WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
I have no hands-on experience of 100TL or TH , but a friend of mine built one a year or two ago, so I'll pass on what I know .
Bear in mind the Ra drops if you are going into A2 . He used a 10K output transformer I believe , and reported very nice results, better overall than VT4C he reckoned. You will need an A2 driver for either 100TL or 100TH .
On that basis 100TH is actually no more difficult than 100TL , in fact the voltage swing for the driver is less , which helps. The 100TH are apparently cheaper than 100TL , I'm told .
I think the start point is deciding on available B+ . My friend used at least 1000, perhaps 1200 V . From that he got about 30wpc with the A2 driver. If you can decide B+ then you should be able to narrow down an operating point with some help .
The driver my friend used was the J.Ross McDonald ACM ( augmented cathode follower ) No.2 variant, using some hefty triode-wired pentodes for the driver (CF) part .