[Jon A.]

Originally Posted by zeno

All from memory so IIRC's apply here

2)Ultrasonic "clickers" used tuned rods hit by little metal
hammers. Used up to mid 70's at least to G line. 1-4
buttons, on/off vol, mute, channel, channel up & down & I
think tint on a few. No standardization of tones,
you could swap rods around from the junk box.
Only repairs were wire spring that held the rods broke
& a few hammer assy's.

3)Battery ultrasonics. Like your pix. IIRC all Zoom & space phone
sets used them. Used til at least M line, abt 6 years.
Tones were finally standardized. If you use a full 0-9
key as a sub for yours you can "random access" channels.

We limited repairs on electronic remotes to battery conectors
& smashed transducers. Also stocked all the battery
covers & gave them away to our "good" customers. J battery
ones would also grow crystals on the connectors & go
intermittant just clean them. All others were sold exchange
for abt. $25 made about $6 on them.

A hand unit collection would be a fun sideline collection. If
you do Zeniths try to find the Space Command cross reference
guide. it had pictures of all the remotes & part #'s & subs.
IIRC RCA also had a similar book.
Enuf

73 Zeno

I have been doing some research on the subject, so let's see if we can pool some knowledge here. Of course I don't claim to be correct on all of it.

Looks to me like the 600 is a re-named 400, introduced with the Space Command color TVs. The only difference I can see between the 600 and the late-model 400 is the labeling. At least some 600s were marked with color adjustment controls. Overall design for these used up to and including the 1973 model year. The really square 4-button ones, apparently introduced when tones became standardized on some remotes (there were two and three button versions, the latter combining the same functions into the same buttons like the earlier 500s, the other I haven't looked at), like Billy Crystal uses in an early scene from Throw Momma from the Train were used from 1974-78, 1976-78 on lower-end models when Zenith battery ultrasonics were introduced.

Not all Space Phone remotes are ultrasonic, I think just the earliest ones were, according to another post I saw somewhere around here. Also, I just purchased an infrared Space Phone remote, remanufactured, in original Zenith box for 7 bucks. It is from around 1981 according to an ad I saw. I don't normally gather infrared remotes, but this one is unique and cheap enough.

Finally, a question: how could anyone smash a transducer without completely destroying the remote?