The Dream is Alive: The CBS 205 Lives On

[John Folsom]

Hello All

In a recent thread, YOUR DREAM TELEVISION http://audiokarma.org/forums/showthread.php?t=159280

Sandy G posed this question "....A 1954-55 era 19" color set-Did any of those survive intact & working ?"

I am very pleased to report I recently completed restoration of my CBS Model 205 19" color TV. This set dates from summer or fall of 1954.

Scott AVitt at Hawkeye picture rebuilt the 19VP22 CRT last February, using an off the shelf 21" round tube gun, as there are no exact replacement guns available for the 19VP22. This tube was rebuilt using the custom made "double cycle " oven control cam, which allows Scotty to process the tube using a 6 hour oven cycle, as opposed to the standard 3 hour cycle, and operates the oven at a reduced temperature. The hope was to improving the chances that the CRT would survive the trip through the oven. The 19VP22 has a large metal flange and glass to metal frit seal around the front of the cRT, similar to the predecessor 15GP22 CRT, but features the CBS-Hytron invention of placing the phosphor dots directly on the screen. The first photo shows an original 19VP22 (left) and the rebuilt 19VP22 (right). Note the reduced length of the neck of he rebuilt tube, due to the shorter replacement gun length. Fortunately, the CRT survived the rebuild, and the replacement gun works very well. The only adjustment that had to be made was to reduce the CRT G3 focus potential from the 9-10KV required by the 19VP22 to the 3-4KV required by the replacement gun. A simple rebalancing of the resistive divider network around the focus pot accomplished this.

The CBS 205 featured a split chassis design, with an RF/IF/Chroma/Video/Audio chassis, and a LV/HV Power Supply Deflection and Convergence chassis. For those of you who like to look under the hood, the next 5 photos show top and bottom views of the chassis.

Rebuild of the chassis was pretty much the standard process. First, replace all the wax paper and electrolytic capacitors. I also replaced the silver micas, as I did not want to be back in the set later on chasing a bad mica capacitor. I replaced any grossly out of tolerance resistors, checked and replaced tubes as required, checked all inductors and transformers for continuity, and then brought it up on the VARIAC to see what it would do.

In actuality, the rebuild of this set has taken place over a number of years. The steps just described were initially completed over the course of several months, and I brought the set up on the VARIAC, and had nominal performance. But the CRT was very weak, and the Beltron rejuvenator would not make it any better. So I set it aside and moved on the greener pastures, hoping someday to find a better CRT.

Eventually I acquired a DUD 19VP22, still under vacuum, from a friend and then managed to get all the ducks in a row required to have Scotty rebuild the CRT. A fantastic video on DVD, captured and produced by Bob Galanter, documents the rebuild of this tube and several others at the Hawkeye facilities. Alas, I was unable to attend this histoic event in person. Bob will debut this fascinating video at the ETF convention.

Upon receipt of the rebuilt CRT, I set up the chassis on the bench with the CRT and brought it up. The only modifications required were to change the focus voltage from the 9-10KV required by the 19VP22 gun to the 3-4KV required by the replacement gun. This was accomplished by a straightforward rebalancing of he resistive divider network around the focus pot. Next I gave the set a swept IF alignment, and now the set works very well.

The convergence is not good at the edges, but the CBS service data for the set indicates this is to be expected. And the purity could be better, but after all, that cRT has has quite a long and rugged existance over the years. And this was the first magnetically converged CRT.

The next 4 photos are vanity shots of the cabinet. Quite a handsome TV, no? When I got the set, the only knobs it came with were the channel selector, UHF and fine tuning (3 knobs on one shaft). A generous friend loaned me one each of the 3 knob types used for the "small" knobs. Using silicone RTV rubber, I made casts of each of these 3 knobs, and cast replicas in liquid plastic. The next photo shows the original knobs (left) and the reproductions. Not perfect, but a lot better than no knobs! I elected to tint the knobs dark black because I could not cast all the knobs simultaneously, so color matching the original dark grey color would have been very difficult. But they look good on the set, and seem to match the channel selector knob pretty well. You serious students may have noticed that my on/off volume knob is actually a channel selector knob. This was the best I could do rummaging around through my knob box. My friend who loaned me the "small" knobs was missing the channel selector knob and the on/off volume knob on his set. So my next task is to reproduce my channel selector knob for him, then make a version of that same knob with the embossed channel numbers removed. This will give both of us a complete set of knobs Hooray! The original on/off volume knob had "on/off volume" embossed on the front of it. Anyone out there seen this knob? I would certainly be interested.

The last couple of photos are screen shots of the set operating. The photos do not do the set justice, it looks better in person.

Well, that is about it for the CBS 205. It has been a long an fulfilling adventure bringing this old gal back to life.

Hope to see many of you AKers at the ETF next weekend.