OK.

Yes, the marker dial does track the counters readings across the dial on all bands.

When you had the IF aligned to 24.3MC, did you try adjusting the oscillator slug for channel 3 (Sams reference A19) while you had your DVD player playing through the rf modulator? Also A8 is the master oscillator adjustment that will offset all channels equally. If you look at the schematic you will see A8 is a trimmer cap in parallel with the fine tuning control. A9-A20 are the individual slugs for each channels oscillator coil. Those adjustments combined are what sets the correct oscillator frequency that in turn is mixed with the input rf, and is sent into the video IF. Another possibility is that if someone had the tuner coils out they may have gotten them mixed up and not installed back in the correct order, in which case channel 3 may not really be creating the correct oscillator freq for channel 3.

No. Maybe I should try that?

I think so. Also see what I just added to my last post. If the tuner is goofed up there's no way it can send out the correct IF frequency for the channel you think you're receiving.

Does this turret tuner look right to you? I would think the inserts would go numerically in order.


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I looked at some other pictures of turret tuners and their inserts are all numerically in order.

Looks like I have to redo the order?

A few are definitely out of order. Are 2,3, and 4 in correct consecutive order? Is one section missing? At any rate they should be in the same order as the channel knob on the front. And since someone was in there messing with them it's even possible they're not all working correct.

Right.

I got them in order. Channel 10 is missing the forward insert. Also there are a few that are not numbered but they went with the ones in that channel number. After reassembling the tuner, I have a decent picture on channel 3 and my bar generator works on channel 6 as it is supposed to. Tomorrow I'll work at getting the double hump curve with the proper freq where they belong. I'm not sure the tuner inserts are the problem because Sams says I can use any channel.

We'll see what happens.

So were the channel 3 coil modules already in the correct location? I'm not even sure if that A8 adjustment can cause the tuner IF to be out by 4MC. Something sure seems to be throwing your tuner IF output off.

I'm not really sure if they were in the correct position on the turret. I lost the metal insert that goes into the plastic channel dial so I can't use the correct dial. I'm using another dial just to be able to turn the channel selector. I looked into the tuner and when the channel 3 inserts were making contact with the wipers, then I used some masking tape to mark the dial. I know it's a bit hokie, but my friend has a metal piece I just haven't gotten to go over his house.

Referring back to the screen shot in post# 197, if he's getting pic and sound correctly with the fine tuning around mid-range, then the osc. frequency is correct. The osc freq varies with the fine tuning, and has no bearing on the IF response curve. In fact the osc should not even be running during the alignment procedure.

(I don't have the schematic.) The tuner may or may not have a mixer plate coil adjustment. If there is, it may have some effect on the IF response curve.

Crist, was there a particular reason you opted to do an IF alignment?

Yes, I wanted to learn how it was done. After replacing all the caps and resistors I thought it could use it.

Well first off, your set uses the old 24 mc IF (vs. the later standardized 45 mc IF). Superhet theory dictates that your set's local oscillator (LO) has to run at 24 mc above the received signal's frequency. Channel 3 video carrier is 61.25 mc. So, 61.25 + 24 = 85.25 mc for the LO. The two signals are mixed, yielding the 'beat' or Intermediate Frequency of 24 mc.

Since the video information on the carrier occupies a wide band width, the IF response must also be broad band, occupying a wide swatch on either side of 24 mc. That's why the IF strip is stagger tuned with an extra stage or two of amplification.

In contrast, a radio's IFs are tuned 'on peak' since audio bandwidth is all that's needed. Since the IFs are not staggered, less amplification is needed.

In a typical AM radio, the LO tracks 455 kc above the received signal, yielding the 455 kc IF. Most all FM radios use 10.7 mc for the IF, meaning the LO tracks 10.7 mc above the received signal.

Most all consumer gear uses 'high side' LO injection, meaning the LO runs above the received frequency. Some specialized communications gear may occasionally use low side injection.

