[F-1540]

I am trying to get a F-1540 back operable for a friend with a 1938 Ford.  The radio came separately with the car purchase and the previous owner had no status on the radio condition.  Cosmetically it is pretty decent shape.
I am a semi retired technician and worked with high power tube transmitters for several years but I have been away from that era for a long while.  I have been reading till my eyes bleed on this site and took the good advice of changing out all the dripping wax caps.  I have recently dealt with the power supply  4/8 uf can by putting a couple of caps on the bottom side … I don’t like the aesthetics but it brought the B+ voltage to about 211 volts.  Not sure if that is correct as I don’t really see any documentation with typical tube voltages.  I’d have changed a few resistors also that were off center value by quite a bit.  
Today I was able to half step and inject 260 kHz in the If producing a nice clean tone.   I eventually got to the point of injecting a 1MHz signal at the grid of the first RF tube and tuned around a bit eventually finding the signal a few hundred KHz off the dial indicator.  The sensitivity I am seeing is around -50 dBm and that is not real crisp.   I can inject into the antenna port also with a bit more loss.

As I am just getting started in this extracurricular activity I don’t have a supply of tubes but may order a 78 and 6A7. I am pretty encouraged about being able to jam a signal through now it may be just a matter of getting it stronger and cleaning the fuzz out.  

I am probably not knowledgeable enough to ask the right questions yet but there is a couple that come to mind.   
What kind of sensitivity should I expect out of this auto radio?
I’m pretty convinced the dial is not tracking right so maybe an alignment would help?  Would a front end tube swap be useful before I went hog wild with a tuning tool.   
Another symptom is the radio seems to produce a good amount of irritating buzzing but when I get the signal tuned in it reduces a lot but a but fuzzy.   The IF to Audio stages were real clean sounding.

I would welcome any comments from the brain trust here as to my next steps.

Regards,

Bill

[RodB]

Hello Bill and welcome to the Phorum. You are definitely a brave person to attack a vintage auto radio. Who knows what that radio went through. Before you can look at sensitivity consider the antenna. The auto antenna must be tuned to peak for optimum performance therfore, the actual antenna from the vehicle, or similar coat hanger, should be used. There's probably a trimmer cap in the antenna circuit.
The buzz is probably coming from the power supply vibrator. Be sure all the capacitors in the vibrator circuit are replaced. You may have to clean vibrator contacts. When you get to the alignment do the IF first. That should improve sensitivity and selectivity. To bring the tracking to where it should be adjust the oscillator trimmer capacitors/coil cores. I'm being general with my comments because I don't have a schematic. I'm sure others will have more specific comments. GL

[Tim Tress]

Do a continuity check on the coils, especially the oscillator coil. Another thing to check are the ground connections, especially at the tube sockets. Make sure that your filament voltage at the 6A7 is correct

[Chas]

Power the radio with a full size auto L/A battery. Use at least #12 wire at 5 feet or so if longer, say, battery on floor, use #10 wire. The battery must not be on a charger and fully charged. When testing be sure all covers over the vibrator circuitry are in place. Use the low capacity cable for the antenna and be sure its shield connections are good route antenna cable (coax) well away from the two power cables, in fact, twisting the power cables will help reduce any errant vibrator hash. Using just a wire inserted into the antenna jack will result in hash.

Most often the Buffer condenser has or is failing. Use the same ratings, the new cap must have a buffer rating or a posted dv/dt rating or it will soon become defective if the wrong type. All bets off if a solid-state vibrator is used, but shielding must remain.

The vehicle may not have RFI protection to support a radio. That is another topic...

[morzh]

Chas


Is there a reason for using AWG 12 or even 10 wire and the battery?

And for the battery, to save space, maybe a 12V SLA, the one they use in UPSes could do?

I mean, a real car bayttery, if something accidentally shorts, will pull an impressive arc, which will make even an experienced person jump. (I have no experience with old tube car radios, so these are the questions from someone who is trying to understand why certain things are done certain way).

[Chas]

(I have no experience with old tube car radios, so these are the questions from someone who is trying to understand why certain things are done certain way).

 
O.P. give that a try, see if noise reduces and sensitivity increases.

[morzh]

Chas,

You've lost me here Starting from O.P. and endingf by the noise and sensitivity. Don't make me feel dumb, I've had enough of that recentl;y

[F-1540]

Thanks to everyone for taking the time to make suggestions. 
I’ll need to revisit the 4/8 uf caps I put in place to take the place of the can. I scabbed in some  Solen PPE series but looking at the data sheet I do not see where they give  a dv/dt  they are physically too big anyways to mount in the can.    I do remember seeing a nice write up on this point somewhere.  
 I  am powering this 6vdc positive ground radio from a switcher power supply on the bench at the moment. Of course all the covers are off also. Probably everything around the workshop is generating some RFI the radio does not like.  Good point about going with the car battery and radio covers to see if things quiet down.  I have a 6 V battery available and I will give this a try.   I do not think the car has any of the Ford Philco noise suppression gizmos but I’ll cross that bridge later. 

