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Old 29th January 2013, 01:14 PM   #2611
Salas is offline Salas  Greece
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Try separate them as much as you have space first. See if the mechanical hum softens with distance.
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Old 29th January 2013, 03:14 PM   #2612
stajo is offline stajo  Sweden
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Hi. This have probably been declared many time but the thread is long and I'm about to bench the scrap trannys laying around, so I wonder if someone can be kind to recover what current each card is likely to draw with a 10 ohm resistor, and what AC under load the tranny is recommended to supply on the secondarys?

Best regards
Staffan
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Old 29th January 2013, 03:34 PM   #2613
Renron is offline Renron  United States
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12x12V 30Vac will work well for stock 63 Ohm //
15x15V 50Vac will work well for mid range hot rod 7 - 10 Ohm
15x15V 100Vac will work well for full blown Nitro Drag strip hot rod 3 Ohm = Fire breathing Dragon

Ron

Edit; Look at your own post #1581, your question has already been answered by Salas
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Last edited by Renron; 29th January 2013 at 03:39 PM.
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Old 29th January 2013, 03:48 PM   #2614
stajo is offline stajo  Sweden
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Well thank you but actually not. I wondered what current each card acrually draws, not the recommended VA on the tranny. Recommended VA according to manufactuerers spec is usually much more then the actual current draw. I also wondered recommended VAC on the secondarys but since I'm gonna dummyload my trannys they might give 14 or 16 under load and I also wondered what might be decent there. Maybe its 15 minimum?

Thanks anyway.

Staffan
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Old 29th January 2013, 04:03 PM   #2615
Salas is offline Salas  Greece
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Each card with 10 Ohm setting resistors is gonna draw +/-200mA max.
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Old 29th January 2013, 06:05 PM   #2616
Renron is offline Renron  United States
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Steffan,
I did not mean to be rude, sorry if it came across that way.
I am using a 15V x 15V 50Vac TX, after regulation my V is -9.5 and +9.7, taken at the 3 holes in the middle the board.
Using 7R0 I'm at 197mA and 179mA.
Voltage across R is +1.377 and -1.325. Measurements taken from the 3 pin output show
R= .0002 and L= -.0016 DC offset. Mezmerise board

Hope this helps.
Ron
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Old 29th January 2013, 08:28 PM   #2617
stajo is offline stajo  Sweden
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None taken, thanks for the helpful info both of you. I have a closit full of retired trannys, some of them unmarked and unmeasured. So today I made me this dummy doll.
Click the image to open in full size.
First tranny up was speced 15 VAC*2,6A*2 on secondarys wich makes 78 VA. Loaded on dummydoll it gave 2*17,7 VAC on secondarys and 2*22,5 VDC over R100 resistors. That is about 2*225 mA.

A little biggy for one card, Ill load it more and see what I get.

With 2*33 ohm load it delivers 2*16 VAC wich makes + - 18,6 VDC and it still doesnt hum or get the least warm. Thats 2*560 mA. It will take 2 cards easy, maybe even 4.

Staffan

Last edited by stajo; 29th January 2013 at 08:58 PM. Reason: another measure
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Old 29th January 2013, 11:47 PM   #2618
Renron is offline Renron  United States
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Nice to know I'm not the only dummy.
Cool bridge you made. Good idea
I've tried 50mA --->300mA, ~200mA is the sweet spot. Sounds great and runs Very cool.
Ron
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Old 30th January 2013, 07:22 AM   #2619
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Quote:
Originally Posted by Erlend Sæterdal View Post
ok then you have to buy new transformers .
these are fine as no hum exists if only one is used.

Quote:
Originally Posted by Salas View Post
Try separate them as much as you have space first. See if the mechanical hum softens with distance.
thank you! will try later.

Last edited by dtses; 30th January 2013 at 07:25 AM.
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Old 30th January 2013, 10:04 AM   #2620
stajo is offline stajo  Sweden
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I tormented the 78 VA tranny a bit more today. At 16,2 ohm load I get 16,9 VAC and 20,0 VDC. Thats 2*1,23 A, so about half its spec. It does not get warm (but load resistors do glow). I can now hear a very tiny hum with the ear close the tranny but thats nothing but normal.

I will run 4 cards and the goal is have it configurable for SE stereo, balanced stereo and 8 channel movie. If I go for the 10 ohm resistors it seems like I will end up on say 2*4*170 mA= 1360 mA total, about half the value that for the last half hour has tormented the loadresistors, and a quarter of the tranny-spec.

I'd say a 225 mA tranny that I was thinking to buy would mostly had contributed to more EMC in the case.

Well, testing with the real Mcoy is the final test but this seems like a plan. Now to glowbug/sand-matching.

Have a good day!
Staffan
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