Perhaps this is a fuitless pursuit, but I'm curious to know whether there is any surviving information on UHF tuner add-ons. By this I don't mean standalone UHF converter boxes, but rather the type that would have been sold as an optional "feature" of one's television set.

There's some interesting information in http://www.antiqueradio.org/art/RCACT-100TunerArticle.pdf which describes a combination VHF/UHF tuner and how they are two separate parts combined.

The service data for my set even makes reference to an attachment point for a UHF signal in the tuner (http://vintagepc.site50.net/site/fleetwoodtv/service/TV_004.png).

Presumably if you went for the option when purchasing the set, your dealer could then install the additional tuning mechanism (for sets with separate knobs for each) and special UHF mixer strip in place of one of the VHF channels, and it would feed the output of the UHF tuner to your IF strip.

My curiosity in how this works has me wondering if one could cobble together a functional UHF adapter in this same fashion with the correct reference literature. A schematic of an external converter could be of significant value since it would essentially be doing the same thing.

Was the crude principle behind it (excluding tuning mechanics and such) simply to frequency-shift the UHF station down to VHF frequencies with a simple superheterodyne receiver, or is there more to it than that?

Looking on a certain auction site the standalone ones seem deceptively simple with only one or two tubes. If shipping from the US wasn't often 2-3x the price of these I'd be tempted to pick one up just to see what the insides are like.

Edit: I see a few BTC-99s floating around for a reasonable price. Are those any good? Is there service literature available?

The only sets with strips I know of were Zeniths but never seen
any with them installed.

If a tuner has a UHF IF jack just about any tuner will work.
Just add B+ usually 12 V & antenna, ground the AFT if it has it.
When you go to UHF the VHF RF amp & mixer are just turned into
2 more IF stages. All UHF tuners are cap tuned as far as I know.

The RCA tuner is an odd ball, never seen anything like it.

Some probably had add on kits but with the added costs I
doubt many were sold. The set-top box is the easy way out.

73 Zeno:smoke:

Philco sets had a center mounted (between the two chassis) UHF tuner that was available as a dealer add-on or factory installed. Early 1953 model shown here: http://www.videokarma.org/attachment.php?attachmentid=168804&d=1291836085
I have seen some of the "kits" for this installation on eBay.

jr

Philco sets had a center mounted (between the two chassis) UHF tuner that was available as a dealer add-on or factory installed. Early 1953 model shown here: http://www.videokarma.org/attachment.php?attachmentid=168804&d=1291836085
I have seen some of the "kits" for this installation on eBay.

jr

That looks nice... and could almost look a match for my own copper plated chassis... Mighty tempted to get one and make it blend in to my own set in a reversible way.

Do they appear for sale often/cheap or are they much sought after by enthusiasts? I only see one at the moment.

Do they appear for sale often/cheap or are they much sought after by enthusiasts? I only see one at the moment.

I think that is the same listing that I saw a year or so ago on eBay... I suspect that they are not in great demand, although some people *do collect* the cute little set top box UHF tuners. Seems as if somebody here had one for sale.

jr

I think that is the same listing that I saw a year or so ago on eBay... I suspect that they are not in great demand, although some people *do collect* the cute little set top box UHF tuners. Seems as if somebody here had one for sale.

jr

The eBay seller churrolady from Wisconsin had some original add-on UHF tuner kits (meant for dealer installation, not consumer) in both the RCA and Philco brands over the last year.

.

The only sets with strips I know of were Zeniths but never seen
any with them installed.

If a tuner has a UHF IF jack just about any tuner will work.
Just add B+ usually 12 V & antenna, ground the AFT if it has it.
When you go to UHF the VHF RF amp & mixer are just turned into
2 more IF stages. All UHF tuners are cap tuned as far as I know.

The RCA tuner is an odd ball, never seen anything like it.

Some probably had add on kits but with the added costs I
doubt many were sold. The set-top box is the easy way out.

73 Zeno:smoke:
Standard Coil made UHF strips, for almost every tuner they built. The strips worked a little better in the cascode tuners, but they were available for the penthode tuners as well. They didn't work as well, plus the UHF transmitting power was rather weak. Once they upped the power, they worked fairly well.
I remember, Zenith used strips, more than other firms. In the Neutrode tuners there was a separate set of contacts, just for the UHF antenna.
I could go on and on about UHF tuners, as Milwaukee was a UHF town, from early 1953.

The eBay seller churrolady from Wisconsin had some original add-on UHF tuner kits (meant for dealer installation, not consumer) in both the RCA and Philco brands over the last year.

.

