As most have mentioned The Eico HF-85 in stock form has some issues that others including myself find to be a nuisance, as far as I know nobody makes any upgrade kits or better replacement potentiometers that fit nicely in place of the original ones. Most of the ones that do get highly praised are the ones that have been rebuilt and modified by D.I.Y. type owners and there are a several here on the AK forum that have achieved that.:thmbsp: The HF-85 can be a very nice sounding preamp but it will require a lot searching and reading with lots of work to be preformed. The ones you see on ebay are usually stock and in need of new caps and most likely other upgraded components to be real good performers yet they do seem to fetch a lot of money in that condition. I got my Eico as a basket case in very poor condition and acquired it a lot cheaper then they normally sell for so it made a great candidate for what I did to it, basically it was just a good parts donor, even the tube sockets were junk and had to be replaced. I am only using three 12AX7 tubes and the one 6X4 rectifier tube the other tubes have been removed from the circuit and so has the selector switch, the unit has been simplified and is just a bare bones preamp with tone controls, and yes I did add some double diodes in parallel each other in opposite direction to bring down the heater voltage on the remaining tubes and that works extremely well and I thank one of the members here at AK for that trick. Along with the preamp out jacks I did keep the tape out jacks because they bypass the tone controls and the level out is controlled by the volume pot and that was the way this preamp was designed stock and I liked the way that works and can be used with or without tone control. All pots have been replaced with much better ones, I used a ALPs pot for the volume and that was a major improvement over the cheap crappy stock one, I had to make short shaft extensions for all the new pots to fit with the Eico's metal enclosure. I did make a new face plate because I moved the tone pots to where was more room on the other side with the new circuit boards for the tone controls mounted over the opening where the selector switch used to occupy, that worked out very nice. The encased printed circuit wafers that sit just behind the tone pots can be upgraded to individual film caps and resistors mounded on a small PCB or breadboards from your local Radio Shack, the schematic for them can be taken from the Eico HF-81 schematic it uses the same printed circuit wafers that also sit behind it's tone pots, for some reason the HF-85 did not show those in detail on it's schematic. I used sheilded wires that are grounded from the new tone circuits to the tone pots, I believe this is part of the problem with this preamps stock noisy characteristics. While I was rebuilding the HF-85 over the past year I kept thinking if this is was going to be worth all the effort and work that had gone into it, but being that it's just a D.I.Y. hobby and after hearing what it sounds like now I think it was worth every bit of it.