The classic Eico HF-87 is a very musical tube stereo amplifier. It has good bass response, and can be bridged for approx. 70W mono operation.
It was manufactured during a time when mains voltages were lower -- typically 117 VAC -- and output tubes were relatively cheap and available. In the original manual, Eico said that a "dullish red glow on the plates was normal."
Well, times have changed. Line voltages are often around 125V and tubes are no longer readily available or cheap. The higher voltages over-stress an amplifier that was already designed to operate on the edge.
This Eico amplifier was professionally rebuilt and carefully modified in order to compensate for the higher line voltages and the costly nature of output tubes, so that they will last a long time. A considerable investment was made to improve the reliability and operation:
1. All electrolytic capacitors were replaced. The two power supply voltage doubler caps are Elna LPS types, rated at 560 MFD @ 400 VDC.
2. The two multi-section caps were professionally rebuilt (with discrete capacitors) by Frontier Electronics.
3. A separate 12VAC filament transformer was provided for the 12AX7 driver tube, and the cathode bias circuits of each channel are now identical.
4. The notoriously unreliable nichrome-wound delay switch was eliminated; a thermistor was substituted to reduce inrush currents.
5. A choke was added to the B+ supply to reduce plate voltage and to stabilize and quite the supply.
6. Premium MusicCaps™ were installed for coupling caps to the output stage.
7. 1K screen grid resistors were added for tube longevity.
8. A new matched quad of Mullard re-issue EL34s (matched for current and transconductance by Jim McShane) were installed. They have very low hours of use (mostly to check for burn-in).
As you can tell, there are good reasons why this particular amplifier costs a little more than unmodified or "as-is" amps found on other auction sites. A lot of time and money went into making this Eico ready to plug in and enjoy, without worrying about tube longevity or premature failure.
I will carefully double-box the amplifier for shipment. A copy of the Owner's Manual will be provided. Look at my feedback and buy with confidence!