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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Fri 07, 2014 3:20 pm 
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That was my concern as well, since the characteristic curves of the two types are very different. I'm sure the set would work fine with a pair of 6FQ7/6CG7 OR a pair of 6GU7 which are preferable, but with one of each there has to be some small difference.

In the meantime it won't hurt anything to leave the wrong type in there but I certainly wouldn't try to compensate for it. Since the black and white tracking seems to be OK and all the colors are present, at least the set is watchable.

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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Fri 07, 2014 6:08 pm 
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I have other 6CG7s. Sounds more than reasonable to use identical tubes for the matrix (specially because they are not 100% compatible) so I will and keep the 6GU7 waiting for his match to come some day :)

Last night I tried to adjust the static convergence (after having setup the purity with reasonable success) but I couldn't get good results. Green and red vertical lines are very far apart. Moving the corresponding two magnets all the way out is not enough to make the vertical lines meet (they start overlapping but just a little). They do get to overlap on the very left side of the screen.

I didn't want to play with any of the dynamic convergence controls yet. Do you think any of them can help changing this situation? I couldn't find documentation related to what each control does.


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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Fri 07, 2014 6:17 pm 
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You should be able to find the convergence procedure, it is pretty much standard and for most sets the controls were located in the same orientation on the convergence board. Note that if yours has a selenium rectifier they were notorious for failure, sometimes but not as often one of the coils on the CRT neck would open, or one of the little wirewound pots opens.

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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Fri 07, 2014 6:19 pm 
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Joined: Aug Thu 07, 2008 1:36 pm
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Location: Orlando
pull one of the magnets completely out of the holder (red or green), rotate it 180 degrees (not end to end the end with the magnet stays near the neck). re insert and try again.

Note the purity must be right before starting or you will be wasting your time. (oops, re read your post you have the purity good so the magnet rotate should allow you to adjust the static).


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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Fri 07, 2014 6:41 pm 
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Joined: Aug Thu 07, 2008 1:36 pm
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a few hints on convergence.

let the set warm up for 10 mim

make sure purity is as good as it can be

make sure height and lin are good

adj focus to best possible

use dots for static

turn down brightness smaller the dot the better

use a hand held mirror (small)

while standing behind the set use one hand to get close up visual of center of screen

adj red and green dot looking only at the center ignore blue

red and green move diagonally so get used to how they move and adj until intersect keep looking at the hand held mirror while adj

after center of screen looks good for R and G dots position the blue dot by moving up and down with the magnet on the conv yoke

move the blue dot left and right with the blue lateral

if it all looks good with the dots in the center of the screen then move on to dynamic, but don't be surprised if you have to touch up.

the dynamic is laid out in the sams. They tell you that you may have to touch up the dynamic while adj the static so keep an eye open for this. this is a lot more complex than the center, so focus on getting the center right before touching the dyanmic.


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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Fri 07, 2014 8:23 pm 
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Thanks, I will get into this during the WHOLE weekend hehe.

Something I forgot (as you mentioned that I should adjustheight and linearity before getting into convergence). I lack of width.
I adjusted vertical linearity and height with a test pattern, also vertical and horizontal position, everything looks fine, except for width. I didn`t find any control to adjust this. Is there a way?


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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Fri 07, 2014 8:59 pm 
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Location: Orlando
typically width is not adjustable, it generally is caused by:

low B+

weak horz out

if the B+ is correct then I would try subbing the 6JE6 and the Damper for starters, and the horz osc as well.

See if that make any difference. check the screen voltage on the horz out pin 1 or 7 should be 140v there is a 47 ohm resistor on it, make sure it has not gone way high (the resistor).

The low 188ma reading you got at the beginning on the cathode of the horz out points to low power thru that tube.

What is the voltage at pin 2-6 should be around -55 v.

IF its more neg than that there could be a malfunction in the hold down circuit from the blanker tube. But my 1st guess is the horz out tube is weak. This is not uncommon and is why you should have a few extra sweep tubes on hand.


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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Fri 07, 2014 9:38 pm 
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try this, make sure you have a 6GU7 in the horz blanking (its shared with the Blue diff amp). Also check the off pin 2 of that same tube, you should see a 270k resistor to ground, check the pin resistance from pin 2 to ground, should be less that 270k. If its higher you may have a crack in the board that connects one side of the 270k to the ground. this is a common problem in RCA, being a clone it may have the same problem. The horz blanking grid voltage is part of a hold down circuit on the HV, it cuts off the horz out if the hv goes to high due to shunt tube failure.

the 270k is part of a voltage divider, without out it the blanker provides too much neg voltage to the horz out thru a 1.5meg resistor connected to the grid of the horz out.

the problem presents as too high a neg voltage at the grid of the horz out. normally you see about -55 but if you see -65 or greater neg, then its likely the blanker is sending too much hold down due to a defect in the voltage divider.


