• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

EL84 Amp - Baby Huey

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sharkey22

Member
Joined 2008
Hi I have just resurected my ecc83/el84 stereo BH project. I have finished the power supply and would like to test it. I need to run it into a dummy load. Please can someone tell me what resistor value and wattage I should use to apply the correct load. I am no good at the maths so would appreciate help in this. Tube line-up is ecc83 x2 & el84 x4.Thanks.
 
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sharkey22

Member
Joined 2008
Testing HT power Supply.

Thanks for the replies but what I should have asked is: I want to test my Baby Huey power supply in isolation from the amplifier circuit. The power supply has choke smoothing. Am I correct in thinking that I need to apply a dummy load from B+ to ground in place of the main amp circuit. I mentioned the tube line-up (2x ECC83 & 4x EL84) so that hopefully someone can tell me the expected current draw. My estimations are about 200-210mA since each of the EL84's draws 45-50mA and the ECC83 draw about 1.5mA per plate.
I am not sure but as the PS has a choke do I need to apply a dummy load in the form of a resistor? If so what value and rating should th resistor be?

Thanks.
 
anatech

anatech

Administrator
Joined 2004
Paid Member
Hi sharkey22,
You're going to need a very high power resistor from B+ to common. The voltage rating will also need to exceed your expected supply voltage. The approx resistance will be VB+/Iexpected= ? R.

Why would you want to run the power supply in isolation? That seems way too extreme. No one I know of does that simply due to the cost of the resistor(s). They also make dynamic loads, but that will be terribly high priced.

-Chris
 
Alastair E

Alastair E

Member
Joined 2004
doctordiesel.co.uk
Why not use a couple of lightbulbs in series?

Current drawn depends on the voltage and the wattage of the bulbs, may take a little thinking out but Ohm's law's your friend here...

TBH--I cant see much point in testing the PSU in isolation to the main amp--Might as well finish it all up then test as a whole--Thats what most (I think) of us do....

Testing with a dummy load isnt going to tell you if there's an odd ground issue causing hum for instance...
 
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sharkey22

Member
Joined 2008
Thank you Alastair and Anatech....As a newbie it just seemed like the thing to do but I must admit that I could not find much on the web about testing a high voltage DC PS in isolation and I am sure that is for the reasons you mention ie. it is not necessary or practical, my particular power supply was custom designed for me by Gingertube who is the co-creator of the BH amp so I imagine it is of sound design. I reckon that it would take a 1500 ohm 60W resistor which is a hefty piece and obviously impractical. I actually thought that people in the know must have some way of testing a power supply to iron out the DC and achieve the correct voltage, however I am new to valve amp building and have limited knowledge of electronic theory so at least thought I would ask. I will now press on with the amplifier construction and see what happens under real operating conditions.
Thank you for taking the time to reply. I am always impessed by and grateful for the advice of members on the forum....Much appreciated.
 
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rhone

Member
Joined 2005
sharkey22 said:
Thank you Alastair and Anatech....As a newbie it just seemed like the thing to do but I must admit that I could not find much on the web about testing a high voltage DC PS in isolation and I am sure that is for the reasons you mention ie. it is not necessary or practical, my particular power supply was custom designed for me by Gingertube who is the co-creator of the BH amp so I imagine it is of sound design. I reckon that it would take a 1500 ohm 60W resistor which is a hefty piece and obviously impractical. I actually thought that people in the know must have some way of testing a power supply to iron out the DC and achieve the correct voltage, however I am new to valve amp building and have limited knowledge of electronic theory so at least thought I would ask. I will now press on with the amplifier construction and see what happens under real operating conditions.
Thank you for taking the time to reply. I am always impessed by and grateful for the advice of members on the forum....Much appreciated.
Click to expand...

If you haven't built many/any HV power supplies before then there is a higher chance that you have made a "beginners mistake" somewhere. Testing the supply with a 60Watt (300V x 0.21 Amps) may just reveal that error. No, you won't get the actual circuit voltages but if the light bulb doesn't glow or the fuse blows you know you have a problem, Huston! If there is light then you can confidently move on to the next stage.
The alternative is you build the whole amp, switch it on and nothing happens. There is a whole lot more circuit to troubleshoot.
I've built a handful of tube amps and I like establishing that my PS is working before I attach the audio circuit. If your a pro whose done hundreds of 'em then you could probably skip it.
 
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