Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Nov Fri 24, 2017 12:24 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 77 posts ]  Go to page 1, 2, 3, 4  Next
Author Message
 Post subject: Crosley 9-407 (DuMont RA-103 chassis) restoration
PostPosted: Jul Thu 24, 2008 8:12 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11848
Location: San Jose, CA USA
Since there are some others working on sets with this DuMont chassis, I'll pass along what needed to be done on mine to bring it back to life.

Here's a shot of it working. My original DuMont 12JP4 is reasonably bright. It has been rejuvinated, so I'm not sure how long it will last, but it seems fine for now. Hardly any ion burn in the center -- you really have to be looking for it to find it.

Attachment:
Crosley 9-407 working - 800 wide.jpg
Crosley 9-407 working - 800 wide.jpg [ 91.53 KiB | Viewed 906 times ]


This set had a special problem, which prevented me from wanting to work on it for several years. The shaft in the Inductuner was broken:

Attachment:
Crosley 9-407 Inductuner shaft broken - 800 wide.jpg
Crosley 9-407 Inductuner shaft broken - 800 wide.jpg [ 34.17 KiB | Viewed 906 times ]


This is a ceramic shaft, broken right near the point where the shaft exits the front of the tuner -- where it needs to have decent strength. Not easily repaired.

This set was shipped to its previous owner by someone who didn't know much about packing. It was boxed in a wooden crate, probably with no padding. Most egregious mistake was that the screws that held the crate together penetrated to the inside and created many holes in the cabinet! (in an otherwise fairly pristine cabinet! :x ) I suspect the tuner shaft and knob were pinned against the front of the shipping crate, which broke the shaft.

Anyway, thanks to Ron (Tahoe TV), I got a replacement Inductuner, from which I was able to borrow the shaft and build it into the one on this set. Assembly of the Inductuner is a little tricky, but with some patience it was done:

Attachment:
Crosley 9-407 Inductuner fixed - small.jpg
Crosley 9-407 Inductuner fixed - small.jpg [ 89.64 KiB | Viewed 906 times ]


This set also has the usual bad B+ relay. For now, I've simply wired across it, and I just might leave it that way unless someone knows a good reason why this set really needs a relay on the B+.

Other notable problems were a bad damper resistor in the HV cage, which I replaced:

Attachment:
Crosley 9-407 damper resistor - 800 wide.jpg
Crosley 9-407 damper resistor - 800 wide.jpg [ 85.62 KiB | Viewed 906 times ]


Also, one of the big Candohm resistors in the main B+ filter was shorted to ground through its housing! Major load on the B+... This is the one:

Attachment:
Crosley 9-407 shorted Candohm resistor - 800 wide.jpg
Crosley 9-407 shorted Candohm resistor - 800 wide.jpg [ 90.39 KiB | Viewed 906 times ]


The rest was mainly recapping and replacing some off-value resistors. One that surprised me was a pair of 2-watt resistors in parallel (two 22K resistors in parallel for 11K) feeding a screen grid in the horizontal oscillator. A bypass capacitor was shorted to ground, and as the resistors overheated, their resistance drastically decreased (which I seldom see), basically shorting the B+ to ground there as well. This took me a while to find, since I did not expect anything with 11K in series with it could have been a sufficient short circuit to kill the B+. But indeed it can when the actual resistance falls to about 200 ohms...

Anyway, that was all there was to it on this one. Will clean up the chassis and try to figure out how to fill the holes in the cabinet without refinishing, since most of the finish is very nice.

_________________
Tom K6VL


Last edited by Tom Albrecht on Jan Tue 26, 2016 7:00 am, edited 1 time in total.

Top
 Profile  
 
 Post subject:
PostPosted: Jul Thu 24, 2008 10:00 am 
Member
User avatar

Joined: Apr Fri 21, 2006 12:49 am
Posts: 9310
Nice picture on that set. Thanks...
Er, do I see a couple of original paper capacitors by the band switch?? That brand of cap is known to suddenly short when it fails....
I wouldn't sweat the relay. I believe this chassis may also have their early special power transformer that is wound in such a way as to be a surge limiter.. Ingenious of Dumont. Unfortunately, expensive, too. By 1951 they quit using that style of transformer. I think it has something to do with the induction core. Otherwise, looks the same as any other transformer to me.... :?

