Old B/W IF Alignments Almost Too Simplified

[jshorva65]

Well, I just found the ultimate alignment instrument for these sets with 23.5 MHz IF center frequencies. The Philco 7008 Visual Alignment Generator is truly the nearest thing to a 23.5 MHz equivalent of the (44 MHz Only) B&K 415. I bought my Philco 7008 on eBay and it was already known to power up per the auction listing. When I received it, things turned out even better than I expected as I found that some prior owner had already installed a full complement of new Orange Drop caps. I added a 1A line fuse, ordered the manual from A.G. Tannenbaum, and set about checking calibration as soon as I got the manual. It was amazingly close to its +/-1% specification for the Marker dial, but the Sweep dial was running about 5%. Since the seller wasn't aware of the need to put two 8-32x3/8" locking screws into holes provided on the bottom and secure them to prevent the EMR modulator from being bounced around during shipment, one of the (still soft and pliable) rubber suspension cushions had slipped out of place and needed re-positioned. After fixing that, I set the Sweep dial to track within +/-1% on both bands. Next, I brought all 3 bands of the Marker dial into factory spec. Next, I finished up by setting the maximum sweep width to exacly 15 MHz and ordered a NOS 3MP1 CRT as a spare since I plan on putting LOTS of hours on the still-usable original tube.

Setting both the Sweep Center Frequency and Marker dials to 23.5 MHz via the built-in crystal calibrator and vernier dial interpolation and injecting a digitally-verified marker for a 750 kHz marker interval (using my Precision E-200-C RF Generator as the second marker source and Elenco frequency counter to verify exact 750 kHz output) via the "chassis eddy current" injection method, the marker points with the sweep width at 8 MHz were 19.75, 20.50, 21.25, 22.00, 22.75, 23.50, 24.25, 25.00, 25.75, 26.50, and 27.25 MHz. I had already pre-set all the IF couplings and traps via the pre-alignment procedure in the RCA 630TS service manual for the pictured Fada 799 chassis. Here are the results of the fine-tweaking of the curve as displayed on the Philco 7008.

[Tube TV]

Interesting , I might look around for one of those myself .
That is the first one of those i've ever seen .
How much would you say it weighs ?

[jshorva65]

Per the Manual, the unit weighs 36-1/2 pounds (with cables stored in the provided side storage compartment), is 16"Hx16"Wx12-1/2"D in Operating position. The CRT is mounted in a compartment which pivots into a recess at the rear of the cabinet for carrying/storage and the light shield also telescopes into the front panel so that the instrument folds to only 6-1/2"D for carrying. It consumes only 70 watts and compensating load resistors are switched into place across its power supply automatically to maintain a constant load and constant output voltages when functions and operating modes are changed via front-panel selectors.

The nearest equivalent to this instrument is the Hickok 610A, although the Hickok unit requires an external oscilloscope for display of sweep output.

I have encountered only three "would be nice if it did this, too" feature omissions.

1 -- There is no provision for the fixed crystal calibrator output alone to be directed to the Output jack (without also having the variable Marker oscillator active).

2 -- There is no provision for connecting an external crystal (the calibrator crystal and its socket are inside the unit with no means of access other than by removing the entire chassis from the cabinet).

3 -- No external connections for the horizontal sweep signal (input or output) are provided. To provide display on an external scope (for example, if a screen larger than the internal 3" display is desired), a scope having the AC Line as a timebase option with a built-in Phasing control or some means (an external variable-phase AC line signal derived from a filament transformer via a phase control network) of providing a synchronizable 60 Hz sine sweep to the scope is needed.

[jshorva65]

One other, relatively minor, shortcoming of the Philco 7008 is that it doesn't use Post-Marker Injection as the B&K 415 and the similar Heathkit unit for 44 MHz IF do. Post-Marker systems insert the marker(s) into the display AFTER the sweep signal passes through the IF stages under test, so that the marker "pips" appear on the display without the marker frequencies actually being injected into the circuitry under test. Only the SWEEP signal passes through the Generator cable into the TV circuitry and the MARKER insertion occurs between the Probe and the Vertical Input of the Scope. This shortcoming of the Philco 7008 makes it somewhat more tricky to avoid distortion of the response curve caused by marker injection. I am not aware of any self-contained Post-Marker type units for the older 22-24 MHz system, however, RCA manufactured a Marker Adder for use with external generators and scope which did actually produce a Post-Marker sweep. Unfortunately, its use of multiple individual instruments and the resultant interconnections which were required represented another potential source of distortion.

Is anyone aware of a self-contained Post-Marker instrument which supports the older IF systems?

[jshorva65]

Per my ongoing research, I have determined that there was at least one self-contained Post-Marker sweep generator system which was compatible with 24 MHz IF systems. That unit was the Eico model 369.

The Eico 369 also produced its sweep output via a fully-electronic modulation circuit, eliminating all of the potential mechanical issues associated with the "EMR" modulation systems used in many other instruments of similar vintage. The only "moving parts" in these units are their operating controls and switches.

