Silly's Salvage Operation :)

[Sillyboy]

Okay, I was inspired by Vikash's webpage: http://www.vikash.info/audio/gainclone/

So, I headed to ebay and a garage sale today... here is what we got so far:

For $7 at a garage sale, I picked up this receiver (Kenwood KR-3130) -- picture attached. I will post a few more pics in reply so you can see the back and insides for inspiration

And this (again Kenwood) KA 2002a http://cgi.ebay.com/ws/eBayISAPI.dll...MEWN%3AIT&rd=1

Lemme just start with question #1, I figure there will be 86 by the time I am done

With reguard to the transformer: am I better off taking some measurements before tearing it out of the receiver? On the 3130, I see no markings on the transformer... someone I need to figure out what is up with it

[Sillyboy]

And a bad pic from the top

I can see a goodly sized transformer and a 50v, 1000uF cap (I assume its the "smoothing cap" a term I learned like 7 seconds ago ) -- those seems nicely reusable.

Who knows what else

[lndm]

Are you trying to fix this, or are you salvaging parts?

Either way for starters, you're probably best ditching that cap. Even if it still works at it's age, it probably won't be doing the sound any good due to the way these things dry out.

[Sillyboy]

Ya, should have clarified the goal

Just like Vikash, on his project at http://www.vikash.info/audio/gainclone/ I want to jump in and learn something by building a simple gainclone... using the cheapest parts humanly possible (with the idea of building a non-ghetto one the 2nd go around).

So, trying to figure out what parts I can salvage out of these two receivers.

[lndm]

Ok, the transformers would be good if they give the right voltages. If not sure of the units you will be pulling them from, it might be safest to pull them then measure them.

Keep in mind that the DC rails obtainable from them will in theory be 1.4 times higher than the measured AC RMS voltages. In practice they will be a little less than this due in part to the limited size of the smoothing caps, and in part to the trasnsformer being loaded. Think in the order of 10% give or take 10% (estimate only).

Oh, and what about heatsinks, volume pot, switches, case. Have you thought about transplanting them into one of these cases? The existing ground platform, mains switching and fusing arrangement might take a little of the pressure off.

[Sillyboy]

Okay, lets do some learning people! (well, you guys do the teaching, I will do the learning )

Attached a new pic, from the underside of the amp. I busted out my voltmeters and started measuring random stuff, most of which I didn't understand

Mr Transformer has 4 pretty colors coming in (white, red, blue and yellow) and 4 pretty colors coming out (2xred, blue and black).

The two reds... head on over to that goofy 4-legged black device in the middle. Legs are marked + ~ ~ - Now, I am not genius, but it seems this device converts AC to DC!

rectifier I assume?

Measure across the two reds, I am getting about 38v AC. So, I assume this says something important about my transformer

Now, here is where I get pretty confused.

Measure across the DC legs... I get about 47v DC. I sorta expected more like 53 (38v * 1.4 ~= 53v). Then on a whim, I measured the DC legs... while switching trusty multi-meter over to AC mode. It measures 105v AC. was i expecting that?

You can see a black'ish circle to the left of Mr 4 Legs, that is the 50v, 1000uF cap (and is where the dc legs head off to, in parallel to their other travels... makes sense... smooth cap, right?).

The blue/black wires from the transformer headed off to an output selector (A, B, or A+B), and I believe come back to those two 35v 1000uF caps. Haven't looked really hard at that part yet.

---

edit: Crap, it won't let me attach. Doesn't give an error, just doesn't show up. Will try again later I guess.

[planet10]

Originally posted by Sillyboy
Measure across the two reds, I am getting about 38v AC.

Is there also a ground somewhere in there -- ie is the 38 V really +19VAC, -19VAC (ideal for a GC) or is it 0-38VAC (not so good)

I measured the DC legs... while switching trusty multi-meter over to AC mode. It measures 105v AC. was i expecting that?

Does the amp actually work? on the DC side you should only be measuring the ripple, which with a working smoothing cap should be considerabley less than 105V

The blue/black wires from the transformer headed off to an output selector (A, B, or A+B),

That can't be right. What do you measure across the blue/black? Is there a voltage across red/black, or red/blue?

two 35v 1000uF caps.

That points towards (+19)-0-(-19) AC rails

dave

[Sillyboy]

Part of the problem is that I have (apparently) no idea what I am doing.

If I set my multi-meter to AC... and take a measurement... I would think that swapping the probes would have no effect. Alas, that is sometimes not the case for me!

Example, measuring across red/blue from transformer output:
- using DC, I get 18v.
- using AC... I get well, 4 values...
blue vs red1: 40v
blue vs red2: 47v
red1 vs blue: 0v
red2 vs blue: 6v.

Anybody want to explain this?

In other voltages:
- blue/black: 7v ac (consistent across swaps, and measure 0v DC)
- red/black: again, crazy: 18vdc -- and measures 41vac 1 way, 0vac the other (consistent between both reds).

As far as ground goes... I'm not qualified to say I am fairly sure the black wire coming out of the transformer is black, as I can simply use the chassis, instead of the black wire... in all cases. What does this imply?

Oh, and I had never tried it out... so I actually hooked up a speaker only station I could get.... Rush Limbaugh! Eeck! but the amp worked fine.

And... slightly tangental, but since you commened on it... voltage across the 35v caps... both show 23vdc across them. I, of course, have no idea why there are 2. A vs B speaker sets... or 2 rails... or something else

Seems to me that my multi-meter just gets grumpy if I measure AC, when there is a dc current? I double checked across the smoothing cap: 47vdc, 105vac one way, but swap, and get 0vac.

Hopefully attachments start working again soon. Will attach here again, just in case

[planet10]

Originally posted by Sillyboy
I would think that swapping the probes would have no effect. Alas, that is sometimes not the case for me!

Example, measuring across red/blue from transformer output:
- using DC, I get 18v.
- using AC... I get well, 4 values...
blue vs red1: 40v
blue vs red2: 47v
red1 vs blue: 0v
red2 vs blue: 6v.

I'm guessing you are reading a voltage thru the circuit board and not transformer lead to transformer lead

[Sillyboy]

Word is... attachments are fixed.

I have re-read planet's comment like 3 times, and it is just now sinking in.

+..........X....??
- ..........X....??

Say X are the points I am measuring, maybe at the legs of mr 4 leg (that really is a rectifier, right? )...

The point is that w/o knowing what what else X is connected to... I can't really accurately measure. The ?? represents the scary unknown

Okay, so... uh... do I really have to disconnect things to measure them?!