You’ve hit a couple of common snags. Old designs using 741 (went out of common use 20+ years ago) and old test equipment (uses unobtainable custom values and parts) and wien bridges that really only work with specific bulbs.
To be honest, I actually am very attracted to old stuff, perhaps because I'm also (getting) old, LOL. At home I have tube radios, reel to reel players, and even three Tefifon players (forgotten technology).
The 741 designs were just what I was finding on the internet and even if they are old (which I know now) I'm guessing they still should work.
Regarding the bulbs, I have a few different ones and some circuits specified some parameters and I did find a match. Some circuits just said to use any bulb within whatever voltage range (or I forgot whatnot). I would still like to put together a bulb oscillator, at least for fun and learning.
So, basically, even if I'm testing circuits with a 741 or with a bulb I'd still like to put together circuits that work out, even if they never end up in an enclosure. I guess at the end of the day, to have a reliable piece of test equipment, I might have to look into more upgraded stuff.
Back to the G-R 1313A. If you really want to clone it, you would probably do better using a good operational amplifier, running on +30V or +/-15V power, instead of the discrete circuit used in the original. With luck and some creativity about the thermal stabilization, you could make it work.
I'd like to clone that circuit and last night I already started compiling a cart on DigiKey. For now I put all the semiconductors in that cart and I was going to compile the caps today.
I would also love to put together an upgraded clone that uses and OP Amp, but my knowledge of electronics is so limited that I would need a lot of guidance on the way. In fact, I wouldn't even know where to start. But let's say the goal would be to build a circuit that produces a natural sine wave (not a converted square wave) and to have the control pot be able to dial in the entire spectrum, without having a separate decade switch. And if it's an upgrade I might want to have a multi turn pot do that job.
I'm thinking, I should probably start a separate thread just on building the General Radio 1313A.
Purchase standard-value C0G/NP0 capacitors lower than the required value and measure them.
I'm not finding anything listed as COG or NPO on DigiKey. I'm sure they are stocking them, but they list their caps as follows:
Aluminum - Polymer Capacitors (10941 items)
Aluminum Electrolytic Capacitors (126208 items)
Capacitor Networks, Arrays (3022 items)
Ceramic Capacitors (741074 items)
Electric Double Layer Capacitors (EDLC), Supercapacitors (1733 items)
Film Capacitors (69732 items)
Mica and PTFE Capacitors (9102 items)
Niobium Oxide Capacitors (476 items)
Silicon Capacitors (267 items)
Tantalum - Polymer Capacitors (13141 items)
Tantalum Capacitors (104071 items)
Thin Film Capacitors (4197 items)
Trimmers, Variable Capacitors (2659 items)
Thanks...