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)
*) 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)
Hurricane Wilma
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
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
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.
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.
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
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
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?
Glad to hear you're allright 🙂
@ Miles - gotta schematic for your 807?
Geek: "gotta schematic for your 807?"
Here ya go: 807 Amp
Screen Regulator
(Still GIMPing up the PS schematic)
Here ya go: 807 Amp
Screen Regulator
(Still GIMPing up the PS schematic)
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.
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.
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.
807 plate suppressors
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
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
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. 🙂
Miles:
I have been through at least a dozen hurricanes, and they are all different. Most don't get real dark though. This one was unique that a cold front came through and actually pushed the hurricane offshore faster. The TV weather people claim that was the catalyst for the destruction. It did have the classic eye, where the wind and rain stopped, and everyone came outside to check out the damage. Things were not too bad. 10 minutes later, someone yelled that halftime was over, and all hell broke loose. Most of the damage happened in the next 10 minutes.
The good thing was that the weather cleared up real quick, and we have had excellent weather for the past three days. This is good, since I have been working outside since the storm. You can see the clear blue sky in the later pictures.
I have been told that the tubes are OK, but I haven't been able to check on them myself. Maybe tomorrow.
When I used to build HF transmitters with 807's or 6146's I used a 10 to 100 ohm carbon composition (important that its non-inductive) resistor with 10 turns of wire wrapped arround it (in parallel). The wire forms an inductor that provides a low DC resistance, but a high impedance to parasitic oscillations. The resistor de Q's the inductor to avoid building a tank circuit.
I have been through at least a dozen hurricanes, and they are all different. Most don't get real dark though. This one was unique that a cold front came through and actually pushed the hurricane offshore faster. The TV weather people claim that was the catalyst for the destruction. It did have the classic eye, where the wind and rain stopped, and everyone came outside to check out the damage. Things were not too bad. 10 minutes later, someone yelled that halftime was over, and all hell broke loose. Most of the damage happened in the next 10 minutes.
The good thing was that the weather cleared up real quick, and we have had excellent weather for the past three days. This is good, since I have been working outside since the storm. You can see the clear blue sky in the later pictures.
I have been told that the tubes are OK, but I haven't been able to check on them myself. Maybe tomorrow.
When I used to build HF transmitters with 807's or 6146's I used a 10 to 100 ohm carbon composition (important that its non-inductive) resistor with 10 turns of wire wrapped arround it (in parallel). The wire forms an inductor that provides a low DC resistance, but a high impedance to parasitic oscillations. The resistor de Q's the inductor to avoid building a tank circuit.
🙂
Sounds like a good idea. I'm not looking for this to take off and make like a HF xmtr. I've had some sand state audio amps go and do that. Although the fix is quite different.
So far, that's something I've missed. Been to Florida to visit, but never had a hurricane hit while there. Although out West, I've seen some hellacious winds come down out of the Sierra Nevadas and blow off roofs.
When a sand state amp oscillates, you can usually tell by the smell of burnt parts. I can remember a Dynaco Stereo 120 that blew up at least 5 times. I couldn't get to oscillate in the shop but in the customers home it would blow up. After a few calls to Dynaco they sent us some special driver transistors that solved the problem.
When a tube amp oscillates, you might not even know it. Sometimes it causes distortion, rarely you get the red glow of death.
I always test my new design by placing it next to an AM radio and a TV set. Try all the channels on the TV while receiving a signal. Then operate the amp normally. Try different volume and bias settings. If there is any interference, the amp is oscillating.
When a tube amp oscillates, you might not even know it. Sometimes it causes distortion, rarely you get the red glow of death.
I always test my new design by placing it next to an AM radio and a TV set. Try all the channels on the TV while receiving a signal. Then operate the amp normally. Try different volume and bias settings. If there is any interference, the amp is oscillating.
Looking at your schematics: I love that DC-couplet driver design. 😉 And it also scares me to death to think that the bias of the output tubes is depending on another set of tubes. (I’ve got the same kind of design in one of my amps).
