View Full Version : Transvision 7FL restoration thread


benman94
09-09-2016, 06:01 PM
When I first made the leap from radios to television sets a few years ago, I rather quickly started assembling a "bucket-list" of television sets. One of the sets very near the top of my list was a circa '47 or '48 Transvision 7 inch kit. Eventually, after some horse trading involving a CT-100, I was able to scratch the Transvision off my list; I acquired this model 7FL.

https://s9.postimg.org/iq5kufjyn/IMG_5813.jpg (https://postimg.org/image/bmxpeteiz/)

https://s9.postimg.org/llio1anyn/IMG_5814.jpg (https://postimg.org/image/r9oys6saz/)

https://s9.postimg.org/9l1teb5xr/IMG_5815_1.jpg (https://postimg.org/image/98af84nnv/)

And shown here sandwiched between two other acquisitions: a DuMont Club 20, and a good 7DP4.

https://s9.postimg.org/be4q2mr4f/IMG_6644.jpg (https://postimg.org/image/4awun0lor/)

I have a good 7EP4 for it. I had initially acquired the 7E for my Viewtone, but ultimately decided to leave it as is, with its shot 5BP4, for sentimental reasons. I'll restore the Transvision instead.

I plan to take better photographs, including under-the-chassis shots, and start assembling a cap and resistor order later. I also nabbed a 5BP4 for use while restoring the set, so as to avoid damaging the much rarer 7E should something in the set go south and take the CRT out with it. The 5BP4 and 7EP4 differ mechanically, but are electrically more or less identical.

In the mean time, does anyone here know how to test either of these tubes? Do they have to be tested in a working pre-war 5 inch chassis or a Viewtone or Transvision, or is there another possible method? I really don't want to go through the effort of restoring the set if the 7EP4 is marginal. It was acquired from a reputable member here, so I'm nearly 100% certain that it's fine. You don't know until you've seen it with your own eyes however...

Electronic M
09-09-2016, 06:07 PM
Do you have a sencore CR-70? I hear those can test scope tubes (which is basically what that set uses).

benman94
09-09-2016, 06:10 PM
I do. I tested both tubes (plus the known dead 5BP4 from my Viewtone) on the Sencore. They all read like new. I'm not putting a lot of stock in the Sencore readings. I think ion burn is likely to render one of these electrostatic deflection tubes useless long before the emissive material of the cathode goes south.

mrjukebox160
09-09-2016, 07:50 PM
Why does it look like the screen is 1/2 full of liquid?

benman94
09-09-2016, 07:54 PM
That's just a mineral oil magnifier. It needs to be cleaned out and refilled.

WISCOJIM
09-09-2016, 08:06 PM
That's just a mineral oil magnifier. It needs to be cleaned out and refilled.

I thought that was part of your "fish tanking" project!

;)

.

init4fun
09-11-2016, 09:55 AM
Hi Ben , I'm hoping for all kinds of chassis shots here when you get into it ! There is something VERY special to me about a TV that has only octals and no 7 or 9 pin "modern" tubes , I really like the prehistoric nature of sets using the big tubes . So , does it have a mains derived HV or is there some type of RF HV circuit in there ?

benman94
09-11-2016, 12:30 PM
Hi Ben , I'm hoping for all kinds of chassis shots here when you get into it ! There is something VERY special to me about a TV that has only octals and no 7 or 9 pin "modern" tubes , I really like the prehistoric nature of sets using the big tubes . So , does it have a mains derived HV or is there some type of RF HV circuit in there ?

This set uses mains derived "brute force" HV. Very pre-war in nature, despite being constructed no earlier than May of 1948 when channel one was dropped by the FCC.

It does in fact use some 7 pin miniature tubes. It uses two 6AU6s and a 9002 in the tuner, and a 6AL5 in the audio discriminator. The original 1947 and early 1948 kits didn't have the later 12 channel tuner, using a 3 or 5 channel tuner depending on when the kit was built. They also used slope detection of the sound carrier, as opposed to the true FM discriminator circuit in my kit.

