807s Anyone? Hydrocodone induced ramble.

[skyboltone]

I like all this talk about big tubes seeing as how nobody buys big amps anymore because there's no place to play them. Have you been watching the Showman and Dual Showman go buy on Eflea lately? No bids on '65 Showman at $650. It just ain't fair.

Anyway, the book says you can run 807s at 750V and 240MA per pair ICAS in AB2. Hehhehhehheh. RCA says that's 120 watts out the pipe. 66.6666% efficiency. It says the PP load ought to be 7300 at 750V. Now here's the interesting part. if you check the nomograph for changes in anode voltage, the PP load should go up as you drop the voltage right? So in the 1962 RCA transmitting tube manual the PP load drops to 6900 at 600 (200ma) volts 4600 at 500 (240ma) and 3700 at 400 (240ma). The nomograph says the PP load at 500 volts should be 1.15 times the load at 600; or 7930 ohms. I've noticed other tubes that seem paradoxical this way. Like 6V6s. Does anyone pay attention to this stuff anyway? EL-34s really are supposed to run at 450V and about 6600 ohms so everybody except Ken Fisher runs them at 3500? What gives?

The 807 is supposed to be a 6L6GC with the anode connection moved to the top of the tube because it can be used in transmitter mode at higher frequencies. Something to do with electron travel distance? ?. Anyway also, the 807 is written up as a 300V MAX screen voltage but the manual goes on to say that you can exceed that if you have a resistor between plate and screen supply etc etc.

So, this is going to be a pedal steel amp for stadium use with about 4 Weber 15" Californians. Super clean. No fuzz face here. But I don't play in stadiums and it will only be twice as loud as a bandmaster anyway. This amp is just for fun, (bother the neighborhood, City) I'm going to build it as a slave with no pre. The pre will be Princeton like

Any thoughts?

Anyway, all the old Standels were 807 and I've got a few of 807s laying around looking for a job. But I hesitate to order the iron. I've got a 400-0-400 at ONE AMP transformer on the shelf. Maybe about 560VDC and 1000ma. That ought to do it for four of them and about 160 watts out, but where am I gonna get the OT? And should it be about 5750/2 ohms primary or use the nomograph? Ultra linear maybe to avoid that screen voltage limitation? I haven't run the curve yet and the RCA transmitting tube manual is highly suspect to me. Besides I'm not sure I want to design for AB2. Try to stay inside AB1 except in severe overdrive; and who wants to do that at 150 plus watts.

So feel free to ramble man. Next we can talk about 813s. I've also seen a single ended 833 OT on Ebay out of Hong Kong for not too bad a price. Imagine 2200VDC on the plate. BIG TRIODE. 350 watts plate dissipation. About the size of a large Mango. Two filament pins sticking out the bottom and the grid and plate pins sticking out the top. Single ended with 12% or so distortion, but you'll never get there because that would be at full power. Takes 20 watts of drive. Bias at -70 then hit them with 400V grid to grid signal. That's class B alright. I've got some of those too. I got a plate transformer for one of those too if I used a voltage doubler.

Dan here, over.

[Trout]

Head over here and check out this 833A amp
http://www.tubelab.com/833SE.htm

I have an old Bogen GX50 PA head in my garage with a pair of 807's that pushes out an easy 50W

The big trick with 807's is not exceeding the screen specs. The Bogen amp I have actually has 2 power transformers, one for the basic amp, and one specifically for regulated screens.

Standell?? Gotta love anything with 807's!

[img::]http://www.diyaudio.com/forums/attachme ... -807-2.jpg[/img][/url]

[skyboltone]

Head over here and check out this 833A amp
http://www.tubelab.com/833SE.htm

I have an old Bogen GX50 PA head in my garage with a pair of 807's that pushes out an easy 50W

The big trick with 807's is not exceeding the screen specs. The Bogen amp I have actually has 2 power transformers, one for the basic amp, and one specifically for regulated screens.

Standell?? Gotta love anything with 807's!

Gotta love that dolt with the 833A project too. MY kind of guy. Your image code is not working, I wonder if it's all those dashes. I'd like to see that. I know a couple of guys that have real 25/15s and they say every one was different!

[Trout]

Ahhh The image shows up here, most likely because I am a member and logged in over where that image is hosted.

DIYaudio.com

They have a detailed photo shoot of the Standell RI

http://www.diyaudio.com/forums/tubes-va ... clone.html

Its on page 7, and worth signing up to see.

[Cliff Schecht]

My first design was a SE amp with an 807 run with a mix of fixed and cathode bias. Doesn't have a very good clean sound (my fault for using two 6AU6's) but has an amazing bloom when overdriven. I plan on doing a Bassman style amp with 807's and some iron I have in the near future, once I find a chassis and time do to so! I have a pretty good stash of 807's as well as 1625's, which are the dual heater versions of the 807. They're very sturdy tubes and are great for audio, it's a good thing they are usually overlooked because of the "goofy" plate caps, it keeps the tubes cheap on the fleabay, swap meets and hamfests.

[Phil_S]

Contact Edcor for an OT. They will probably do it better and cheaper than anyone, and might even have a design in the file cab. It won't be cheap, though.

[M Fowler]

Here is a weber version using 807.

[skyboltone]

Hey Trout:
It shows up now for me. I registered. Interesting.

[Trout]

Hey Trout:
It shows up now for me. I registered. Interesting.

There is a heck of a lot of interest in the 25L, but so far I have not found much actual data until they posted that over at DIY.

But as one poster pointed out over there, the big key is still the speaker which is really getting both expensive and hard to locate.

[UR12]

Don't for get the "my favorite martian tube", the 815. Kind of like having 2 x EL34s in one tube. I have a friend building a amp with a quad of these and should get about 220 watts.

[skyboltone]

Hi Dana
That's a nice lookin' tube you got there dude. Is it really two Beam Power Valves in one package? Wait I just looked it up; it is indeed. Would you run it at 450VDC 6600 load or 3400 load. It's an eight pin socket but is it octal? Hmmmm. Might have to hard wire it in eh?

Notice how nobody has come down on that question yet? Where's Vacuum Voodoo when you need him. I'm sure he has an answer.

[skyboltone]

Hey Trout:
It shows up now for me. I registered. Interesting.

There is a heck of a lot of interest in the 25L, but so far I have not found much actual data until they posted that over at DIY.

But as one poster pointed out over there, the big key is still the speaker which is really getting both expensive and hard to locate.

I would not be the least bit surprised if in double blind testing behind the curtin test that nobody could tell the difference between a JBL and a Weber Neo 15" or even the California 15"

Anyway, like I mentioned, I brought the amp up on the Steel Guitar Forum and there are a couple of guys who have them. One fellow who responded to me said he's had access to more than one at a time for comparison and they really did differ amp to amp. What's his name, I already forgot, Bob Crooks, did voice every amp as he went along.

I would just like to know if Crooks looked at UL and rejected it for the series screen resistor for a reason or he was just cheap and bought off the shelf Stancor stuff that would not have been available in UL?. I'm cheap too, but ultra linear stuff is old hat now. A guy could try it both ways huh? No big deal.