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Old 07-04-2002, 07:54 AM
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Production-Run Variations, B/W Sets

After looking at pictures of two RCA 8TS30's, I noticed some variations between early-production and late-production runs that I thought were somewhat interesting. Both sets had 13-channel tuners, though. The first 8TS30 that I looked at had the familiar black-on-gold channel selector escutcheon and plain black knob, while the second set featured a white-on-black escutcheon and black kbob with a white pointer. Things got more interesting with the inside pictures. The first set had an electromagnetic ion trap like the one in the 721TS I just restored and sold, while the second set had a PM ion trap that resembled the one in my Crosley 9-408. If this thread takes off and I write more about these two sets, I'll refer to the first one as the "1948" 8TS30 and the second as the "1948-1/2" 8TS30. I would like to know what production variations, if any, have been noticed by other vintage b/w set collectors who have seen or owned multiple examples of the same model. I plan to email the current owners of both sets and find out as much as possible about these two classic tv sets..

John
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Old 07-04-2002, 07:55 AM
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Here's the outside pic of the 1948 8TS30
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Old 07-04-2002, 07:57 AM
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Here's the outside pic of the 1948-1/2 8TS30
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Old 07-04-2002, 07:58 AM
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Inside the 1948 8TS30
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Old 07-04-2002, 08:00 AM
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Inside the 1948-1/2 8TS30
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Old 07-04-2002, 09:33 AM
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John,

Interesting thread. My channel 1, 8TS30 would classify as your 48-1/2 as far as the tuning selector knob, although there is no white on the brass pointer. Inside however is the same single strap ion trap as in your 48 model. My chassis s/n tage says C001560. It would be interesting to compare everyone's s/n's with the rest of this information. I'll ad a photo of the s/n tag when I can.

As far as the tuning knob and escutcheon, those are so easily swapped around their existence in a particular set is somewhat arbitrary today, but not serial numbers.

Did you observe any chassis differences at all between the two models? Perhaps there aren't two models and just different ion traps were put in based on manufacturer's stock. You might just have an odd channel changer that someone added once if the original became misplaced at a service shop perhaps?

Rob
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Old 07-04-2002, 10:24 AM
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The knob and escutcheon could be swapped, but I really doubt it. The different ion traps indicate that there are definitely electrical differences between the two chassis. You see, the ion trap on the 1948 is an electromagnetic type which I recognize by its pole pieces and the type of thumbscrews as being the same type that was on my 721TS. This ion trap, instead of having a permanent magnet, has a pair of coils (located on the underside) which connect to the power supply via two wires. The bleeder network in the power supply must therefore provide via additional resistors and/or value variations some means to compensate for the absence of the ion trap's field coils from the circuit of the 1948-1/2. I suspect, although I haven't actually seen the speaker of either set, that there is a field coil on the 1948's speaker and a PM speaker in the 1948-1/2 which would have no field coil and require the addition of a filter choke and/or resistor to maintain proper filtering. As for an explanation of the variation, I suspect that the first production run of 8TS30's (the 1948's) contained leftover 630TS chassis which used electrodynamic (field coil) speakers and electromagnetic ion traps. Later productions may have contained a chassis designed specifically for the 8TS30 which was modified to operate with a PM speaker and PM ion trap. I also believe that the design which was licensed to companies such as AirCastle, Crosley, Fada, etc. was actually the later variation (8TS30) chassis. I own a Crosley 9-408 and Fada TV30 which support this theory since both sets use PM speakers and PM ion traps. Both sets feature the same 13-channel tuner and the black-on-gold escutcheon, but the actual selector and fine tuning knobs differ between the two sets. The Crosley's selector knob does not look line any RCA knob I've seen, while the Fada's selector appears to be like the knob on the 721TS except that the Fada's knob is painted gold to simulate a brass finish. Photos of the 721TS which I recently restored and sold can be viewed in the vintage b/w forum with more pictures and info about the 721TS and the Crosley 9-408 located at http://home.earthlink.net/~amptechsys/serv03.htm

John
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Old 07-04-2002, 10:45 AM
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In this photo of the underside of the 721TS chassis (to the right of the chassis) is the electromagnetic ion trap. It's also possible to see the leads for the speaker's field coil if you look closely. I've noted 3 different types of ion traps which were used on many 1946-1948 sets. The first is the double-field electromagnetic type used in the 621TS, 630TS, 721TS and the 1948 8TS30's which is secured by two thumbscrews which are located on top. The other two that I've seen are PM types, one being the ring type which is on the 1948-1/2 8TS30 and my Crosley 9-408 and the other is a clamp type secured by two wing-nuts and often has pieces of blue tubing on the front pole piece and black tubing on the rear.
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Old 07-04-2002, 10:48 AM
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My Fada TV30 has the clamp-type PM trap with the blue and black tubing as did both GE 800C's that I've owned.
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Old 07-04-2002, 11:56 AM
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For the technically-curious, study the power supply sections of the RCA 630TS / 1948 RCA 8TS30 schematic (Sams 54-18) and the Fada TV30 / 1948-1/2 RCA 8TS30 schematic (Sams 74-3) and note the absence of the speaker and ion trap field coils from the Sams 74-3 schematic and the presence of speaker and ion trap field coils in the Sams 54-18 schematic. Also note how the focus controls operate by increasing resistance as the control is rotated in the CW direction ... increasing focus coil current by shunting less current away from the focus coil. On the 54-18 schematic, the speaker field coil will be between the +300V and +280V points, the focus coil and ion trap are between the -18V and -100V points. On the 74-3 schematic, the speaker field will be replaced by a filter choke and some resistors, the focus coil and control network will be between the -18V and -100V points with some resistors substituted for the ion trap coil.
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