And, in my view that Mallory inductuner was ingenious.
I still don't fully understand how it works.
I have a really ratty RA-103D I still don't know what to do with.
Finnish basket case.
That same resistor under the chassis is hanging on wires. It had exploded, and, shorted to chassis.
I know why this resistor, and, a similar cheaper one popularly used that I call a "candy kiss" resistor due to it's shape had a tendency to short.
The insulator was merely some sort of cardboard wrapped around the resistor inside. That cardboard eventually burns away, and, allows it to short.
One time I had an Airline AC DC table radio that had that resistor standing on end above the chassis. It was pop riveted on by one leg. It was in the hot end of filament supply.
Chassis was connected to B-through a capacitor.
That resistor shorted to chassis.
Radio played, but, had a terrible power supply hum.
The resistor was the reason....

Hope you can fix that case, but, it sounds like you'll be refinishing it.... :(

Bill Cahill :D

_________________
http://www.tuberadioforum.com/
PLEASE visit Tube Radio Forums-The best forum in the World!


Top
 Profile  
 
 Post subject:
PostPosted: Jul Fri 25, 2008 6:49 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11848
Location: San Jose, CA USA
Hey folks,

When I was putting the set back together, I notice there is a small permanent magnet attached to the inside of the cover of the HV cage. It looks original. It sits right next to the horizontal output tube when the cage cover is on.

What is it for and what does it do?

_________________
Tom K6VL


Top
 Profile  
 
 Post subject:
PostPosted: Jul Fri 25, 2008 10:11 am 
Member
User avatar

Joined: Apr Fri 21, 2006 12:49 am
Posts: 9310
I'm not sure, but, I think it was supposed to make the tube have more output. It wasn't really a good idea.
Bill Cahill

_________________
http://www.tuberadioforum.com/
PLEASE visit Tube Radio Forums-The best forum in the World!


Top
 Profile  
 
 Post subject:
PostPosted: Jul Fri 25, 2008 10:52 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1539
Location: Manitowoc, WI USA
Maybe it was to make the TV more attractive...

_________________
We improve things by making them worse...


Top
 Profile  
 
 Post subject:
PostPosted: Jul Fri 25, 2008 12:33 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 369
The magnet helps eliminate Barkhausen interference.
Another trick was to put an old ion trap around the
horizontal output tube.
Regards,
Swanson


Top
 Profile  
 
 Post subject:
PostPosted: Jul Fri 25, 2008 4:38 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11848
Location: San Jose, CA USA
Hi Swanson,

Barkhausen noise is caused by erratic movement of magnetic domain walls in a magnetic material. So I could imagine that a magnet placed near the core of the flyback transformer could have some influence on Barkhausen noise there. But I don't think I understand how a tube could have Barkhausen noise. Do you have some insight into that?

_________________
Tom K6VL


Top
 Profile  
 
 Post subject:
PostPosted: Jul Fri 25, 2008 5:33 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 669
Location: Crystal Bay, NV
Tom,
This quote is from the old Rider publication "Troubleshooting and Repair Guide Book" from 1952.

"Barkhausen oscillations appear as one or more black vertical lines at the left-hand side of the picture-tube pattern. Barkhausen oscillations occur durning the time that the plate of the horizontal-output tube is negative, due to ringing and overshoot of the plate waveforem. The oscillations are usually radiated to the frontend tuner. Some suggestions for reducing or eliminating this effect are:
1. Try shielding the yoke leads coming from the high-voltage compartment. However, this may not be practical, since the added capacitance in the sweep circuit can cause foldover.
2. Select another horizontal-output tube that does not oscillate.
3. Mount an ion-trap on the horizontal-output tube.
4. Shield the screen lead of the horizontal-output tube. The plate lead usually cannot be shielded due to foldover.
5. Insert a 100-ohm parasitic-suppressor resistors in the control- and screen-grid leads of the horizontal-output tube."


Obviously, any repairman would first try the tube substitution, then the ion trap. Your set seems to have a fix similar to the ion trap, and it might not be necessary now.
=======
Ron


Top
 Profile  
 
 Post subject:
PostPosted: Jul Fri 25, 2008 6:51 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11848
Location: San Jose, CA USA
Very interesting! I don't really understand how it works, but I can see that there is some definite basis for this in the literature.