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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Sat 08, 2014 12:26 am 
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Great, thanks! I will do all those test during the weekend.

These are some pics of test patterns.
The DVD goes to the TV through a VCR to transform video output to RF on channel 4.

Tuning channel 4, the yellow looks a bit weird. If I tune channel 3, moving the fine tunin I hear a distorted sound and the picture is not clear but the yellow looks great. Is there something I should adjust in the chroma circuit or should this be related to the mismatched tubes?

Something else. With a crossbar all the lines (V and H) are perfectly parallel. With a signal pattern with something else on the bars they bend a bit (check the pics below):

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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Sat 08, 2014 1:31 am 
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Location: Orlando
did not see the horz width issue on that last set.

AGC can often cause distortions, best thing to do is adj it to what ever the device you are planning to be driving it with.

That yellow is not that bad, personally I would leave it be and just enjoy it.

If you want to mess with it you could try swapping some of the IF tubes, maybe shift around the IF response enough to make it work better, with a scope and a proper signal generator like a BK415 you maybe able to improve it, but even then there is lot of experience needed to get it right, and more of a chance to mess things up.

If it was mine I would prob try subbing some tubes but I know you have a limited supply, bottom line, leave it alone.


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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Sat 08, 2014 1:36 am 
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Location: Asheville, NC USA
Id leave it alone for now, and let it run for awhile.

The picture you have looks mighty fine for a nearly 50 year old color TV.

Step away from the screen, and you won't notice much of the convergence troubles.

You've got a keeper, there. I wish I could find a Maggie roundie combination set like what you have.

Bruce


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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Sun 09, 2014 12:26 am 
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Wow, this convergence process is more painful than being down on your knees over rice for 24 hours... :) Specially without the instructions!

I didn't succeed finding online instructions on how to adjust the dynamic convergence, but in the convergence board the controls are numbered and there are arrows between them so I just played with them in the specified order (many, MANY times). I also had to re-adjust the static convergence from time to time.

The result I got is not at all as good as other cases I've seen online, but I declare myself unable to do it better after having tried the whole day this recursive never ending exhausting job!

Just to let you know, I had got to a point where I could not do anything to improve the vertical convergence. In the center everything was ok, but getting away from the center the separation between red vertical lines was becoming non-linear. On the right side of the screen, red lines were more to the right than green lines, and on the left side of the screen red lines were more to the left than green lines. There was no way to compensate that effect with static convergence, and playing with the controls of the dynamic convergence didn't help at all.

I checked components, voltages, everything looked normal. While I was adjusting purity I pulled the yoke towards me all the way, and I never got to see that red spot in the center of the screen together with the other colors around it. That made me think that maybe the purity coils were way too far to the front of the CRT away from its normal position, not letting the yoke to run enough to the back of the CRT neck (and also maybe not letting me adjust the convergence correctly?)... So I just pulled the coil's assembly together with the purity rings a bit towards the end of the CRT's neck and voile! I was able to improve the vertical convergence, and the three coil controls on the convergence board started acting.

SO, I am happy with what I got though for many of you this could not be called a success. I included a pic of the "after" (the same round color pattern I posted before) to compare. There is a blue column on the right and a green one on the left, those are like that on the pattern, it is not a purity issue.

About the yellow, I changed the VCR's RF output channel to three, and there I had more range on the tuner of the TV to adjust the fine tuning. It seems that in channel 4 the fine tuning was reaching a maximum and I was not able to go further (channel 3 allows me to go to both sides with a good margin). I could see that fine tuning affects the colors, not only intensity but a bit their temperature. So, I just wen a bit to lower frequencies with the fine tuning and I got a nicer yellow.

I am getting the patterns from Youtube, maybe the one I used last time to adjust height and lin had a slightly biased aspect ratio (it was a b/w old test pattern).

@Bruce: I wonder how this set ended up down here... It is absolutely one of a kind here, I am so curious to know what's the story behind it but I got it in The Salvation Army so no chances at all. I must consider myself very lucky. These sets were not being imported to here, where color TV broadcasts started around 1978. Maybe it comes from an expat who just moved here together with all his stuff (something really uncommon).

