Old B/W IF Alignments Almost Too Simplified

[forjack842]

All,
I've pinged John on this and should hear back shortly. He might be on a trip.
I just worked with him on purchase and shipment of his 741PCS.

I'll post as I find out and if nothing else start on modifying one of mine.
I didn't come across a 415 manual as of yet. I probably have one its just in what safe place I've put it. Am always protecting stuff, usually its from me when I need it! If one of you has a electronic copy please send it.

In the mean time any of you math wizards out there try and figure out if a easily available crystal could be digitially divided/multiplied to provide the marker frequencies. THis would make it alot easier then getting every crystal.
There's alot of digital synthesizer chip possibilities I just don't have time to work it right now
Thanks

[Tube TV]

sansui200A , Thought this thread might be of interest to you .

[jshorva65]

Glad this thread is still active. I still have two B&K 415's (one for performing 44 MHz IF alignments, plus a "spare" to modify for 24 MHz once someone with more RF circuit design background develops a set of modification plans to follow), so I'm still following the thread. It's a shame that the dial drives used in the Eico 368 and 369 weren't as precise as those used in the Philco 7008. A unit combining the all-electronic sweep system of the Eico 368 with the post-marker upgrade I described earlier and dial precision equivalent to that of the Philco 7008 would be the ideal instrument.

I have heard good things about an instrument used by Dumont for RF/IF alignment in a Production environment called a "Wobbulator" and have heard that the unit was factory-configured to Dumont receivers' standard marker frequencies as used circa 1947 (21.9 MHz Audio IF, 26.4 MHz Video IF) via front-panel "pushbutton" presets. Rumor has it that the unit was dubbed "model 1200A" and that Stromberg-Carlson may have been involved in its development or production. The unit is also mentioned by name in the Alignment instructions provided in technical literature published by J. F. Rider for several Dumont receivers of the time. In addition, I have noted that Rider manuals for Dumont receivers (particularly for the RA-103D and RA-104A) provided more information than was included in the Sams folders for the corresponding models regarding the Mallory Inductuner units.

[jshorva65]

Since all of the frequencies of the "old" IF band (at least for RCA sets and RCA clones) are EXACTLY 20 MHz below the B&K 415's built-in markers (21.25 MHz Sound vs. 41.25 MHz Sound, 25.75 Pix vs. 45.75 MHz Pix, 24 MHz Sweep Center vs. 44 MHz Sweep Center), it follows that perhaps an "add-on board" containing a single 20.000 MHz crystal-controlled Master Oscillator and a set of buffer/mixer stages could be constructed as a means of modifying a B&K 415 for 24 MHz IF. I'm a little rusty with Transistor/IC Circuit Design and PC Board Design/Fabrication, so I'll ask for expert input on that aspect. It's been YEARS since I designed/built any multi-stage "solid state" circuits. At least theoretically, though, a "board" wired in for pick-off and beating of the Sweep and each Marker individually against a 20 MHz reference and accomplishing re-insertion of the "new" frequencies into the appropriate Output circuits of the 415 seems most logical. This is, of course, based on the assumption that there are many great new IC's available featuring small size, low power drain, excellent performance at the frequencies required, and requiring very few support components other than ordinary Vcc decoupling. Am I over-complicating, or perhaps over-simplifying, the goal of creating a 24 MHz version of the B&K 415?

It seems like a reasonably straightforward POOGE project (Progressive Optimization Of Generic Equipment) at least from my viewpoint. Perhaps even providing some means to switch the Master Oscillator from 20.00 MHz to 19.35 MHz (RCA's 21.25 MHz and 25.75 MHz or Dumont's 21.9 MHz and 26.4 MHz) or an In/Out switch could be incorporated? Perhaps even a combination of all those features (RCA B/W / Delta-F=20.00 MHz, Dumont B/W / Delta-F=19.35 MHz, Standard Color / Delta-F=0.00 MHz) with a three-position selector?

[jshorva65]

This past weekend, I scored a second Eico 368 without the post-marker upgrade as described in the April, 1969 issue of Service magazine installed yet. I plan to recap this one, replace some terminal strips to facilitate a "star ground" configuration which will break up internal ground loops in its original construction, rewire tube heaters with twisted-pair wire to further reduce line-frequency noise, and complete a customized version of the post-marker upgrade featured in Service, but accomplishing a less-cluttered panel layout by using a dual-concentric pot for the Trace Size and Marker Size controls and subbing a pot with a pull-on/push-off switch for the 10K Sweep Width pot, switching the Blanking tube's cathode circuit to enable mirroring two "S" curves into an "X" pattern for FM Discriminator alignment so that the "X" display makes the center of the "S" curves much easier to spot when viewing the scope trace from a distance. In its original pre-marker configuration, the effect of the internal ground loops present in the original construction on the scope trace was far less. The addition of the upgrade without also eliminating the internal ground loops, however, tends to worsen the appearance of the noise introduced by those ground loops on the trace due to the tendency for the upgrade's marker-adder circuitry to amplify the unwanted ground loop noise along with the composite trace and marker signal which the post-marker upgrade was constructed to produce. The amplified 60 Hz ground loop noise appears on the scope screen as a tilting of the trace. The degree of tilt is proportional to the input sensitivity setting of the scope. The goal of upgrading this one to star grounding as part of the upgrade procedure will be to eliminate the "tilt" which I was only able to diminish significantly on my other Eico 368, which I purchased with the upgrade already installed.