Futterman. Jump in? Or, not so fast...

Harvey worked with Mr. Futterman before the latters passing, and bought the rights to the Futterman name and OTL design shortly before that came to pass.

One of the reasons the NYAL amps were unreliable was Harvey used surplus photoflash capacitors in his power supplies. They were rated 600uf @360V; about an inch in diameter and about 5" long. These parts were not suited for power supply duty as they didn't survive ripple current very well. So even if they were new when installed they would not have been reliable. If you see these parts in an NYAL amp they all need replacement.

Go for it!!
When I spoke to Julius about my H3aa, he said:
- Matched tubes weren't needed.  The tube set can be "Balanced" via the balance pot and measuring pins in the 7pin socket to ground.  Pins 5 and 7 comes to mind.  But it has been a few years. No specific value.  Just equal.  But having a spares is a good idea.  6LF6s are getting harder to find.  I notice a source for them in this thread.
 -Of course test the tubes.  Especially for shorts.   
- If the balance voltages are way off,  check the wire fuse in the cathode circuit.  He had placed some replacements in a sleeve inside by the fan.
-may have to swap an upper tube with one of the lower to dial in the balance.  Do one pair at a time.  He had always been able to balance them.  As have I.

Other little info as memory serves  The "Bias" adjustment pot is not output tube bias.  They are "self biased".  It adjusts the plate voltage of the, phase inverted tube?  90 volts? Measured on that 7 pin socket.  Pin2 again comes to mind.  Have to trace it out.  Be very careful.  Those photoflash caps can do harm.  Even if the unit has been off for a few hours.  The B +or- bus under those 6 capacitors run close to the edge of the top cover/chassis.  Arced a good part of my 1/4" flat blade out.   Feedback came up in the thread.  The number 60db of feedback rings in my memory.  I contacted George Kaye to source replacement tubes. None.  But he has a modification to convert the 6LF6s to Triode.  Eliminating the need for the Screen regulators.  Another pair of 6LF6 would be installed their sockets.  If a problem arises with the screen regulator/s, this might be a way to go.
And finally LOL, Julius was my kind of guy.  "Sailor mouthed".  Some may take offense.  Made me chuckle throughout the conversation.
  

I will look for them but recently I saw the hand typed instructions Julius provided for making adjustments to the H3. This was one of the areas where Roger simplified the design, using a 6 position switch and meter so one could easily take readings and adjust accordingly.