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Old 5th January 2004, 05:27 PM   #1
tiagor is offline tiagor  Portugal
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Question Beginners question(help!)


I'm currently building an EL34 PP design from Van der Veen "Modern high-end valve amplifiers" book(70W pentode/30W triode with 4xEL34 per channel). Since my electronics knowledge is very basic I must admit I could have chosen an easier amp to build but.. I just couldn't help to going the hard way

Well.. here are the questions: as I would like to be sure everything is well connected, I was wondering if I can test the Power Supply circuit first(just the power supply and check the voltages for the expected values), then connect the phase splitter and test, and only then the output stage and hope nothing blows.
Is there any problem if I connect the power supply to the mains without any load? will this kill the mains transformer or just be ok?
As to the phase splitter, may I test it without the ECC82 in the socket, or is it a no go? same with the output valves.

Thank you very much in advance, and please bear with my weak electronics skills.


PS: By the way, any DIY'ers in the Lisbon area?
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Old 5th January 2004, 06:21 PM   #2
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Default A thing or two

Hi Tiagor.

As long as the PS and coupling capacitors are not stressed by over voltage, no problem. When the splitter tube is installed, the voltage maybe a little high, so the performance, like clipping, will be slightly different then when the Output tubes are installed, loading the PS voltages down. Other than that you should be ok.
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Old 5th January 2004, 06:28 PM   #3
dhaen is offline dhaen  Europe
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Without a load, the power supply caps will hold their charge for longer. Use a meter to check that they are discharged before touching
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Old 5th January 2004, 06:38 PM   #4
SY is offline SY  United States
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Testing the amp in blocks is a fine idea.

When testing the power supply, you can substitute a power resistor as a dummy load, simulating the current draw of the circuit. Use Ohm's Law to determine a suitable value, given the total idle current draw and the nominal rail voltage. You don't have to be too exact, but mind the power rating! The advantage of this is that it draws the supply down to its actual operating voltage, will show up excessive ripple, and will also discharge the caps after you power down the supply.
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
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Old 5th January 2004, 06:44 PM   #5
miguel2 is offline miguel2  Portugal
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PS: By the way, any DIY'ers in the Lisbon area?
Yes there are, but I am in Coimbra

Do you have a schematic? Discharging the psu with a resistor is always a good thing (once got a discharge of 100u at 300VDC in my fingers, but the dark spot it left has long gone...). Which output transformers are you using?

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Old 5th January 2004, 07:14 PM   #6
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Hi Tiagor!!

As to the phase splitter, may I test it without the ECC82 in the socket, or is it a no go? same with the output valves.
Yes you can...but expect the voltages will be a litlle higher that with normal load..
And when testing put a hand in your pocket...just in case...
Good luck!

Hi miguel!
Yes there are, but I am in Coimbra
Me too!!!
I am from Coimbra too...besides now i am living in Aveiro.
Very near.
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Old 5th January 2004, 07:49 PM   #7
tiagor is offline tiagor  Portugal
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Thumbs up thanks for the replies

Thanks for all the replies, they'll most certainly prove helpful.

Miguel, the output transformer is the Amplimo(Plitron) PAT4004. It yelds 70W(30 when connected in triode mode). It has neat specifications, with a bandwidth of 22.7 Hz - 187.4 kHz. I only wished it was less expensive
For the mains transformers i'm using the Amplimo 6N606.

I'm not posting the schematics here because i do not know if it is copyrighted in any way, but you may check it on:
This is the page of a guy who built it. Just take out the bypass caps on his schematics, and you have the original thing.

By the way, I'm using silicon coated copper wire(rated up to 3A) for all the wiring but the filaments. Just coudn't find any shop that sells teflon insulated wire
As for the filament wiring, I'm just using a thick wire I found around, though I feel a bit unconfortable about it's quality for the purpose, as it's supposed to feed 6.3A through it(Should i use any special purpose wire instead?)

Take care,

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