Maybe the magnet affects the cutoff behavior of the tube (less sharp cutoff?). I'm guessing the actual Barkhausen phenomenon is still in the flyback or yoke (where there are magnetic materials present), even though it is being affected by a change to the tube.

_________________
Tom K6VL


Top
 Profile  
 
 Post subject:
PostPosted: Jul Fri 25, 2008 7:03 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 669
Location: Crystal Bay, NV
Here is another explanation of Barkhausen oscillation from a Coyne servicing encylopedia:

"As the output amplifier grid voltage goes suddenly less negative, plate voltage drops momentarily below screen voltage and electrons between plate and screen move toward the screen. But before all electrons reach the screen the plate becomes more positive, and electrons between the elements move back toward the plate. This back-and-forth movement of electrons or charges constitutes oscillation within the tube and in capacitances and inductances of connected wiring."
=========
Ron


Top
 Profile  
 
 Post subject:
PostPosted: Jul Fri 25, 2008 7:06 pm 
Member

Joined: Jun Fri 01, 2007 12:54 am
Posts: 266
Location: douglassville PA
My HV cage has this magnet as well. Thanks for letting us know what it does!


Top
 Profile  
 
 Post subject:
PostPosted: Jul Fri 25, 2008 7:17 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11848
Location: San Jose, CA USA
Thanks, Ron. I'm learning some new things here. Up until now, I was only familiar with the term "Barkhausen" in the context of Barkhausen noise that we encounter in magnetic sensors (see for example http://en.wikipedia.org/wiki/Barkhausen_effect or http://wagner.ucsc.edu/Papers/barkhausen.pdf ).

A little search right now reveals that Barkhausen oscillation is actually a more widely applied term for certain kinds of oscillations that occur in unstable feedback loops (see http://en.wikipedia.org/wiki/Barkhausen ... _criterion ).

The "Barkhausen" phenomenon being referred to here is clearly the second category. Apparently the tube is momentarily unstable, and oscillations can arise.

What particularly confused me is that a magnet is used to affect the problem (pointing me in the direction of the magnetic Barkhausen effect that I was familiar with), when in fact the magnet is being used to affect what happens to electrons inside the tube, which has nothing to do with any magnetic materials in the tube or other associated components like the yoke or flyback.

I am often surprised at what a treasure trove of information ARF members have lurking in their minds. A lot of knowledge floating around here!

_________________
Tom K6VL


Top
 Profile  
 
 Post subject:
PostPosted: Jul Sat 26, 2008 5:43 am 
Member

Joined: Jul Sat 12, 2008 4:31 am
Posts: 25
Location: San Diego
Hi Tom,
I was surprised to see the Crosley 9-407 TV. My father bought this model in December 1948 and I still have the TV and the original receipt. Over the years, I replaced the picture tube and some of the capacitors. It suddenly "died" in the 1980's and I later found the flyback transformer had failed. I called (before the internet) Thordarson and they told me of their "Gold List" where the remaining old transformers could be found. I called a place in Connecticut and they actually had two. I asked them to send one and they said if it didn't work, to send it back and they would send the other. The first did work and the TV picture worked again. The last failure was another transformer in the vertical section. I haven't replaced it for lack of a part. I used a capacitor or some part to connect the burned out section. The picture is a little messy at the bottom, but it still works. The Inductuner always worked and most of the earliest problems were the electrolytics and some tubes. I have ordered the HD coupon for this TV and hope to keep it going. I will need to again replace the capacitors that I replaced about 30 years ago.
Do you know of a source for 60 year old vertical transformers (it might be a blocking or sync transformer). Good luck with your set. The picture looks great.


Top
 Profile  
 
 Post subject:
PostPosted: Jul Sat 26, 2008 5:06 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11848
Location: San Jose, CA USA
Hi Ken,

Interesting that you mention the transformer in the vertical section. On mine, that part has obviously been replaced (probably the only nonoriginal part on it when I received it), so that must have been a weak link in these sets. I presume you're talking about the vertical interstage transformer, rather than the vertical output transformer, which is still original on mine.

I don't know what the characteristics of that transformer are, but since mine is still on the bench, I could try to measure the turns ratio and then you could look into using some kind of audio transformer in place of it.

