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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Feb Sat 24, 2018 2:24 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 441
The set will run without the width coil. You could then scope around to find a candidate for the ref pulse.


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Feb Sat 24, 2018 3:29 am 
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Posts: 4675
Location: Ann Arbor, MI
robert1 wrote:
this is why i asked if i could replace the coil with a standard width coil & try to find another source for the horizontal sync pulse. i notice that the later Admiral chassis designs use a different method of sourcing the sync pulse

One problem with using a standard width coil is getting one with the right inductance. Now if schematic for your set specifies the inductance, than you could try to get a new coil to match. Or you could try whatever you can find and see if it works. You could always wind a new secondary on to a standard coil. The secondary would not have to be precision wound and would not have many turns.

_________________
Tom


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Feb Sat 24, 2018 4:53 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 156
Location: parkersburg west virginia
Tom Schulz wrote:
robert1 wrote:
this is why i asked if i could replace the coil with a standard width coil & try to find another source for the horizontal sync pulse. i notice that the later Admiral chassis designs use a different method of sourcing the sync pulse

One problem with using a standard width coil is getting one with the right inductance. Now if schematic for your set specifies the inductance, than you could try to get a new coil to match. Or you could try whatever you can find and see if it works. You could always wind a new secondary on to a standard coil. The secondary would not have to be precision wound and would not have many turns.


Both the Sams & Riders manuals do not specify the inductance, but Sams shows it as 80 ohms for the Primary & .5 ohm for the secondary.
i really don't have any parts like that here so i would have to look (& guess) online for something that might be close.
as for the the winding, can it be wrapped around the outside of the width coil winding?


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Feb Sat 24, 2018 7:33 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 314
Location: Elkhorn,Wisconsin,United States
Hi Robert,
I did some checking on 20b1 set I have, and found that the primary inductance adjusts in the 9 to 12 mh range. The secondary adjusts through 530 uh. I took these readings with the wires removed from the coil. Also remember that the adjusting core of the coil increases overall inductance. I noticed that the secondary coil is wound with heavier wire, 26 to 28 gauge wire. I measured 78.8 ohms for the primary winding.
If you get a standard replacement coil , it shouldn't be too much trouble to wind the secondary over the primary. Just try and count the secondary turn off the original coil.
Ed


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Feb Mon 26, 2018 7:21 pm 
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Joined: May Fri 29, 2009 4:35 am
Posts: 2071
Location: Chicago, IL USA
Perhaps this Workman T121 width coil available from Talon will work ?

http://www.talonix.com/shop/item.aspx?itemid=3660

Chassis mount, Transformer,
Primary resistance 102 ohms,
Primary Inductance 9 - 24 mH

Secondary (AGC winding) resistance 1.2 ohms
Secondary Inductance .25-1.1 mH


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Feb Mon 26, 2018 9:12 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 156
Location: parkersburg west virginia
bandersen wrote:
Perhaps this Workman T121 width coil available from Talon will work ?

http://www.talonix.com/shop/item.aspx?itemid=3660

Chassis mount, Transformer,
Primary resistance 102 ohms,
Primary Inductance 9 - 24 mH

Secondary (AGC winding) resistance 1.2 ohms
Secondary Inductance .25-1.1 mH


Wow, Thanks, Bob. i believe that may fix it. i just ordered it. i will post back on this topic once i get it installed (which may be a couple of weeks)


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jun Mon 25, 2018 6:08 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 156
Location: parkersburg west virginia
Hi
I finally got around to working on this set around three weeks ago. i got that part from Tylon electronics over a month ago.
after installing this coil & powering it up, i got the raster back, however, i noticed that i had some serious fold over on the right side of the screen. adjusting the horizontal drive did not help at all.
I then remembered watching one of Bob Anderson's video of servicing a similar chassis, & decided to check that 7500 ohm 25 watt resistor. sure enough, it was open. i got another one from Mouser (It was half the size), & i had to buy the proper size screws so i could mount it in the same place & way as the original.
I powered the set up, & got a much uniform raster.
I then connected the cable that i have with a channel-3 output to it & i immediately got sound out of the speaker. the picture, however, was weak. when i grasped the tuning knob, i noticed that it made lots of noise in the picture. i found that if i grasp the turret & slightly turn it off the detent, my picture quality would increase, apparently, i am going to have to deal with the tuner...But, here's another problem. i don't think that the coil that i installed works well with the horizontal sync circuits as this is what i am getting on the screen.
Image

