"One note is that while modifying a used sealed beam by installing a new bulb will produce "light", it's not likely you'll have a headlight that is actually usable, safe, or legal, to ride with in the dark. The bulb filaments are precisely located by the factory at focal points of the reflector which is unlikely to happen when installing a different bulb into the old reflector."

No argument from me there Mark although, with my facetious hat on, I could say that argument applies to the original 6v headlight as well!   Not even the 12v headlights of that period were up to much and, over here in the UK/Europe, we were quick to be ditched in favour of Cibie ones. Thank goodness headlight technology has moved on since then.

Even though none of my bikes with the headlight repairs are running yet, I must rig up something in order to check out if and how effective they are.

Gr8uncleal...  the originals might not be great...  and "logically" it sounds like it "couldn't be that bad".  In reality, the results I've seen and had with this modification of replacing the bulb in an original sealed beam are dismal.

Not an exaggeration to say the headlight beam pattern is completely unusable and even "dangerous" as the stray light seemingly scatters everywhere except where it needs to be.  (This "danger" is admittedly not much as the wattage of these early lights is not that high...   still could blind an oncoming driver a little)

I did the  6v H4 conversion in my 1971 CT-1 headlight, and can confirm it does NOT create a usable or legal light for night riding, but does provide a bright enough light for daytime riding. This video shows the "beam" shining onto my driveway. It's best on low beam, and on high beam it scatters. Do make sure you fit a voltage regulator, in fact that's the reason I had to replace it. If you want to usable legal light for night riding, do is MarkT suggests and get a new sealed beam, using the W clips.

youtube.com/shorts/3cwwrpjd17U?feature=share
 

 Thank you so much for all the help guys!  I’ve been riding modern dirt bikes for a bit, but these vintage ones have stolen all my attention. Very grateful for this community making it possible to keep them going. 

I going to go ahead and get the 4020 bulb MarkT recommended.  Does anyone have a link to the how to?  I searched and couldn’t seem to find anything. My 74 DT175 has that style, and I’m curious as to how the clips will work.

Thanks!

See my post #4, plus others, here.

1970 ct1 headlight replacement - Vintage Enduro Discussions (yamaha-enduros.com)

Oh okay that makes sense now with the picture. I was over complicating it in my head. Thank you so much. 

 I’ve herd these bulbs work well and are pretty affordable. Although they don’t come with the needed W clips. I’m going to get both coming and I’ll report back on quality. 


 

MikesXS.com should have the clips or you can get them from Yamaha.

I just ordered the Amazon bulb. Found the clips on partzilla. Thanks again for the help.