Yes, I bought one of those NOS Philco convertors from churrolady and did a video on it. http://youtu.be/ucJym4IYmpk?t=10m42s

https://farm9.staticflickr.com/8183/8104219811_15c1b89313.jpg (https://flic.kr/p/dm9fcM)

WOW! that's a really nice looking pair of Philcos! Interesting that they both have the slide-rule dial rather than the rotary style that both of mine have. I think that mine were both dealer installed... perhaps these are factory? I have also seen another style that is a slide-rule type, but the scale is tilted (prism perhaps), for better viewing from above.
jr

I have this brown metal box set-top converter RCA made. Connects like the Blonder Tongue units but is much older, like the Mallory units with the slide rule tuner and glass dial
Its got two channels, selected by a large gold plastic knob. 3 positions; VHF, UHF1 and UHF2. It definetly uses strips, not a variable CAP tuner.

Most of the towns (beyond fringe of 60 miles from Philly and Baltimore) here had exactly 2 channels, so this set up worked well. You likely could not get UHF more than 35 miles away, with the lower effective radiated power of these UHF's, which always shared call letters with the town's AM stations, in the early 50's.

When power increased and antennas got better:thmbsp:, the markets got larger, so some in-between smaller stations went away.:sigh:

I have this brown metal box set-top converter RCA made. Connects like the Blonder Tongue units but is much older, like the Mallory units with the slide rule tuner and glass dial
Its got two channels, selected by a large gold plastic knob. 3 positions; VHF, UHF1 and UHF2. It definetly uses strips, not a variable CAP tuner.


Interesting! Likely a model U2 (Ch KCS79), which can be pre-set to two different UHF channels and outputs on channel 5 or 6. These were also installed (sans cabinet) *inside* various RCA TVs, perhaps a dealer option.
I have a 17" metal cabinet table model RCA 17T200 that has one installed on the right side, just behind and below the speaker.

jr

Standard Coil made UHF strips, for almost every tuner they built. The strips worked a little better in the cascode tuners, but they were available for the penthode tuners as well. They didn't work as well, plus the UHF transmitting power was rather weak. Once they upped the power, they worked fairly well.
I remember, Zenith used strips, more than other firms. In the Neutrode tuners there was a separate set of contacts, just for the UHF antenna.
I could go on and on about UHF tuners, as Milwaukee was a UHF town, from early 1953.

Interesting. I gather this relied on your tuner being able to oscillate at the correct frequency - so you had to have an oscillator tube that could handle it? Or was it so that nearly all VHF oscillators could work at UHF frequencies?

Also... does anyone have comments on single-tube vs 2-tube UHF converter boxes? I heard folks say the 2 tube ones were better/less finicky, but does that still make a difference for signal quality if you feed it cable?

Interesting. I gather this relied on your tuner being able to oscillate at the correct frequency - so you had to have an oscillator tube that could handle it? Or was it so that nearly all VHF oscillators could work at UHF frequencies?

Also... does anyone have comments on single-tube vs 2-tube UHF converter boxes? I heard folks say the 2 tube ones were better/less finicky, but does that still make a difference for signal quality if you feed it cable?
It seems that the 6J6 was usable at UHF frequencies. Some sets used a 6J6 as a UHF oscillator and they lasted a whole lot longer, than the 6AF4.
Regarding: the set top convertors, the Blonder-Tongue and the Granco one tubers worked fairly well, the Regency's, not very well, if at all.
The hottest two tube units seemed the Turner's and the Radio Receptors.
I don't know how many different brand names that the Mallory's were sold as. :scratch2:

It seems that the 6J6 was usable at UHF frequencies. Some sets used a 6J6 as a UHF oscillator and they lasted a whole lot longer, than the 6AF4.
Regarding: the set top convertors, the Blonder-Tongue and the Granco one tubers worked fairly well, the Regency's, not very well, if at all.
The hottest two tube units seemed the Turner's and the Radio Receptors.
I don't know how many different brand names that the Mallory's were sold as. :scratch2:

I have my eyes peeled for a BT 99 which seems to be common and cheap.

Alternately... there's probably no reason one couldn't fabricate a UHF channel strip with a 3d printer, a few small brads for the contacts, and some calculations to figure out what the coil inductance should be....

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.

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

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. :)

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.

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.

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.

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.

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....

Would anyone be offended if we took this in the direction of tuner theory? Given the tuner schematic at http://vintagepc.site50.net/site/fleetwoodtv/service/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.

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

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/fleetwoodtv/service/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.

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?


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

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. :)

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/RCACT-100TunerArticle.pdf

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

jr

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

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. :)

Sorry for the double post... anyone have a schematic for said BTC-99? Web tells me it is Sams 259-3.

Thanks in advance. Should be simple enough to do without but I like having reference material on hand, and so I can pre-pick my parts drawer for the correct caps it needs replaced. :)

Just to see if it would work at all, I connected a tube based UHF to VHF converter to an antenna, and the output to a HDTV converter box tuned to channel 6. The tuning was rather fussy, I think because the converter box doesn't expect the digital carrier to be that much off in frequency. Also the UHF converter may add too much noise. With the UHF converter, the resulting digital carrier on channel 6 could be anywhere. A vintage TV set with fine tuning could cope easily.

