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In Reply to: RE: apologies ... posted by rage on January 22, 2015 at 20:26:53
In my view your results are actually satisfactory having in mind that the sim does not take into account a real world transformer. It's more like "this is what you could get, now it's up to you and your choice of OPT".
Plus, 6k is more suitable and was used in the sim, and with pentodes and beam tetrodes primary impedance is more important than with triodes, i.e. there is a "sweet spot effect".
The OPTs you have used are extremely cheap and probably worse than some scavenged or recycled OPTs from old radio receivers. Just compare your results with a standard 2A3 SE amp and you'll get what I mean. Or, compaee it with other EL84 SE amps and you're going to understand why it had so much success.
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http://rh-amps.blogspot.com/
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this rh84 measures better than the last el84 amp I built. I think I ended up around 2.2% distortion at 1 watt using el84 UL with edcor iron... 12at7 led biased... so alex, I Like your design! I think i'll switch my el84 amp to it and give it a listen.
I built a RH84 from a console amp I found next to the road with a FREE sign. I was driving my pickup so I stopped and took it home.
I have a scope, function generator, dvm. Can I measure distortion with only these instruments? I'm more curious than anything.
The amp works great for what I'm using it for. Sorry for the lousy pic.
looking for some jazz and a little libations - joe strummer
Sure a scope can tell you lots, you will be able to visually see distortions. IMO for us amateurs a visual representation is more useful then a static number.Anyhow I won't spend a lot of time on it in this thread, but make sure your scope and DVM can be used at those voltages and don't float the ground.
You should find a suitable power resistor for your OPT. 8Ohm? high wattage.
Have a look at the link, it shows you what phase and symmetry and 10% harmonic distortions look like.
Farther down it shows what noise, parasitic oscillation, clipping and reservoir capacitor ripple look like.It also has a nice section on square wave testing, shows you what the altered squares mean. Also shows the effect of differentiator and integrator (tone controls) circuits.
Take your time, maybe google around a bit, check out youtube this will give you a better feel for what you might be comfortable testing.
Edits: 01/23/15
Thanks. I do have a 50w dale power resistors and heat sinks I use for a loads.
looking for some jazz and a little libations - joe strummer
I have a few other OPT:
Trancendar SE 5K/8 10W, Heyboer 5K/8 14W and Hammond 125ESE.
The only other end users of AES PT-31 have indicated trying them in low power guitar amp circuits.
For biamp with 811B at 1500 cycles up, the AES PT-31 sounded pretty good in the test amp.
Thanks for your input and review of this thread.
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