EL84 PP Diy. Pls help me!!! - diyAudio
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Old 10th May 2006, 06:22 AM   #1
BigOx is offline BigOx  Viet Nam
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Default EL84 PP Diy. Pls help me!!!

I'd like to biuld an PP amp using EL84/6bq5 tube with 12ax7 driver. I'm a beginner, still not choose any schematic for my project. Can any one help me from beginning to build this amp? Please guide me from point to point, schematic->PSU->OPT, auto bias or fix, UL or no UL ...in short everything the best for EL84 PP. Now I have 2x12ax7, 8xel84, 1x 5u4gb, 2 5z3p. PSU: propose DIY, OPT: DIY. Thanks a lot mfs!!!
this is my proposal chassis
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Old 10th May 2006, 07:04 AM   #2
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Hi BigOx!

I think you can't go wrong with EL84 and ECC83/12AX7, at least experienced people from this forum are working with those tubes and topology - and lots of innovative ideas. Gingertube has recently published a complete schematic for a PP with EL84 and ECC83 (he uses E803CC, a similar tube).
EL84 Amp - Baby Huey

SY, another great and active member, is preparing a paper in which he describes an EL84 amp - well, that is what I think

I am making a kind of 'universal' breadboard where I will be able to test and compare the different circuits posted here. When I am finished I will post some pictures!

Erik
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Old 10th May 2006, 08:27 AM   #3
BigOx is offline BigOx  Viet Nam
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Unhappy Oh thanks

Oh! that's great to hear infos from you, thanks alot, i'll check it out.
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Old 11th May 2006, 05:08 AM   #4
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Hi, BigOx,

You might like to have a look at the Mullard 5-10 circuit, which I'm sure you will be able to find using Google. It uses EL84s in PP, with ECC83 driver and EF86 front end.
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Old 11th May 2006, 06:26 AM   #5
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Quote:
Originally posted by ErikdeBest
SY, another great and active member, is preparing a paper in which he describes an EL84 amp - well, that is what I think
I have a bag of red LEDs i'm laying up for one of SY's "red light district" PP EL84.

Another one to check out is Eli Dutton's El Cheapo... all different tubes but a lot of general info applicable.

dave
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Old 11th May 2006, 09:19 PM   #6
chrisb is offline chrisb  Canada
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Quote:
Originally posted by planet10


I have a bag of red LEDs i'm laying up for one of SY's "red light district" PP EL84.

Another one to check out is Eli Dutton's El Cheapo... all different tubes but a lot of general info applicable.

dave
Dave & I have built a pair of EL84 P/P loosely based on Eli's above mentioned design.

Note the El Cheapo uses 12AT7 for the LTP, and with a hot enough input or high gain linestage, you might even get satisfactory results with 12AU7.

A lengthy thread on the evolution of the design, and current schematic:



http://www.decware.com/cgi-bin/yabb/...;start=259#259
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Old 11th May 2006, 11:12 PM   #7
EC8010 is offline EC8010  United Kingdom
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Try to avoid 12AU7. If the circuit calls for 12AU7, substitute the far lower distortion 12SN7 or 6SN7 instead (completely different base and heater requirements, but far better).
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Old 12th May 2006, 12:02 AM   #8
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EC8010,

In a SE amp, I agree with your advice about the 'SN7. In a PP amp, I have reservations.

The 12AT7/ECC81 is not particularly linear, but works WELL combined with PP "finals". Look at the distortion spectrum of the entire amp, not any given stage.

Like the 'T7, the 12AU7/ECC82 is not highly linear. I'd like to see a HD spectrum plot of an amp using a 'U7 LTP splitter driving PP finals. IF the "waterfall" of 2nd>3rd>4th, etc. HD is present, as is the case with 'T7s, the amp will sound GOOD.

It's NICE when the whole exceeds the sum of its parts.
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Old 12th May 2006, 12:33 AM   #9
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Quote:
Originally posted by: EC8010
Try to avoid 12AU7. If the circuit calls for 12AU7, substitute the far lower distortion 12SN7 or 6SN7 instead (completely different base and heater requirements, but far better).
Yup, and if you don't wanna go octal try a 6CG7/6FQ7, same as a 6SN7 but same base as a 12AU7.

Eli, I believe arnoldc has built a PP EL34 w/ a 6SN7 going into a 12AU7 LTP. But doing a HD spectrum plot of it...
A 12AZ7 would be better than an 'AT7 due to the higher permissible (200V) cathode/heater voltage, and dirt cheap right now.

Cheers
Wayne
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Old 12th May 2006, 12:42 AM   #10
SY is offline SY  United States
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Quote:
The 12AT7/ECC81 is not particularly linear
Actually, it's quite linear. With a CCS load (Morgan Jones's "irreducible distortion"), I measure better than 0.03% THD at 15V out with current-production JJ, dominated by second HD. A little worse (0.06%) for several NOS genera.
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