There are a number of octal tubes missing from my set, so I'm going to have to sit down with a schematic and determine whether my set uses the "late-model" horizontal sweep circuit or the original version from 1947. If it does in fact use the late version, then I think I can safely say this is probably among the last of Transvision's 7 inch kits sold and constructed. I can't find any reference to 7 inchers with the 7EP4 post 1949. The original JAN tubes still in this set all have 1949 or 1948 datecodes.

init4fun
09-11-2016, 05:23 PM
Oh well , at least it's still mostly octals :D

I'm impressed with the amount of iron on that chassis , I see at least one big and two smaller transformers (or chokes ?) . I see no 5U4 so at least one of them is missing , and just curious what rectifies that evil HV supply ?

benman94
09-11-2016, 08:25 PM
On Saturday, my father and I drove down to pick up this Transvision, the DuMont Club 20, and a good 7DP4 for my blonde 621TS. The 7DP4 and Transvision weren't an issue. The DuMont is going to continue its visit at the museum for at least a little while longer; I couldn't fit it into the car. I must have transposed the dimensions wrong when I jotted them down...

https://s17.postimg.org/45dsn9byn/20160910_121744.jpg (https://postimg.org/image/tbequ3d8r/)

https://s17.postimg.org/6nzhnxxov/20160910_121749.jpg (https://postimg.org/image/k4wg6t80b/)

https://s17.postimg.org/ryx1s7ftb/20160910_121759.jpg (https://postimg.org/image/lxzcv4t6z/)

https://s17.postimg.org/5ods5z7wv/20160910_121804.jpg (https://postimg.org/image/97zpvsamj/)

The CRT tests weak but usable; perhaps when it finally dies rebuilding at the ETF will be a possibility. I have to thank Steve McVoy for allowing me to have the sets stored there temporarily, and Larry at the museum for his help in loading the sets. It was greatly appreciated.

After grabbing lunch in Hilliard, my father and I made a side trip to Cynthian Township, Shelby County, Ohio, to the site of the former Moyer homestead and visited the graves of my great-great grandparents, and great-great-great grandparents, among other relatives. We returned home late Saturday evening, and I dug into the Transvision early Sunday morning.

benman94
09-11-2016, 08:25 PM
As promised, more photographs of the set....

https://s10.postimg.org/sqcxajfq1/20160911_180245.jpg (https://postimg.org/image/n26mjnbdh/)

https://s10.postimg.org/j738h2s7t/20160911_180312.jpg (https://postimg.org/image/oii51sead/)

https://s10.postimg.org/y4bpi35g9/20160911_180348.jpg (https://postimg.org/image/owjh1dydx/)

https://s10.postimg.org/8mtayhnq1/20160911_180520.jpg (https://postimg.org/image/huljf6us5/)

https://s10.postimg.org/z95rngrx5/20160911_180528.jpg (https://postimg.org/image/ec9jistw5/)

https://s10.postimg.org/4szupc6e1/20160911_180607.jpg (https://postimg.org/image/nlbpsx2s5/)

https://s10.postimg.org/ksii8w2ft/20160911_180615.jpg (https://postimg.org/image/yyy944dat/)

https://s10.postimg.org/4isc5zrrt/20160911_180631.jpg (https://postimg.org/image/gxf46bj9x/)

https://s10.postimg.org/g969ndkk9/20160911_180653.jpg (https://postimg.org/image/fjnhb0k0l/)

https://s10.postimg.org/if0khvo0p/20160911_180836.jpg (https://postimg.org/image/nqfh2la39/)

https://s10.postimg.org/5p0xij5g9/20160911_180916.jpg (https://postimg.org/image/5c9jccn6d/)

https://s10.postimg.org/6sl1uhq3d/20160911_180922.jpg (https://postimg.org/image/5djh5rp05/)

https://s10.postimg.org/5rkt5d93t/20160911_180928.jpg (https://postimg.org/image/wpeq73tqt/)

https://s10.postimg.org/vbn3bsuhl/20160911_181116.jpg (https://postimg.org/image/nvntq06s5/)

https://s10.postimg.org/dmvck6iqh/20160911_181127.jpg (https://postimg.org/image/jnt1h95cl/)

I've determined that this set does in fact use the later FM circuit as I had originally thought. The 6SQ7 socket was rewired for a 6SN7, a 7 pin socket was added for the 6AL5 diode, and the 6V6 and sound IF tube, the 6AC7, were left as-is.

This set also has the later sync circuit which changed both the vertical and horizontal sweep circuits. The vertical and horizontal oscillators were changed from 6SN7s, to 6N7s. Luckily these changes to the kits were documented in the J.F. Rider's data.

Now for the worrisome part: the tuner. I have zero documentation on this thing, and I've never seen another like it. I strongly suspect it was Transvision specific. I hope to hell there isn't anything wrong with it, otherwise I may have to bypass it and the IF strip entirely and feed video and audio from line level into the set. Tuner repair still scares the hell out of me...

