How much power for a SE 807 amplifier?

[6BG6GA]

OK, I just purchased a stereo 807 SE amplifier that was supposed to be a "one of a kind" and the ad stated it puts out 10watts per channel.
After listening to it I became very disappointed and decided to check the output. I got a whopping 1.125 watts out of it driving a 8ohm load and 3% distortion with a 1K signal. It features the following tubes 1) 5R4, 2) 807's,1) 6sn7,1) 6sL7 and is supposed to be running in triode mode. As the ad stated "Quasi Triode mode".

Any ideas here?

Joe

[MIKET]

Being a close cousin to the 6L6 you should expect about 8 watts as a SE amp. Less as a quasi triode. See the following article:
http://www.lundahl.se/claus_b_se.html
Hope this helps

[Sch3mat1c]

Whatever quasi-triode is, it sounds just like it's in triode mode. 6L6 can only do about 1.6W in triode, IIRC. A side-effect of having little heater power (around 5W), essentially; the only way around that is to use grid current or make use of the screen.

I've always wondered how they manage to slap on odd ratings like that. Maybe you can sue them for false advertising.......

Tim

[SHiFTY]

Simple- wire the 807 in tetrode mode for about 6-7 Watts of power. Of course, the distortion will be higher, but you could apply a bit of negative feedback to bring it down.

I am using a PP 807 amp, it is pretty grunty!

[Brett]

Joe,

Find out for yourself.

Here is the best and most comprehensive datasheet I've ever seen for the 807. It's 5.5M though.

[6BG6GA]

Brett

Thank you for the link. Unfortunately it didn't quite work for me. I got code one time and the next time the computer just sat there stupid.

Am I to understand that the power I am getting out of this pos is normal? I have several line amps and I'm wide open just to get any kind of output from it.

With the distortion analyzer I have to hit it with 3volts input just to get 3 volts out. There has to be something wrong with the design or the amp. I think I will draw up the schematic and post it. I have sent an email requesting to return the unit and obtain a refund.


Joe

[Positron]

An 807 has at least the same plate dissapation as a EL34. An EL34 will put out up to 6 watts RMS in triode mode. Mine puts out 4.6 watts RMS in triode mode, running fairly easy.

Of course the high screen voltage required by the 807 may limit the output power when running normal plate voltages. But I cannot see, at this point, the output power being so low unless the tube is run easy.

[Sch3mat1c]

Apples to oranges.. EL34 takes a bit more heater power, which means it has more perveance, which means it can do more plate current at lower voltage, with less grid voltage (i.e., no positive grid voltage for instance). 6L6 and related are pretty wimpy when it comes to triode mode.

Obviously, if they have the same plate dissipation, but one has more power output, then one must be more efficient at producing power.

Tim

[Positron]

Somewhat true, but the efficiency isn't that low. The 6L6, listing in the tube manual, is run somewhat easy. I could probably get 2 watts out without too much trouble. The GC version, more yet.

The 807 is a much stronger version and one could easily get 2 watts output, or more.

The limiting factors in both tubes is the screen dissapation. Plate dissapation and plate voltage create no problem.

[6BG6GA]

Ok, did some checking and got a few voltages. The 807 is running 48ma across its pin 4's resistor to ground. The r value is 500ohms and the voltage is 24volts. The plate voltage is 304volts. The B+ feeding the output transformer is 315volts. The G3 r value is 680K going to ground. The cap value running from the second tube is .022 and that is feeding the G3.

With the tubes in the correct positions I get 3.82v out into an 8ohm load with a 1.25 input signal at 1K.

I know that Brett has probably furnished a very good link to information on the 807. Unfortunately I cannot get it. I will try the sat link at work as it is faster than my modem.

Now, I am trying to learn so please be patient with me. The triode connection I assume is the 100ohm resistor going from the G2 to the plate? If this was connected differently to the B+ supply would this provide around 8watts? As always, thanks for the input.

Joe