Congrats to both of you on your progress.
No 6JN6s here. A pair of 17JN6s that I haven't tested. I've got 6LB6, 6LF6, and 6LQ6. Too bad they are all top hat tubes.
Spent the afternoon raking wet leaves, brewing beer and simulating an HV power supply. Didn't even fire up the soldering iron.
No 6JN6s here. A pair of 17JN6s that I haven't tested. I've got 6LB6, 6LF6, and 6LQ6. Too bad they are all top hat tubes.
Spent the afternoon raking wet leaves, brewing beer and simulating an HV power supply. Didn't even fire up the soldering iron.
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George,
Sounds like a nice relaxing day for you and sounds like you had some fun. Great way to spend the evening. I am glad you got a break. Play more work less, all us tubelab.com people just waiting for the Simple PP can wait. You, a Sherri could use the R & R after the year plus you both have had.
Cheers,
Alan
In case anyone is interested, these are possible equivalents to the 6cb6. Roll at your own risk. At least check the pinout and heaters before plugging any of these in!!! I don't recall the site where I got this list, but this is the cut/paste I had saved.
6AW6, 6CF6, 6DC6, 6DE6, 6DK6, 6HQ6, 6676, 7732 7CM
6AG5, 6AU6, 6BC5, 6CE5, 6BH6, 6HS6
6AW6, 6CF6, 6DC6, 6DE6, 6DK6, 6HQ6, 6676, 7732 7CM
6AG5, 6AU6, 6BC5, 6CE5, 6BH6, 6HS6
OK, you brought it up. Here is my short list for input tube testing. These are just the ones that I have. All have been verified for proper pinout only. Experiment at your own risk. I don't mind watching something smoke, others don't always share my enthusiasm. I intend to try most of these.
Sharp Cutoff Pentodes:
6AU6, 6AH6, 6AK6, 6HS6, 6AS6, 6BH6, 6661, 6CB6, 6676, 6CF6, 6DE6, 6DK6, 6EW6, 6JK6, 6AG5, 6186, 6AK5, 6AN5, 6BC5, 6CE5, 9001
Remote Cutoff Pentodes (not usually too god for audio, but may work here):
6BA6, 6660, 6BD6, 6HR6, 6BJ6, 6662, 6BZ6, 6DC6, 6GM6, 6JH6
Dual Control Pentodes (no idea if they will work):
6DT6, 6GX6, 6GY6, 6HZ6
Tetrodes (again, no clue):
6CY5, 6EA5, 6EU5
Hexodes (the 6GU5 has been proven to be a good audio tube):
6FS5, 6GU5
Here is my list for output tube duty. I have some of each, but in some cases only 2. The first batch has been quickly screened to verify pinout compatibility. Double check before using, there are two possible choices for the grid stopper. Use the right one for the tube being used. In most cases you can't have both in the board.
Pinout compatible sweep tubes:
6JN6, 6JM6, 6HF5, 6JS6, 6LR6, 6GV5, 6GY5, 6KD6, 6LF6, 6KN6, 6LB6, 6JZ6
MODS REQUIRED TUBES. These tubes require board modification, including cutting the trace connecting pin 2 to pin 4 which is under the socket. A wire jumper is added between these pins to use the compatible tubes listed above. The 10 ohm cathode resistors must all be connected from pin 4 to ground. This requires relocating 2 resistors. In some cases the grid and screen stopper resistors get installed into the wrong holes. In other words don't try it unless you know what you are doing, and are willing to risk some parts or worse. I have some of all of these and will test them eventually.
Medium sized sweep tube:
6GE5
Bigger sweep tube with same pinout:
6HB5
Little Runt with same pinout:
6GF5
Pint sized vertical output tubes said to be "special". I bought some a long time ago on recommendation, but haven't tried them yet.
6JA5, 6JB5, 6JC5, 6HE5
Beam Triodes (35 watt monsters with a Mu of 300) I have several and haven't made them sound good yet. I believe that A2 will be required, so I may sky wire in some mosfet drivers. I told you that I got this thing to experiment:
6JH5, 6HS5, 6HV5, 6HZ5, 6JD5, 6HF5
I am sure that I will dig up some more as time goes by.
