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Old 16th October 2001, 09:37 AM   #41
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Join Date: Oct 2001
struck gold!
took apart an old amp (10 yrs kenwood) and found what looks like a largish 100VA type transformer that weighs a ton..
Its a Kenwood A-522, with a 2 sets of D2340 and D1531 mated to a largish heatsink with little plasticky whitish pads
: ^) guess I dun have to worry about the heat now.
I found the Power transformer stuck on a sticker in the case. It says, Connectors F3,4,5 2A, 250V. Connectors F6, 4A 250V. PCBs with leads stuck to them are also mounted on the transformer, labelled with the F numbers. How can I use this type of transformer? There's another smallish trans nearby...
Is it possible to use this transformer as a power supply, and what do I need to buy to convert it into a suitable one?
I'm now pretty confident about placing my stuff in this amp
cos the transformer is screwed down securely, there's a largish heatsink with 4 holes for my ICs and more than enough space for my caps and circuits
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Old 16th October 2001, 11:18 AM   #42
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after removing the parts, clearing out the case, I've still no idea of the ratings of the transformer, anybody knows any links where i can identify my transformer model? the numbers on the top are L07-0328-05 JK 05h SMD
the heatsink's huge. 20 cm by 10 cm.
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Old 16th October 2001, 01:29 PM   #43
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How is VA calculated.. all the sites I visit say Voltage X Amphere. However, my transformer sez 18-0-18 1.1A 20VA. Should I trust the transformer or should I trust the sites? Looking back, I saw that paulb calculated my transformer's rating as 40VA. I think that's wrong now.. after reading more on transformers...

2nd. In Elliot's designs, he always specifies a smaller transformer voltage than what he requires as input. Will i be upsetting his design if I use a larger voltage transformer at the same VA rating? I cannot see how the filter caps or the rectifier diode can raise a +-18AC supply to a +-25 DC supply.

Thanks alot! I've gotten my case up, wired up the board, and waiting for the power supplies to make their appearance.

Now considering Monoblocking, placing two smaller transformers close together in the same case, running two channels, or using the large transformer, if I figure it out(highly unlikely.)
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Old 16th October 2001, 02:17 PM   #44
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I think I figured out the large transformer
it has 4 input pins labelled 9 10 11 12
and 11 output pins labelled from 1-5 and 7-12
Somehow I'm betting 9 and 12 are the connections for 240V and 10 and 11 are connections for 110V
But as it is, I have no way of checking the number of turns on the output, and what the numbers 1-5 and 7-12 mean
anyone has any experience with transformers like these?
Repairman or DIY fanatic?
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Old 16th October 2001, 02:43 PM   #45
paulb is offline paulb  Canada
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I think the sticker with F3, F4, etc. on it just tells what the fuse ratings are.
The VA rating should definitely be secondary voltage * amperage. I don't know why your transformer is apparently 36V, 1.1A, 20VA. Hmmm.
If you use a full-wave rectifier, the output DC voltage will be roughly 1.4 * the input AC voltage. See Rod's article on power supplies.
Maybe this page will help, it shows a dual primary transformer: Although the numbers seem to match up with what you've got, don't assume this is true.
If you're not SURE which is the primary, or what the secondary voltages are, you can do an experiment. Run a lower voltage (from your other transformer or preferably a "variac" adjustable transformer) into the "primary" and measure the voltage (you need a multimeter set to AC volts) at various points. The ratio between primary and secondary will be the same regardless of the actual voltage you apply.
Example: if you apply 12V to a 120V primary, and you see 6V on one of the secondary windings, that secondary winding will be 60V when you actually run it from 120V.
Always use a fuse when doing this experiment, and please be very careful, especially if you have 240V line voltage. If you stop posting I'll think you electrocuted yourself.
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Old 16th October 2001, 03:52 PM   #46
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Hehz I'll be careful..
I realized that after reading further..
went to TNT audio and found their article on calculating amp specs
I found that for 20W on 4ohms I only need 3.17A for 2 channels, and another 10 bux worth of caps if I plan to have rectifiers for each channel. so I'll be setting that as my target. Seperate bridge rectifiers or a single one? have you tried that? results? Think I can get a simple 50VA unit that'll give me 2.7A + the 1.1A I'll get from my 20VA trans. Should I put them in the same case next to each other or should I seperate them? plenty of space for the both of them.

I just bought mylar caps and metal film resistors.. found out that they were kept behind the counter and you had to just ASK. DOh.

I think VA's rated on the AC voltage which is 18V x the Amperage which is 1.1 = 20
can't really use 36 cos you only get a difference of 18V per peak.

Yup it does look very much like the hammond scheme. I think all manufacturers have their own datasheets and serial numbers, unless mine was made inhouse by kenwood which is Quite unlikely. Don't think any manuals from that time would have survived anyway
and I'm not paying 2.99 for a photocopy that'll reach me a mth or 2 later. Think I'll just get a slightly larger trans and leave the large trans for the next 63W project
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Old 17th October 2001, 02:50 AM   #47
paulb is offline paulb  Canada
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After thinking about, I'm not sure that paralleling two different transformers will work. I'm going to start a new thread to ask the question so others will notice, they've probably been ignoring our banter. Look for the new thread.
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Old 28th December 2001, 07:05 AM   #48
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dont use 2 non identical transformers ....... it'll cause you more troubles than you can imagine.
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