Need info for Kenwood power transformer MU8604H1

[Lewis Moon]

I just pulled this out of an old Kenwood receiver that went Pfffft (smoked cap). Can anyone tell me about it? I'm thinking of building a gainclone and was stripping the carcass for the heat sink.

[dave_gerecke]

Hello Lewis, If you remember the model # of the receiver you pulled it out of that would help a lot. Then people can figure out the output rating of the receiver, approx age, etc. This can usually help a lot in determining the usefulness of a particular transformer for a purpose.

Peace,

Dave

[Lewis Moon]

It's an old KR-A4060 From what I remember it was 2X 60W into 4 ohms.

[Lewis Moon]

Looks like the direct replacement from Kenwood is the KHR-MC8601H1. Beyond that I can't find anything. Anyone out there with more skillz/knowledge than this plodder want to take a whack at this? If it's a big, copper paperweight, I can deal with it.

Added: Is there a way to test the output without serious brain fry potential?

[h_a]

Is there a way to test the output without serious brain fry potential?

Dealing with mains power is always a certain risc, it's certainly not fool proof.

Technically, you need only to connect primaries and measure secondaries with a multimeter in VAC-mode. Remember, that VAC-value is usually shown as RMS, not peak (multiply with 1.42 for Vpeak).

Use a light bulb wired in series or at least a weak fuse as power limiter.

If you have no clue which wires the primaries are, it's usually the pair with highest resistance, also usually made of rather thin copper-wires.

Also, I'm not so sure wether that thing is worth the effort (in case you feel uneasy) as many consumer amps save very much on the transformer. As the amp is only 2x60W into 4R, the transformer is probably even rated below that (as it usually has only to deliver this as peak power, not continous).

Last, if the transformer is not a toroid, I maybe would not bother at all as that regularly brings more problems than it solves (humm).

Have fun and take care! Hannes

[Lewis Moon]

Time to glove up and don my rubber shoes and Dr. Horrible goggles.....

Is this a good place to start?

Black = primary
Black/ tracer = primary return (tracers are usually white, red or yellow)
Brown = secondary 6.3 V heater
Brown/yellow = SHCT
Red = B+
Red/yellow = B+ center tap
Yellow = 5 V filament (for rectifiers)
Green = primary 6.3 V heater
Green/yellow = PHCT
Blue = bias winding (independent of B+ winding)
Slate = bias tap on B+ winding

[dave_gerecke]

Hello Lewis, I don't know if the color coding you posted will help. That one appears to be something from the days of vacuum tubes, I doubt it's applicable to the transistorized stuff from the Japanese. I did a quick look up of your amp, Kenwood claimed 80w a channel into 8 ohms, on a 2 channel amp. Then they list the power consumption as 190watts total. Assuming this Kenwood was class A/B then it was probably about 50% efficient at best. Thus (80w x 2) x 2 again (this for the 50% eff.) you would need around 300-350w in to get 80w out on both channels continuous. That isn't happening with the consumption listed.
Now on to the next part, assuming 80w in 8 ohms, we are going to need about 25 volts DC to get 80w into one speaker. This is peak on the transformer. So the AC out is probably going to be around 18-20 volts. If they were giving you an honest 80w into both channels, the output current would be around 3-3.5 amps x 2 channels, so around 6 to 7 amps total. We know that isn't likely with the total draw.
Figuring out which wire is which is difficult without a picture of the transformer showing the colors coming out of it. Even then it might be a pain in the ****. If you do figure out the pinout of the transformer, and the voltages are around what I listed above for the AC, it might actually work for a gainclone, depending on what device you would use for the amp, and what sort of load you are planning on driving with it.

Peace,

Dave

[Lewis Moon]

Wow Dave, that's a thorough answer. Thank you! I really appreciate it. I take it you're an EE?
There are 11 wires total:
1 white
2 grey
2 blue
2 orange
3 red
1 black

None with any sort of stripe. All 22 awg.

[Lewis Moon]

Here are some pics:

[star882]

The red and white look like the primary but check. It should be the highest resistance winding. Then connect a 100w light bulb in series with it when testing. The bulb should remain off if everything is right. Then measure voltages to determine turn ratios.
EDIT: the transformer has a copper band like some switching power supply transformers. Could there be a circuit with a pair of SCRs as a primitive switching power supply? Post pictures of the original circuit board.