Well, not quite so fast. The preamp in the picture is without a doubt a mono Heathkit WA-P2. However.........
As I have reported elsewhere on AK (and the seller may have read), with a couple of obvious exceptions, the WA-P2 preamp circuit is an exact Copy of the original Fisher 50C preamp design. So identically close that no doubt permission was required. What are the differences you ask? Well:
1. The Fisher 50C is self powered containing its own power supply, which includes a small heater supply that powers all the audio tube heaters with DC voltage. As a result, the Fisher execution has no hum. By comparison, the Heath version powers all the preamp tube heaters with AC voltage taken from the power amp it operates from, with a hum balance control provided to balance out as much of the AC noise as possible in the high sensitivity (phono preamp) circuits. Of course, it wouldn't be too terribly hard to build a small outboard power supply complete with DC heater supply to power the Heath preamp, so that it would be just as quiet as the Fisher version.
2. The volume control in the Fisher 50C is a complex 3-gang device that adjusts loudness as it adjusts level. Back in that day, some manufacturers (like Eico for example) included separate level and variable loudness controls, so that with the loudness control full up, the level control was then set for the maximum desired sound level, and as it was desired to reduce the sound level from that point, the loudness control was used to reduce it all the way to zero if desired. In this way, the loudness function always worked optimally for any given sound level, and regardless of the strength of the signal source plugged into the preamp (which can very much affect the operation of a loudness function if only a simple on/off loudness switch is provided). Fisher simply combined the level control and loudness control onto a common shaft, resulting in the complex control installed in 50C preamps.
By comparison, Heath simply used a simple, non-loudness-tapped volume control. Three terminals, no gangs of controls, easy peasy, that's it. So no loudness function is even offered with the Heath version of the Fisher 50C. Other than these points however, the Fisher 50C and Heathkit WA-P2 are dead wringers for each other circuit wise. As I've said then, if you're looking to find or build a very inexpensive preamp that comes with a definite pedigree, then the Heath WA-P2 is it!
Dave