Or perhaps someone here knows more about the characteristics that are typical of this kind of transformer.

Regarding caps, you may want to replace the 30 year old electrolytics, but the other caps you replaced should be fine for a long time. Old paper caps deteriorated rapidly, but if you used new caps 30 years ago, they were not paper, and will hold up for a long time.

It's great that you'be been able to keep a set like that in the family so long. Hope you get it working again.

_________________
Tom K6VL


Top
 Profile  
 
 Post subject:
PostPosted: Jul Sun 27, 2008 6:10 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11848
Location: San Jose, CA USA
Found one more quirk with this set that may be helpful for others working on similar sets using this chassis:

Operating the set with the speaker unplugged is hard on the audio output tube, since the output transformer is on the speaker. Unplugging the speaker removes B+ from the plate of the tube. After you do this a while, the tube is toast.

When this tube goes, the whole set can develop quite an interesting set of symptoms, since loss of plate current on this tube throws all the B+ voltages off. Contrast goest way too high, and the focus control goes out of range.

Replacing the 6V6 audio output tube, and running only with speaker connected solves the problem. Need to physically remove the speaker from the cabinet and leave it plugged into the chassis all the time.

_________________
Tom K6VL


Top
 Profile  
 
 Post subject:
PostPosted: Jul Sun 27, 2008 6:37 am 
Member

Joined: Jun Fri 01, 2007 12:54 am
Posts: 266
Location: douglassville PA
I was just wondering what the crosley and the DuMont set sold for when new? Anybody know?

Thanks, Kyle


Top
 Profile  
 
 Post subject:
PostPosted: Jul Sun 27, 2008 8:07 am 
Member

Joined: Jul Sat 12, 2008 4:31 am
Posts: 25
Location: San Diego
Hi Tom,
Three things:
1. When I replaced the capacitors I used old caps that were removed from other old sets. They were paper too. Too bad now.
2. I remember operating the set with the audio output plug disconnected with no problems. It was probably for short intervals when I made part changes and forgot to reconnect it.
3. I found the old Sams for the this TV and the only transformer it could be is marked T3, the vertical blocking oscillator transformer. It also affects the vertical sync. The Sams has the DC resistance of the windings and a Crosley part number: D-160015-2. Unfortunately, it has no cross reference. I remember the primary is good and one of the secondary windings is open.
Any ideas for repair are welcome.

Kyle: The receipt for the Crosley dated 12/17/48 shows the TV costing $334.75 and the installation with a roof antenna for $75. This set was purchased in NYC.


Top
 Profile  
 
 Post subject:
PostPosted: Jul Sun 27, 2008 3:49 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 369
Hi Tom,
When I was working on my RA-103D many years ago I
used an old 6K primary single ended output transformer
for the output tube load.I screwed one side of the transformer
to one of tne inductuner cover screws and put a 10 ohm
1 watt carbon resistor on the secondary.The output tube
was loaded properly and I was able to keep the fragile
speaker in the cabinet.Check your junk box and see if you
have an old output transformer kicking around and put that
speaker back in the cabinet.
Regards,
Swanson


Top
 Profile  
 
 Post subject:
PostPosted: Jul Sun 27, 2008 6:45 pm 
Member

Joined: Jun Fri 01, 2007 12:54 am
Posts: 266
Location: douglassville PA
Would the DuMont be more expensive than the crosley?


Top
 Profile  
 
 Post subject:
PostPosted: Jul Sun 27, 2008 7:19 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11848
Location: San Jose, CA USA
Ken,

I also got away with running the set with the speaker disconnected for actually quite a long period of time.  But eventually it did kill the 6V6 in my case.  Maybe you were a quicker repairman than I was! :)

Swanson,

Using a temporary output transformer is not a bad idea.  The speaker is a bit fragile -- the cone paper is quite brittle, so I've had to add a few glue dots here and there to keep the cone from rattling where it's cracked at the edges.

_________________
Tom K6VL


Top
 Profile  
 
Post New Topic Post Reply  [ 77 posts ]  Moderators: 7jp4-guy, Mr. Detrola Go to page 1, 2, 3, 4  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 9 guests



Search for:
Jump to:  


















Privacy Policy :: Powered by phpBB