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
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
807 is a cousin to 6L6
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
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
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
I've always wondered how they manage to slap on odd ratings like that. Maybe you can sue them for false advertising.......
Tim
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!
I am using a PP 807 amp, it is pretty grunty!
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
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
possibly that particular design
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.
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.
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
Obviously, if they have the same plate dissipation, but one has more power output, then one must be more efficient at producing power.
Tim
Somewhat true
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.
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.
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
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
Hi Joe,
Further to my e-mail to you:
It is recommended to use a 100R resistor as a plate stopper, this can be soldered in directly on the topcap.
A series R of 100R isn't necessary for pin #2, topcap (plate) and #2 can be strapped together.
Recommended plate voltage for the 807 SE Class A1 is 250V, Rg should be no higher than 500K (yours is 680K it seems) and when cathode bias is used a 500R resistor with appropriate capacitor bypass should be used.
Primary load impedance at 6K THD would than be 4% at max power of 1.1W.
If you can't download the sizeable file Brett posted, let me know and I'll e-mail you a much smaller one.
In fact all of the above can be found verbatim in the datasheets.
Provided the cathode resistor of the 807 is adjusted so you have the tube idling at around 65mA plate current and screen current at around 3mA, yes that would yield about 8W with THD at around 12%.
Cheers,😉
Further to my e-mail to you:
It is recommended to use a 100R resistor as a plate stopper, this can be soldered in directly on the topcap.
A series R of 100R isn't necessary for pin #2, topcap (plate) and #2 can be strapped together.
Recommended plate voltage for the 807 SE Class A1 is 250V, Rg should be no higher than 500K (yours is 680K it seems) and when cathode bias is used a 500R resistor with appropriate capacitor bypass should be used.
Primary load impedance at 6K THD would than be 4% at max power of 1.1W.
If you can't download the sizeable file Brett posted, let me know and I'll e-mail you a much smaller one.
In fact all of the above can be found verbatim in the datasheets.
Provided the cathode resistor of the 807 is adjusted so you have the tube idling at around 65mA plate current and screen current at around 3mA, yes that would yield about 8W with THD at around 12%.
Cheers,😉
Somewhat
I worked with 807s for several years, back in the 60s, and 304 volts on the plate/screen is no problem, as the design itself testifies.
However, with that said, the screen dissapation is the critical factor, so overdriving the tube could, it could put the tube in peril.
In general, triode mode is easier on the average screen dissapation than pentode mode as the screen voltage never goes higher than the plate, thus the peak screen current is lower.
In pentode mode, the screen voltage can be higher than the plate, depending on how much the plate swings (at low signal levels the plate voltage always remains higher than the screen).
I worked with 807s for several years, back in the 60s, and 304 volts on the plate/screen is no problem, as the design itself testifies.
However, with that said, the screen dissapation is the critical factor, so overdriving the tube could, it could put the tube in peril.
In general, triode mode is easier on the average screen dissapation than pentode mode as the screen voltage never goes higher than the plate, thus the peak screen current is lower.
In pentode mode, the screen voltage can be higher than the plate, depending on how much the plate swings (at low signal levels the plate voltage always remains higher than the screen).
Run the screen to B+ instead of the plate. I don't know the pins, but someone else mentioned them already.
B+ will be found on the not-connected-to-plate side of the OPT primary (usually a red wire).
Since the voltages are the same, you won't have to rebias or anything.
Tim
B+ will be found on the not-connected-to-plate side of the OPT primary (usually a red wire).
Since the voltages are the same, you won't have to rebias or anything.
Tim
You need to connect the screen to its own stabilised supply. In the schematic below, the author uses Zener diodes to keep a constant voltage, however, you would need to calculate what voltage you need (your B+ is much lower.)
You could just try using a 5-10K or so resistor and a 10uF cap without the zeners, that would work fine...
Also your distortion would be higher, you might want to use some feedback.
All these things are very easy to do, you might as well experiment!
You could just try using a 5-10K or so resistor and a 10uF cap without the zeners, that would work fine...
Also your distortion would be higher, you might want to use some feedback.
All these things are very easy to do, you might as well experiment!
Attachments
No, his B+ is only 315V? 😕
Actually, come to think of it, your 807 is only dissipating 13.4 Watts (280V * 48mA)
You could decrease the value of the cathode resistor, and increase the current, giving more watts. 807s are rated at 25W maximum, so running it at 20-22 W dissipation would give you more power...
Just another idea 😀
Actually, come to think of it, your 807 is only dissipating 13.4 Watts (280V * 48mA)
You could decrease the value of the cathode resistor, and increase the current, giving more watts. 807s are rated at 25W maximum, so running it at 20-22 W dissipation would give you more power...
Just another idea 😀
ShiFtY said:
Running it through Tubecad (trioded)
B+ = 315
Rl = 3k
Ia = 70mA
Pout = 1.87Wrms
Plate diss = 20.6W
Vg = -19.1V
2H = 5.2%
3H = 0.4%
807's sound really nice at these sort of op points, not like most 6L6's used at traditional 'max power output' op points. Not very efficient though.
I don't recommend using resistors: you loose regulation, and this means the screen voltage will be pulled way south at maximum output. Besides that, any lower screen voltage than as before will require a rebias, and maybe even a different load impedance for maximum power output as well (not like that will make much difference anyway though).
Tim
P.S... Huh... didn't notice a new page of replies on this thread... workin too fast, boys
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