Below there are some pics and links to two videos. The colors look great to me, much nicer and pleasant than the colors in my other modern TVs. The videos are low quality and there is also this moiree effect on them, the pic looks much better in person than in the video. There is a kind of "ghost" to the right, but I recalled later on that the sharpness control was all the way to the "sharp" side. That in general causes this effect; I turned the control all the way to the opposite side and it got much better.

Things that I noticed (last questions, I promise!!! After these I will put the back cover back on the set, clean the living room and enjoy it as is!):

- The screen shakes mainly on the left side, up and down, and a bit diagonally too at regular intervals, quickly like if the power supply transformer's magnetic field was affecting the vertical deflection (the transformer is right there on the left side in this set, but there is no shield and it was designed like that so.....). It is very noticeable and a bit annoying. If I reduce the height, I see the sweep lines shaking up and down. Can it be a cap? I've seen this effect on other TVs when getting a power transformer close to the CRT.

- The can of the fly-back is really hot! Even on the side opposite to the H-out tube. I didn't touch the FB yet (I will do it) but at this point I guess I should try to play with the "eff" control to reduce the current? Should I just turn it to one side or the other and see what happens with the current? Should I stop looking for any effect on the screen or be careful somehow?

- The varistor connected to the degaussing coil is not working (measures several Kohm cold). Do you know what's the normal resistance value, or how can I look for something compatible? In the schematics that I have there is no number for it.

- The focus could definitely be better (I think). I tried turning the plastic bar to both directions several turns but I didn't notice any change. I am afraid of taking the magnet completely out of the coil because I can't see what I'm actually doing inside of the metal can. Should I notice something right away when adjusting this knob?

Thanks in advance and have a great weekend!!!

https://www.youtube.com/watch?v=S5bQ0xusIEc&feature=youtu.be

https://www.youtube.com/watch?v=W6eIhF9iMBA

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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Wed 12, 2014 2:29 am 
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Posts: 328
Location: Somewhere on Planet Earth
Hi all....

So then, the items I wanted to work on (addressed in my last post) will be carried on sometime in the future for many reasons.

Some final pics. One showing the back of the set with the 220/110 V transformer installed on it, another one with an upper view showing a piece of wood (not solid so the heat will go through it) that I added to give it a better look (between the wall and the edge of the furniture originally there are around 7"), one showing the controls at the back of the set (they should have been placed in the front together with the other knobs according to my opinion), and one showing the set in place with a colorful video of ELO.

The last one is to say goodbye :)

Thanks a lot for all your help and encouragement!!!!!!!!!!

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Last edited by normende on Mar Wed 12, 2014 4:07 am, edited 3 times in total.

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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Wed 12, 2014 2:36 am 
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That console looks right at home with the furniture you have.


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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Wed 12, 2014 2:44 am 
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I still can not believe that I found this set down here, thanks :)


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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Wed 12, 2014 3:10 am 
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Just like the stars and planets in alignment, everything just fell into place. Congratulations on your success. You did very well.

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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Wed 12, 2014 3:39 am 
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Very nice, I bet its a real conversation piece as well. I hope you have some LP's you can play on it as well.


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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Wed 12, 2014 11:50 am 
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Normende, did you ever fix the phono speed problem?


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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Wed 12, 2014 12:06 pm 
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For sure this is a great piece of conversation here. It is, between my friends fans of stuff from the USA from the 50s, 60s, and 70s (the kind of people who love digging into every corner of the "Popular mechanics" magazine), between my friends who are into repairing old radios and TVs, and between those curious people that just get attracted to unusual things like this one, a console that has a TV on it! (here we only know consoles that are a radio-phono combination).

Supplementing the motor shaft worked really well. The plastic cylinder-shaped ring that I added was completely even in terms of width on all the 360 degrees and it entered the shaft very tight, so the speed remains uniform. I know I should increase the speed just a little bit, but so far I couldn't find something with the exact width I need (something only less than a tenth of a millimeter wider).

I would really like to finish the adjustments I mentioned in my other post sometime in the near future (I'll be back for some advice specially on the eff control adjustment), so I am including the speed fine tuning of the turntable in that package :)


Last edited by normende on Mar Wed 12, 2014 2:21 pm, edited 1 time in total.

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 Post subject: Re: Alternatives for tubes on a Magnavox color roundie?
PostPosted: Mar Wed 12, 2014 1:00 pm 
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Would it be possible to find a record changer for the console that is made to operate on 50 Hz or a motor spindle for 50 Hz operation?


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