Hi, all. I have a 1973 Kasino guitar amp that needs some work. I've had it for a few years now. I got it at a pawn shop for $40. The guy couldn't tell me if it worked or not. It did (after some tinkering) for about 9 months. Then, one day it stopped. I found the problem, but haven't been able to find the part to fix it with. It was a germanium transistor with only two leads, and the number 61008 on it. Is there any way to repair this amp? Or, should I just write it off as junk? Thanks
ljn wrote:
I'm pretty sure the part in question was a PNP germanium transistor. It only had two leads, though.
Then it isn't a transistor.
From another site same question......
U100... Isn't that the "Club", right? You know that Kasino amps are largely just Kustom amps in different cosmetic appearance. They recycle largely the same PC board modules. Club, according to my references, holds PC105 (preamp), PC803 (reverb & f/s control) and PC900 (power amp & +/- 8VDC regulators).
You can verify pretty easily what board numbers are of interest.
I can find a crossreference to 61088, which is a 1N3754 diode, but not a reference to 61008.
Another useful resource:
http://www.vintagekustom.com/literature/Tech/tech.html
Thanks.I have posted about this in another forum. Part of what you said was also written on there, but not all of it. Thank you. I'll have to try and find one of those, although it's extremely unlikely that I have one. And yes. I'm aware that it's just a rebranded kustom. That's why I wanted it in the first place. I'm a CCR fan. That being said, I constantly played through it until it died. The reverb was amazing. I never even put a grounded cord on it, either. I was going to, but couldn't find one that was long enough.
1) yes, Kasino was rebranded Kustom, owner had some Divorce trouble, inside they were exactly the same.
2) I very much doubt they used germanium for anything at all, specially in a Kasino which came later.
3) please post a picture of your mystery transistor, I'm just guessing you refer to a TO3 (or TO66) metallic transistor, which of course "has 2 legs" .
4) what exactly is the problem, symptoms, and why you think that particular transistor is the problem?
Look for PCB labels and post a couple pictures, it certainly must match some regular Kustom amp, specially because of their modular construction ... which I find an excellent idea..
Thanks, Juan. I can't get a picture of the transistor because I lost it. It had some kind of fluid leaking out of it, which I noticed once while working on the amp. Shortly after, there were intermittent popping sounds, and loss of output when the amp had been on for a certain amount of time. Then one day I turned it on and ...nothing. The part had a clip that it sat in, and when I moved it to get the number from it, the leads broke off. I tried to keep it, but it was eventually lost. I read that this amp is supposed to be identical to the Kustom K 100 (internally) . When I get the chance, I'll try and get some pics.
2 legs / mounted on a clip points to a diode, probably a biasing one.
Post a picture anyway showing where it used to live, of the clip (and measure its diameter, as in , sometimes you don't have the girl but the bra gives you an idea of size) and both sides of the PCB where it was originally connected.
That way we might guess a little more accurately.
And of course the goldmine would be to have PCB codes matching known Kustom ones :cheesy:
Thanks,Juan. It was exactly the same size as the metal can germanium transistors. I'll try to get some pics, if I get a chance. Thanks again
That nails it.
It must be the then very famous and popular 1N3754 , "the king of biasing diodes" ;) ... or so they thought.
(http://www.radiomuseum.org/images/tubephoto_klein/1n3754.jpg)
That looks just like it, except for the number. I can't get those pics yet, but I will as soon as possible. I don't really feel up to moving the amp right now. Thanks again, Juan. :)
Someone on ebay selling those 1N3754 has the spec listed as:
100 PIV, 125mA, Vf = 1.0-1.1V
Does that sound right?
Quote from: g1 on December 12, 2014, 08:30:44 PM
Someone on ebay selling those 1N3754 has the spec listed as:
100 PIV, 125mA, Vf = 1.0-1.1V
Does that sound right?
Thanks, but I have no idea about any of the specs for the original part. I guess the amp may just have to sit there and look pretty for a long time. I appreciate your help, though.
We can clearly see that the 61088 diode refers to an IN3754 diode, see attached sheet(kustom semiconductor infomation 2). That semi-conductor reference is clear back in 1971 and is from Kustom, which we know is possibly the same amp. Here is the data sheet for the RCA IN3754 diode too. Seems like your closer than you think. Attached is the Kustom K100C and perhaps that relates to this amp, I don't know. There is one IN3754 in there and a special note that it clips on to chassis, CR902*. 61088 was a house number perhaps and the actual name of that part is IN3754. Just throwing it out there... :tu:
Quite possible and thanks for posting :dbtu:
I would be very surpriseed if Kasino K100 were not Kustom K100 :o
I remember unsuccessfully trying to get 1N3754 in Argentina ... and eventually replacing it with plain old 1N4002 :o
In your case, maybe a fatter 1N5402 will fit that clip , although its legs will be too fat for original PCB holes if direct soldered.
