I am looking for your thoughts and opinions on how, cosmetically, to restore an EICO HF-87 I recently acquired. I picked up the HF-87 that had been in Sheffield Lab Recordings (sheffieldlab.com). Some of you may have seen this advertised, but I got it for much less than advertised, partly because of my previous restoration of one. The studio had converted the amp to rack mount and fixed bias. While quite competently done from an electrical standpoint, it leaves a lot to be desired on the cosmetic side. No matter what happens, I am doing a 100% full strip down restoration. While functional, the caps are shot and so are the tubes. It needs a complete overhaul.
My big question is, do you think I should revert it back to the original condition chassis (no rack mount) and self-bias or restore it as the studio had it with the custom rack mounting, but in a way that looks very nice? Definitely a new front panel.
I have attached a pic of one I did years ago that had a bad power transformer. Either way, I will likely lose the green paint... but I am really split on restoring to original(ish) vs. leaving it with its unique history from the company. I really could go either way and be happy.
What does everyone think?
My big question is, do you think I should revert it back to the original condition chassis (no rack mount) and self-bias or restore it as the studio had it with the custom rack mounting, but in a way that looks very nice? Definitely a new front panel.
I have attached a pic of one I did years ago that had a bad power transformer. Either way, I will likely lose the green paint... but I am really split on restoring to original(ish) vs. leaving it with its unique history from the company. I really could go either way and be happy.
What does everyone think?
Attachments
I would go back to fixed bias for sure. The cosmetics are a personal thing, but
there's no real need for a front panel unless you want to arrange the output tube
biasing from the front panel. If you make all that effort to restore the amp, then
you might as well see it too.
there's no real need for a front panel unless you want to arrange the output tube
biasing from the front panel. If you make all that effort to restore the amp, then
you might as well see it too.
Cycline3, aesthetics is a personal choice, but for my taste I like the current rack mount look. I also would keep the fixed bias if it was implemented well. (See Gillespie mods below for performance enhancement, check version of output transformers). Of course, if you prefer to restore it to original design and operating conditions you will please many.
Rayma, please explain why you would go back to fixed bias “for sure”. I have one too and thought “for sure” to perform Dave Gillespie’s modifications which includes conversion to fixed bias and GNF adjustments. See attached schematic and discussion here:
https://audiokarma.org/forums/index...e-modifications-to-the-hf-87-nfb-loop.937912/
Rayma, please explain why you would go back to fixed bias “for sure”. I have one too and thought “for sure” to perform Dave Gillespie’s modifications which includes conversion to fixed bias and GNF adjustments. See attached schematic and discussion here:
https://audiokarma.org/forums/index...e-modifications-to-the-hf-87-nfb-loop.937912/
I think fixed bias is much better than self bias. Individual bias per tube (or a DC balance control),
definitely improves the sound in the bass by equalizing the currents and minimizing DC
in the output transformer.
I would only change the nfb components if you have a scope to verify the operation.
definitely improves the sound in the bass by equalizing the currents and minimizing DC
in the output transformer.
I would only change the nfb components if you have a scope to verify the operation.
Rayma, good we agree then. I was not sure, because the HF87 comes with a bias tap on the power transformer, but it is unused and comes standard with self-bias. I believe the Gillespie modification that switches it to fixed bias and improves the NFB loop provide a good increase in performance. Dave Gillespie had done all the tweeking of the NFB components, so no need for guesswork.
Thanks for the opinions so far, if anyone else stops by, please share. Because I have lose the rack chassis and keep it. 🙂 Right now I am for keeping the fixed bias setup - since the other is original self bias, but I have several other self bias amps that sound fantastic too and require no maintenance... so I don't have a strong preference there. I don't need the little extra bit of power so that's not a deciding factor. I do like better setting of tube current.
Normally I have a very strong opinion on design and looks and this would be easy... but I am really back and forth on this one.
Normally I have a very strong opinion on design and looks and this would be easy... but I am really back and forth on this one.
It is a bit of history in itself if it was being in the recording industry? ('Provenance' they call that in the antiques trade). I think the handles could be replaced with ones could have been produced in the 60s, they look a bit out of place.
What is your goal? To sell on? In which case its history could be a selling factor, and keeping it as it is could be a factor?
What is your goal? To sell on? In which case its history could be a selling factor, and keeping it as it is could be a factor?
I don't have any plan to sell it, as much as I love the one I have already I imagine it will hang around. I too find the handles odd. The rack mount is hand made... and it is cut 4U (7") high and the handles go right to the edge. I believe they were sourced from something that was 5U or larger, as they do not look like they belong.
I like the history of the amp thing... and the convenience of biasing by pressing a button, but I really like looking at glowing tubes while I listen to music. I think I am leaning at this point on returning the EICO to its proper status, and I have a set of old Scott transformers that with a few cut sheets of aluminum, could find a nice home in the rack chassis frame.
On the other hand, the current VU meter is for bias only and I have a beautiful new pair of VU meters that in a rebuild could be both bias measurement and VU meters... hmm.
I like the history of the amp thing... and the convenience of biasing by pressing a button, but I really like looking at glowing tubes while I listen to music. I think I am leaning at this point on returning the EICO to its proper status, and I have a set of old Scott transformers that with a few cut sheets of aluminum, could find a nice home in the rack chassis frame.
On the other hand, the current VU meter is for bias only and I have a beautiful new pair of VU meters that in a rebuild could be both bias measurement and VU meters... hmm.