On Tuners and UHF Mods/Adapters

[jr_tech]

Originally Posted by Jeffhs

UHF television in the 1950s was crude compared to the '60s to now, as the stations operated with low power on very high UHF channels, 70-83. Youngstown, Ohio's first UHF channel, WFMJ-TV, now on channel 21, for example, began its operations on channel 73.

Crude and low power; Yes I agree!
Channels 70-83; No way! The Jan 1954 Radio Electronics magazine (the one with a CT-100 screen photo of Faye Emerson on the cover) has a listing of the channels on the air as of Nov. 23, 1953... It lists about 108 UHF channels on the air at that time. Most are concentrated at the lower end to middle of the UHF band (14-50), with *only 4* shown in the 70-83 range.
These were:
WLOK-73, Lima
WFMJ-73, Youngstown
WTPA-71, Harrisburg
WTVU-73, Scranton
It was likely better to use the lower end of the band at that time, for best reception.
The *first* commercial UHF station on the air in the US (after the Bridgeport experiments) was a low Ch number; KPTV-27, Portland Oregon (Sept. 20 1952).

jr

[VintagePC]

As always I'm fascinated by the amount of knowledge that folks here have. I have a UHF converter on order now and I should also be obtaining a 3D printer at some point in the future...

I do intend to take a crack at fabricating a UHF strip for my tuner (because why not? worst case it doesn't work, best case it does and may prove useful for folks wanting to do the same) and I'll be sure to make a thread here because I'm sure others will be interested in that too.

[dieseljeep]

Originally Posted by Jeffhs

UHF television in the 1950s was crude compared to the '60s to now, as the stations operated with low power on very high UHF channels, 70-83. Youngstown, Ohio's first UHF channel, WFMJ-TV, now on channel 21, for example, began its operations on channel 73. It is safe to say that these early UHF stations didn't have much range, due to their very low ERP outputs.

I did not realize that, in the early days of commercial television, most cities only had, at most, two television channels. However, I do remember seeing early editions of TV Guide and other television listings which, in many cases, showed one station being affiliated with two or more (!) networks. Some stations, located in smaller cities, were affiliated with all four commercial television networks of the time--NBC, ABC, CBS and the now-defunct DuMont network. This was often found in cities which only had one TV station; the programming from each network was carefully selected and was probably rotated from time to time, to fit into the station's broadcast schedule which wasn't that long to begin with; the stations didn't sign on until late in the day, and probably signed off as soon as prime time ended, as there were no local newscasts (as we know them today, anyway) in the very early days of commercial TV.

BTW, I did not realize, either, that Milwaukee has always had mainly UHF TV stations. The city's NBC affiliate, WTMJ-TV, for example, began and is to this day on channel 4. (One station in the city did switch to a UHF channel a couple years ago, when FOX purchased several stations in various cities and switched them to that network.) If there were any UHF stations on in Milwaukee in the early fifties, they may well have been on channels 70-83, which today is no longer used for telecasting, but for land-mobile and probably other non-video radio services.

Living in Milwaukee for my first 58 years, I remember how these channels came about.
WTMJ-TV was originally on channel 3. IIRC, Chicago and Green Bay both had channel 2. Because of the close proximity of Milwaukee to the other two channels, there was co-channel interference to the other channels, so the FCC requested WTMJ to switch to channel 4. WTMJ was another channel that carried programming from all the networks.
The next two channels were UHF. That was in the 1953/54 time frame.

[bgadow]

I have a 53 Emerson with a UHF strip installed for ch.16, which came on air locally in 54. I discovered this by accident, when I got the set working I discovered I could pick the station up great on one channel (probably 6, can't remember.)

Also, my Predicta (cheap 17", probably from a motel) has labels on it that say "use 6 for 21 and 4 for 27". I figured out at one point what city had those stations.

I think I might have some ch.16 strips in a jar somewhere, I think for a Zenith tuner.

[Dave A]

The venerable CT-100 had spaces for UHF strips usually installed with blanks unless you had a UHF station in your city. The channel dial will confirn that. And I have about a dozen NIB of the pre-tuned strips somewhere. Channels 33 and 51 I think. I think the paperwork shows how to re-tune. Not that we could see the results anyway unless you have the ultimate stars-are-in-alignment setup of a working CT-100 and a BT modulator with UHF. I will try to find one and post a photo.

[dieseljeep]

Originally Posted by bgadow

I have a 53 Emerson with a UHF strip installed for ch.16, which came on air locally in 54. I discovered this by accident, when I got the set working I discovered I could pick the station up great on one channel (probably 6, can't remember.)

Also, my Predicta (cheap 17", probably from a motel) has labels on it that say "use 6 for 21 and 4 for 27". I figured out at one point what city had those stations.

I think I might have some ch.16 strips in a jar somewhere, I think for a Zenith tuner.

I heard that Zenith made UHF strips for their early sets, such as the porthole models. There was always an empty slot in the turret, next to the channel two slot. I've never ran across one.

[DavGoodlin]

Originally Posted by bgadow

I have a 53 Emerson with a UHF strip installed for ch.16, which came on air locally in 54. I discovered this by accident, when I got the set working I discovered I could pick the station up great on one channel (probably 6, can't remember.)

Also, my Predicta (cheap 17", probably from a motel) has labels on it that say "use 6 for 21 and 4 for 27". I figured out at one point what city had those stations.

