Single 813 Driver?

[Carl WA1KPD]

For all too long I have been collecting parts and dreaming of a HB single 813 rig.

Anyway the VFO exciter  is 3/4 done. It is on a 19 inch chassis and uses parts from a VF-1, Johnson Adventurer (6AG7 to 807) and a Mullti Elmac carcasses.  I was planning on a big variable screen resistor in the 807 and  reduced plate voltage to bring it down to a better drive power for the 813. The 813 RF deck, HV supply (done) and  speech amp/mod will each be on separate racks

However it is beginning to look to me like the 807 is real overkill and I am now considering driving the 813 with a 6L6 with the variable pot for the 6L6 screen voltage. 

I have plenty of 6L6s and 807s so the choice is academic to me. The advantage I can see with the 807 is it would loaf along as a driver  and could also run as a sweet little stand alone AM rig if conditions warrant.

I just don't want to end up with too much or too little power so would welcome thoughts from the group.

Thanks
Carl
/KPD

[W3SLK]

Hell, go with the 807, Carl. Should you find yourself wanting to add another 813, (which you may), You'll have the headroom to drive 2 comfortably. I guess a 6L6 would fit the bill but it would be another circuit to redesign should you want more power. Besides, an 807 is a buzzardly old tube from way back. 

[WBear2GCR]

Ummm... in general terms 807 = 6L6!

The 807 will handle more plate voltage, and the 6L6 may handle more plate current in later incarnations... although a water jacketed and cooled metal 6L6 is said to be rather incredible in terms of power handling!  

The 807 is better at HF RF apps...  

 afaik that is...

is this for the RF drive or the modulator drive??

               _-_-bear

[Carl WA1KPD]

Thanks
It is for the RF drive
160, 80  and 40 only at this point. Never cared for UHF AM (20 to 10)
Carl
/KPD

[K9ACT]

However it is beginning to look to me like the 807 is real overkill and I am now considering driving the 813 with a 6L6 with the variable pot for the 6L6 screen voltage. 

.....
I just don't want to end up with too much or too little power so would welcome thoughts from the group.

The answer is in the question.... a change of screen resistor deals with over kill but under kill is a bit of a hassle.

The 807 is a real man's tube anyway.

My 807 ran out of poop when I switched from an 8000 to an 810.  I could get a new 810 for $45 but an 8000 goes for about $125.  The 810 is a drive hog but switching to a 6146  gave me the additional 10W I needed without changing anything else.

I now am forced to lie on the air because I like saying it's an 807.  6146 is right up/down there with a 6L6... they do the job but lack buzzardness.

js

[KL7OF]

I used to use a 2E26 to drive the pair of 813's class c  and now use an 807 in the same rig.....either tube provides plenty of drive.... good luck...Steve

[John K5PRO]

807-->813, a real combo from the 40s. Roll with the pair of eights! All you have to do is back 'er off if the 813 grid I is excessive on the low bands.

[k4kyv]

The 807 is basically a glass 6L6 specially designed for rf use, with the plate lead coming out the top instead of the base, so it would not be overkill to use an 807 instead of a 6L6.  Besides, the 807's control grid-to-plate shielding is much better than that of the 6L6 which was designed for audio use, so there is less likelihood for self oscillation with the 807, if an external shield is used per RCA's instructions. Plus, the 807 (at least the early ones) has better rf insulation. 

Later, more cheaply made 807's are much more 6L6-like, with the little internal shield at the bottom of the plate structure missing, and the ceramic insulation  holding the plate/grid structure together replaced with mica sheet.

[KM1H]

The 2E26 was used in the classic ARRL HB/QST 813 rig of the 50's. When the sun spots come back you will want the higher bands unless you prefer listening to static crashes on 75.

Carl
KM1H

[KE6DF]

The 6BG6 is a beefed up octal variant of a 6L6. It was beefed up for use as a sweep tube in early 50's TVs and has a plate cap, and higher voltage ratings than the 6L6. I've heard it described as an octal 807, although the plate to grid capacitance is higher than the 807 -- closer to that of a 6L6. I've found 6BG6's to be cheaper than either 6L6s or 807s on epay -- probably because the audio hobbiests haven't "found" them -- although they are used in some broadcast transmitters as audio tubes.

As for driving two 810s, you could use an 828. It was used in the BTA250 transmitter. It's a pentode 1/2 way between an 807 and a 813. Plus it's plenty impressive and funky looking. 828's are also good AB1 modulator tubes and a pair are used to modulate the 810s in that transmitter.

Probably overkill to drive 813s which was the initial topic of this thread.

[k4kyv]

828's are a little pricey and hard to find, but a very similar although slightly less powerful tube is the 814.  They were widely available after WW2 as military surplus.  A  single 814 will easily put out 100 (real) watts.

Don't confuse those with the Taylor 814, which is a triode somewhat similar to the 810.