Here's a listing of TV channel frequencies.. http://wiki.radioreference.com/index...on_Frequencies

Agree with all that. I was simply suggesting that the beat frequency that the tuner is generating may not be what the IF is looking for(something other than 24MC). If I'm not mistaken Crist thought he had his IF aligned to a center frequency of 20.3MC, which he's based on what his marker generator is telling him. When he aligned it to where it's suppose to be he's not getting video. He also mentioned that he has changed caps and resistors in the tuner circuit.

OK I see what you're saying now. I shoulda re-read those prior posts closer.

Be good if he could post the tuner schematic showing the parts that were replaced.

I can post a scan of the tuner from Sams later tonight, gotta run now. It's really close if not the same as the 20Z1 chassis tuner which is available on the ETF.

Here is the schematic.

I replaced all of the resistors except R9. It was too buried to get to. I also replaced C15A and C15B. Then the only other cap that was replaced was C17, a mica cap. C17 was replaced with a 120pf 500v mica cap. C15A/B was replaced with 2 of these:

https://www.digikey.com/product-deta...5-1-ND/5812010

Just so you know, I used the same type of caps to replace those in the IF section but only with 1500pf for 1500pf and 3900pf for 4000pf caps.

C17 couples the tuner to the IF section.

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Great. The two critical frequency-determining caps, C12 and C13, have been left alone. But I would double-check resistors R18 (10K) and R19 (4.7K) for correct value since they could affect LO frequency. (It's not necessary to disconnect those for checking.)

I checked those resistors and here are the pictures of each one installed. The first picture shows R18 a 10K and the second shows R19 a 4.7K.

I keep notes on each resistor removed and installed.

10K R18 was 9.81K and was replaced with a 9.8K
4.7K R19 was 4.92K and was replaced with a 4.64K

http://i1060.photobucket.com/albums/...pstjvq55xv.jpg

http://i1060.photobucket.com/albums/...ps4bg0fzhi.jpg

Can you verify that by adjusting the Ch 3 oscillator slug, that it will in fact alter your sound and picture tuning? There should be a definite point where both at their best. It's the same effect as adjusting the fine tuning control, only this should have a coarser range.

Yes, it does exactly like you said.

I went over to channel 6 and my pattern generator and the video was unsettled. I tweaked the channel slug and got a great pattern. I only tweaked it just about a 1/4 turn or less.

Beings they're that close it's hard to imagine the IF is off as far as your marker generator is indicating. I suppose you could slowly tune your IF back in the direction of 24MC, intermittently checking if you can still get good sound and video by readjusting the Ch 3 oscillator coil. I don't know what else to suggest. Maybe Old Coot will have a suggestion.

OK. We'll see what he has to say.

I was gonna suggest essentially the same thing.. incrementally 'walking' the IF adjustments back, while looking for the best rendering of fine detail in the pic, with no ringing or smearing of fine detail. Probably have to re-tweak the Ch 3 osc slug along the way, to keep the fine tuning range centered.

There was a guy on here two or three years ago, a total newbie with a late 40s Dumont (I forget his name. Phil Nelson probably remembers). The guy did an IF alignment totally by eyeball, no instruments, no nothing. But damn if he didn't end up with a perfect pic, just as good as with a full instrument alignment. That might be the way to go with this one.

If you want to go the eyeball route and have a frequency counter that'll read 85.25 mc, set the Ch 3 osc slug to that frequency. (A turn or two of wire taped around the osc/mixer tube oughta provide a decent pick up.) With the fine tuning at mid range, the osc wants to be at 85.25 mc for a 24 mc IF. That way, you have a 'target' to walk the IF adjustments toward.

(Ch 3 carrier is 61.25 mc.)

OK, I'll try walking back the IF and tweaking the CH 3 slug.

I've got a pretty good picture now, I know what you mean by doing it visually. We'll see what happens.

Thanks for the suggestions guys.

I was hoping you'd explain to us how to do that. :)

Also a B&K 1076 or 1077 Television Analyst would be really handy right now too. With that he could inject the Analysts IF output directly into the sets IF and manually sweep through 24MC, so he could see exactly where the TV's IF response appears to be optimized for best sound and picture. A very handy and educational tool for anyone planning to stay in the TV restoration hobby.

