Is my Dynaco Stereo 400 worth repairing for resale?

Your Dynaco 400 might not need any immediate work. Put it on a variac to reform the power supply caps. Then use a multi-meter to check the DC voltage on the two speaker outputs. If those show only a few millivolts of DC try the amp with a pair of speakers. Not all old amps need parts replacement. My 40 year-old Sumo Andromeda - another Bongiorno design - has been in use 24/7 for seven years now without a hiccup! 

Under no circumstances should anyone buy "restoration" parts from Hi-Fi-Audio-Rocks on eBay.  He's notorious for send poor or wrong components and providing weak or nonexistent documentation.  There's a long thread mover at Audiokarma about this seller.

I built the Ampzilla in 1975. I paid for a rebuild 12 years ago after a 2 hour conversation with Mr. Bongiorno months before he died. I subsequently used it until I finally replaced it with a Spread Spectrum Analysis (SSA) Son of Ampzilla II amplifier, circuitry designed by Jim and finished in partnership with Jim by Wyred for Sound who physically built it and designed the beefy power supply.

A note about his name: I have only seen references to “James” Bongiorno in the last 25 years, with pictures of him usually wearing a wild colored suit with an extravagant shirt. When I met him as an 18 year old in late December 1984, he introduced himself to me as Jim and was wearing a white T shirt with a leather jacket, very biker like.

The original Ampzilla had a “dual-differential input” and had completely complimentary symmetry from input to output. I think the SWTP Tigersaurus had a complentary output stage with differential input. Others may know better, but the lineage of the Ampzilla runs through the Dyna400 to SAE 4 to Marantz 500 chain most directly. I think that the Marantz 500 was the first to use both high powered PNP and NPN transistors in its output stage.

@mswale 

Did you use fancy dancy caps and could you hear a big difference in the sound? If so, was it a good or bad difference?  I’m still trying to decide whether I want to keep the 400 or hopefully sell it.