 I can push a strong signal through the receiver and the oscillator seems to track decently so I am encouraged there may be some hope. I have a pretty clean signal from the IF to audio and rocked the padders a bit per the alignment procedure, The alignments seem to be peaked.  I do not have any tubes to try nor a tube tester but I may order a 78 and 6A7 just in case it is a weak RF or DET/OSC.   I have more stuff to buy from ARS anyways.  
I’ll take the suggestions offered here and add them to my checklist of things to ponder over.  I’m sure I’ll formulate more questions while partaking in an adult beverage.
Thanks All. This is an awesome resource!

Bill

[morzh]

>>do not see where they give a dv/dt

Use a typical value of 20-30V/us for polypropylene; poluester is better, 100-400V/us.

[David]

Some info hope it helps. Just to be sure the set is 6 volts!!   http://www.nostalgiaair.org/resources/00...014008.htm

[David]

Tried to post a link to  you tube.  https://www.youtube.com/watch?v=CM_m1MNTTsU

[Chas]

Thanks for update,

It is the buffer condenser that has to have a pulse rating Part #60, 7500 pf, the OEM may be paper or mica but it is of foil electrodes, the foil can easily take the kickback pulses of the power transformer, metalized capacitor in this service cannot and in time metalizing separates and looses capacity. If the required value cannot be found two of double the value in series are fine. For example two .015 at 630 Cornell or equivalent: 0.0150 mf WPP6S15K–F. If a single cap at .0075mf can be found do go to 1kv or more. Deviating more than 10% from the MF value risks shortening the life of the mechanical vibrator as far an an electronic vibrator, dunno?

The radio uses a electrodynamic speaker, that field coil uses about an amp by itself, it is possible to replace with a PM speaker as the field is not part of any voltage drop or power filtering.

The +6 volts will be via a #10 wire from the auto ACC terminals, the ground or return is the chassis, sometimes assisted with a #2 braid from the radio chassis to the firewall. There should be a much heavier braid from the chassis to the frame/battery as the body is or was rubber isolated. The heavy cabling is to reduce voltage drop to the supply for the radio, reduce the impedance at RF and allow for the heavy current surge when turning on the radio.

There is no indication of the type of antenna wire used. I suspect it is the very low capacity type that is basically a braid over a hollow tube and a 24ga copperweld center conductor "flopping around" inside.

Modern coax is around 22 pf per foot, no matter if it is terminated at its characteristic impedance but in the auto that capacitance may put it out of resonance so the signal will be marginalized. If a replica FORD antenna assembly for that model type/year is available, that, should work fine... Try 50 ohm coax it the antenna trimmer can peak properly and radio is sensitive across the band then fine...

This a quality Philco radio, with a fully tuned RF stage. Its sensitivity should be awesome on the bench and in the vehicle...

Caps #41 and #42 could also benefit from a dv/dt rated type, static crashes cut off the OPT and the collapsing magnetic field can puncture OPT windings. Same static pulse can degrade common metalized caps.

Oldest auto radio I rebuilt was a 40 Ford for a friend now SK. He had to find replica plastic indicators for the dial...

Oh, last word, any new part that may be on long leads, tag down to chassis with blob of electrical silicone. Auto vibration can work harden component leads until they break off...

GL

Chas

[F-1540]

F-1540 progress report.
Thanks to this Phorum and the great wisdom from the members that took time to answer my questions, I am able to declare significant progress made on this 1938 receiver, and pleased to inform it has be accomplished over budget and way over my time expectations. The directions I received here the other night were spot on.
Today I got a 6 volt Optimum gel cell auto battery and built a short, fused, power cable. I turned off all the shop led lights and anything electrical built after 1930, put all the covers on the radio and hooked up an antenna . I then scanned the band and soon was listening to the first off the air reception on this radio. I’m not really sure how many hours I have in reading till my eyes bleed, looking for service data, reading old Rider troubleshooting books and service bulletins for every like receiver I could find. My wife has been curious about all the little component purchases, soldering odds and ends, test cables, etc. Curiously she had the audacity to question why I would purchase a signal generator just to fix an old radio. I will admit the challenge of getting mediocre AM noise out of this old radio became a bit of an obsession over the last month or so.

Tonight I was sitting in my man cave siping a Bourbon Manhatten, all the Chinese LED lights off, and tuned into Clear Channel WBZ out of Boston. I was basking in the glow of the single amber tuning dial pilot light oozing the spirit of determination, and accomplishment.f

Next I need to attack the cosmetics, the speaker grill cloth needs replaced along with the tuning indicator bezel. I also want to stuff the power supply 4/8 uf capacitor can with new electrolytics if I can locate components that will fit. I don’t like the bottom chassis scabbed in capacitors. There are a couple resistors that are a bit off value and I may replace them. Hopefully I will not break anything in the process. At my NASA job I was always careful not to technician things to death.
I expect when we put it in place in the 38 Ford Woodie it will be noisy as I do not see any of the suppression components on the vehicle. Really this will be more to fill the dash holes and have something to brag about at the car shows.
The help I received here was top notch and it is much appreciated. Now that I’ve taken your time reading this, please have a Happy New Year.

Regards

Bill
Ford F-1540 … on the air

[Chas]

Congrats!

You may find friends at the auto shows will want you to repair their radios too

Sorry I missed WBZ this evening, I tune in every so often, but with a G-E "Super" radio.

Chas in S. Dartmouth...

[David]

Glad the radio is up and running. I also like the GE super radio. One can never have to many super radios. David