.
Even better, hand draw a schematic of at least the end of the power amplifier: output transistors, driver transformer, and very specially the string of biasing resistors (it might include some thermistor ) from +B to -B. Probably most of it is in the board you posted. Bye.
Did some measurements.
Speaker output is still reading 47VDC. This voltage seems to be everywhere. there's a six pin molex connector that comes from the amp/transformer section that has that voltage on every pin but the ground wires.
All of these voltages are read with no load, i.e. no speaker connected. They don't really like the voltage.
All -# just represent that they are the same transistor, just different location. They are the same model transistors.
The power transistors.
TIP3055-1 30mVDC and 28mVDC
TIP3055-2 Pretty much have nothing reading on that transistor. Like nothing is feeding it any power.
The rest of the transistors.
2N3397-1 37.9VDC 38.7VDC
2N3397-2 47.5VDC 38.3VDC
2N2955 47.5VDC 0.01mVDC
MPSU57-1 30.2mVDC 0.01mVDC
MPSU57-2 0.01mVDC 0.01mVDC
I'm still not sure what the heck is going on with this thing!
p.s. The more I look at that schematic and the more I look at this amp... they don't really go together. Need the Sano 1000R schematic.
What voltage should be present at the speaker output? I assume something minimal.
I replaced half of the diodes by the transformer output and I'm now down to 13VDC at the speaker output with a 10ohm load.
Yet another update...
Replaced the rest of the diodes by the transformer. Got rid of the 47VDC at the speaker output.
But.... now the light bulb glows quite brightly and without the bulb in the circuit it blows the fuse. Now I have to figure out where this crazy current draw is coming from.
In all cases you should read a maximum of few millivolts across the speaker terminals. As what comes to other readings you might want to read (especially page 84):
http://www.pacificrecone.com/files/Darr6.PDF
Rest of it here:
http://www.pacificrecone.com/JackDarrBook.html
If you desperately need a schematic why don't you just sketch it out? That doesn't look like an overly complex circuit at all. Once you get into it it will likely take only a bit more than half an hour. Couple of hours max. You can easily spend days in trying to find a schematic from somewhere while the circuit is right in front of your eyes. Even if you eventually find something you can't trust it to be correct. However, if you trace out the circuit you will have a diagram that is 100% accurate.
Looks like it wasn't the power output portion at all. I'm not sure where the short is. Need to discharge the caps and unwire them and test them.
Then after that the OT??
Dear Muttomatic: please don´t get desperate and start changing parts at random. I guess you misplaced some of the power diodes at the power supply, that´s why now it blows fuses straight away. Return it to the original state. You need that power supply working before you can proceed with anything else.
I´m posting a refried schematic, the very poor one seen before. We´ll have to use it for now, we have none other. Please do: 1)Label the transistors with their real names. If in doubt, copy every inscription on them, not on the schematic itself (it will get very cluttered) but on the text of your post. Also label them on the board or chassis as "Q5" ... etc. with some Sharpie or Magic Marker to always be sure what are we talking about. 2)tell me the real world value of the resistors R15 to R22 ¿Did I mention I don´t trust the schematic very much? 3)Draw the Molex connector on the schematic, number the pins (they´re usally labeled somehow) and then measure the voltage to power supply ground from every pin. I strongly suspect that your -B (-47V) is missing, making *everything else* measure close to +47V. Other possibility is that both R20 and 22 are open. 4)Please measure some voltages for me. The red ones (V01/2/3) should be measured with the black probe on the power supply ground itself and the red probe where indicated. I suspect V03 (-B) will be missing at the board, in that case trace its path , specially on both sides (male and female) of the Molex connector. IF that is OK, measure V04 to 09, placing the black and red probes where indicated by the respective colors. Good luck.
Looking at the photo of the power board, the circuit doesn't seem to resemble the one in the schematic at all. There are only two TO-3 cased devices mounted at the sides of the U-profiled heatsink. I suppose there are no more output devices – at least I see no wires running to them. Also, I see only two power emitter resistors. The two un-heatsinked TO-218 devices on the board are likely the output drivers and in between them - on the board - looks to be two diodes (at least they seem to have that red-ish glass package typical to diodes). If they are indeed diodes then they are likely part of the biasing string. It doesn't look like this circuit would be using an interstage transformer at all. The rest of the transistors at left are most likely parts of the input stage and voltage amplifier (the one in metal package) and I see no wires running to a transformer from them. I see no wires running to the speaker either so I suppose the connection is through the molex. What the heck is that round thing next to the big capacitor at top left? So, all in all, this looks like a much newer design than the one depicted in the schematic.
