[ARC5] Calling All Smart People: "To Drive or Not To Drive?"

[David Stinson]

Here's one for the many people on these lists 
smarter than me (Nick, you're still my hero ;-)

This is the xtal oscillator/x4 multiplier from an
AN/ARC-5 VHF transmitter.  The tube is a 1625
https://goo.gl/photos/MsagwCjmHGCz7Yep6
I can drive it to good transmitter output with a 
little programmable oscillator, a 4:1 UNUN and
some DC blocking caps.  Grid currents on
the stock test set read in normal range.
Note that the tapped grid resistance is for metering.

Here is the TX Xtal oscillator from a BC-669.
It uses a 6L6 in straight fundimental mode:
https://goo.gl/photos/6Ttf7Qej3j22o6qf9
I've build a transistor buffer to boost the voltage:
https://goo.gl/photos/DNUbU5uCmPqx5qqG7
Please note that I removed R12 at the output 
because the input of the driven stage is resistor
loaded already.

I can still drive the transmitter only to about 
half rated output and the PA grid current is 
very low compared to an xtal.
To be fair, I think my buffer's output inductor
is faulty and I'm replacing it.
But here's the question:
Why is driving the ARC-5 stage so much 
easier than driving the BC-669 stage?

TNX OM DE Dave AB5S