Step by step scratch build of a modified Eico HF-87

[kcdonahue]

I meant to ask you, what did you think of Dave's FB loop mods? Were you as impressed as I?

Somehow I missed this post!! After rebuilding my HF-87 essentially stock outside of the HF-89 bias setup, I found it to sound to be good but not great. After making Dave's feedback mods it transformed the amp making it more balanced and listenable over the long term. I just wish I would have isolated my grounds better as it has the normal eico issues with ground loops...

Your project is moving along very nicely and looks amazing! I am looking forward to future posts for more ideas I can apply to my amp.

KC

 

[BuzzK]

Thanks KC.

I agree -- the stock HF87 was mediocre at best. Dave's mods removed all traces of listener fatigue for me, but also brought it to a level where I think it rivaled my finest tube amps.

 

[BuzzK]

Now that the power supplies and the connections to the input / output jacks have been made, it's time to puzzle over the circuit and try to figure out the best use and placement of terminal strips for the connections to the tubes.

 

[Pio1980]

EICO OPTs were some of the best made. They usually put their money in the trannys and somewhat saved on the cosmetic side of things.

One of the Battradio projects was to be a Mullard implementation of the HF-20 OPTs, have you worked with them?

 

[BuzzK]

I never have worked with that Eico model or transformer, if you intended the question for me.

 

[Pio1980]

I never have worked with that Eico model or transformer, if you intended the question for me.

OK, thanx.
I miss the hamfest days when these things could be had for $10-$20.

 

[primosounds]

One of the Battradio projects was to be a Mullard implementation of the HF-20 OPTs, have you worked with them?

Sorry, i have not had the impetus to rebuild my HF20s. For me the problem is that the 20 as you know, are a mono integrated amp. I don't really use an amp like that although by virtue of a separate power supply they should theoretically perform better.
Anyway, the pluses for the hf20 is that the OPT is potted and was made to the same quality as the whole line of Eicos like the hf87 and hf81, etc. I guess the problem is that the original manufacturer for the OPT is variable between 3 or 4 companies, but they were all good ones.

 

[RS Steve]

My experience with rebuilding two HF-87's fell flat, both units had a bad OPT so I sent both bad ones to the fellow in Maine. Received an email saying he tried twice to build new ones but failed both times, and he was returning them. About a week later I received the box and set it aside and wondering where I'd find any replacements. Decided the other day to open the box only to find one OPT in pieces with the failed new winding included. So now I'm missing a set of bells to boot. I could combine the two good OPT's and create one working unit, but still holding out searching for a pair. Both amps are completely restored other than needing transformers, they are a bit different looking with one having a notch in the iron and the other does not. One must be an earlier version I guess.

Sorry, didn't want to hijack the thread, love what your doing with yours!

 

[BuzzK]

My experience with rebuilding two HF-87's fell flat, both units had a bad OPT so I sent both bad ones to the fellow in Maine. Received an email saying he tried twice to build new ones but failed both times, and he was returning them. About a week later I received the box and set it aside and wondering where I'd find any replacements. Decided the other day to open the box only to find one OPT in pieces with the failed new winding included. So now I'm missing a set of bells to boot. I could combine the two good OPT's and create one working unit, but still holding out searching for a pair. Both amps are completely restored other than needing transformers, they are a bit different looking with one having a notch in the iron and the other does not. One must be an earlier version I guess.

Sorry, didn't want to hijack the thread, love what your doing with yours!

Hi Steve,

I think I may have some spare bells if you need them. Let me know and I'll have a look.

 

[RS Steve]

Hi Steve,

I think I may have some spare bells if you need them. Let me know and I'll have a look.

Thanks, it might be a mute point since nobody can rewind any of these from what I have learned. Hoping to find a parts unit one of these years.

 

[Squidward]

Have you talked to Heyboer about rewinding the TX? They seem have a pretty good track record of such things.

 

[nj pheonix]

 

[Pio1980]

Pix online show at least two different styles OPTs, one center clamped and another corner clamped.
Btw, HF87 topology strongly resembles Mullard-Marantz 8.

 

[dcgillespie]

There were two versions of the HF-87 -- the earliest version had a frequency response to 100kHz, while the latter version's response was only to 50 kHz. The output transformers were different between the two versions -- reflected impedance was the same with both, but the HF characteristics were different. This was also true with the HF-89, which had two different versions as well.

Dave

 

[Pio1980]

There were two versions of the HF-87 -- the earliest version had a frequency response to 100kHz, while the latter version's response was only to 50 kHz. The output transformers were different between the two versions -- reflected impedance was the same with both, but the HF characteristics were different. This was also true with the HF-89, which had two different versions as well.

Dave

I see pix of OPTs with and without the lamination core center slots, does this identity which is which?

 

[RS Steve]

Have you talked to Heyboer about rewinding the TX? They seem have a pretty good track record of such things.

I was told by many that Gary in Maine was the go to guy, he failed and I contacted quite a few other places recommended by others, with everyone saying they couldn't help me. OPT #'s are S32019 and M32019
I believe Dave G. said these could be used together, but it's been some time since I was dealing with all this and memory is not great about it.

 

[RS Steve]

I see pix of OPTs with and without the lamination core center slots, does this identity which is which?

I think one style had 32 ohm capabilities and the others 16.

 

[BuzzK]

QUESTION:

Which driver-to-output tube coupling cap should I use, and why? (Russian PIO; Theta Audio Cap (polypropylene); or Orange Drop (polypropylene).

Thanks for your input (or output).

 

[Pio1980]

What does the Theta feature besides polyprop film? Foil vs metallized, lead metal and internal termination, ect?
Are these the only caps directly in the signal path in the amp?

 

[Pio1980]

BTW, how convenient will bias checks be on the amp in place?