This is of course just my first impression. Detailed photos would help a lot in determing what each part is and what the circuit likely looks like.
I really encourage that you trace out that schematic. The one with interstage transformer doesn't seem to be any good and it is very unlikely that you would find the one for this circuit from somewhere. Having the schematic would help you – and us – a lot. Plus, you would get a clear insight of the circuit's architechture and figure out which part does what. Also, there's never too much schematics to old transistor amps around so in the future your effort to trace out the circuit might help other people who are in a similar position as you are now.
Dear Muttomatic: now I know that the schematic and questions I posted before are useless in this case. My browser only showed me part of the picture you posted, I wrongly assumed that the board (and U shaped heatsink) were *much* longer, possibly containing other two TO3 devices and some other stuff (and a chassis mounted driver transformer). Now I "pulled" the full picture, opened it into Irfanview and sharpened it as much as possible. I´m posting a sketch of what I think the power schematic looks like, you´ll have to correct it and "fill the blanks". I assume the input transistors are NPN and the "Class A" PNP but the reverse is also possible. I´ve also drawn both outputs NPN, but they might be complementary (NPN/PNP). Please redraw the schematic as you see it on the actual board; also a couple more sharper pictures will help a lot. If possible also include a bottom one (solder side). To begin with, the amp has no short protection at all; not so bad within a combo, but if you add any external speaker, it becomes very dangerous. We still need that Molex drawing and voltages.Still suspect your -B is missing, also +-47V is too much for 2n3055/2955 devices. Bye.
Argh! The exact same thing just happened to me!! I was playing through my supernova, and a huge buzz ensued. The 50 Ohm 10W resistor (R14) was smoking! I shut it off immediately, and now I too can measure about 40 VDC at the speaker output. HELP! Did you ever get to the bottom of yours? It seems like we have different models slightly, based on your pictures, but maybe the same problem. . .
Those symptoms are almost a sure sign of an output transistor/stage failure.
One or several of the output devices fails by short circuiting, hence basically hooking the speaker load directly to one of the power supply rails. The resulting massive current draw will cause supply voltage to sag and ripple voltage to increase. DC can nicely burn a voice coil but it can not motivate the speaker back and forth - however, the AC ripple voltage riding on top of the DC can and you hear it as hum coming from the speaker.
The repair procedure should be rather obvious and easy: Locate the failed transistors and replace them.
Thanks! So here's what's in there:
4x 22-3773 - power transistors mounted 2 each on two large aluminum heatsinks
2x SEN T-73 - mounted underneath the main power supply board - no heatsink
1x 156-043 - also mounted underneath the main power supply board - no heatsink
I found an old Sunn schematic that calls out for 22-3773, and lists 2N3773 as an alternate part number, which is easy to find for sale. It also seems that 156-043 is sparsely available. But after talking with tech support at Motorola, Onsemiconductor, and Westinghouse, no one has ever heard of any part number resembling SEN T-73. Any suggestions?
My plan is to replace the four 22-3773's and R14, and hope for the best. Parts of the schematic (downloaded from the link provided in the thread - thanks) seem to match my Supernova very well, but none of the transistors have part numbers. Are these three TO-3 packages (2x SEN T-73 and 1x 156-043) as likely to be shorted as the 22-3773's? Does anyone know their function, or have different part numbers for these?
I'm pulling all of them out now so I can check them for shorts. I'll report whatever I find.
Thanks,
-James
P.S., I've taken nearly 100 pics of this thing, so if anyone needs a picture of anything, I've likely got it, or would be happy to photograph any part of it from any angle.
Sure enough, Collector-Emitter short on one of the four power transistors. Just ordered 4 new 2N3773's to replace these 22-3773's. . . hope they do the trick!
Is there anything I should be looking for as a potential cause? I've read pages 84-89 (from the above recommended book) about 10 times, and now I want a DC ammeter, an ACVTM, and a nicer scope (I have a Heathkit from around 1960. . .)
Thanks again for the help - you were dead right.
At last - my transistors arrived! And now it's working deliciously! Thanks!!
The ones that were in there read 22-3773, and my working <3) 2N3773's are well, working well!!
I can't remember it sounding any different - fantastic dynamics, and completely silent when not playing. As soon as the oil comes in, I'll fill the cans up (they're supposed to get about a tablespoon each?) and report back.