A 6JF6 may be worth a try too, but uses a Novar socket. If you cut the heater traces you could possibly use alternate heater voltage variations too. I got one of those boxes of 22JF6's from RES, but won't likely try any with this amp. They look an awful lot like 6GV5's and have similar specs too.
I got just about all the parts, but haven't soldered anything yet.
Totally different circuit, but the 6CB6 sounded better to my ears in my Marantz 8b over the 6BH6 it normally uses. The 6BH6 is cooler in the bass dept.
I got just about all the parts, but haven't soldered anything yet.
Totally different circuit, but the 6CB6 sounded better to my ears in my Marantz 8b over the 6BH6 it normally uses. The 6BH6 is cooler in the bass dept.
It may be possible to use a 12 volt input tube so that 12 volt sweep tubes would be a drop in. I have never seen a 12CB6, but 12AU6's are common. There are several of the smaller sweep tubes available with a 12 volt heater. I have a few. These are usually real cheap too.
I have already taken mine off of the workbench. I doubt that I will get back to it any time soon. I should be able to finish the first Simple P-P chassis in Thursday nights wood shop class. I have two amps planned and a third one in my head based on the Simple P-P boards.
After those are done you can expect to see the plate caps blown off of some crusty old sweep tubes! I'll be a little nicer to the useful tubes.
I bought a box of 81 6BQ6GA's from RES, and I got some 6BQ6GA's and some 6BQ6GTA's from AES when they were selling them for 98 cents. I also bought some 6CB5's and I found a good size stash of 6CD6's and 25CD6's in my warehouse. They all have an octal base, but I have already got one "test" amp ready, and I may slap together another one based on what I learn from this board.
I have only one 6BZ6 here at the house. I will grab some the next time I go to the warehouse. If they are anything like the 6CB6's I'll need a big handful to get 4 good ones.
I was expecting a box of parts from UPS today which were rescheduled to tomorrow due to "adverse weather conditions". Yeah it must be too hot and their truck died! So without the parts I need to finish my Simple P-P build, I decided to hook the red board back up.
I made a few measurements turned a few knobs, and then blew the board up with a BIG BANG! OK, Details.
I set everything up just like it was and got the same results. Output power was 50 WPC with 450 volts. Knob turning didn't make any real improvements. Petes suggested 40 mA bias current seems to work the best. A bit more power can be obtained by turning up the current, but 60 mA only gives 53 watts, so it isn't a good trade off.
I did make a few observations. Connecting the GNFB improves the distortion up to the edge of clipping, then the driver goes mad trying to keep the output tube from clipping, so the GNFB was disconnected for all testing. I discovered that the driver was distorting at the 45 watt level even though the amp makes 50 watts cleanly, why? The output tubes are being driven into AB2. Yes, the grids go to +15 volts. Now there are two reasons to stuff some mosfets in this thing.
The amp ran for almost an hour at 50 watts while I poked around inside it with scope and voltmeter probes. No hint of redness was seen in a totally dark room. So, what to do? Turn the knob to the right. 450 volts was cool, so I try 500. No problem here, 67 WPC at 5%, no glow either. 550 volts, 72 watts, ten minutes of continuous running, no glow, none. OK, I dialed up 600 volts still idling at 40 mA (readjusted) and cranked up the drive. 80 WPC came easy and the THD was 3.2%. Again, no glow whatsoever. I was getting ready to dime the power supply when there was a very loud bang and the pungent stink of an exploded electrolytic cap. Instead of the usual venting, the top blew off of it, but I think most of the noise was made by the lightning bolt that blew a resistor in half!
OK the big dumb blonde one used 450 volt caps, and was cranking 600 volts into the board, DOH! C24 is partly dissasembled, R48 is now just a black stain on the board. C27 is a bit bigger than it used to be. No big deal, just a few parts offered up for science! I have some 500 V electrolytics, but I really need something good for a bit more!