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.

Slightly before the CT100 came out, the RCA all channel sets were equipped with a tuner similar to it. It either was factory, or field converted. They were equipped 19, 25 and 31 strips. Back then, channel 31 was only proposed and never materialized.
The tuner had, 2 6BQ7's, 1 6AF4 and a 6S4, voltage regulator. The 6AF4 was used as an oscillator for both, VHF and UHF and lasted a lot longer, than the ones in the UHF only tuners.
I like the tuner a lot, truly overkill at it's finest. :thmbsp:

Just to see if it would work at all, I connected a tube based UHF to VHF converter to an antenna, and the output to a HDTV converter box tuned to channel 6. The tuning was rather fussy, I think because the converter box doesn't expect the digital carrier to be that much off in frequency. Also the UHF converter may add too much noise. With the UHF converter, the resulting digital carrier on channel 6 could be anywhere.
Were you able to get any sort of stable reception of the DTV channels? I tried the same thing with no success. :(
It would be *really fun* to be able to turn the UHF knob or Converter tuning on an old tv to tune the digital channels.
jr

Were you able to get any sort of stable reception of the DTV channels? I tried the same thing with no success. :(
It would be *really fun* to be able to turn the UHF knob or Converter tuning on an old tv to tune the digital channels.
jr

Don't most converter boxes act just like a cable box in that you tell it what channel and it tunes to that and outputs on CH3? From what it sounds like you are trying to do... you'd need a box that "de-digitizes" the DTV streams on the fly and outputs them to their appropriate frequencies...

Were you able to get any sort of stable reception of the DTV channels?

Think I should have said "extremely fussy". Think I only got the strongest signals about 5% of the time. Not at all a practical thing to do. Otherwise I would have though of using an old TV tuner inside a vintage TV set, then feed its IF to the ATSC converter (upconverted to a channel it could tune, or maybe find the IF strip inside the box and feed it directly), and take the resulting demodulated video and audio and feed it to the audio amp and video amp of the TV set (bypassing the TV set's IF amps).

Don't most converter boxes act just like a cable box in that you tell it what channel and it tunes to that and outputs on CH3? From what it sounds like you are trying to do... you'd need a box that "de-digitizes" the DTV streams on the fly and outputs them to their appropriate frequencies...

And indeed, many set up a number of ATSC converters feeding B-T modulators to provide an in-house source of converted-to-analog ASTC channels for vintage TVs to "tune" on the "correct" channels with their own tuners.

What I was considering was "bass ackward" from the normal configuration, something like this:
1. Antenna connected to vintage UHF converter.
2. Converter down converts the digital signal (most are UHF) to channel 5 or 6 (common output channel).
3. Output from UHF tuner is connected to ATSC converter box, fixed tuned to ch 5 or 6.
4. ATSC box then converts the ch 5 or 6 digital signal to audio & video, which feeds the TV set.

The novelty here would be that the ATSC converter could be mounted out of sight (and out of mind) inside the TV, while the digital channels would be tuned with the UHF tuner. TV would "appear" to function as designed, without resorting to a rack full of ATSC converters and B-T modulators.
jr

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.

Yet another reason I could kick myself for letting this set slip through my fingers: I accidentally discovered a Zenith 19" porthole I once had would receive UHF channel 35 when tuned to channel 2 (or was it the empty slot? Can't verify--set's gone :( ).

And indeed, many set up a number of ATSC converters feeding B-T modulators to provide an in-house source of converted-to-analog ASTC channels for vintage TVs to "tune" on the "correct" channels with their own tuners.

What I was considering was "bass ackward" from the normal configuration, something like this:
1. Antenna connected to vintage UHF converter.
2. Converter down converts the digital signal (most are UHF) to channel 5 or 6 (common output channel).
3. Output from UHF tuner is connected to ATSC converter box, fixed tuned to ch 5 or 6.
4. ATSC box then converts the ch 5 or 6 digital signal to audio & video, which feeds the TV set.

The novelty here would be that the ATSC converter could be mounted out of sight (and out of mind) inside the TV, while the digital channels would be tuned with the UHF tuner. TV would "appear" to function as designed, without resorting to a rack full of ATSC converters and B-T modulators.
jr

That's an interesting idea. In theory there's no reason it shouldn't work... in practicality, however, I suspect that the analog first stage just isn't clean enough for what the ATSC box is expecting.

Re channel strips: It's odd you don't see more info on them floating around, but then again they're also not something that went bad easily so it's not like repair shops had jars of them on hand to service customers. OTOH... you'd think they would pop up occasionally since dealers and service folk did replace or customize them for the local stations and would therefore amass a pile of spares.

