[Amps] Alpha 77Dx two hole

[Mike Keller]

Hi,

Last week I purchased a “77Dx" from an SK estate.
The 3CX1500A7 was the final in my first FM broadcast transmitter, so I have always had soft spot for one.
In this case with no ability to test it before purchase and no first hand history, I rolled the dice.

When we got it home, I set about to inspect the interior and was shocked to find a tube in the second socket.
The front panel is clearly marked as a Dx, so I assume this was an after market conversion to Sx lite.

It runs daily well, making legal limit and then some, but the tune / load dial settings and some of the meter reading are wildly different from those in the manual I downloaded.
On 160 and 80 the loading control is completely at the end of range.

With two tubes in parallel perhaps the output circuit was designed to transform the combined impedance?

I really have no desire to run excess power and am thinking about converting it back to original condition. 
Opinions?
Where could i find a description of the conversion?

There is one immediate problem that I could use some advice on. The vacuum variable binds hard and stops well before reaching minimum capacitance.
This prevents operation on 20 meters and above.
I have heard that it could be a dried great problem.  Any tricks to get free it up or am I in for a teardown?
Are there any mechanical drawings available?

73
Mike
W1BNC