Since the Eico 369 was available in factory-built and kit form, there are potential "workmanship issues" with a unit which was built from a kit. Most of these are easy to spot and correct during recapping and calibration, however. Also, if the Scope cable is missing, the "Twinax" connector (similar to the one RCA used for RF Out on the WR-69A) required for making a replacement cable may be difficult to find.

Post-Marker upgrade instructions for the model 368 were also featured as a project article the April, 1969 issue of Service magazine. I have just bought an Eico 368 with the Service magazine upgrade installed and with all accessories and documentation included. The unit was shipped Monday afternoon via USPS, so I expect its arrival in about a week.

In my original post on this topic, I described one method of obtaining a multi-marker display using two marker sources, and the IF system used in the example was RCA. When aligning a Dumont receiver, the 750 kHz "Interval" frequency will remain constant and the "Master" marker frequency should be set to 24.15 MHz per the following calculation, where "F" is the unknown Master frequency to be used and "P" is the known Picture Carrier IF value from the Service Manual of the set to be aligned (P = 26.40 MHz for most Dumont chassis):

F=(P-25.75)+23.50

The third marker on each side of center will be the correct Sound and Picture carrier marker respectively for the chassis under test. The fifth marker from each side of center will be at the correct Adjacent Picture and Adjacent Sound trap marker positions.

[jshorva65]

Tuner alignment is seldom required unless capacitors and/or resistors inside the tuner required replacement during the recapping of the chassis or some other "major surgery" on the tuner was required for other reasons (as correcting a previous repair which had been done poorly). A response check of individual channels can be set up in a manner similar to the IF setup described above, but with the Sweep center and Master marker settings changed to those of the channel to be checked or aligned and the injection point moved to the Antenna terminals. Service manuals generally include the basic procedure.

Oscillator alignment using the Sound Carrier frequencies of each channel as Sweep center and Master markers, turning off the Interval marker, and narrowing the Sweep Width to about 200 kHz can be accomplished with great accuracy on sets having Discriminator sound circuits by viewing the S-curve at the Sound Detector output and setting the marker at the center of the S-curve for each channel. This applies to switch-type tuners such as those used in RCA models 621TS, 630TS, 721TS, and similar which have provisions for Oscillator alignment on individual channels.

Also, the RCA Service Manual for the 630TS includes a procedure on Page 18 to diagnose and correct Oscillator Pulling. If the correct settings of individual Oscillator adjustments become progressively farther from center and/or entirely out of range of the trimmers with each of the channels below 13 or 6, Oscillator Pulling is the most likely culprit.

RCA tuners (and many others) of late-1940's vintage use push-pull circuitry in the RF and Oscillator stages, and a proper "balance" between the two triode sections of the 6J6 tube used in each stage is critical. A properly-balanced 6J6 is also important in the Mixer stage, but is absolutely critical for RF and Oscillator tubes, just as proper balance is essential in Driver and Output stages of push-pull circuitry in Hi-Fi amplifiers. Oscillator Pulling effects may be reduced by employing a Dynamic Mutual Conductance tube tester to identify properly-balanced 6J6 tubes for use in these critical stages.

If preliminary tests indicate that the tuner does not need alignment and all tubes are "Good" this indicates that any imbalance observed with the tubes' test results had been compensated adequately and has not changed since the tuner was last aligned. In other words, "If it isn't broken, ..."

[jshorva65]

First, a question. I remember having read somewhere that either Tele-Matic or Channel Master marketed a line of replacement tuner shaft and detent assemblies for various makes of TV tuners and seeing a listing of available types (with photos and part numbers) somewhere online. I also remember that shafts for the RCA 630TS and similar models were available and that there were two versions of the RCA-type shaft having very similar appearance. Is anyone else aware of these or know which site had that old catalog listing? In 2006, my HD crashed and some of my Web resource links were among the files I wasn't able to restore from my backups.

On a recent 630TS restoration (a "severe shipping damage" casualty), I encountered absolutely pathetic signal strength (slightly better on channels 12 & 13 with a high RF output from a B&K 1077, but still highly degraded), after replacing all the paper caps, re-forming, and performance-testing all the electrolytics. Accompanying this was a medium-loudness, brief, single "pop" sound from the speaker during warm-up, followed by good picture and sound with signal injection into the IF. What I found with a 7-pin tube socket test adapter inserted between V1 (RF Amp) tube and socket was 0.5V on each 6J6 plate. Resistances checked OK the FIRST time. Subsequent testing, after removing the tuner from the chassis, revealed that V1 pin 2 intermittently went from infinity to about 18 ohms to chassis ground. R14 measured 7.6K instead of 4.7K and one of C14's leads was too close to and intermittently rubbing against the ground connection at the center of V1's socket. Carefully re-positioning the displaced C14 lead and replacing R14 fixed that issue. Since the short was at the plate end of R14, V2 and V3 still received enough B+ to (barely) continue functioning; C13 and C14 coupled some signal to the grid of V2 due to the not-quite-zero-ohms short, hence the overall pathetic performance but slight improvement at the upper end of the high band.

