What are the differences between the straight Recording and the Recording w/F? I know the bells are different (8 vs 8.5), but how about the tuning slides? Are they interchangeable? Would it be feasible to add a valve to a straight horn? It looks like you'd have to at least remove 2 braces, but if the distance from the neckpipe to the bell centerlines is different, it would require a different tuning slide, and wouldn't really be feasible.

I think the tuning slides are the same. Olds compensated for the larger bell by having an offset between the mainline valve knuckles on the R-20.
<ATTACHMENT filename="knuckle.jpg" index="0">[attachment=0]knuckle.jpg</ATTACHMENT>

I'll try to remember to measure my R-20 this evening.

I've considered the possibility of fitting an R-15 bell flare/tail to a R-20, but I wouldn't want to hack up a working instrument (or two) just to appease my curiosity, and the necessary parts haven't come my way.

Ah, I see, so you'd have to extend the main bell brace. There's a Recording valve and wrap for sale on ebay. I was thinking about it, but I don't think ill do it if it's not just a drop in replacement. Thanks for pointing out that offset. I didn't notice that.

[quote="hyperbolica"]Ah, I see, so you'd have to extend the main bell brace. There's a Recording valve and wrap for sale on ebay. I was thinking about it, but I don't think ill do it if it's not just a drop in replacement. Thanks for pointing out that offset. I didn't notice that.[/quote]
There might be enough extension in the R-15 brace to compensate for the offset (I think it's less than 1/2") - or you could just use a piece of copper tubing to extend the brace (the advantage of three-piece braces vs. the one-piece design used on Supers). You'd still need to find the saddle for the lever, though.

I think a better use for this setup would be someone who has an R-20 (or close cousin, like an A20 or V-20) with a cracked/twisted knuckle.

Tuning slide width is not the same for the R15 vs. the R20.

~4.69" for the straight Recording.

~5.24" for the Recording w F- attachment.