Image

This is where the horizontal locks at. it will not drift, even after a half hour warm-up. I also notice that the width is still a little wide.
I suspect that the coil that i installed may be causing this as the ratings on the secondary of that coil are different then that of the original.


Attachments:
Admiral 20A1-6.JPG
Admiral 20A1-6.JPG [ 62.17 KiB | Viewed 1080 times ]
Admiral 20A1-8.JPG
Admiral 20A1-8.JPG [ 177.27 KiB | Viewed 1080 times ]
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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jun Tue 26, 2018 3:02 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 441
Simple!
Reverse the connections to either the primary OR the secondary of the width coil. NOT BOTH!


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jun Tue 26, 2018 5:26 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 156
Location: parkersburg west virginia
irob2345 wrote:
Simple!
Reverse the connections to either the primary OR the secondary of the width coil. NOT BOTH!

Thanks for the response. That thought occurred to me shortly after i made my last post the other night. I got right back on the set early this afternoon & the first thing i did was reverse the leads on the secondary of the width coil. That appeared to fix that problem.
I still have a couple of issues that i still have to tackle as well as find someone on the forum who has the proper equipment to do a alignment on the IF stages. otherwise, it appears that this set could produce a decent picture once completely done


Attachments:
Admiral 20A1-9.JPG
Admiral 20A1-9.JPG [ 124.52 KiB | Viewed 1046 times ]
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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jun Tue 26, 2018 7:50 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 441
From what I can see I would not touch the vision IF alignment. It looks fine to me , you are resolving the 3.58MHz color info and there is no ringing, overshoot or smear on the white/black transitions. No further improvement is possible - it ain't broke so don't fix it! The sound IF you can do with a meter, no special gear needed.

There is a bit of snow, check your tuner AGC delay. There will be a high value resistor on the tuner AGC line that possibly has gone open circuit.

Vertical needs work. Cathode and screen electrolytic bypass caps bad? Or maybe just low emission vertical output tube.


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jun Wed 27, 2018 6:43 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 156
Location: parkersburg west virginia
irob2345 wrote:
From what I can see I would not touch the vision IF alignment. It looks fine to me , you are resolving the 3.58MHz color info and there is no ringing, overshoot or smear on the white/black transitions. No further improvement is possible - it ain't broke so don't fix it! The sound IF you can do with a meter, no special gear needed.


Thanks! I also noticed that there was no smear. just snow. However, i do think that there still is a problem in the tuner. At least, It's good to know that the I.F. stages are working within specs.

irob2345 wrote:
There is a bit of snow, check your tuner AGC delay. There will be a high value resistor on the tuner AGC line that possibly has gone open circuit.


I did check the test point on the tuner for AGC voltage & it is measuring -4 v to -4.2 volts (depending on the changes in the signal), however, i'm gonna connect a DVD player (via rf modulator) & re-check the voltage on that checkpoint & see what goes on from there.

irob2345 wrote:
Vertical needs work. Cathode and screen electrolytic bypass caps bad? Or maybe just low emission vertical output tube.


I did change the 6K6 vertical output tube with a NOS tube as well as replaced the 6SN7 vertical osc as well
I think i know what the problem is, i believe the two .0047 mfd epoxy encapsulated capacitors that replaced the .005 mfd capacitors in the vertical integrator circuit may not be up to snuff, even though they were NOS.
I will post the results tomorrow evening.
I appreciate you helping me, Irob2345


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jun Wed 27, 2018 7:54 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 441
OK, I think I can see where your problems are.