I think I might have some ch.16 strips in a jar somewhere, I think for a Zenith tuner.

Many places had the UHF channels about 6 (or 36 MHz) apart, after re-assignment of the initial generous allocation of 70 channels, when actual conditions made the lower frequency channels more available and desirable.

Harrisburg PA area channels: 15 WLYH (formerly WLBR), 21 WHP (which moved from channel 55 in 1961), 27 WHTM (which was WTPA, moving from 71 in 1957) and 33 WITF came later in 1965 as the PBS channel.

Philly area:17, 23, 29, 35....

Thanks to VintagePC for bringing up a fun subject, good exercise for aging minds....

[VintagePC]

Would anyone be offended if we took this in the direction of tuner theory? Given the tuner schematic at http://vintagepc.site50.net/site/fle...ice/TV_004.png as an example... is my understanding correct?

I gather L4 is what sets the frequency for the RF amp, and the resulting RF signal is coupled via L5/L6 to the oscillator (6J6) in prep for the IF strip at 21Mhz. L7 is presumably for fine-tuning the oscillator frequency.

It looks like if one wanted to feed in a UHF signal it would be done on J1 and fed in to L4 at a downshifted frequency to match the frequency of the RF amp on that channel strip?

Sorry if this is too specific, I'm just interested in understanding the theory of operation and also what the meaning of the 'UHF XTAL MIXER' label is and how it would be used in application.

[jr_tech]

Do you have a schematic showing the same tuner with a UHF strip? I believe the design of the strip was quite different, using the extra contact (1) to switch the UHF mixer diode into the circuit for UHF mixing. IIRC, there were also more coils that were used to double or triple the local oscillator frequency, since the 6J6 likely was a poor oscillator in the UHF range.

jr

[VintagePC]

Originally Posted by jr_tech

Do you have a schematic showing the same tuner with a UHF strip? I believe the design of the strip was quite different, using the extra contact (1) to switch the UHF mixer diode into the circuit for UHF mixing. IIRC, there were also more coils that were used to double or triple the local oscillator frequency, since the 6J6 likely was a poor oscillator in the UHF range.

jr

Alas I do not. Very little is known about the fleetwood sets from Canada; I was fortunate to have the manual with this one else I would have been up a creek without a paddle restoring it. (full scan here: http://vintagepc.site50.net/site/fleetwoodtv/service/) It shows a picture of the tuner (P. 5) and that's about it. The only other mention is on P.2 (http://vintagepc.site50.net/site/fle...e/TV_002.png):

Cascode Tuner - for clean pictures without snow, high sensitivity in fringe areas. Easily adaptable to UHF reception.

I've tried googling "Cascode tuner" in the past expecting it was a particular design or brand implementation but that was trying to find a grain of sand in a manure pile.

(Edit: whaddaya know- dieseljeep mentioned those in his post on UHF strips by standard coil. Now I'm even more interested in trying to reverse engineer something out of this)

GE's 6J6 datasheet says it can run up to 600 Mhz if configured in PP mode with the two halves tied together... which might be doable with bridging some pins on the strip, and certainly covers _some_ of the UHF range.

There may be some info in the RCC service info, I asked JustRadios but I don't think they had any info on this set.

[jr_tech]

Originally Posted by VintagePC

I've tried googling "Cascode tuner" in the past expecting it was a particular design or brand implementation but that was trying to find a grain of sand in a manure pile.

I believe that the "Standard Coil" tuner as shown in your schematic was used in a number of sets... somebody here must have more info and perhaps UHF strips for certain channels. What channel are you trying to get, anyway? nearly all of the Low Power UHF stations in the US have converted to digital...do you still have some left in your area?

Originally Posted by VintagePC

GE's 6J6 datasheet says it can run up to 600 Mhz if configured in PP mode with the two halves tied together... which might be doable with bridging some pins on the strip, and certainly covers _some_ of the UHF range.

Since the top of the UHF band went to 880 Mhz, it seems likely that some sort of frequency multiplication circuit would have been part of the UHF strip esign.

jr

[VintagePC]

I'm feeding the set basic cable and I was curious whether I could replace some of the standard VHF channels with garbage to a UHF strip for some of the higher channels which are actually worth watching.

Overall it just got me thinking about VHF/UHF and tuner operation theory and I realized how little I knew and that I was interested what knowledge had survived.

[jr_tech]

Here is a link to a PDF about the strip tuner used in the RCA CT-100 (and I suspect other RCA sets of the early 50s:

http://www.antiqueradio.org/art/RCAC...nerArticle.pdf

The design is quite different than the "Standard Coil" (Standard Kollsman, mfg?) but interesting reading for theory and operation.

jr

[Electronic M]

Cascode was a circuit topology. IIRC it meant cascaded cathode follower.

[VintagePC]

Found this tidbit in another thread here, http://www.videokarma.org/showthread.php?t=257651

IIRC, the Q strips were used in the tuner, when the RF amp was a 6BQ7.
The "Q" tuner was also designed to be used with UHF strips.

Thanks very much for this information. I did not know about this.

The tuner does have a 6BQ7 for the RF amp and a 6J6 local oscillator and mixer.

It also does have 3 UHF strips installed.

Cliff

Seems I have the Q type tuner.

It wouldn't bring much fruit until I actually have a means to fabricate the mounting strip, but does anyone have (any) corresponding UHF strip they'd be able to post some high-res photos of and measure inductances/other component values? Doesn't have to be immediately.