In that case, use 1N4148 or 1N914 which have skinny legs but you'll have to epoxy it to the heat sink to have some thermal coupling.
That said, a blown bias diode usually means certain death for outputs and drivers ... check them.
Thank you both very much. I've tried several diodes in there, but got a distorted sound and alot of heat coming from the amp, so I had to shut off power very quickly. I became somewhat disenchanted after several attempts, and left it alone. Externally, the amp looks great other than a bit of rust on the corner caps. I wonder if someone had been driving the amp too hard over the years. Thanks again guys.
So we can't blame a plain old vanilla diode for these types of problems. As Juan stated the diode being bad typically indicates other greater problems. Are you running this amp on a light bulb limiter when you are testing it?
Agree.
But no problem, it's quite repaireable.
Just a little homework:
1) check that the power amp schematic actually matches what DrGonz posted.
2) sometimes the electrical schematic is the same, but parts designations, as silkscreened on the PCB do not match (say schematic Q103 is screened Q47, etc.) ; in that case relabel parts so they match your PCB , to avoid confusion.
Although it's highly probable they will match.
Thanks ,Juan. But there's two problems. I don't have a schematic for this amp, and I can't download a PDF file. I really appreciate all your help.
Quote from: LJN on December 13, 2014, 06:48:30 PM
Thanks ,Juan. But there's two problems. I don't have a schematic for this amp, and I can't download a PDF file. I really appreciate all your help.
Then you have NO problems (lucky guy !! :lmao: ) because here it is:
just print it as large as possible , grab good light and a pencil to check how well it matches your actual PCB and if necessary rename parts in schematic with PCB labels.
Thank you very much, Juan. I just downloaded it. Not sure how closely it matches mine, but it does have all the same jacks, so I think that may be a good sign. Much appreciated. :dbtu:
The cherry on top of the cake: the official Kustom amp testing procedure.
Notice the signal generator attenuation to easily get instrument level signals, the series 100k at the input to better simulate a real world pickup (driving guitar amps from very low impedance generators, typically 600 ohms or less often leads to inaccurate results) , .... and he also implicitly acknowledges that he cheats a little with rated power.
"100W" amps are around 65W RMS ; maybe 70W on a good day, to reach 100W he has toallow quite a lot of clipping.
Oh well, typically "100W Twins" were around 85W RMS at clipping start and so on so way back then that was the name of the game.
Thanks again, Juan. I don't have any testing equipment, or any idea how to use any.
Quote from: LJNI don't have any testing equipment, or any idea how to use any.
Which are problems for somebody intending to work on amplifiers. But they can be overcome.
Without a multimeter you are flying blind. It doesn't have to be expensive, quite reasonable (yellow) Digital MultiMeters, DMM's, can be had for under $10, but you've really gotta have
something.
The only other thing you really need in the way of instruments (c/f tools) is a
signal source. You can use your guitar, but you'll find it a lot easier to be able to play test tracks from your MP3 player, radio, laptop, or whatever. You can just use music, but you can also download test sound files, or record your own using freeware like
Audacity.
There are also freeware "instruments" that will turn your (old/spare) 'puter or laptop sound card into a test oscillator, an AC millivoltmeter, an oscilloscope, or a spectrum analyser. These are very limited in their capacity and application, but they can still be useful if you have no other such instruments.
An instrument you can busk which is the "poor mans CRO" is a signal tracer, and modding an old unwanted amplified computer speaker is a great starting point.
One of the things you build up over time is a rack full of test leads, leads with different ends, every type of connector you can think of to the connectors in common use in your workshop, 1/4-inch, minijacks, RCA, insulated croc clips, etc, etc, made up as needed and archived on the rack.
You can learn to use whatever instruments you can acquire or build by presenting repair problems to a forum like this and be instructed on how to apply what you've got to get the results you need. {a lot of the time when you're a tech it's about improvising with whatever is to hand to do the diagnostics and repair.}
thanks,Roly. I actually do have one of those cheap yellow multimeters. It's really all I have. I don't really see it as a piece of testing equipment.
Quote from: LJNI actually do have one of those cheap yellow multimeters. It's really all I have. I don't really see it as a piece of testing equipment.
Aww, that's a bit cruel, it beats having to stick your tongue on it. :lmao:
For the moment we are only concerned with restoring the
DC conditions, so even the most basic multimeter will serve. We will tell you what measurements to make.
I think we need to bring a bit of formal order to this faultfinding. Questions pending, your homework;
Quote from: J M FaheyLook for PCB labels and post a couple pictures
In particular, is the power amp board marked "PC900"?
