807 Audio Amp Progress Report

[Miles Prower]

After two months of RL getting in the way, the 807 amp construction is finally underway. So far, here's where things stand:

*) I have a dead quiet DC supply for all heaters. (6.35Vdc measured, full load) Calculated ripple is -100db(v) below full wave unfiltered ripple. Trying to o'scope the output with all heaters glowing doesn't show any ripple out of the noise (5.0mVp-p, courtesy of a 50KW, clear channel AM station about 30 miles from my QTH). The FAN1084 voltage regulator runs quite cool with the home made heatsink.

*) 2.0mVp-p ripple on the main HV supply.

*) First preamp done. This needed a slight modification: 4.7K grid stopper to kill slight 666KHz oscillation, and to help keep the aforementioned AM RF out of the amp.

Av= 10.0 (measured)
12.0 (calculated) Slightly below calculated plate current: 1.0mA (calculated) 0.9mA (measured).

THD= ? (this, too, was below the noise floor) 2.38% (calculated)

f(l)= 8.0Hz (-3.0db)
f(h)= 40KHz (with grid stopper) (-3.0db)

[tubelab.com]

I went to the warehouse and retrieved a large bag full of 807's, but hurricane Wilma has put an end to all Tubelab experiments for quite a while. FPL (power company) is saying we might get electricity by Nov. 21. That is almost 1 month. There are currently 3 MILLION people in the dark.

I have posted some pictures on the web site. I have enough gas to run the generator 2 or 3 hours each night, for the next few days, and I have one of the few working phone lines.

At this time I can't get to the warehouse to check on my tube collection. Roads are closed and I am saving the gas for the generator.


http://www.tubelab.com/hurricane_wilma.htm

[Miles Prower]

WHUDDA MESS!

It's good to see that you came through OK. Hope the VT's did likewise. A whole month without power? Can't imagine that, and I get disgusted when it goes off for a few hours (happens just about every summer when one of those big storms brews up). Oh well, you have hurricanes, and we have tornados (just dodged that bullet five years ago when one hit no farther than a mile-and-a-half).

Interesting thing: in those pics taken during the storm, the sky doesn't look all that dark for the wind and rain. You'd think it would get nasty dark, like one of those big Midwestern thunderstorms.

Glad to see you're safe and well.

[kevinkr]

Hey tubelab.
Have enjoyed reading your posts for a long time, glad to see that you made it through ok. Hopefully your warehouse of tubes did as well.

Maybe FPL will get the power back on before you run out of gas for your generator.

Thanks for posting all these pix, the media have not provided a whole lot of coverage locally.

Good luck!

Kevin

[Geek]

All of a sudden, the cold, wet, west coast doesn't seem so bad

Glad to hear you're allright

@ Miles - gotta schematic for your 807?

[Miles Prower]

Geek: "gotta schematic for your 807?"

Here ya go: 807 Amp

Screen Regulator

(Still GIMPing up the PS schematic)

[Geek]

Very nice, thanks!

Outta curiosity, if those resistors in series with the 807 plates are for parasitic suppression, you might wanna parallel a 10 to 47uH choke with them. It just seems to work on 807's that way.

[Tom Bavis]

It shouldn't need plate suppressors, and they waste output power. When used (parallel output tubes), winding an inductor on the reasistor works well, and minimizes the losses. Screen stoppers, though are very likely required.

[Andrewbee]

The application note for the 807 calls for it. I put them on my 807 SE amp as well, IIRC they should be 100R.


Andrew

[Miles Prower]

Outta curiosity, if those resistors in series with the 807 plates are for parasitic suppression, you might wanna parallel a 10 to 47uH choke with them. It just seems to work on 807's that way.

Yup, that's what the plate resistors are for. The 807 STC recommends 100 ohm resistors for class AB1 and 47 ohms for class AB2. Since this is a class AB1 design, that's what they are.

"...you might wanna parallel a 10 to 47uH choke with them."

Will take it under advisement.