That tuner AGC is a bit too negative for anything but a really strong signal. Get a clip lead, short it out, and see the difference.
I don't have the circuit, but I bet there is a 10meg or thereabouts resistor from the tuner AGC to B+. I bet it's open circuit.

The vertical fault will NOT be caused by the integrator capacitors.

Try adding a 100uF cap in parallel with the one in the cathode of the 6K6 vertical output. See if that stretches the bottom out.
If not, get a 47uF or thereabouts electro 300v rating or more. Use it to bypass the B+ supply to the vertical output at the vertical output transformer.

If neither of these make much difference, observe the crushing top and bottom of that raster as you increase the height. Does it seem to hit an invisible wall?
If so, your vertical output transformer probably has a shorted turn. You'll need to replace it. Same thing happened to me recently with an HMV F series.

Shorted turns were common in the days before polyester winding wire. The vertical output transformer is vulnerable because it has a large number of turns of very fine wire in its primary and high peak voltages are developed during the retrace.


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jun Wed 27, 2018 3:54 pm 
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Joined: May Fri 29, 2009 4:35 am
Posts: 2071
Location: Chicago, IL USA
The vertical looks fine to me. This is a 4:3 aspect ratio set and it's not supposed to fill the screen vertically. A mask will cover the top and bottom when it's in the cabinet.


irob2345 wrote:
OK, I think I can see where your problems are.

That tuner AGC is a bit too negative for anything but a really strong signal. Get a clip lead, short it out, and see the difference.
I don't have the circuit, but I bet there is a 10meg or thereabouts resistor from the tuner AGC to B+. I bet it's open circuit.


You can get a free copy of the service info here: http://www.earlytelevision.org/pdf/admi ... er_tv4.pdf


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jun Thu 28, 2018 1:45 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 441
Quote:
The vertical looks fine to me.


Given, but have a closer look at the line spacing - it's way out, crushing top and bottom.


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jun Thu 28, 2018 2:03 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 441
Re the tuner AGC and the snow:

That circuit has NO delay on the tuner AGC at all. That fact, and the use of a 6AG5 (pentode) as the RF amp, would make the noise performance of the set (snow) poor by later standards.
You may be able to modify the tuner AGC to add delay, or just use a stronger signal. If you S/C the tuner AGC you will S/C the AGC to the IF amps and kill the picture.

If you have a choice with your modulator, use a LOW VHF channel (i.e. band 1) because the performance of the 6AG5 will be better at lower frequencies.

Would you like some advice on how to add adjustable AGC delay? It might help.

I checked the vertical circuit and my earlier comments apply. It's a pretty standard circuit.


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jun Thu 28, 2018 4:36 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 156
Location: parkersburg west virginia
irob2345 wrote:
OK, I think I can see where your problems are.

That tuner AGC is a bit too negative for anything but a really strong signal. Get a clip lead, short it out, and see the difference.
I don't have the circuit, but I bet there is a 10meg or thereabouts resistor from the tuner AGC to B+. I bet it's open circuit.


From what i ascertained from the schematic is that there is no reference to B+ anywhere in the AGC buss. I did remove one lead off of each resistor in the chain & they were all within their ratings.
I also checked the voltage on the plate of V305 (6AU6) & got around 190 v p-p

irob2345 wrote:
The vertical fault will NOT be caused by the integrator capacitors.
Try adding a 100uF cap in parallel with the one in the cathode of the 6K6 vertical output. See if that stretches the bottom out.
If not, get a 47uF or thereabouts electro 300v rating or more. Use it to bypass the B+ supply to the vertical output at the vertical output transformer.


I will most likely try that out when i finish with troubleshooting the AGC problem

irob2345 wrote:
If neither of these make much difference, observe the crushing top and bottom of that raster as you increase the height. Does it seem to hit an invisible wall?
If so, your vertical output transformer probably has a shorted turn. You'll need to replace it. Same thing happened to me recently with an HMV F series.

