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Old 30th June 2003, 01:43 AM   #61
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Hi,

Quote:
I don't need to be concern with current surge as the first resistor which is a 100ohm will prevent overload of current. right?
Correct.

Quote:
The xformer use is a 369GX (can accomodate 240VAC mains). Specs are 225-0-225 65mA for plate and 6.3V 2.5A for filament.
Easy peasy: you have 2*27 mA for the plates + the heaters: 600mA + 3*365ma (assuming a standard 6DJ8)

54+600+1.095 = 1749 > 2A slo-blo should do.

Cheers,
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Old 30th June 2003, 02:11 AM   #62
jarthel is offline jarthel  Australia
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thanks for all the help. I hope you wouldn't mind more questions in the future.

Jayel
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Old 30th June 2003, 02:15 AM   #63
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Hi,

Quote:
thanks for all the help. I hope you wouldn't mind more questions in the future.
'Course not.

Happy building,
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Old 30th June 2003, 02:33 AM   #64
jarthel is offline jarthel  Australia
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heh I have a question again. I was doing some reading on Frank's website and I found some inconsistencies with the heater requirements of the 6DJ8 family (including 6922 and 7308).

Well I plan to tube roll but 6DJ8 and 6922 have different heater current ratings. 6DJ8 has a current rating of 365mA as you mentioned. 6922 has a current rating of 300mA. 7308 has a 335m
A current rating.

Should I spec the fuse based on the 6DJ8 or 6922 or 7308?
--------------

Let's say the total current requirement for the whole circuit is:

2.349A = 54mA (for the amp) + 1.2A (for 5852) + 3x 365mA (for 6DJ8).

should I get a 2A slow-blow or 2.5 slow-blow?

Thanks again.
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Old 30th June 2003, 09:08 AM   #65
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Hi,

Quote:
should I get a 2A slow-blow or 2.5 slow-blow?
At 2.35A you better go for a 2.5A fuse.

In an ideal world one would have to change the fuse according to what tube is used to be on the safe side.

BTW, there are also the Russian 6N1P-EB/6H1P-EV at 600 mA heater current that you may want to try.

They'll all work provided the heater winding of the powerxformer is up to it, in the case of the 6N1P : 3*600 mA + 1.2 A = 3A

The slo-blo fuse will act on a fault condition such as a short.
Eventually it will melt on overcurrent as well, it will just take a little longer.

Hope this helps,

P.S. For the 6DJ8/ECC88 heater current varies from 300mA to 365mA depending on the brand.
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Old 1st July 2003, 05:08 AM   #66
jarthel is offline jarthel  Australia
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just a thought

don't I have to translate the power taken by each component and translate that into amperage passign through the primaries?

2.5A on 230/240VAC translate to 575/600W which is highly suspect as these are low power tubes.

Thanks

jayel
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Old 1st July 2003, 11:01 AM   #67
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Hi,

Quote:
2.5A on 230/240VAC translate to 575/600W which is highly suspect as these are low power tubes.
That would be correct if the 2.5A were consumed at 240VAC which they aren't.

I forgot about that completely but the fuse, when put on the primary side needs to be derated.

Luckily for us the powerconsumption seen by the powermeter is transformed back by our power transformer ratios.

So, if we assume our heater supply runs at 6.3 V and consume 2.5 A it will consume: V*I= 6.3*2.5 = 15.75 W.


You need to do the same for the rest of the circuit and than we need to find out what it looks like seen from the primary side.

It's been ages since I've done that kind of thing but I'll see if I can dig it up somehow.

Cheers,
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Old 1st July 2003, 12:26 PM   #68
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Hi,

Quote:
So, if we assume our heater supply runs at 6.3 V and consume 2.5 A it will consume: V*I= 6.3*2.5 = 15.75 W.
Using the above as an example:

Current (Amps) = Power (Watts)/Voltage (volts)

I = 15.75 W / 240V

I = 0.06666 A

Allowing some margin for inrush current at switch on, a 0.1 A slo-blo should do the trick IMHO.

So all that's left to do is calculate the total powerconsumption of the preamp, convert that back into amperes, allow some margin ( I've read upto 167%, don't know if this is correct) and off you go.

Hope this helps,
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Old 2nd July 2003, 01:15 AM   #69
jarthel is offline jarthel  Australia
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thank you frank

ps. please check my attenuator thread
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