general and specific amplifier building questions

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Bernhard

Bernhard

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Joined 2002
#1
Transformer secondaries are 24Vac, recommended fuses 6.3A slow blow, 25A rectifier, 10.000 µF first cap, 140.000 µF second cap.

The toroid only 300 VA for mono, no inrush current limiter needed.

For raw testing I would like to keep it as simple as possible.

So the obvious question is, can I turn that on without blowing something ?

Does it make sense to put a 5W 0,33 ohms resistor between the caps ? and will it withstand power on surge ?

I could cut the 140.000 down to 120.000
 
#2
Hello,
If you make a crc network it will limit the current. You can take a look at the hiraga 20 watt power amp which also uses big caps. Maybe you can try putting two 5 watt resistor in parallel.
Depending on the current flow they will get hot. Lower value the current will be bigger but the charging will be faster.
Most of the time the 6A fuse will blow if something is wrong.
Greetings, Eduard
 
#3
You'll be alright
I would skip the R unless it's wirewound/ceramic
I don't think the R would limit much anyway, then if you were to increase it, it would defeat you.
I've done 1500VA with just a heavy duty power switch and that thing still works.
S
 
#5
synonymous said:
I would skip the R unless it's wirewound/ceramic
I don't think the R would limit much anyway
Click to expand...

The secondaries have about 0.2 ohms, so a little more resistance would limit the current a bit ?
Also I could measure bias at that resistor.

The transformers are a mystery, they measure 15cm x 8cm and are pottetd in plastic, but only 300 VA, that size usually has 600 VA at least.
 
#6
Bernhard said:
The toroid only 300 VA for mono, no inrush current limiter needed.
Click to expand...
- you are a bit wrong here, unfortunately. The good news is that the primary current inrush limiter will limit a charging current too. So I would propose to use an inrush current limiter (in the primary circuit) as a universal and quite simple answer to all questions.
 
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#7
Perhaps on a similar vain to the halogen lamp, I once used a small motor between a transformer and a car 1 farad cap, it was quite amusing to observe the motor suddenly buzz into life, then get slower and slower as the cap charged up.
 
#10
You could think about installing one of THESE inrush current limiters between the 10.000uF capacitor and the 140.000uF capacitor. At power up, when they are cold, these are 50 ohm resistors. Their high resistance limits the rectifier current at power up, to (24*sqrt(2)/50)=0.68 amps. Loooong after power up, when they have heated up to steady state, their resistance when 6A is flowing, is 0.3 ohms.
 
#17
Hello,
Usually a 300va toriodal does not trip the fuse.
What will trip the fuse is a to big cap after the rectifier. If you will change it into CRC network like the one used in the Hiraga there will be no need for the Ntc mentioned a few minutes ago. It is not in stock.
Greetings,Eduard
 
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