Louis Stangle of Quality TV Tuner Repair told me earlier this year that he no longer services low-IF tuners, only the 44-MHz types, since he no longer has the equipment on hand to support the low-band IF systems. This came as very unwelcome news to me since I had two low-IF tuners in need of repair at the time. I am equipped to fix SOME problems with RCA-type tuners of the 630's vintage, but am hesitant to attempt any "major surgeries" (ie: rewinding a burned-out segment of the wafer-mounted coils) without more practice on sets from my own personal collection.

[jshorva65]

Some parts of these RCA tuners (identified as KRK-2B per 721TS service manual, no part number specified in Sams for 630TS for the "RF Unit") can be replaced without separating the wafer switch and side/rear fibre pieces from the main tuner chassis. A magnifier, very small "pencil" soldering iron, and "surgical-type" forceps are highly recommended.

[jshorva65]

In other related news, I recently acquired a Hickok 610A TV/FM Alignment Generator. This model seems to be among the better quality self-contained instruments of the time for this purpose. Recapping and calibration are in progress.

The upgraded Eico 368 seems likely to become my primary alignment instrument for pre-color IF systems, although the dial gear drives seem less precise than those of the Philco 7008. On the Philco unt, there is almost no mechanical backlash in the dial mechanism, while the Eico drives' backlash is quite noticeable. The lack of a 1/10-division vernier for its 0-100 linear scale on the marker dial was another minor inconvenience, although I have since created a decal having the correct markings printed to proper scale which is now affixed to the faceplate in the proper location.

Regarding the Eico 368 in general, the unit bears some signs that the manufacturer's Engineering and Accounting departments may have had some disagreements in which Accounting seems to have overruled Engineering The schematic, for example, shows the 6.3 VAC tube heater circuit having neither side grounded to chassis, while the kit assembly instructions and ultimately the construction of the unit itself not only had one side of the heater circuit directly connected to chassis ground, but actually employed the chassis as a conductor for heater current. Having also studied the manual for the Eico 369, it appears that Accounting and Engineering reached a compromise of sorts regarding heater wiring, since the heater circuit of the Eico 369 is shown wired in twisted-pair configuration with one side tied to ground. Isolating the heater circuit in my Eico 368 from the chassis, making its ground connection to a single point, and ultimately converting cathode and grid returns of some of the most sensitive circuits to star-ground configuration significantly reduced 60 Hz noise content of the Scope Vert output. Prior to the improved configuration, the Vert output consisted of the desired output riding on 60 Hz AC of 150mV p-p. After the breaking of internal ground loops, the amplitude of the 60 Hz noise on the Vert output is down 20dB at 15 mV p-p. The only way to improve further upon that figure would seem to be to reverse the assembly instructions of the kit step-by-step, replace all heater wiring with twisted pair, and change all ground connections to star configuration. If I were to eventually do that, I would probably also add a Hum Balance pot for good measure.

Since I'm partial to the "X" (actually, a mirrored "S" curve) display for FM Detector alignment, I'll be replacing R28 (10K-linear "Sweep Width" pot) with one having a "push-off/pull-on" switch and wiring the switch between pin 3 of V3 and R23. With the knob in the "out" position, blanking will function normally. Blanking will be disabled with the knob pushed "in" so that the "X" pattern can be displayed with proper scope settings.

[forjack842]

I've been collecting crystals for a few years planning to take one of my 415's and converting it to 24mhz. Since all markers are post IF injection. they are basic oscillators. Coil rewind and cap size increase verified with transistor grid dip should get all the markers onto frequency. Redesign the sweep circuit inductor/cap might be the major hurdle, but not impossible. The rest is pretty straight forward.

Any thoughts??

[ohohyodafarted]

Contact John Folsom. I think he modified a B&K as per your inquiry.

[forjack842]

I vaguely remember picking it up off Ebay couple of years back. IT arrived just before I moved so I cleaned it up and put a coat of wax on the it and wrapped it up in a blanket popped it into a crate and off it it went.
THe more I read this thread the more I had visions of the CRT door in the back and the front bezel pushing out as the back crt door was extended. I kept remembering things no picture showed so I must have one. THe hunt was on and tonight and found the crate buried back in the garage. Opened it up and was thrilled! All the cables neatly tucked in the left bottom compartment. Everything was there but a manual.
I don't think I did an electrical restore as of yet either. Am wondering about a manual. Any sources available?
Its time to get this baby up and running. I've got a Philco 48-700 on the bench and a 48-1000waiting.


Also dropped a line to John for his experience on modifying a 415.

Thanks All Great Thread!!!!!

[Dave A]

And I am sitting on one of these I picked up at Kutztown. No cables though. Have not powered or restored. Power cord shot for starters.

[dreyfoos]

Hello forjack842,

If you or John come up with a frequency mod plan for the B&K 415, please let the rest of us know the details. I've always wondered if anyone had ever tackled such a mod. I don't have the background to design such myself but I could probably follow a good recipe.

Roger

[Tube TV]

Im still sifting through ebay & craigslist looking for a Philco .
Eventually I will find one .

Im glad this thread is back up , I had lost track of it .