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Philco CT-2 for 1930's Plymouth PJ
#1
I have a Philco CT-2 that was restored and ready to install in a 1934 Plymouth PJ and is now acting strangely.

When 6 VDC on a positive gorund is applied, the tubes light up nicely (except for possibly the #77 tube, I can't get a good vantage point to see if it lights) and the vibrator begins to hum. At first, when using a signal generator, I wasn't able to pull a signal in. I then gave the side of the radio a few good thumps and it seemed to jar the vibrator into a better working state. I was then able to pick up freq's from the sig. gen.

Before thumping the side, the radio was drawing about 3.5A and post-thumping, the raio was drawing 4.6A. Possibly a bad vibrator?

The problem other than the above:

#1 - I can only get a good signal down to 800 KHz. I have no problem pulling a good tone in the uppers but it cuts out when I get down to 800 and below.

#2 - When I was taking voltage readings from the underside of the chassis (the tubes), I thought that I might have heard a little arcing, could this also be the Vibrator?

#3 - If I rock the radio while at a "good" freq. above 800, the radio tends to cut in and out.

#4 - If I touch a screwdriver to the grid cap, tube shield or case, it seems to change the amplitude of the signal. Could this be a ground problem?

#5 - The #77 tube doesn't appear to be lighting, but I can't be 100% sure. When I measured between pins 1 and 6 I got continuity (heater)

I'm fairly new at playing with antique car radios and still have a lot to learn. These seemingly multiple problems are really confusing. Part of me says that I should replace the Vibrator / take it apart and clean up the contacts.

Any help on this topic would be greatly appreciated. Thanks!
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#2
CT-2 is a 1935 radio ,I've restored a few . A good rule of thumb is a 6 volt car radio will use one amp pre tube + an amp for the field coil on the speaker, check tube sockets for possible shorting, that may be your arcing , low voltage you will get some signal but not enough to get station check your voltage from your secondary side of the power transformer, this set has been recaped?First thing you need a new buffer! also there is a condenser block ,replace them all , old Transitones had OSC coil troubles check it , Vibrator can be brough back by buzz it on 110 AC in line with a 40 watt light bulb lets first start by getting your B voltage up
BILL
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#3
Thanks for the quick advice! Yes, the radio has been recapped. I'll give the vibrator "re-gen" a try.

How do I go about checking the "OSC Coil"? If the OSC Coil turns out to be bad, are there replacement available for it or can it be rebuilt?

I'm still curious as to why I can't get any signal below 800 KHz, anybody have any ideas as to why this is occuring?
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#4
Check for continuity, there is a primary and secondary, OSC. problem could give you your signal droping but ,get your B+ up first
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#5
Just my .02, but I have found that the old mechanical-type vibrators are worthless at best, and not dependable at all. I have had to take the old mechanical vibrators apart, clean the points, and then find they still arent dependable unless you give them a good "slap" to wake up.

The good news is, new type solid-state vibrator replacements are now avail from several sources. I buy the new solid-state replacement 6v vibrators from: <!-- w --><a class="postlink" href="http://www.radiodaze.com">www.radiodaze.com</a><!-- w --> . They have a very good selection for any type application (neg or pos ground types). As far as "alignment" of your stations on a already recapped set, check to make sure the alignment was done properly using a good trustworthy accurate RF generator to "peak" the IF sections. If all that checks OK, then check point-to-point contacts on all the push button tuning (mechanicals). WD40 works well as many other high-dollar electronics contact cleaners. Weak,..( but still working) pentagrid-converter tubes can sometimes also cause wierd-issues in any vintage tube radio. ( get a schematic if possible) ,... try for a free one at: <!-- w --><a class="postlink" href="http://www.nostalgiaair.org">www.nostalgiaair.org</a><!-- w --> , ... then double check previous electronic restoration very closely!! If you have some "spare tubes",.. you can try subbing them (one-by-one)into the circuit starting at the front-end. Your getting audio, so the amplifier section is working? Seems your not far away from total perfection if a orig coil isnt open? Also, make sure you have a good antenna connection. A simple 4' piece of wire connected to a small screwdriver inserted into the ant connect should be enough to receive local stations (daytime). Also, follow all BILLs recomendations! He knows lots more about vintage auto-type radios than I ever will! He is is the PRO indeed!! Im just tryin to help out if I can!! Best of luck on your radio restoration!! Im still learning also, for over 35 yrs!! Nothing surprises me anymores working on these old sets!! Icon_wink
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#6
Bill & Texas,

Thanks for the hint's and help, I really appreciate it!

Instead of just using a freq. gen. (the building that I was originally testing the radio in is unable to receive any real signals) I brought the radio back home and hooked it up to my newly acquired power supply and connected an antenna like you had said and was able to pull in stations from 1500 KHz down to 800 KHz loud and clear but still nothing lower.

Just to verify that I wasn't crazy and just hearing things (or in this case not hearing things!!) I used my freq. gen. to verify my operating range and it is still 800 KHz and up.

I do have a schematic coutesy of Nostalgia Air (I love that site!) and will go back through the radio to verify that the re-cap job was done correctly
and it is 100% correct electronically.

I don't have any extra tubes laying around. I would love to have a spare set to swap in and out to see if that is the problem.

I will more than likely go the Solid State route on the vibrator and forego messing around with the old one seeing as how it's a single point of failure.

