Follow up to EICO HF81 or Rogers PP EL84 Clone build

Tube DIY Asylum

Do It Yourself (DIY) paradise for tube and SET project builders.

I finally settled on building an EICO HF86 clone on a recycled console amp chassis. This was chosen because of the 3 tube front end on the existing chassis. Wait a Minute! the EICO HF86 uses 7247 front end tubes. Well, that tube is a 12ax7 and 12au7 in one tube so i separated out the tubes into 1 12ax7 for the input and 1 12au7 per channel for the phase splitter. I am only using 1 section of the au7 of each tube.
Interesting thing about the original amp i discovered that it was using 6cz5 or 6973 power tubes. I found this out when doing an early power up test and i had a WTF moment when i had no Anode voltage on the el84. This freaked me out for a minute until i checked the pin out on the tube sockets and found the problem. After that i had to reroute some wiring for the el84. The power supply is a little different in that i made a CLCLC of 10uf x 630v Solen, 4H x 100R potted inductor, 33uf x 450v Nichicon, 1H x 50R, 2 x 83uf x 450v Nichicon. With a 5v4ga rectifier the plate voltage on the el84 is spot on at 355vdc.
The amp was finished today and it sounds pretty sick! Very clear, clean, natural, and lots of head room. It will effortlessly go from pianissimo to fortissimo in an instant. One thing i have against PP is the artifacts that are present from phase inversion and reconstitution and global negative feedback. This amp seems to have very little of that. Whether due to the overkill power supply, the EICO HF86 circuit, or the OPT from the 6973 tubes, I never really expected it to sound this good. I will post pics in a couple of days after a thorough break in. Cheers and thanks for the help and suggestions! Dak

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Topic - Follow up to EICO HF81 or Rogers PP EL84 Clone build - DAK 17:51:54 08/20/17 (7)

EL84Ms will last longer in that role and sound great as well. - Timbo in Oz 16:28:20 08/22/17 (2)

RE: EL84Ms will last longer in that role and sound great as well. - DAK 23:11:23 08/22/17 (1)

PP EL84s are great though! :-)! - Timbo in Oz 23:33:11 08/22/17 (0)

RE: Follow up to EICO HF81 or Rogers PP EL84 Clone build - SteveSchecter 11:27:01 08/22/17 (0)

RE: Follow up to EICO HF81 or Rogers PP EL84 Clone build - Eli Duttman 01:38:37 08/21/17 (2)

RE: Follow up to EICO HF81 or Rogers PP EL84 Clone build - DAK 02:21:51 08/21/17 (1)

RE: Follow up to EICO HF81 or Rogers PP EL84 Clone build - Eli Duttman 02:36:51 08/21/17 (0)

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