• 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.

The Red Light District - another PP EL84 amp

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#184
6EU7 is much closer (maybe identical) to an ECC83 rather than an ECC81. It will work, more or less, but will take some juggling of circuit values to optimize it, and it will still be not as good. ECC81 is cheap and readily available; the current-production JJs are easily the best ones ever made.

Good luck with the build. I've had one in my main system for some months now and have no urge to change it.
 
#185
Hi SY,

Can you elaborate more on how it will not be as good? Then I can weigh it and see if I can accept the limitations? I'm currently using the Magnavox EL84 circuit (which explains the spare 6EU7s), just wondering how this will be different?

thanks again! 🙂
 
#186
Less linear as a voltage amp which will increase overall distortion; higher source impedance which will impact bandwidth and high frequency distortion performance. You'll also have to readjust the biasing in the first stage and play around with getting the phase splitter's operating point to a reasonable spot.

Two new ECC81 are $20 here...
 
#187
SY said:
the current-production JJs are easily the best ones ever made.
Click to expand...

I agree! We use them in our kits, a design loosely based on your circuit 😉 Zero microphonics, and very low distortion before applying feedback.

Btw, I can't understand how they connected pin 9 on them. I see 6.3V on it (I'm heating them with 12.6VDC between pins 4 and 5), so it must be the center tap of the heaters, but it appears to be connected to the shield between sections (as common frame grid tubes, es. ECC88).

Have you tried ECC83s and ECC803s from JJ/Tesla? I'm interested in opinions, especially in critical phono stage use. The standard ECC83s has plates like a frame grid tube, and it appears that this technique can further reduce noise and microphonics, very important in a phono amp.
 
#189
Yes, that could probably be done, but the idea of 20 times bigger hunks of dielectric having its electron density shoved back and forth by the signal gives me heartburn from an esthetic point of view. And you are taunting the Overload Recovery Gods. I'd keep an eye on low frequency stability.

Hey, give it a try, the worst case is that it doesn't work as well as you like and you're out five bucks for some new caps. Best case is you love it and you can tell me all about it.

😉
 
#194
I was not clear enough, sorry. The LS well outperformed the Dynaco transformer (a pretty good unit itself) in high end extension. It's excellent iron. I've also done builds with James iron and am delighted by how it performs, again noticeably better than the Dynaco.
 
#195
SY said:
I was not clear enough, sorry. The LS well outperformed the Dynaco transformer (a pretty good unit itself) in high end extension. It's excellent iron. I've also done builds with James iron and am delighted by how it performs, again noticeably better than the Dynaco.
Click to expand...

Thanks SY for the clarification. Rereading your statement I now understand the inflection.

BTW, only had a chance to skim your article. Looking forward to a cold one later in front of the fire and take my time with it.

Happy Thanksgiving to one & all!

speaker
 
#196
SY said:
I was not clear enough, sorry. The LS well outperformed the Dynaco transformer (a pretty good unit itself) in high end extension. It's excellent iron. I've also done builds with James iron and am delighted by how it performs, again noticeably better than the Dynaco.
Click to expand...


Pardon my ignorance, you are referring to the OPT and not the power trans correct? For the driver stage, the transformer is not critical IIRC from your writeup?
 
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