Eico HF-81 question for those that have one and moved on from it or returned

A Stereo 70 will have more power of course.
But if your Eico is as heavily rebuilt as you say, the sound differences will be mostly about the output transformers and other parts quality. Eicos came stock with ceramic disk caps for coupling caps but it sounds like those have all been changed out; OTOH the HF-81 had pretty good output transformers. The only big difference I see is the Mapletree stuff uses the 6SN7 family which IMO/IME is a better sounding tube than 12AU7s.
So my opinion is that you will be making a bit of a change for more power, not more bandwidth and otherwise slightly different sound (you'll have to play with interconnects between the preamp and amp which will affect things). I don't think it will be a dramatic improvement; with your amp you don't have to deal with the interconnect issue. It might be possible to have your amp set up with 6SN7s - that would be possible if the power transformer can support their filament requirements.

I owned a stock refurbished 81 in the 70's 80's.

The can caps were replaced and something feeding the rectifier tube was changed.  

The coupling caps were also replaced with Yellow Illinois brand caps which I was told would sound similar to the originals.

Sources were various Thorens TT's, Nakamichi cassette decks and believe it or not Beta and VCR video decks used to record LP's and to record/mix live music.

The only thing I found lacking was the 81's phono section.

I patched in the phono section of an Advent 300 receiver which easily bested the stock Eico phono section.

So maybe just try an outboard phono preamp for starters.

Though I haven't used it for years I now own a Pilot 240 integrated amp and the same thing goes.

The line inputs sound great, but the phono section is lacking.

During the time I owned/used the 81 I also used Mac 30's and various modified Dynaco Stereo 70's (in mono block and stereo versions).

The 30's were stock/refurbished and the 70 mono blocks had a tiny transformer and other parts added to the power supply (maybe used as a choke).

The above were used with the preamp section of an Advent 300 and sometimes a Dynaco PAS 3X preamp.

The 81 held it's own against the Mac and Dynaco gear.

I sold them all in 1986 and didn't own another decent rig until the late 1990's.

DeKay

thanks guys for the responses. It has been helpful.

Been a long time since I rebuild it (maybe 2002_2003).

My recollection is I used cardas wire for the signal paths, Sprague 716p to replace the coupling ceramics and Angela oil for the .1 uf caps, Riken carbon resistors in EL84 grid network with new carbon comps for others, replaced the phono section ceramics with upgraded caps and kept the metal film resistors marked West Germany as they were within 1% of value.

Upgraded the negative feedback resistors and caps and el84 bias caps (Blackgate) and resistors (Mills wire).

I found a schematic for the tone control wafers and build new ones with upgraded caps and resistors. Power capacitors were replaced.

Replaced all the rca sockets and upgraded the speaker terminals (8 ohm) to modern banana gold plated types and replaced all the tube sockets.

Oh and replaced the EZ-81 rectifiers with NOS Mullards. Only thing I didn’t touch were the vol, balance, and tone controls.

I’ve got a spare HF-81 and have often thought about using it for a custom unit without all the tape and mic stuff, tone controls, and with a modern input selector and ALPS volume control I have.

Maybe after I retire and am looking for a project. :-)

One option would be to do what I did and go with EICO HF monoblocs and a more modern preamp with a phono section. I am using a Croft 25R with rebuilt HF-35s and they are unbeatable if not somewhat hard to come by.