Retrace Lines on 1948 Admiral 20x1

[Unimatic1140]

Hi everybody, I am in the process restoring my second vintage television set which is a 1948 10" Bakelite Admiral set. This is the same set as seen Rob's first post under the "Show us your vintage B&W sets!" thread. Its chassis 20x1, I recently found a brand new 10BP4 picture tube for the set and it is now has a wonderfully bright picture.

I have recapped the entire set and have cleared up most problems, including a troublesome sound issue that was cause by someone turning the Sound IF slug nearly all the way in at some point in this sets past. My one main issue with the set is I seem to have a problem with white diagonal retrace lines which appear generally on the top 1/2 of the screen, but at times can go almost to the bottom of the screen. On some stations I can get the lines to disappear, but during the momentary dark periods in-between commercials, I can still see these lines. In order for the retrace lines to completely disappear I need to turn the brightness control down to the point that the picture is too dark to be viewed comfortably. Does anyone know where in the circuit I would need to troubleshoot to try and minimize or completely remove the retrace lines? :dunno:

Another interesting issue I have with the Admiral is when I turn the contrast control all the way down (counter-clockwise), I loose both picture and sound. I heard this was normal on some early receivers, but I sort of find that very strange that they would be designed with that flaw.

Anyway, thanks in advance, any help will certainly be appreciated.

Robert (Unimatic1140)
http://www.classicappliances.com

[Rob]

Robert,

I see you got an answer to this same question on that other forum, however I, as you know have this same Admiral and although I experience slight the loss of all functions when the contrast control is turned way down it is not a problem because I never use the control that low. However the chassis that preceeded this one, the 30A13 has this problem really bad, turn down the contrast and sync gets lost, sound disappears and the picture goes away, I guess it is a manual screensaver control. :)

I guess one could design a blanking circuit fix for retrace lines by examining the schematic and poking around with the chassis on the bench. I've not felt it necessary.

Another cause for visible retrace lines is the lack of a DC restoration clamp circuit in the video output stage where it drives the CRT. Without a clamp circuit, and many of the earlier sets did not have one, it is a scientific impossibility to achieve full grey scale dynamic range without seeing the retrace lines. My 30A13 has a DC restorer (half of the 6AL5 used as the video detector) but my book covering the 21X12 is out in the shop so I cannot say. I suspect it does. Perhaps your restorer is faulty.

Rob

[Unimatic1140]

Well thanks for your help Rob, I'll take a look for the DC restorer this week and check it out. All the tubes have been replaced with new or known good ones so it might be a resistor problem in one of the video circuits. I'll let you know what happens when I figure it out.

[jshorva65]

This is somewhat on-topic since it deals with the contrast controls on late-1940's sets, but I've noticed that high settings of the contrast control resulted in severly-overloaded video and loss of sync on ALL of my sets when connected to my home's amplified antenna distribution system. Setting the control fully CCW would kill the sound and video on most of the sets. I found that these sets all lacked modern AGC circuitry and were designed to make the most of fringe reception. In fact, the alignment instructions for the 721TS call for connecting a VTVM into the circuit near the contrast control and setting the control to give a reading of -3V as a preliminary step in the video IF alignment procedure.

To minimize overloading on all sets, my display room is now fed from the same distribution system via a switchable attenuator and that has cured the problem. Channels I've received are Cleveland channels 3, 5 & 8 and then by rotating the antenna I can pick up 2. 4, 9, 11 and 13 which are from other cities mostly to the east.

[DBerning]

The dc restoration is an interesting issue. I have not played with many pre 1950 sets, but from what I have seen, some of the early sets included the restorer diode, but once the larger-screen sets of the early 50s appeared, the dc restorer had been abandoned (for cost reasons I assume). I don't recall seeing a B&W set with dc restoration until I saw a Sylvania circa mid to late 60s perhaps. Some later sets, including color, had partial dc coupling. It wasn't until Consumer Reports Mag. made an issue out of dc restoration in about the early 70s that all of the manufacturers got on board and put the dc restoration back in the sets. The CR article was prompted by Sony (and perhaps Sylvania) being the only manufacturer having 100% dc restoration at the time. The picture quality of the Sony was rated the highest of the sets tested. I had just purchased a 1973 Zenith, and that or a similar Zenith was rated as having only 10% dc restoration. I bought the Zenith (hybrid) because I liked the way it was built, and would not have touched a Sony. Shortly after I read the CR article I set about eliminating all of the coupling capacitors in the video signal path and adding appropriate level-shifting transistors to achieve 100% dc coupling, which give the same result as restoration. I have done a similar operation to a number of other sets, including a vintage CBS Columbia that I used in my bedroom for many years. The only set that I have in house that I have not done this to is a 1948 Admiral 7-inch round CRT table-top unit that I want to keep original.