I was amazed that these little tubes can pump out 80 WPC without stress, I can't wait to try some big ones.
Just curious about the Plate-to-Plate loading...
I see there is 8K load with 18W output...
When I reviewed the plate curves, I figure a 3K plate load can be used under the same operating conditions resulting in 40 watts output....
The average plate dissipation could be an issue...
How good is the power supply regulation at full power output???
WHat B+ and screen voltages do you get at full power output???
Best Regards
Chris
I see there is 8K load with 18W output...
When I reviewed the plate curves, I figure a 3K plate load can be used under the same operating conditions resulting in 40 watts output....
The average plate dissipation could be an issue...
How good is the power supply regulation at full power output???
WHat B+ and screen voltages do you get at full power output???
Best Regards
Chris
I have a 6.6K ohm OPT. I have used these transformers in several other circuits as 3.3K ohm transformers by connecting the 8 ohm laod to the 16 ohm tap. That produced a loss of power (only a few watts) and an increase in distortion with the 6JN6's. I did not attempt to find out why, or even try it at a different idle current.
The plate, screen and bias voltages are being sourced by regulated supplies.
The screen supply is my Fluke 407D which is in the same condition that is was in when I got it off of Ebay for $25. I have seen some stability issues in this supply when operated above its rated current output, but here it is set at 150 volts and the current meter reads between 20 and 40 mA, so I doubt that the voltage changes much.
The plate supply is a monster Hewlett Packard variable supply rated for 0 to 600 volts at 0 to 1.5 amps. It will do 650 volts and 1.7 amps maxed out, so it can really blow the lid off of some little electrolytics! Again I was nowhere near taxing the limit of the supply, since I was experimenting on a single channel.
At full tilt the current meter was reading about 320 mA. Since the idle channel was drawing about 95 mA (40 + 40 + 15), the active channel was eating about 225 mA. The input stage eats about 15 mA leaving about 190 mA for the output stage. 210 mA at 600 volts is about 126 watts input to the output stage. I was getting 80 watts out at 3.2%, so the output stage was dissipating 46 watts. Assuming that the two tubes were sharing the load evenly and the OPT losses were 6 watts (just a guess) or so each tube was dissipating 20 watts, which is slightly over spec. The output stage efficiency is about 64% which is good so the 6.6K ohm load is a good match for these conditions. It is interesting to note that the output tubes dissipate 24 watts each at idle, so this amp cools off when you hit it hard. This is often the case with class AB amps, and always the case with class A amps. Many class AB P-P amps will dissipate the most heat at about half the rated power output, which was not tested.
These numbers may be off a bit since I was taking my readings off of the little meters on the face of the power supply, and it is now obvious that some of that current was being used to heat up two capacitors, and two resistors!
As a rule I abstain from anything with alcohol in it and usually drink a bit of something caffeinated before soldering or testing. Otherwise I often look at my work the next day and wonder what the heck I was thinking and then have a lot of clean up to do. Be safe.
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As a rule I abstain from anything with alcohol in it and usually drink a bit of something caffeinated before soldering or testing. Otherwise I often look at my work the next day and wonder what the heck I was thinking and then have a lot of clean up to do. Be safe.
Maybe he meant a 12-pack of RedBull or Jolt?
cheers,
Douglas
I am not a big consumer of alcohol. I probably cosnume less than 12 beers in a given year. Saturday was one of those rare occasions where I consumed more than one in a day. I used up all of my 'altered state' time much earlier in life! No useful
I know better than play with electricity even when I am tired, and I fully remember stuffing the board with 450 volt caps, thinking that I would never go past 450 volts. Yeah, right. My big power supply will make 650V and I thought that I wouldn't turn it up.
Now, I am thinking that I will add the mosfet regulator on the PCB, set it for about 400 volts and use it to drive the input tubes. I have some really big 900 volt mosfets. I bet that the input tubes and their plate load resistors were getting toasty as well with 600 volts of B+.
The UPS tracking site says that my parts are "out for delivery" so this amp will get put back on the shelf for a while. Its back to Simple P-P for the near future.
