Thomas's  "check connections" and PowderMonkey's comments are both good, the latter if you have an AVR with 120V, single leg sensing, which is a bad idea. 

You didn't mention an AVR.  Is is using the stock harmonic excitation?
Is this a new problem or have you never tested large 120V , asymmetric loads?  I ask because many (smaller than your ST-7) ST heads moan and vibrate badly with such a load, and regulation not good.

My first thought is to go over the basics via ohm meter:

I'd check the resistance of each set of the stator windings looking for a difference in values and documenting the resistance for future reference..

I don's see brushes or  the rotor as likely culprets due to the 120V leg voltage asymmetry.  But it never hurts to check connections, and document resistance of the rotor coils for future reference.

Best Wishes,
Bruce


 

Butch, I'm not aware of a universal voltage indicator lamp of any kind. 
I checked and it seems small neon night lights are no longer being made, they are LED instead.

The neon bulbs Glassblower linked to seem a perfect replacement element for your ST power indicator.

Bruce

Hi Butch,
My health has been poor so struggling to keep up with the basics.  Not much going on to post here.  I did replace my UV wrecked Dorman plastic radiator overflow tank with an aluminum one to keep the Listeroid 6/1 going.

Its fantastic what you've done to restore those Bamfords!

Best Wishes,
Bruce

Running a line shaft for an Amish wood shop-  What a lovely application for your 16/2 restoration, Butch. 
Lucky woodshop owner!

Very sorry to hear you're having serious health problems, 32Coupe.  I hope you'll get a reprieve. 
Best Wishes,
Bruce

https://www.caranddriver.com/features/a36062942/evs-explained-charging-losses/

This is a bit more current on actual charger/battery losses.... and they are seeing about 20% losses for charger and battery, which is way better than starting at 35%. 

ST head efficiency is more likely around 80% despite the simplicity and high THD. So add another 20% to the 80% for charger and battery losses, and it's still 60% efficiency.

So 6 gallons of diesel for 4 gallons of gas mileage is reasonable.  Cold weather is another story; the present LFP batteries need heating in cold temperatures which eats into the charge power/efficiency dramatically.  But if the fuel is free that isn't a deal breaker.

The 6/1 is pretty small for car battery charging. 
Many Chevy Bolt drivers see 3.7 miles per kilowatt hour.  Assuming 3Kwh per hour of 6/1 charging, 12 hours of charging would be 12x3kwh =36 kwhrs x 3.7= 133 miles.  If you estimate your full load fuel use for those 12 hours at 0.33 gallons per hour thats 5.2 gallons for those driven 133 miles.   133 mi/5.2 gallons= 25.5 mpg using the CS as generator for an EV.

This is consistent with my previous estimate.  The fuel consumption at 0.33 gallons per hour at 3KW is something you can check yourself as this may be off.  Plug in your own number and see what you get.

I think we are painting a darker picture than is warranted.
Using the same fuel in a diesel engine car will only result in 30% efficiency as well, so the IC engine loss is a wash; you lose it either way so it does not count.

A 65% charge/battery charge combined efficiency is often reported.  So the only question is whether that 35% loss is really a loss considering that the fuel is essentially free.  I'd say so.

This also lends itself to adding some solar so that in sunny parts of the year, the oil can be conserved and CO2 reduction is provided.