Deleted. My bad. It's the B&K 415 that's the 'gold standard' for learning IF alignments. With a decent scope, it makes doing IF alignment actually fun. https://www.google.com/search?q=b%26...nerator+images

The 1077 Analyst is a stablemate to the 415 and does everything under the sun except IF sweep alignment. Phil Nelson refurbished one not too long ago. http://antiqueradio.org/BK1077BTelevisionAnalyst.htm

The BK 415 is for the higher freq. IF TV's. It won't work for mine. Later today I'll get back to this chassis.

Unfortunately true. And as far as I'm aware there was never a rival service grade unit made for the old 24MC band.

IIRC the markers on the 415 were crystal based (I need to dust mine off and make it work) so with the right crystals and mods to the sweep section the 415 might be convertible to the older IFs...Could be an interesting project trying to make a 415 mod to switch back and fourth both IF freqs...Though it might be reinventing the wheel.

I recently picked up an example of that EICO generator you were using ($5 at Goodwill)....That makes ~6 pieces of 'as found' IF alignment gear I have sitting waiting for the day I decide to try and teach myself IF alignment...I really need to block off some time for that some summer or winter...

By golly you're right. I had to look up the specs just to be sure. Amazing that it doesn't cover the old band.

I looked into that and came to the same conclusion. The correct crystals are very difficult to find, and the project would get very involved before it was all said and done. A better use of time might be to design from the ground up a digital programmable 5 frequency marker generator that could be used as an add on with any of the service grade post marker sweep generators.

Taking a mini-break from this for a few days. Another quickie project has popped up.

Not the first time I heard of "eyeballing" the IF strip. When I was a kid helping at a TV shop, there was a tech that did my Motorola TS905 and a RCA CTC16. Both sets turned out great! Amazed me to watch as he did them. He was a older ham operator who also designed and built a good bit of his gear. As a kid, that shop was a blast!!
I just wish I still had that old Motorola. It's biggest problem was it was huge! My mother was not fond of it in my bedroom. Took up way too much room!

Besides my mini project this week I worked on getting the back reconditioned. Much to my surprise it really didn't fit too good! I know when I got the TV it was barely on the TV and it really didn't fit so good.

I got to looking and the left vertical brace was installed to the back too high. It contacted the upper left mounting screw boss by a lot. OK, so I relocate the brace to match the good right side. I place the back into the cabinet and it is too high! The cutouts for the upper mounting holes won't line up. Hmm....

I decide to mount the chassis into the cabinet to see where the problem is. Well it looks like the outline of the back is correct, but all the holes, etc are about 1/4 inch high! My guess during manufacture, the blank outline wasn't inserted fully into the jig or machine that drills/punches out the holes! I also thought that there might have been some rubber biscuits that go under the chassis but there can't be because the controls shafts are centered on the cabinet holes.

There is no way to locate the elongated holes that mount the back to the chassis. I run out off the bottom edge of the back.

So I drew up a new back using my CAD program. I double check all the mounting holes to the chassis and to the cabinet. Much, much, better. Of course I have to make a new back now.

I've included some pictures of this whole mess.

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Nice job on the drawing. Yes that back design is a bit of a mystery. I wonder if the Masonite actually shrunk to the extent that the top screws pulled the corners off? I also don't understand the need for what appear to be so many extra screw holes, as if that back spent some time on some other cabinet. :scratch2:

That looks like the incorrect back. There also needs to be a lot more ventilation holes near the bottom to get a decent draft on them hot tubes.

It is the correct back. The elongated screw holes and the interlock connector fit perfectly. Also the cutout for the antenna terminals fits perfectly.

Kevin, the extra screw holes in the pictures are for the screws that hold on the 3/4 x5/8 braces which were removed when I was measuring the back. In my drawings, you can see them as dotted lines.

Ah. Funny how quickly I can forget stuff. I had to go back to where I we originally discuses the set on CL to see what the back originally looked like mounted. Makes sense now that the corner hole were elongated for expansion and contraction, and then the large washers to cover the holes. But I also have to agree that that back doesn't allow for very good ventilation, but since it's spaced out from the chassis at the bottom I suppose it's suppose to work like a convection oven.

http://videokarma.org/attachment.php...8&d=1470097105