So I got my amp up and running with iron from a Heatkit AA-100. B+ was a bit high (although not 600V!) so i knocked it down with a couple of 235 Ohm resistors on each HV leg of the secondary.
The plates of the output tubes are sitting at ~345 V, bias is dialed in, and most all seems well. Gain is slightly different between channels, but acceptable. No NFB. I'm getting 13.25V (~20 WPC into 8 Ohms) at 5% THD.
It's just together on the test bench right now, still need to get a chassis together.
A couple of oddities:
@ ~2V out I'm at 0.07% THD in one channel and 0.4 % in the other. Thoughts here? Tube to tube variation?
With my B+ @ the aforementioned ~345 V I'm getting ~200V on the plates of the driver tubes. Pete's schematic calls this out at ~130V. With the B+ well within the ballpark, I was surprised this was so out of whack.
I hope to actually listen to the thing this evening, and I'll try and get some pictures up soon.
The plates of the output tubes are sitting at ~345 V, bias is dialed in, and most all seems well. Gain is slightly different between channels, but acceptable. No NFB. I'm getting 13.25V (~20 WPC into 8 Ohms) at 5% THD.
It's just together on the test bench right now, still need to get a chassis together.
A couple of oddities:
@ ~2V out I'm at 0.07% THD in one channel and 0.4 % in the other. Thoughts here? Tube to tube variation?
With my B+ @ the aforementioned ~345 V I'm getting ~200V on the plates of the driver tubes. Pete's schematic calls this out at ~130V. With the B+ well within the ballpark, I was surprised this was so out of whack.
I hope to actually listen to the thing this evening, and I'll try and get some pictures up soon.
I have several hundred unboxed 6CB6's of unknown origin. They were supposed to have been pulled from military spare equipment, and many did have JAN or USN markings. I brought about 15 home from the warehouse and had to play musical tubes for a while before finding 2 sets where the plate voltages could be equalized without the pot being cranked all the way to one end. One channel had plate voltages of 165 volts and the other had 195 volts. The distortion was quite a bit lower in the 165 volt channel. The distortion and voltages followed the tubes. This led me to believe that there was considerable tube to tube variation. Previous experiments with 6AU6's from the same source showed similar variations, so the whole lot (50,000+ tubes) may be suspect. Try swapping the input tubes from one channel to the other. Then try swapping the output tubes, mine are somewhat unbalanced also. I put all of the good tubes in the channel that I have been experimenting on. That channel measures about half the distortion of the other at high power, but they both sound the same.
I have some NOS 6CB6 tubes stashed somewhere, but I haven't found them yet. There will be no new experimentation on this amp for the next few days. The Simple P-P is on the bench now. Got to take a few hundred more pictures.
I see no reason why they wouldn't work, unless the charging current of the downstream caps exceeds the 3 Amp drain current spec. 2SK2700's are becoming extremely scarce, so I am saving the few that I have for other experiments. I have found the 2SK2700's fairly easy to blow, but just about any semiconductor becomes a fast blow fuse at 400+ volts. When they fail they short out, bad for the downstream caps.
I have not been able to blow any of the Fuji parts (post #82) yet, but I was using the Fluke power supply. The HP can blow things in half (like 1K 2 watt resistors). I have several HV mosfets to try, I'll figure that one out when the time comes.
Whitelabrat. Someone that works in the plant where I work announced today that he is leaving (by choice!). He got a job at the APL starting in early December.
Belgian Single. My lagering refrigerator died a couple of years ago and I just do Ale any more.
1.050 OG, 59% pils malt and 39% Vienna malt, 1% Carapils. Styrian Goldings and Czech Saaz hops. 20IBU. Chimay Yeast.
It doesn't like the garage at 62F though. It has slowed down to a crawl. I don' t need it for a month or two so I'll let it take it's time.
Mean time I'm playing with my HV pass regulator. For some reason it won't regulate. It just goes to full outpu,t even though the Simulation looks fine. Must mis-wired but I can't find it.