What I was considering was "bass ackward" from the normal configuration, something like this:
1. Antenna connected to vintage UHF converter.
2. Converter down converts the digital signal (most are UHF) to channel 5 or 6 (common output channel).
3. Output from UHF tuner is connected to ATSC converter box, fixed tuned to ch 5 or 6.
4. ATSC box then converts the ch 5 or 6 digital signal to audio & video, which feeds the TV set.




That's essentially what I did in post 32, but I found the tuning very fussy to get the ATSC box to do anything. Seems the DTV signal needs to be nearly dead on frequency for an ATSC box to lock onto it and decode it properly. I don't think any DTV set comes with an analog tuning front end.

The novelty here would be that the ATSC converter could be mounted out of sight (and out of mind) inside the TV, while the digital channels would be tuned with the UHF tuner.
This is definitely a fun concept, but it would not work as described even if/when the UHF converter was correctly tuned to an ATSC channel, unfortunately. The catch is that ATSC stations have digital codes as part of the signals, to identify the main channel as well as any additional channels in the signal (the 4-1, 4-2 and so on you may have seen on a digital TV or converter). Normally, this information is stored for each channel during the "channel scan" typically done with a new TV set. Even if some digital tuners can re-check for these codes each time a channel is selected or re-selected, almost certainly none can do a search "on the fly" when a signal is lost (such as when turning the knob on the UHF converter in the proposed setup). It would be cool if they could, though.

Think I should have said "extremely fussy". Think I only got the strongest signals about 5% of the time. Not at all a practical thing to do. Otherwise I would have though of using an old TV tuner inside a vintage TV set, then feed its IF to the ATSC converter (upconverted to a channel it could tune, or maybe find the IF strip inside the box and feed it directly), and take the resulting demodulated video and audio and feed it to the audio amp and video amp of the TV set (bypassing the TV set's IF amps).

The digital decoder has enough pull-in range to handle expected offsets:
the frequency steps of a synthesized tuner; transmitter co-channel offset (+/- 10 kHz); crystal tolerances. These offsets add up to considerably less than 1 MHz (probably on the order of +/- 100 kHz max). You could get there reliably with an analog tuner system with AFC (which would have to include the analog IF), or with a synthesized analog tuner, but not with a simple continuous-tuning analog tuner running open loop.

I've received my UHF converter box and finished recapping it (also replaced the selenium with a modern diode+100 ohm dropper).

It appears to work, but not particularly well. Incoming signal should be strong (fed via cable). Schematic is available on last page of Sams 259-3, which is on the ETF page here (http://www.earlytelevision.org/tv_schematic_diagrams_postwar.html) - Tip of the hat to Tom Albrecht for that!

Symptoms are as follows, all resistors check OK but haven't tested the capacitors. Electrolytics replaced, others are ceramic and can't be measured in-circuit. 6AF4 is also unknown state.

1. The entire tuning range of the converter spans about 8 channels. (62-64, got 70 once).

2. Some regions on the dial pick up FM radio stations. I attribute this to not having a proper tube shield on the 6AF4 since it is much less if I temporarily wrap it in grounded tinfoil, and said regions are likely multiples of the station's frequency. (e.g. 88.9 FM when Ch55 (~716Mhz) is onscreen).

So far there are a few things I suspect it could be, and I was hoping someone here could point me in the correct direction. As I'm interested in learning, even if you don't have an answer but just some basic circuit theory explaining how the setup works, I'm happy to listen. I do get the higher-level principle of superhet down conversion/how an oscillator works but I don't think I grasp all of the circuit blocks quite yet (e.g what the intent of each of the traps are).

I gather from the tuning range that the oscillator isn't spanning to the correct frequencies (based on the channel seems to be stuck in a narrow band of them.

B+ measurements seem reasonable. They do seem to vary a bit depending on the tuner, from about 115V to 135 as called for on the schematic. Voltage drop across the dropper resistor indicates we're drawing about 25mA B+.
The 6AF4 plate voltage (at 80v in the Sams) varies from 70-90 in a similar way as the B+. Grid voltage I have seen go from near zero up to -10 as I tune the dial.

1. Bad 6AF4? I don't have a replacement on hand, but that might be the most logical, but not the cheapest place to start... They're plentiful and can be had for a few $ but since they come from the US I pay upwards of $10 for shipping a single one... which isn't particularly cost-effective.

2. Bad UHF diode? I really don't suspect that's the case given I do get reception, but I'm curious what kind of symptoms a bad crystal mixer (1N82) would cause. I remember reading about it in a thread either here or elsewhere, but can't find it any more.

3. The tuning 'gimmick' (labelled as such below L3 in the schematic). It's comprised of two wires, one insulated, twisted together. Any idea how sensitive that is to misalignment?