In fact, this Admiral is an interesting set in that it uses electrostatic deflection, and has relatively low power consumption. Power is supplied with a 5Y3, and the high voltage is supplied with a 6V6 resonant RF oscillator. Another interesting feature that lowers power consumption is the way power is supplied to the IF and tuner. The main B+ is perhaps 300 volts, but the voltage used by the IF is reduced to 150 V not by a power resistor, but with the audio output tube. Thus, the audio output tube is used sort of like a series pass voltage-regulator tube, but at the same time doing the work of the audio output.

Dave

[jshorva65]

I have one of those Admiral sets that I bought on eBay as a recapped, working set with no cracks in its Bakelite case. When I received it, it was not at all as it was described from the 10" crack in the top of the case, broken back-cover screw posts, insufficient vertical sweep and the fact that turning the volume up to an audible level would cause the video and sync to go nuts. Needless to say, I wouldn't have paid over $200 for the set if I had known half of this before I placed my bid and I expressed my dissatisfaction to the seller who responded by promising to send a copy of the schematic which I received almost 2 months later after reminding him several times Needless to say, I haven't bought anything else from this guy. Since he put the words "as-is" in his listing, there wasn't much point in posting negative feedback although I didn't include the usual high recommendations in my feedback that I normally do. I've placed that set fairly low on my priority list due to the condition of the cabinet, but I'll eventually restore it. I prefer 10" electromagnetic-deflection sets, possibly because I still have one good spare 10BP4 plus a rebuildable dud just in case I find one that needs a CRT. I had two good spare 10BP4's before I used one of them in the 721TS that I restored recently.

[Rob]

Originally posted by DBerning
.....In fact, this Admiral is an interesting set .... Another interesting feature that lowers power consumption is the way power is supplied to the IF and tuner. The main B+ is perhaps 300 volts, but the voltage used by the IF is reduced to 150 V not by a power resistor, but with the audio output tube. Thus, the audio output tube is used sort of like a series pass voltage-regulator tube, but at the same time doing the work of the audio output.

Dave

Hi Dave,

Welcome to the Vintage TV Forum! Your knowldgeable contributions will be appreciated. The clever DC B+ divider scheme using a 6AS5 miniature pentode in the audio output stage was not only employed in the 19A11 Admiral chassis but in some of their larger magnetic deflection chassis as well in 1949 for sure. I had a 12" set with a badly gassy 6AS5 with incandescent screen grid and not having an exact replacement found that more common similar tubes like 6AQ5 whch I did have in stock unfortunately had different pinouts. Determined to enjoy the set I raised a couple of resistor values in the audio output circuit to decrease the current through the tube allowing it to function until I could get a replacement. Before the mod it would suddenly avalanch completely into cutoff with no sound from a mild audio excursion. After replacing the tube I never bothered changing my resistor values back to stock. It worked fine.

That Tesla coil type HV supply in the 19A11 using a 6V6 is a real powerhouse compared to the T-54 series Hallicrafters 7" electrostatic sets. Halli does the same thing using one tiny 6C4!

BTW, I am very impressed with your very unconventional OTL amp design and sure would love to have the opportunity to hear one of these some day!

Rob

[Unimatic1140]

Well the guys at rec.antiques.radio+phono helped me update the circuit in my Admiral and my Retrace Lines are completely gone! YAY. Apparently Admiral was always in a big hurry to get their products to market. It turns out that my chassis was part of Production Run #3 and there were 13 different production runs in total on this model. By Run #13 there was a fix in the circuit to prevent Retrace Lines and someone was kind enough to look up the fix and explain the necessary circuit changes to me (in easy to understand newbie terms that is). :)

And to think before I started learning how to restore vintage television sets I acutally thought of taking the old chassis out and sticking a new remote controlled color TV in the cabinet. That would have been a terrible thing to do to this wonderful antique, it is so much more fun to have the original working beautifully again.

Look how beautiful it came out! I just installed it in the dining room. Here is the Admiral playing a 1949 commercial for Joy dishwashing liquid from when the set was barely 1 year old...

http://www.classicappliances.com/TV/Admiral-Completed.jpg

Thanks again guys for all your help and replies.

[Rob]

Unimatic,

Wow! Beautiful restoration there. The Admiral looks and works just like new. Why not post this picture in the "Show us your vintage B&W TV's' thread?! It is easy to attach the photo. Just click on the browse button in the attach file box below the text writing area and find the picture in your computer.

Rob

[Wedweb]

I saw one of these in a local thrift store for $100.00. The only difference was that the tv tube was on the left. If anyone is in the St. Louis driving area and interested in it I can tell you how to get to the store. I did not try it.

http://www.tvhistory.tv/1949-Admiral-32X15.jpg