I can see that you have a 2.2M resistor connected from the wiper to the negative side on the bias pots. That’s in case of any kind of glitches in the pots?
How low is Vkk -- about –250v?
Is it your plan to drive the 807s into AB2?
I can see that you have a 2.2M resistor connected from the wiper to the negative side on the bias pots. That’s in case of any kind of glitches in the pots?
How low is Vkk -- about –250v?
Is it your plan to drive the 807s into AB2?
"And it also scares me to death to think that the bias of the output tubes is depending on another set of tubes. (I've got the same kind of design in one of my amps)."
Not too worried about this. In the vast majority of cases, VTs fail open, not shorted. If the 6SN7 fails open, the 807's are biased way into cutoff. Of course, the only way to be 100% sure would be to isolate every stage with capacitor coupling. That's something I wanted to avoid as much as possible. "I've got the same kind of design in one of my amps": then it really can't scare you all that much, now can it? 😉
"I can see that you have a 2.2M resistor connected from the wiper to the negative side on the bias pots. That's in case of any kind of glitches in the pots?"
Yuppers, the 2.2M resistors are in case the bias adjust pot fails open (which they are wont to do).
"How low is Vkk -- about -250v?"
-300Vdc, actually.
"Is it your plan to drive the 807s into AB2?"
This is a Class AB1 design. The 6SN7 driver is included to get the slew rate up. At 30KHz, the 807's require ~0.6mA of instantaneous current to charge up the input + Miller + stray capacitance. That'd be asking a bit too much of the 6SL7's. Class AB2 807's would be power overkill, I think. Anyway, I'd go with a different driver for Class AB2 operation. Something like an SRPP, perhaps, although my preference would be to use a MOSFET source follower for that. I've done quite a few solid state designs, and so am not "sand-o-phobic", so that wouldn't be a problem. 🙂
Not too worried about this. In the vast majority of cases, VTs fail open, not shorted. If the 6SN7 fails open, the 807's are biased way into cutoff. Of course, the only way to be 100% sure would be to isolate every stage with capacitor coupling. That's something I wanted to avoid as much as possible. "I've got the same kind of design in one of my amps": then it really can't scare you all that much, now can it? 😉
"I can see that you have a 2.2M resistor connected from the wiper to the negative side on the bias pots. That's in case of any kind of glitches in the pots?"
Yuppers, the 2.2M resistors are in case the bias adjust pot fails open (which they are wont to do).
"How low is Vkk -- about -250v?"
-300Vdc, actually.
"Is it your plan to drive the 807s into AB2?"
This is a Class AB1 design. The 6SN7 driver is included to get the slew rate up. At 30KHz, the 807's require ~0.6mA of instantaneous current to charge up the input + Miller + stray capacitance. That'd be asking a bit too much of the 6SL7's. Class AB2 807's would be power overkill, I think. Anyway, I'd go with a different driver for Class AB2 operation. Something like an SRPP, perhaps, although my preference would be to use a MOSFET source follower for that. I've done quite a few solid state designs, and so am not "sand-o-phobic", so that wouldn't be a problem. 🙂
I went to the warehouse today, all of the tubes are safe and warm. There is a fine dust made of powdered roof material (particle board and tar paper) all over everything, but the tubes are all in closed boxes. I can't figure out how that stuff got in the closed warehouse bay.
Still no power. FPL came through the area and fixed the easy stuff. Said that the rest would come later.
Still no power. FPL came through the area and fixed the easy stuff. Said that the rest would come later.
Good deal. Now the experiments can go on. 🙂
"Still no power. FPL came through the area and fixed the easy stuff. Said that the rest would come later."
