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Old 27th August 2008, 08:51 PM   #11
DRC is offline DRC  United Kingdom
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Quote:
... and a little more to the right there seems to be some corrosion on the little silver cap?
that looks more like a leaky electrolytic cap

might be worth replacing any small value electro caps, especially any near hot components or any that don't have much polarising voltage ...

i didn't find the manual on BAMA
it'll be real tough without a schematic !!

my guess would be the OP stage - possibly that area of the PCB with the 4 trans with heasinks - maybe you can trace back the OP wiring ?
did you test with both unbal (both + and -) and bal OP ?

dave

PS: just fixed a fluke 1953A for the cost of a junkbox 74S74 - thx BAMA
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Old 29th August 2008, 05:31 AM   #12
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yeah, its going to be tough without the schematic, maybe ill end up getting one off ebay, but they are about 20 dollars or so..mehh.
I checked BAMA too, I love that site, soo much information.
Ill start poking around with the meter to see what i can find out, but it seems this might have had someone else with thier fingers inside as well!

For the trace on the scope, I had it coming out of the unbal output, for the bal output on 600 ohms its positive, not negative.
Could anyone ask Anatech if he has a copy of the manual? I asked him but he hasnt replied yet and that was two weeks ago.

There might be a bunch of things wrong, though, because the meter still has no movement (slight movement when you change the attenuator, so I know it still works)

I hope I didnt get a dud!
But we will fix it, you guys are great!

thanks again
-chris
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Old 29th August 2008, 05:58 AM   #13
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The positive part of the balanced output you saw is the negative output just inverted. you are still missing the positive half of the waveform, once you have that sorted out the balanced output will fall inline.
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Old 29th August 2008, 07:08 AM   #14
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( I feel kind of a noob about this.. ) on the output bnc terminals there is one that says unbal, and then going to both of them it says bal...sooooo do i need to use two test cables??

im sorry for my lack of knowledge..haha..but I start electronics engineering school in 5 days!

when i have one test cable into the first channel of the scope from the bal/unbal jack, and one other into channel two of scope from the bal only jack i get a psudo sine wave, but it doesnt match up and its not ..i dont know. its all over the place, ill post a pic later ( gotta go to work now) but so when im on 600 ohms the two different output terminals is just for having two outputs to different things...like one to a scope and one to the amp-dist analyzer-scope?

i havent had a chance to trace out the impedance selector circuit to see if its parallel or what..haha

-chris
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Old 29th August 2008, 10:46 AM   #15
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A quick explanation might in order ...

(1) in UNBALANCED mode the output signal is generated between the signal output and ground, ie between the signal and screen of a single BNC connector

(2) in BALANCED mode the output signal is generated between the two signal outputs, ie between the signal of both BNC connectors. In this situation you should NOT assume any relationship between either signal outputs and ground. Often, each output will be an inverted version of the other but this is not guaranteed to always be the case.

Since you connecting the generator to a standard scope input you should connect both outputs to the scope, ie to channel 1 and 2. If you then select “subtract” on the scope you will see the difference signal when the generator is in BALANCED mode.
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Old 2nd September 2008, 06:51 AM   #16
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I ordered a service manual for it, so I will have to wait until it arrives, unless anyone else has a copy!
I dont want to start poking around and changing parts and mess up the cal if I dont have the manual first.

Thanks again guys, ur great!
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Old 19th September 2008, 10:05 AM   #17
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okay, so I recieved the service manual in the mail, finally. If anyone wants a copy of it, just ask. I should get it put up on BAMA.
so power supply is dead on right. been poking around and it seems the problem is in the balanced amplifier section...? I havent traced it to the component yet. I dont have too much free time ( too much school work to do. gotta love electronics engineering courses)
I get a perfect sinewave out of the Counter Output, so those are my indications so far.
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Old 19th September 2008, 04:01 PM   #18
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Old 20th September 2008, 06:31 PM   #19
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Ooooookay. So I am getting more near the cause of the problem. I have found quite a bit of effects of the problem so far. C10 is no good, C40 is no good (C40 is the one I said had corrosion on it) and C10 is the small capacitor by the transistor with heatsink on the small board. It's part of the Amplitude Control Integrator. The rails are dead on +31.0V and -26.0V.

So the problem is in the Balanced Amplifier, I am pretty sure. I just ran out of time last night to work on it, Ill do some more probing and see what comes of it.

Does anyone know what would be a good compliment to this device?? I am starting my little venture into tube audio amplifiers and I would love to get numbers on my builds and see how I can improve them or whatnot.

I know alot of you have a 33*A distortion analyzer..are they worth the price? And having to potentially repair them as well? ( I do like that they have an AC voltmeter built in that you can use by itself.)
What other things do I need? I have a good DMM, a Tek 422 scope (20Mhz dual trace), this test oscillator...I do have a Heathkit 'harmonic distortion analyzer' but it doesnt work and Im not sure if its worth fixing it as well...its all tube too.

soo, any suggestions to what else I need before I really dive deep into tubes?

(oh, I have a variac, lightbulb current limiter, and the odds and ends..thats about it.)
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Old 20th September 2008, 11:55 PM   #20
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so I took a closer look at it and I am pretty stumped as to what to do with the Balanced Amplfier. I cant locate it down to a single transitor, so maybe I will just replace them all! haha.

But like i said before A3C10 (sprague 22uF 10% 25V Tantalum) and A2C40 (Sprague 180uF 20% 10V Tantalum) are both no good, so should I possibly replace these first before I replace the transistors and see how it is then?
I just cant seem to find the 'root' of the problem. Which part was the one that made it all fail...

If any of you have those capacitors, I will purchase them off of you. Seems that Digikey doesnt stock them, and they want a high price for them as well.
The full part numbers for the caps are:
22uF- 109D226X9025C2
180uF - 109D187X0010F2-DYP

thanks again you guys for spending the time helping me!
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