Shorted turns were common in the days before polyester winding wire. The vertical output transformer is vulnerable because it has a large number of turns of very fine wire in its primary and high peak voltages are developed during the retrace.


Actually, i can adjust the linearity & hight controls to cover the whole screen & the crushing at the top will disappear. it really never had compression at the bottom, just the top.


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jun Thu 28, 2018 4:43 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 156
Location: parkersburg west virginia
irob2345 wrote:
Re the tuner AGC and the snow:
That circuit has NO delay on the tuner AGC at all. That fact, and the use of a 6AG5 (pentode) as the RF amp, would make the noise performance of the set (snow) poor by later standards.
You may be able to modify the tuner AGC to add delay, or just use a stronger signal. If you S/C the tuner AGC you will S/C the AGC to the IF amps and kill the picture.


Well, the signal is a strong clear signal that i have that set connected to. just to make sure, i connected another portable set just to verify why kind of signal i was getting.

irob2345 wrote:
If you have a choice with your modulator, use a LOW VHF channel (i.e. band 1) because the performance of the 6AG5 will be better at lower frequencies.


I use channel 3 on both the feed from my bench, as well as the output of my modulator
Also, when i run the modulator, it appears to over load the video on that set.i can tune it to the point where i can get the picture, however the sync becomes unstable & i lose my audio

irob2345 wrote:
Would you like some advice on how to add adjustable AGC delay? It might help.


Yes, i would be very interested & i would appreciate it


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jun Thu 28, 2018 5:22 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 441
OK, I'll draw it up and post it.

Attachment:
AGC_Delay.jpg
AGC_Delay.jpg [ 68.78 KiB | Viewed 956 times ]


What this does is reduce the amount of AGC being applied to the RF amp until the signal strength is too high for the IF amps to handle. That way the mixer always operates with the largest possible signal and the IF amp gain is reduced in proportion. This improves the signal to noise ratio.

You will find a similar circuit in almost all tube type TVs.


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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jun Thu 28, 2018 8:04 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 156
Location: parkersburg west virginia
I found the cause of the problems with both the AGC & with the snow in the picture last night.
i did a trace on the AGC line in comparison with the Riders schematic & found that someone in the past had removed a .001 capacitor that connects from the plate of V305 (6AU6) to terminal 1 on the horizontal width control (secondary winding) & replaced it with a jumper wire. i removed the jumper & attached a .001 capacitor in place, powered up the set & noticed a big difference in the picture, however, i still had snow. i changed the channel up to the next channel, which was unused & switched back again to see how the sync would lock. i then discovered that the detent was not aligned & after jiggling the tuner knob, the picture cleared right up. i had to re-adjust the spring on the turret lock. now, i do not have any more snow in the picture.


Attachments:
File comment: This is connected straight from my bench cable
Admiral 20A1-12.JPG
Admiral 20A1-12.JPG [ 85.34 KiB | Viewed 929 times ]
File comment: This is with my DVD player via RF modulator
Admiral 20A1-11 DVD.JPG
Admiral 20A1-11 DVD.JPG [ 90.56 KiB | Viewed 929 times ]
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 Post subject: Re: Admiral 20A1 recap - Need Advise
PostPosted: Jun Thu 28, 2018 8:07 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 156
Location: parkersburg west virginia
irob2345 wrote:
OK, I'll draw it up and post it.

Attachment:
AGC_Delay.jpg


What this does is reduce the amount of AGC being applied to the RF amp until the signal strength is too high for the IF amps to handle. That way the mixer always operates with the largest possible signal and the IF amp gain is reduced in proportion. This improves the signal to noise ratio.

You will find a similar circuit in almost all tube type TVs.


This is a good idea. i will try that circuit out once i address the two remaining issues on that set (vertical & low audio)


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