Quote from: J M Fahey1) check that the power amp schematic actually matches what DrGonz posted.
To confirm that we are all on the same circuit page.
Quote from: DrGonz78Are you running this amp on a light bulb limiter when you are testing it?
This is a "must" - see
Limiting Lamp (http://www.ssguitar.com/index.php?topic=2093.0).
Also
disconnect the loudspeaker and leave it disconnected for the time being.
This circuit includes the locations of the transistor on the PCB (on p2);
https://docs.google.com/a/olenik.com/file/d/0B1FxxpOmGO8vZXZWQV9rOTBpNm8/preview?pli=1&rm=demo (https://docs.google.com/a/olenik.com/file/d/0B1FxxpOmGO8vZXZWQV9rOTBpNm8/preview?pli=1&rm=demo)
I don't think this is a germanium-based amplifier but silicon-based, which will hopefully make repair a bit easier.
The mystery diode 1N3754 is a
silicon diode and marked on the circuit as CR902. Can you please confirm (or otherwise) that the board overprint is this number?
In any case,
install a temporary wire link where this diode was fitted.
Power up the amp via your limiting lamp (say around 40W or less).
Does the lamp settle to a dim light, or seem to be full brightness? (dim is good, bright suggests there is a short somewhere)
Measure the three following voltages;
The main +ve supply. Should be a red wire coming from the power supply. It may be as high as +40V, but could be anything if there is a fault.
Ditto for
the main -ve supply, green wire. May be up to -40V, but as above.
The voltage on the half-rail, that is the output to the speaker, blue. This should be about half way between the +ve and -ve supply, that is very close to ground, only tens of millivolts, but again could be anything from full +ve to full -ve under fault conditions.
Post results.These measurements should give us a much better idea of what we are dealing with. And don't fret pet, most of us have been servicing amps without the benefit of a circuit since Noah called to have the stereo on the Ark fixed, and we've walked people through to happy conclusions many times on this site. :dbtu:
I appreciate all the help. It's been a while since I looked inside the amp, but none of the parts are labeled on the board. I do remember seeing the PC900 Mark, though. I tried several diodes, but each one caused the amp to sound distorted and the board got very hot.
Quote from: LJNI tried several diodes, but each one caused the amp to sound distorted and the board got very hot.
Uh huh.
Now when you run out of hair to pull out, try it my way;
Quote from: Rolyinstall a temporary wire link where this diode was fitted.
Power up the amp via your limiting lamp (say around 40W or less). Does the lamp settle to a dim light, or seem to be full brightness? (dim is good, bright suggests there is a short somewhere)
Measure the three following voltages;
The main +ve supply. Should be a red wire coming from the power supply. It may be as high as +40V, but could be anything if there is a fault.
Ditto for the main -ve supply, green wire. May be up to -40V, but as above.
The voltage on the half-rail, that is the output to the speaker, blue. This should be about half way between the +ve and -ve supply, that is very close to ground, only tens of millivolts, but again could be anything from full +ve to full -ve under fault conditions.
Post results.
We can provide you with hundreds of years of experience, but it is up to you to apply it so we can make progress. 8|
Did we ever determine the board number for the circuit we are looking at?
Not yet. I'll get to it as soon as I can. The amp is in an awkward place right now and I'm fighting a cold. I'll get to it soon.
Hi, all. I just wanted to report that the amp has been working for over 20 days now. It turns out there were a few solder joints in the power section that had come loose. Old age, I guess. Thank you all very much for your help. I' m now working on a tremolo pedal to use with it. :dbtu:
I do have a question regarding the monitor Jack on the rear panel. What's the purpose? By that, I mean, what type of monitor will work with it? Thanks,again.
Well, um... if we knew what boards the circuit used, we could look on the schematic.
In all likelihood, it is a line out to drive a slave amp.
Quote from: LJN on May 28, 2015, 11:12:09 PM
I do have a question regarding the monitor Jack on the rear panel. What's the purpose? By that, I mean, what type of monitor will work with it? Thanks,again.
To drive a monitor cabinet which it sort of implies it *should* be in parallel with the main speaker out or have its own dedicated power amp , because you need
power (voltage *and* current) to move a heavy cone and voice coil back and forth, but I guess that in this case it's a glorified name for a Line/Preamp out (or worse, a 20:1 attenuated tap from speaker out) to drive an external power amp and speakers .
Which yes, could be used to "monitor" what's coming out of main speakers.
Remember these amps were designed and made Looooooooonnnnnngggggg ago, they were charting unknown territory, and some of then acceptable "solutions" are not so today.
Very true. I don't play anywhere, so I don't really have any use for any monitor. I was just curious about it. My amps are actually overkill for my tiny bedroom, but they sound good.