single ended output - hammond 125 SE?

[Old Tele man]

does rp = "Plate Resistance" when I'm looking in a RCA tube manual?

...yes. The FULL name is Dynamic Plate Resistance (rp), but its often shortened to just plate resistance.

how do a I get from 60k to 8k by multiplying by 2?

...the answer depends upon what circuit you use the tube in--Single-Ended (SE) or Push-Pull (PP), ie:

I) for Single-Ended (SE), you multiply rp = 60K times 1/8 and by 1/10:

rp = 60K/8 = 7.5K
rp = 60K/10 = 6.0K

...so, ANY SE-OT between 6.0K and 8.0K will work; with most likely 8-ohm secondary (speaker) but 4-ohm could also be used if available. So, the SE-OT specs would be anything between 8.0K:8 and 6.0K:8 or anything between 8.0K:4 and 6.0K:4. (SE must have "gapped" core!)

II) for Push-Pull (PP), you do the same math, multiply rp = 60K times 1/8 and by 1/10:

rp = (60K/8) = 7.5K
rp = (60K/10) = 6.0K

...but, now, the PP-OT primary must have a center tap, and any PP-OT between 6.0K and 8.0K will work. The same output load selections apply (4 or 8 ohm secondary). So, the PP-OT specs would be anything between 8.0Kpp:8 and 6.0Kpp:8 or anything between 8.0Kpp:4 and 6.0Kpp:4 (PP must have center-tapped primary).

...the 1/6-to-1/10 "range" illustrates how non-picky vacuum tubes are when using output transformers.

[mike_mccue]

Thanks very much, this is exactly what I've been trying to understand.

best,
mike