FYI - 6 Volt Bulbs
 

When I replaced the strange mix of bulbs in my car after buying it, I found little to guide me as to their proper equipage. The vendor catalogs were no help; they indicate you can put any bulb wherever it will fit. After extensive googling I put together the following list (subject to correction) (but then I never make a mistake :D). So I thought I would share:

LIST OF 6 VOLT INCANDESCENT BULBS
(OE = Original Equipment; DO = Dealer Option)

HEADLIGHTS (BA15D base):

H-TYPE (before 3/29):
#1158 - 21/3 CP (S10) OE
#1170 - 21/6 CP (S10)
#1114 - 21/21 CP (S10)
#1118 - 32/21 CP (S10)
Apparently, of these only the #1158 survives but in the smaller S8 glass, which I suspect is not designed for parabolic reflectors. Snyder's sells part # T-13007-D (for Model T, 50/32 CP) which may be compatible, but see Note below.

TWOLITE TYPE (3/29 onward):
#1110 - 21/21 CP (S10) OE, A-13007-C
#1116 - 32/21 CP (S10) DO 11/30, A-13007-D
#1000 - 32/32 CP (S10) DO 11/30, A-13007-E
#1188 - 50/32 CP (S10) - See Note below
The S10 bulb profile was extincted early on, superseded by the RP11, with a wider, flatter top and no ridges.

BA15S base:

STOP LIGHT/SPORTLIGHT:
#1129 - 21 CP (S8) OE
#1680 -32 CP (S8) DO 6/31, A-18570
COWL/PARK:
#61 - 2 CP (G6)
DASH, TAIL:
#63 - 3 CP (G6) OE
DOME:
#81 - 6 CP (G6)
TAIL:
#81 - 6 CP (G6) DO 6/31, A-13466

AVAILABLE BA15S REPLACEMENTS:
---- - 10W* (G6)
#87 - 15 CP (S8)
#209 - 15 CP (B6)
#1133 - 32 CP (RP11)
#1183 - 50 CP (RP11)
* The "10 CP" bulb vendors sell is actually 10 Watts. MSCP of these bulbs is unspecified.

BA9S, Turn Signal Pilot:
#44 - 0.8 CP (T3.25)
#51 - 1 CP (G3.5)

Note: The 6V generator is designed for 12A output, 96 watts at 8 volts. Maximum authorized 32 CP headlights and 6 CP taillights draw a total of about 10A, leaving 2A for coil current. Intermittent brakes and/or horn requires another 5A each (32 CP brakes = 8A). Operation in this condition will draw down the battery until you shut off the lights to allow it to recover. Compare 50 CP headlight filaments which require approximately 6A each. You can see this may be a problem.

If you see any errors or can add any information (e.g., part numbers), let me know so I can update this list. Enjoy.

Re: FYI - 6 Volt Bulbs
 

Badpuppy,

per SAE std. J573d Mar. 1918, rev. 12/68:
@6.4V (full charged lead antimony battery only@ 68F) all lamps at rated circular candlepower output were driven to 2725K:
21cp = 2.63A
32cp = 4.01A
50cp = 6.27A
____________________
@7.1V (correct generator setting to maintain full battery charge) all lamps produced 2875K averaged spectral output.
21cp(now driven [email protected]) = 2.68A
32cp(now~34cp)= 4.08A
50cp(~54cp) = 6.34A
_____________
The purpose of the original circular ridges on the top (front) of the Ford and Lincoln spec. lamps was to diffuse direct point emission from the forward 138 degrees of the lamp. That part of the light would not strike the reflector and could not be focused into the parallel beam necessary to produce the driving beam. The ridges reduced glare to oncoming traffic.

All headlamp bulbs had a L.C.L. of 1.25". This is an exact match for the 1.25" focal length of the Ford parabolic reflector. Being equal, you could focus any Model A headlamp when OFF!!! All you had to do was to look at the reflector base and make sure the top edge of the bayonet pins were flush with the crimped ring of the socket guide in the reflector.

Many pre-1932 original headlamps were in S8 (8/eighths, 1" diameter) envelopes.

S10 envelopes followed later in an attempt to decrease the concentration of vaporized tungsten deposition (blackening) as the lamp aged.

The RP envelopes followed in a further attempt to change and reduce the blackening pattern as lamp aged. You may notice many RP envelope lamps have black dots or caps (skew caps) attached. These are more effective than the ridges in reducing glare to oncoming traffic.

As a side-note here, you will notice 'modern' halogen headlamp assemblies all have mechanical caps in front of the envelopes to prevent direct line of sight.

Re: FYI - 6 Volt Bulbs
 

Re: FYI - 6 Volt Bulbs
 

An effective skew cap on RP11 envelope lamps that does not reduce any of the focused beam pattern can be made by attaching a 1" diameter anything to the top of the envelope with a little hi-temp silicone rubber. You could also cut a 1" hole in a piece of sheet and use it to spray hi-temp aluminum paint on the glass.

FWIW, for those unfamiliar with them, the "Ron Francis" 125/75 lamps are actually 75/50 cp. You only get the 125 by wiring both filaments to illuminate simultaneously. Additionally, they come in '12V' only. My own testing of them in 4pi mode in an Ulbricht integrating sphere shows they must be driven above 15.5V to produce the claimed cp. At that point they are at about 3025K and will not last long as they are conventional vacuum/inert gas lamps.

If you wired the two-dollar 50/32cp lamps, either 6V or 12V in a similar way you could have an 82/50cp lamp. 50cp dipped and 82cp high beam, more focused lumens than the 35W halogens the vendors sell.

Re: FYI - 6 Volt Bulbs
 

Badpuppy,


Thank you for starting this thread and posting that wonderful list of Model A lamps!

Sorry if things went a little off-track from original lamps because of my comments.

Re: FYI - 6 Volt Bulbs
 

Thank YOU Mike, for posting the SAE data. Good information, could have saved me some arithmetic.

Light emitted from the parabolic focus produces parallel rays off the reflector. Moving the bulb forward from that point condenses the beam to form a conic, the nexus of which should be set at 25 feet forward. Per instructions this is accomplished with lenses in place, perhaps to avoid scorching the far wall.

Re: FYI - 6 Volt Bulbs
 

I like these sideways/slightly off topic discussions. Always interesting, and learn a lot.

Re: FYI - 6 Volt Bulbs
 

Re: FYI - 6 Volt Bulbs
 

Thick praise for this diligent work!

Re: FYI - 6 Volt Bulbs
 

Re: FYI - 6 Volt Bulbs
 

Thanks for the post - a great reference for future use!