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Old 27th January 2004, 10:46 PM   #1
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Default measuring wattage?

hi, ive got a realy old haker valve amp for my guitar, i would like to find out what wattage its producing? i have a basic grounding in electronics (qualIfied 15 years ago grade 3 technicin, gave it up though.DOH) but i havent done any thig with valves and its been a while :-)

i know theres some deadly stuff going on inside this valve stuff but i want to learn. its so old it has no markings. was going to build my own(see other posts) so thought this would be a good one to maybe strip down and play with

thx in advance for any help
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Old 28th January 2004, 09:19 AM   #2
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What are the output tubes?
What is the plate voltage on the output tubes?

Do you know the impedance of the loudspeaker?
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Old 28th January 2004, 11:36 AM   #3
SY is offline SY  United States
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You'll need a sine wave generator, a dummy load (like an 8 ohm power resistor), and an oscilloscope. Substitute the dummy load for the speaker, hook the 'scope across it, run the output of the generator into the input of the amp (use a midrange frequency like 1kHz), then turn it up until you see clipping at the output (i.e., when the tops of the sine wave start to flatten out). Reduce the level until the flattening just goes away, then look at the peak to peak voltage at the output. Average power can be calculated by squaring the voltage, then dividing by 32 (assuming an 8 ohm dummy load).

You don't need to dig into the hazardous high-voltage guts of the amp to do this measurement.

And as FB says, you can at least get a ballpark idea if you know what the output tubes are and their B+ voltage, though that requires a bit of probing around potentially lethal voltages- take precautions against the possibility of shock.
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Old 28th January 2004, 02:11 PM   #4
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there r 3 valves in there 2x Mullard(MADE IN BRITIAN) ECL 86 and a smaller Mullard E280

are they any good?

how do i measure the base voltage at the tubes?

theres is 16 ohms on the speaker

thx
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Old 28th January 2004, 02:53 PM   #5
SY is offline SY  United States
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Quote:
how do i measure the base voltage at the tubes?
Don't take this the wrong way, but if you ask that question, you shouldn't be doing it without someone experienced supervising.

In any case, with those tubes, you're probably in the 10 watt range.
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Old 28th January 2004, 03:06 PM   #6
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Default Re: measuring wattage?

Quote:
Originally posted by dudemyster
hi, ive got a realy old haker valve amp for my guitar, i would like to find out what wattage its producing?
Do you mean Hacker? If so I know the amp chassis made by this company. I've seen several in the past, and the ECL86s are run well within their limits, so I doubt that the output is above 6-8 watts.
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Old 28th January 2004, 11:48 PM   #7
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no thats fine, i didnt take it the wrong way :-). yea it is hacker , sorry spelling mistake.( god looked through post, imust look at the creen when i type :-))

i have knowledge of electronics its just i have never worked on valve stuff before! i was trained in "semi" stuff and low voltage. i just want to make sure iam going to do it correct. do the caps in these sorts of amps act like those in tv sets by holding there charge after switching off?

iam going to have a go at buiding the p1 AX84
and that is supposed to be a beginers project. iam just gathering as much info as i can b4 i start :-) iam going to get hold of a book called "the tube amp book" by aspen pittman. my guitar teacher recomends it.


thx
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Old 29th January 2004, 09:46 AM   #8
svokke is offline svokke  Belgium
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Making the P1, then I recommend you read the theory document on the P1 project page.
After that you could read the tech info on aikenamps
and If you want to dig deeper in theory, these excellent articles:
audioclass
tubecad journal
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