The AM Forum

Still working on my Globe King 400B - atleast I think its a B model - someone installed 816 rectifiers in the modulator, lots of other mods too, still trying to reverse engineer this before I apply the AC.  I understand why they did that, I guess, but was wanting to know if there were other subs such as the 3B28 tubes?  I put the 3B28's in the RF power supply but didnt know if there would also go in the modulator.

Thanks, 73, Tim K8WBL

816's in the modulator tube sockets?

 ::)

better check the wiring first. Sounds like  Ham Hambone got to that rig.

From what I saw on line the 400 uses 866AX on the mod deck PS. 816's should work ok if they are good.

Watch the 816s.  If the coating on the anode if flaking off, they will flash over.  They seem to be a fragile tube.  The bad thing is the 816 requires 2.5 volts at 2 amps and the larger 866 requires 2.5 at 5 amps, as does the 866jr.

The King 400 diagram says that 866s are used.  Verify you have the proper filament transformer in there.

They used 816's on the mod deck. The hv supply for the final are 866A. According to franks tubes, the 866AX uses 3 amps to heat one tube. The 816 can use up to 2.75 amps per tube. I generally replace them with solid state rectifiers if they can't be seen but if they are out in front, they gotta glow  ;D ;D

3B28 are better than 866A's because they can operate in a wider temperature range with out flashing over or short life from running too hot. Just my two cents worth  8) 8)

3B28's are the bomb. used em for years in the derb HB rig and nver any trouble under any operating conditions.

he made it sound like he 816's were in the actual mod deck itself, not in the PS for it.

If you want real vintage rectifiers, use a pair of 866jr's.

I think the 866AX has the same characteristics as the 866A, with a full 5-amp filament.

The page below compares the characteristics of the 866 family of tubes.  For other tubes, delete the 866 in the url and type in the desired tube type.  It is a Japanese site, but most of the data is in English.  My browser displays the Japanese characters as question marks. Some good photos of the tubes are displayed.

http://homepage.mac.com/ryomasuda/VT/num/866/index.html


The following one lists most types of rectifier tubes, with a thumbnail photo of each.  The electrical data listed on this site is sketchy, but a lot of historical information, physical descriptions and comparisons between brands is given.

http://home.comcast.net/~nwilson343/tubes/rectifiersindex.html

For other tubes on this site, click on

http://home.comcast.net/~nwilson343/tubes/master2.html

A bit of trivia on this site is that the "W" designation on certain tubes, e.g. 807W, reportedly indicates that the tube is "Warized" and ruggedized to meet JAN-1A specifications.

Is there any issue with series-ing 866s etc with solid state diodes? You'd get the cosmetic glow without possibility of flashback . Or is there some reason this wouldn't work?
                                                                Ian VK3KRI

Never thought of this concept. I think you may still get a flash over depending on the condition of the tube but the rectification would continue. You could call your idea a "Diode Buffer"  ;D

I have come into a big dusty box of those 866/3B28 replacement solid state stick rectifiers.. so many diodes, so little time. Probably sub for 816's, if the height is not too great. PM if you can't find what you want.

Thanks guys, in considering this, the 400B I have DID have 866jr. as rectifiers in the Mod Deck before Mr. Hambone changed them out to the 816's...  - but 866A's in the HV PS - I was going to go for the 3B28's but did not know if I could use them as well in place of the 816's - schematics look like they would.  But if can buy enough of the solid state plug ins, without busting the bank, I might just do that. 

Now the big decision is the audio chain - both the 400B and 400C mod decks have tube and circuit changes, and can I snip out those couplates or maybe just leave them in for now and see how she plays?

73, Tim K8WBL