The power supplies, to answer init4fun, are pretty straightforward. The big transformer on the rear is a 750 VCT transformer for B+ and filaments. The B+ is smoothed in part by the smaller choke nearer the front of the chassis. The small transformer on the opposite side of the chassis is the HV transformer. It supplies 1700 volts at 4 mA of current to a 2X2 halfwave rectifier, in addition to the 2.5 volts for the 2X2 filament.

baursam
09-11-2016, 11:11 PM
Lucky about the Dumont 20BP4, those are often dead and very hard to find!! Great thread, look forward to reading your progress

init4fun
09-12-2016, 08:56 AM
Ben , Today is your lucky day , at least 2X2 wise .....

I just so happen to have a brand new 2X2 that I know beyond a reasonable doubt I'll never use , and I'd like to donate it to your project here , no strings attached . In fact , if you PM me your shipping address I'll send it to you totally free , shipping included .

Just so ya know , my interest here is that when I was a youngster , I watched an Uncle up in Ellsworth Maine get blown clear across the room by reaching into the back of a Transvision TV kit back in the early 1960s and that began my fascination with all things electronic . I just had to know what great force could have been in there to send him flying like that ! I collect tube radios mostly and at my age I'm reaching the end of my collecting days and I know I'll not be restoring any antique TVs that need a 2X2 , that's for sure . This tube came to me in a group purchase of radio tubes years ago and I kinda joked to myself "well I guess this one ain't ever gonna get used" and to see a set that actually needs it means it's just gotta get sent to you . I tested it on my modest little Superior TV-11 tube tester and it checks out fine , well up into the green area on the scale .

Kevin Kuehn
09-12-2016, 09:30 PM
Now for the worrisome part: the tuner. I have zero documentation on this thing, and I've never seen another like it. I strongly suspect it was Transvision specific. I hope to hell there isn't anything wrong with it, otherwise I may have to bypass it and the IF strip entirely and feed video and audio from line level into the set. Tuner repair still scares the hell out of me...


Ben, It looks like you have the same tuner that was used in the models A1 and A3 as shown in Riders 2. Unfortunately there's no tuner schematic shown there either. :scratch2: Very interesting set you have there.

benman94
09-13-2016, 08:01 PM
init4fun, I went to send you a PM regarding the 2X2, but couldn't. Shoot me a PM or an email from my profile page.

The first order of caps is in, I just have to order the micas and the HV caps now. The 0.2 μF 2.5 kV HV filter cap is going to be a real pain to find. I may end up having to parallel two 0.1 μF 2.5 kV film tubulars. I see no reason why that shouldn't work...

benman94
09-13-2016, 10:26 PM
Ben, It looks like you have the same tuner that was used in the models A1 and A3 as shown in Riders 2. Unfortunately there's no tuner schematic shown there either. :scratch2: Very interesting set you have there.

I think you're right Kevin. I pulled my copy of Riders 2. Good eye! :) It seems the tuner in the Sightmaster and Transvision 10 inch kits is identical, with the exception of the fine tuning knob. My version has a small window cut out above. There's a small plastic wheel with the FM band frequencies painted on it so it can function as a tuning dial for the FM band. The Transvision and Sighmaster 10-15 inch sets with the same tuner just have channels 2-13, no FM, so there's no need for the fine tuning dial.

benman94
09-13-2016, 10:48 PM
Kevin is 100% right. The tuner assembly in this Sightmaster 10 inch set is the same as the tuner in my kit. Only the mechanics of the fine tuning knob differ slightly.

https://s12.postimg.org/4rr8uswp9/finetune.jpg

The large pulley on the fine tuning shaft of the tuner pictured is replaced with the aforementioned painted dial on mine. Somebody HAS to have seen documentation on this tuner at some point. Anybody?

Kevin Kuehn
09-14-2016, 01:36 AM
I assume your fine tuning control will fine tune the individual TV stations as well as tuning for the FM radio band. Just makes sense that it would remain active on all channels, don't you think?

bandersen
09-14-2016, 09:52 AM
The first order of caps is in, I just have to order the micas and the HV caps now. The 0.2 μF 2.5 kV HV filter cap is going to be a real pain to find. I may end up having to parallel two 0.1 μF 2.5 kV film tubulars. I see no reason why that shouldn't work...

Allied has an ASC film 0.22uF rated for 4,000 volts.
http://www.alliedelec.com/asc-capacitors-x675-22-10-4000/70006925/