I have two of these variable VHF-only attenuators, one Blonder Tongue and one Channel Master. Both are very similar in construction - the BT has a 220 ohm resistor across both the input and output, with a 1K pot between the input terminal and the output terminal. The writing is worn off the case, so no model or attenuation factor.
The Channel Master has 240 ohm resistors (1/2w film types) and a 1.2K pot between the input/output terminals. It is obviously Asian made - there was an earlier model with a slide pot, but mine has the rotary pot. It's a carbon or cermet element. I had to desolder the shield to get to the guts - not service friendly.
Down East Microwave has the schematic to follow, about half way down this page:
www.downeastmicrowave.com/journal.htm
Just make sure it's in a shielded encosure. Hammond and Pomoma make nice little boxes for this kind of use.
Cheers,