Oh well, hopefully they'll get it done before the next hurricane blows through. 😉
Phase Inverter/Preamp Done
Finally have the second preamp/phase inverter done. (see attached) So far, so good: no oscillation, just some residual AM from the 50KW station up the road. Seems particularly bad today. No distortion evident with 40Vp-p output (as high as the o'scope goes) triangle wave input. The Sovtek 6SL7's are measuring a bit on the low side:
Ip: 0.575mA (calculated)
Ip: 0.5mA (measured)
Av: 26.75 (calculated)
Av: 25.0 (measured)
May be a Sovtek thing since the plate curves came from an RCA data sheet. Still not getting any second or third harmonics out of the noise. Nothing blew up, and the performance is looking quite good. 🙂
The tail CCS is built with Fairchild MPSA42 high voltage (Vceo= 300V) small signal transistors. These came with a 15-pack of "transistors anonymous" from Rat Shack. The bias diodes are still the basic 1N941's, also from Rat Shack. (Helpful hint here: check them before installing. There might be a bad one in there. 😡 ) Just about any small signal NPN's with a Vceo of 45V or more should work here, though the extra margin that the MPSA42's provide is quite nice since without the load of the finals, the PS overvolts by about 40Vdc, or so. That put the cathodes of the 6SL7's at 82.5Vdc instead of the expected 56Vdc.
Finally have the second preamp/phase inverter done. (see attached) So far, so good: no oscillation, just some residual AM from the 50KW station up the road. Seems particularly bad today. No distortion evident with 40Vp-p output (as high as the o'scope goes) triangle wave input. The Sovtek 6SL7's are measuring a bit on the low side:
Ip: 0.575mA (calculated)
Ip: 0.5mA (measured)
Av: 26.75 (calculated)
Av: 25.0 (measured)
May be a Sovtek thing since the plate curves came from an RCA data sheet. Still not getting any second or third harmonics out of the noise. Nothing blew up, and the performance is looking quite good. 🙂
The tail CCS is built with Fairchild MPSA42 high voltage (Vceo= 300V) small signal transistors. These came with a 15-pack of "transistors anonymous" from Rat Shack. The bias diodes are still the basic 1N941's, also from Rat Shack. (Helpful hint here: check them before installing. There might be a bad one in there. 😡 ) Just about any small signal NPN's with a Vceo of 45V or more should work here, though the extra margin that the MPSA42's provide is quite nice since without the load of the finals, the PS overvolts by about 40Vdc, or so. That put the cathodes of the 6SL7's at 82.5Vdc instead of the expected 56Vdc.
Attachments
Glad to hear of your success. I can't speak about Sovtek 6SL7's but I have tried Sovtek 6SN7's. They appear to be relabled (after the fact) Russian tubes since you can see faint Cyrillic characters under the red Sovtek logo on some of them. They don't look like any American 6SN7 and don't exactly work like them either. I don't remember the details but they did exhibit lower gain than the American tubes, and they weren't as microphonic as the American tubes either.
Our electricity was restored last weekend. I am slowly cleaning out my lab (it was used as a storage shed during the storm). Hopefully experiments will resume in a few weeks. There is still a bag full of 807's waiting to be fired up!
Our electricity was restored last weekend. I am slowly cleaning out my lab (it was used as a storage shed during the storm). Hopefully experiments will resume in a few weeks. There is still a bag full of 807's waiting to be fired up!
The Sovtek 6SL7s and 6SN7s don't have any red logos, and I'm not seeing any wiped out Cyrillic characters either. Just the usual type identifiers, "Made in Russia", and "Sovtek". As for how they compare to US NOS, I can't say as I've never seen them before. (Although the 6SN7's have substantial grid cooler "wings".) I'll have to wait to see how the 6SN7s perform when I get the driver stage complete. These operate as followers to drive the 807s. Hopefully that will work as well as everything has so far. 🙂
Good going on getting the power back ahead of schedule. 🙂
"There is still a bag full of 807's waiting to be fired up!"
All at once
That'd be one helluvan amp! 😀
Good going on getting the power back ahead of schedule. 🙂
"There is still a bag full of 807's waiting to be fired up!"
All at once
That'd be one helluvan amp! 😀- Status
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