August 29, 2023 at 10:20 am #25301
Well, the title says it all. Im looking for a L49B ballast tube for a Majestic Model 651.
Thanks.August 29, 2023 at 5:01 pm #25302Dan WalkerCVRS Member
Hi Ben; I am looking for the same tube.
From the research I have done, I have found that a sub for that tube is a L55B.
I have not found one of those either.
If you find a couple of these tubes please let me know.
Dan in Calgary
August 30, 2023 at 11:54 am #25304
- This reply was modified 1 month ago by Dan Walker.
I guess ballast tubes weren’t made for a long time, so there aren’t many left.
looks like I will have to fashion my own.
BenAugust 30, 2023 at 12:41 pm #25305John GreenlandCVRS Member
I guess the question is how original did you want to keep the radio ?
For example if you replace the ballast with a 50L6 and add a 330 ohm resistor across the heater you would effectively turn the tube into a 300 ma tube instead of a 150 ma tube.
The resistor would be 7.5 watts and I am sure a 10 watt one would do very well.
If you had the space, two 25L6’s in series would also work without a resistor but you need another tube socket.
Just food for though from my slightly off brain !
John G. VO1 CATAugust 31, 2023 at 8:10 am #25306
I’m leaning toward the diode resistor combo. Radiated heat is drastically reduced, and the components will fit in the original L49B case maintaining original appearance. (Of the chassie at least)August 31, 2023 at 2:47 pm #25307John GreenlandCVRS Member
Now you have me very curious.
How are you using a diode in an AC circuit to drop 50 volts at 300 millamps ?
John G.September 1, 2023 at 6:06 am #25308Dan WalkerCVRS Member
Here is a link to ARF about this tube.. I am not planning on building a new tube , but the information is here for you guys that are.
Dan in CalgarySeptember 1, 2023 at 8:33 am #25309Jim SirtonskiCVRS Member
The diode/dropper resistor is definitely an option but be aware that a diode failure in many cases will result in a in a short and should that happen it could take out other tubes in the string. You may want to investigate the use of a capacitor dropper. Have a look at this write-up on droppers https://www.vintage-radio.com/repair-restore-information/valve_dropper-calcs.html
There are several technical articles available on the use of capacitors as droppers but few mention that you cannot use electrolytics or DC capacitors. You have to use an AC motor runtime capacitor. Good luck.
JimSeptember 8, 2023 at 2:58 pm #25350
Thanks everyone for the info. I’ve done both, dropper cap and diode. Both have there their modes of failure.
I plan on using a 3A. diode, so its 10X bigger then is required. I’m going to look into adding fast blow fuse.
- You must be logged in to reply to this topic.