I will also check the coils and if worse comes to worse, get them re-wound to ensure that it will never be a problem.
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#7
Change that mixer/ocs tube, I've seen this problem many times, this will most offen cure it
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#8
Brian, I really dont think you have any orig coil probs worthy of going to the trouble of rewinding, period. If anything, below 800kc not working, is most prob a weak tube, (try replacing the osc/mixer tube) as Bill suggested first and foremost!! A weak tube in the front-end can "shut down" a perfectly aligned set from the factory. Messing with alignment on these vintage auto radios is usually not necessary, as most have never been serviced before, or alignment "changed" in most cases! As Bill said, you most likely need to replace the 1 tube, and will find your stations ALL, loud & clear across the full dial!! You bet, auto radios need a good antenna when servicing them indoors a metal type bldg etc! String up a good 4'-20' insulated pc of insulated wire out thru a nearby window to your workbench! (horizontal) as high as possible. Get you a couple good used "spare tubes" to interchange in these cases, so you can be sure the tubes are strong enough to give good performance all across the dial. Tube testers can "lie" sometimes also!! The best "test" for any tube, is while inserted into the set it is intended for! Also, recheck ALL the tube-socket pin-connections! Make sure they are clean,snug, & shiny!! Always improves any vintage radio!! Icon_wink
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#9
A couple of things you need to check on those old Philco Transitones. As with all auto sets, the filaments are returned to chassis, generally with a ground lug held by one of the mounting eyelets for the socket. Over all those decades, there is a barrier of corrosion that forms between the grounding lug and the chassis. The filament is no longer grounded, and often does not light. It might be a good idea to make a soldered connection directly on the chassis, and wind a bare wire pigtail to the filament terminal and the solder pool on the chassis.

One other part of the above is that if the connection to chassis is bad on the power amp tube (41 or 42), the cathode and filament pins are tied together, then grounded with that ground lug. Now, if the connection is poor, a whole volt may be measured from the filament (and cathode) pins to ground. The filament is lit OK, but there is virator hash in the output of the set. If you have that bad connection, you are feeding the vibrator hash into the cathode of the tube, and you have a sort of "grounded grid" signal feed into the power amp stage.

Second thing. Check the grid capacitor in the oscillator, and the grid resistor. They could be the source of weak or dead oscillator.

And lastly, don't get bent out of shape over old style vibrators. I'd never send a radio out with a solid sate one.
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#10
The only reason I use solid-state vibrators in these old 6 v dc type auto radios, is #1, Ive never had a prob using them before at all for several yrs past! Absolutely no probs at all!
#2: the points in the orig-types vibrators will most definately fail again in the future, due to oxidation & corrosion...guaranteed!
#3: if spending a xtra $30 bucks or so for a dependable S/S vibrator installed in customers auto-type tube radios for "reliable" operation in the future is a issue?? so beit. To each his own indeed!
My customers vintage auto type radios wont leave my shop "without" a S/S type vibrator installed,period! S/S vibrators are Much more reliable than the originals! .. and most customers dont know how to open the old vibrators to file & clean the points, and/or apply voltage to make them operable again.
The n.o.s. 0Z4 tubes we use in these type radios has a bad history also! Always install a new buffer-cap, in these type radios, and never fear "updating" the vibrator while the radio is on your bench. Ive never had a S/S vibrator fail yet since they have been in production, but then again, use your preferred choice! "Choice & Time" is what proves new components types integrity in the 1st place! I dont throw away my mechanical type vibrators at all. I use them for "test" purposes only!
As a general rule on vintage auto tube radios, the tubes all use about 1-amp each, so if you have a 5-tube set operating properly after full recap, your amp meter should be around 5 amps total DC current draw for the radio after warmup of the tube filaments.Monitor all tube filaments (string) test for exact 6.3 volts on slow variac DC power applied. These type radios have a higher "surge draw" from initial power-on. The reason for so many 6v DC type "on-off" switches being bad being bad buffer caps also. For a 6v auto tube type radio, use a 14-15 amp fuse as most mfgrs did back then on the 6v DC line into chassis which will more than cover the power-on surge at the on/off switch. If you have "noise-hash" issues, while unit is connected to a vintage Ac to DC bench test supply, remember that the "hash" is from the AC converter to DC supply, and once Radio is connected properly to the auto-battery, that noise is gone, unless the antenna has probs, or the autos generator or voltage regulator needs a added capacitor to chassis ground to rid hash. Using a .47/600 v bypass cap replaces the old metal-cased expensive auto-store types! Just my .02 only. Icon_wink
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#11
Just my .02 as an FYI. while working on my CT2 radio, I found that the Rider diagram for the component layout for the CT2 and CT3 shows slightly different tube layout and IF cans location.
My CT2 has some of the CT2 layout and some of the items are like the CT3 layout. You have to pay attention to that if you haven't worked on one of these radio before (like me).
If you have tube voltages for plate and gids and cathodes on a working chassis would you share them with me?
Jay Icon_lol
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#12
I agree with Doug Houston, the sets that used a 6A7 sometimes had a problem known as a critical oscillator. Try other tubes as Doug suggested, Sylvania seemed to be a better brand of tube here. As Doug also pointed out, there can be corrosion in the ground connection at the tube sockets so I also suggest running a ground wire directly to the chassis from the pins that are supposed to be grounded. Also there was no model CT-3, the first letter of the model number indicates the car(line) that the radio was designed for, the model T-3 was made for Pierce-Arrow MT-3, Reo RT-3, and Studebaker ST-3. I have never seen the osc coil go bad in any 34 or 35 Philco car radio, the 36 thru 38 radios are a different story, check with an ohmeter for continuity to make sure.
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#13
The loss of signal below 800 KHZ may be due to the variable condenser having warped plates that touch causing a shorting out and loss of signal. I found it not unusual for this to happen. It is around this point where the greater amount of meshing occurs between the plates. If the moveable plates comes in contact with the stationary plates of the tuning condenser you may hear intermittent scratching or experience complete signal loss. A close examination under good light with the aid of a magnifying glass may be of help.
Hal
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