The AM Forum

I was browsing at a flea market and came across several "vintage tubes" in their original boxes (which the booth owner had thoughtfully pasted his masking tape price/booth sticker on, right over the tube type!) There were a couple of relatively useless replacements for TVs, but - I found a brand-new 2E26, and the other a shiny new 829B still in the original crepe wrapping. Those I bought.

Right now I don't have a use for either, but figure I'll need them for a project someday ;)
What neat things could I do with the 829B (besides first looking for a socket)?  :D

-Charles
WB3JOK/0

push pull amp! audio or RF. The low screen voltage requirement is a benefit.

http://amfone.net/Amforum/index.php?topic=46518.msg333478#msg333478

Thanks for the link! There are several interesting articles in that post.

Maybe I'll build an amplifier for my 2m FM handheld. That would be a neat combination of old and new(er) tech.
I already have the 4 x 4-125A amp in my profile pic that I started many years ago when I feel like running AM with my Command Sets on 40 and 80m  8)

Hold onto it as a spare for when you buy a TDQ transmitter for some 2 Meter AM.

Those sockets are easy to find on eBay or just put out a request here and someone probably has them? The nice thing about the sockets is that if you get tired of the 829B, the 4-65A or the 4D32 among others will fit the socket and then go for higher power :o :o :o. If you decide to build with that 829 and it goes bust for some reason, I'm sure I have some around here to back you up.

Thanks for the info. I used a 4-65A as the screen shunt regulator for my 4X4-125A amp. Maybe I bought a spare socket  ;)

Note that the 829B is a dual beam-power tube with 40 watts dissipation, but the 4-65A is a single... would take some redesign for more power  ;D

Great! When using 829  for RF the proper socket is made out of metal and part of it resides below chassis.The tube specs states to keep it tame, one must put the pins and part of the glass area below the plane of the chassis otherwise it will be a nightmare to neutralize. My thought-unless you went GG. Of course there is a porcelain socket located within the metal mount. You would not have to re-design the circuit if you went parallel on the plates of the 829, you just would have to use coils of a larger gauge for future upgrades. 

Do you have any pics of your 4X4-125 rig or a schematic? Your 4-65 regulator sounds interesting. The last tube regulator I built had a bunch of 0A2's with an 811 triode, that was a 750 volts screen regulator for a pair of 813's. 

Thanks Terry

Not sure where the schematic is, maybe on paper. I'll try and dig it up.

It's just a basic AB₁ amp with the four tubes in parallel. The power supply is an old 900 VA Thordarson plate transformer, bridge rectifier to a 56 uf defibrillator cap, 3.2 kv key-down. Center tap ("economy" circuit) goes through a hefty dropping resistor to the 4-65A (grid bias supplied through a string of Zeners and a pot at the bottom to set the screen voltage). I used a shunt regulator since tetrodes can exhibit negative screen current and it can absorb it without the screens soaring, and I already had the 4-65A which can easily handle both the power and the voltage. Pi-net with two stacked Amidon T200 cores, Jennings vacuum variable for loading.

The output capacitance of the 4 tubes might be too high for 15 or 10 meters but I was only interested in running Command Set transmitters on 80 and 40... with 500 watts of dissipation I can make a couple hundred watts of carrier.  8)

   I picked this beautifully built home brew CW transmitter up at a swap years ago and pulled it out a few days ago to see if I can get it working. The tube line up is a OA2, two 6AG7's and a 829B with both sections in parallel as a final.


                                               W6TOM

Back in the late 80's early 90's 2M AM days here in the Boston area, lowered the socket in my SCR-522 and popped it in place of the 832 for a few more Watts to the antenna. I think I got 20-22W out instead of the 8 to 10 W - All that for 3 dB.

73's Mike WU2D

There is a socket for that tube at high VHF which is not only recessed as mentioned but also has bypass caps built onto it. I don't know if I have any still but have seen a handful of them. Maybe some military design? How about siome under chassis images of thise transmitters to see if that special socket can be spotted?

I don't recall if it was like these:
https://www.ebay.com/itm/Lot-of-8pcs-Jan-829B-3E29-Tubes-with-Sockets/274393046452?hash=item3fe3199db4:g:gHUAAOSwB4Je4GyB
or something different.

Yes, they are the correct sockets. If I were into building in my old age, I would snap them up!

Most of the applications that I have seen them in was with the 832 tube so I don't know if those built in caps are correct for the 829 in some circuits? I wonder if there is data to be found on the sockets?

Images of the 4 diferent basic kinds of 829B sockets so far.

You could save a derelict Viking I. The 829B make abt 85wts out of AM in one. And it's a kewl looking tube. Got one in mine...

Terry