Now I want to build a custom cabinet for it. . . The original advertisements hail:
"two-12 inch heavy duty eminence (Altec Lansing optional)"
and then it says:
"150 R.M.S. 425 watts peak power into 2 OHM load"
Is it advisable to run this amplifier into a 2 Ohm load (I'm guessing two parallel 4 Ohm speakers)? I've been running it through a single 10", 8 Ohm cabinet, and it sounds fine. What's the safest choice? If I want a 2-speaker cabinet, what speakers/overall cabinet resistance make the most sense?
Also, I'd like to add a line out to make it possible to record directly to tape. I've read about cabinet emulators that accept a power amp output and then simulate the non-linear resistance dynamics of a speaker. . . not too concerned about all that! What I'd like to know is, can I just tap the pre-amped signal someplace and get a line out? I'd rather not use the amplified signal at all - not even to the speakers sometimes. Will this hurt the amp (disconnecting the speaker load)? Is there a special dummy load for old transistor amps?
I thought about just making the input to the spring reverb into a y-cable, and recording that! Any recommendations on a good spot (if any) to tap the preamped, effected signal, and get it into shape for a nice, juicy, balanced ProTools input?
I'm so glad it's working again - thanks again for the help.
Mixed report:
:)
- When the oilcan effects are off, I get beautiful, dynamic, noise/distortion-free tone.
- The Reverb and Tremolo effects sound great.
- I bought a Tektronix 465B oscilloscope, a Lambda triple DC power supply, and a Fluke bench meter.
- I built a custom 4-switch foot pedal with parts from Home Depot - works great!
:'(
- The oilcan effects are noisy. There is a regular pop, synchronous with the rpm of the Rotating Sound motor, that can be heard even if the Rotating Sound effect is off. It can be heard when either the delay or the rotating sound effects are on at all, and gets louder as these effects are turned up.
- There is some noise that I can hear and see on my scope when the effects are on. It is (in addition to the cyclical pop) very high frequency, and sounds like static/grounding noise. I have replaced all of the components on both of the two amp cards mounted to each motor, with no noticeable effect.
- The Long Delay setting yields unimpressive results compared to the Short and Multiple settings. The long delay send wire that comes from the selector switch was broken off. It looked like the break had happened at the top (backmost looking at the amp), two pins away from the input wire. There are a few caps and resistors wired into this messy switch - doeas anyone have a hi-res picture of this switch wired properly? The scematic I have differs from the electronics inside - not sure if it's been modded or if it's just a different version.
I have completely disassembled both motor assemblies, inside and out, and meticulously cleaned everything right down to the screws and washers (used up two toothbrushes, five 00 brass wool pads, a brass brush, a steel brush, and more than 1000 two-sided Q-tips (no joke)). In fact, in addition to cleaning, resurfacing, and polishing literally everything, I also resoldered every connection in the entire amp. I replaced the power transistors, all of the electrolytics, the power resistor (which was killed by one of the original(? 22-3773) power transistors that shorted out), and completely restored the hardware, skin, and the crumbling original wooden deck. She looks like new! Again, I've got over 150 pics if anyone's interested . . .
In fact, playing through the clean channel, or the effects channel with both the Echo and Rotating Sound effects off, it drives an 8 Ohm 12" or a 4 Ohm 15" beautifully. This tells me that the preamp and power amp are clean and fine. All of the components on the can-cards are new, and still test ok taking them out of the circuit. The insides of the cans were completely disassembled and cleaned, and 20 ml of special-order oilcan oil was added. I put new belts on. Could the AC motors just be tired/old and leaking noise?
Anyone have any guesses/ideas/inklings? I'm out, and really excited to have that "AHA" moment worth 2000 Q-tip swabs.
My last idea is to replace the 2-prong AC plug/wire with a proper, three-prong, grounded set. There's no harm in doing this is there?
Thanks for all the help, this Supernova may as well have been called the Odyssey!
I'd start with proper grounding, I think you are right on there. No damage done by replacing the 2 prong with a 3 prong plug, make sure to ground the chassis with the 3rd prong, it doesn't do any good if the ground wire isn't attached anywhere :tu: (yes - I've seen people do this)
I believe Temuk is refering to a "light bulb" limiter used on the mains input to limit current in the case of a fault. The circuit consists of wiring a low wattage bulb in series with the amplifier.