12 volt to 6 volt tube conversion

[dozerman]

Maco was famous for using wimpy, too-small Load controls.

Adding a disc capacitor in parallel with it will help, but only if it's big enough to take the current. You won't find that number printed on it, but higher-voltage disc caps, like 3000-Volt rated types have more metal in them. A cap that doesn't have enough metal in it will overheat and fail. A value around 100pf is a good place to start. Making it much larger than 150 pf may create the opposite situation, with the peak setting at the full-minimum end of travel. Your mileage may vary.

The Plate Tune control is the one to pay attention to. If the plates are near center when it's peaked for max output, you're good to go. And if that control goes all the way to one end or the other, that indicates the need to adjust the coil, and bring the peak position on the Tune control back into range between the max and min extremes.

Just be nice to that Load control. The spacing between the plates is so small, they're easy to bump and throw the plates out of parallel alignment.

73

the tune was a bit off center but in the time i had the box, sold it and bought it back, the coil had been spread. for whatever reason.. i brought it back to a more stock appearance and it made a slight difference but not much. adding a .0047uf cap centered the load back up. the box does really well. time to put it back on the shelf.

 

[dozerman]

dozerman,
Re-reading post #11, it seems you may be a bit confused about series/parallel filament wiring.



Just to be as clear as possible, the way the above is written would be strictly series wired filaments. If your 4 tubes were wired in this manner, the 3rd and 4th tube in the series would have 0 voltage on the filament. (Experts, Please chime in!)

See the filament wiring section below of the following link from CBTricks. It is a Maco 200B with 6LB6's.

http://www.cbtricks.com/Amp/maco/maco_200b/graphics/maco_200b_redraw_sch.gif

View attachment 24106

V1 & V2 above are in Series with V3 & V4 also in series but parallel to V1 & V2. Or Series/Parallel. (This is what I meant by referencing "Tube 1, Tube 2" etc in post #13.)

Please don't misunderstand my intentions. I am not trying to be "Holier Than Thou" or anything like that. I make my share of mistakes (See post #4 and about every other post I have made!) Comes with the Old Age thing. Computing with one hand is very slow and chockfull of do overs! I tend to believe my memory instead of researching due to the cumbersome task with my limited ability. (In other words-"Classic Laziness!)

I believe wiring all 4 of these tubes in Series and turning on the high voltage may fry at least 2 of your "cheaper" replacements for the 8950/M2057. Last I knew these 6LB6's were about $40.00 each! Too rich for my wallet.

AND

ABOVE ALL ELSE-BE VERY AWARE OF THE HIGH VOLTAGES IN THIS UNIT! PROTECT YOURSELF AT ALL TIMES WHEN WORKING ON THIS UNIT! DISCHARGE THE CAPS, PULL THE FUSE AND PUT THE POWER CORD PLUG END IN YOUR POCKET TO BE SURE YOU ARE SAFE!

I have been lucky enough in the past to survive unscathed a 400vdc jolt (from all else-the awesome Golden Eagle Mark lll). It wasn't pleasant and I vowed not to repeat that stupid mistake. The best lessons learned are taught by repetition and/or Trauma Impact!

Please also seek advice from some experts. There are many of them on this forum. I am not one of them. Just a lucky Old Dude who is still kicking despite all the Trauma Impact lessons I have learned in life.

Have fun, Good Luck and Learn Things!

73's
David

yeah thats right. i re wired mine per that schemo. and i dont know how i forgot about it, but ive got a maco 750 thats been converted to 6 volt and a quick peek inside couldve helped me a long time ago. lol maybe someone in the future will get some help from this. thanks fellas

 

[Dmans]

maybe someone in the future will get some help from this. thanks fellas

I hope they do too dozerman.

There is a load of great information on this forum. I believe there are a lot of good people on the forum that participate and are more than willing to share and teach.

If I had a nickel for every time I wished I could have asked a question of my neighbor/mentor that got me hooked on this hobby prior to finding this forum, I'd be retired already!!

73's
David

 

[442]

Hello, This thread was INVALUABLE in helping me with my 12v to 6v conversion of a 300 Skipper. I have a sleeve of 6LF6's , and the 8950's in the Skipper were becoming soft after 50 years in service. What a breeze to do!
I got a LDO version I think I will do next !

73's
Kyle