Well, the LED in the other channel is round. In reality I put some aligator clips where the LED should go and started trying LED's. I picked the ones that gave the lowest distortion. I had an orange rectangular one in there first, but a shorted tube blew it out, so in went the triangular yellow one. It was left over from a satellite TV receiver that I designed about 25 years ago.
I tried two Sears branded Sylvania USA made tubes. They consistently made about 1 watt less power and showed faint color at 26 watts of dissipation. They lit up brightly at 40 watts.
I tried one really crusty old looking RCA tube. It made 14 watts at 5% under the 500 volt test. It also barely glowed. When I removed the drive it developed a glow similar to the Japanese tube.
Both the RCA and Sylvania tubes glowed the brightest on the plate surface that faced the other tube section. I would expect this since the path to radiate heat is blocked. The Japanese tube glowed the brightest on the outside face of the plate.
All of these tubes exhibited even glow, no hot spots. This is good. Any hot spots on the plate can cause a quick tube death.
Attachments
I put the cracked tube back in and wired up a second power supply to the screen grid. This way I can set the plate voltage and the screen voltage independently. I could not find any set of conditions that worked any better than UL mode. I get lots more gain in pentode mode (expected), but no more power output (unusual, but I have seen it before). I have also seen tubes (the 307A - VT225) that make the same power in triode as in UL, but pentode makes more power. The best results were always obtained when the screen voltage is the same as the plate voltage.
Note, Never operate the screen at voltages significantly above the plate voltage. Dead tubes will result regardless of what the magazine article said.
Man I go out to the garage to fabricate some tranny brackets and you go off again!
WHOO HOO I love it!
Wow...., just looking at those smallish plates of these guy's had me leary of "pushing" them very much.
By your testing, these tubes loafing along at say ahhh 18 - 22 watts of plate dissipation and 350v - 375v (plate to cathode)
in UL mode wouldn't be unreasonable for someone actually running them like that. Dam pretty scary!
(Yes Yes I know YMMV and your on your own if you push them)
But many thanks for the torture/testing.
WHOO HOO I love it!
Wow...., just looking at those smallish plates of these guy's had me leary of "pushing" them very much.
By your testing, these tubes loafing along at say ahhh 18 - 22 watts of plate dissipation and 350v - 375v (plate to cathode)
in UL mode wouldn't be unreasonable for someone actually running them like that. Dam pretty scary!
(Yes Yes I know YMMV and your on your own if you push them)
But many thanks for the torture/testing. 
I've been following the thread on AK as well and in looking for sources for 6lu8 and 6lr8, it looks like the 6lu8 is available nearly everywhere, but very few folks list the 6lr8.
Prices for 6lu8 run $5 to $10 each and average about $6, with most of the premium audio tube services charging from $8-$10. The only 6lr8s I found seem to be between $8 and $10, but again, very few places to find them.
Is there a matching dissimilar triode tube to fit the 12 pin compactron socket? If so, it might be a better choice based on apparent availability of tubes.
I certainly don't want to tell you how to do things, but I do know that availability of tubes is one of your top concerns -- which we certainly appreciate.
-- Jim
P.S. - 12 pin compactron sockets also seem more widely available.
Prices for 6lu8 run $5 to $10 each and average about $6, with most of the premium audio tube services charging from $8-$10. The only 6lr8s I found seem to be between $8 and $10, but again, very few places to find them.
Is there a matching dissimilar triode tube to fit the 12 pin compactron socket? If so, it might be a better choice based on apparent availability of tubes.
I certainly don't want to tell you how to do things, but I do know that availability of tubes is one of your top concerns -- which we certainly appreciate.
-- Jim
P.S. - 12 pin compactron sockets also seem more widely available.
AES had them for $1.65 each! Another forum member bought a bunch, and then I bought the remainder (only 9).
I have talked to a dealer who "has thousands". The price is still up in the air, but it looks like $5 or less. New production ceramic sockets are "in customs". I will post details when I have them. I won't proceed with the PC board unless plenty of tubes are available from a source that ships world wide, and I have a bunch myself.
While looking through my collection of sweep tubes I came across a 10JA5. It looks like the pentode half of a 6LR8 all by istelf. In this package with better radiation capabilities it is rated at 19 watts.
Hey Tubelab,
Just curious are you running the LED for biasing the driver just as is?
As I'm experimenting with it, and I'm going to try "steeling" a bit of voltage/current
from the output tubes cathode for an extra 7ma or so to get 11ma total on the LED.
(just a straight 3k resistor from the output tube cathode to the top of the LED)
Curious your thoughts on this.
Later,
Keg
Just curious are you running the LED for biasing the driver just as is?
As I'm experimenting with it, and I'm going to try "steeling" a bit of voltage/current
from the output tubes cathode for an extra 7ma or so to get 11ma total on the LED.
(just a straight 3k resistor from the output tube cathode to the top of the LED)
Curious your thoughts on this.
Later,
Keg
In this case the LED is used as is. The LED was added because both tubes (6LR8 and 6GF7) want about 2 volts of bias but at different current and plate voltage. You can't get there from here with a resistor, but you can with an LED.
I have used LED's in my other amps (Simple SE and Tubelab SE) without needing "boost" current. I tend to run my driver stages at higher that "normal" current (5 to 10 mA) so "boost" is not usually needed.
You can measure your LED's and see if "boost" will help. Connect a suitable resistor in series with the LED, and hook both up to a variable power supply. Increase the voltage until the LED just begins to glow. Measure the voltage across the LED and the current through the LED. A current meter is a big help, but the current can be computed from the voltage drop across the resistor. Increase the voltage and take a new reading repeat until you are well past the current that you intend to use. Choose a convienient current increment (such as 1 or .5 mA). Then plot this data (I used Excel). You now have the I/V curve of the LED. It should be nonlinear up until a point at which it becomes very linear. Is your chosen operating point safely inside the linear region? If so "boost" will not help. If not, now you know how much "boost" you will need. You can pick two points an equal distance from the chosen operating point (but both in the linear region) and compute the dynamic resistance of your LED. Lower is better.
I have used LED's in my other amps (Simple SE and Tubelab SE) without needing "boost" current. I tend to run my driver stages at higher that "normal" current (5 to 10 mA) so "boost" is not usually needed.
You can measure your LED's and see if "boost" will help. Connect a suitable resistor in series with the LED, and hook both up to a variable power supply. Increase the voltage until the LED just begins to glow. Measure the voltage across the LED and the current through the LED. A current meter is a big help, but the current can be computed from the voltage drop across the resistor. Increase the voltage and take a new reading repeat until you are well past the current that you intend to use. Choose a convienient current increment (such as 1 or .5 mA). Then plot this data (I used Excel). You now have the I/V curve of the LED. It should be nonlinear up until a point at which it becomes very linear. Is your chosen operating point safely inside the linear region? If so "boost" will not help. If not, now you know how much "boost" you will need. You can pick two points an equal distance from the chosen operating point (but both in the linear region) and compute the dynamic resistance of your LED. Lower is better.
Probably where the main diference is, our plate loads, with my using of
a 47k I get just barely 4ma through the tube and it's LED. Your 22k will
definatly put you better at say 6.5 - 7ma for the both.
So I see why your's works well, I think mine needs a bit more "boost"
(I've got to try some more LED's as well here)
Again more experimenting to follow, thanks for the info.
Later,
Keg
a 47k I get just barely 4ma through the tube and it's LED. Your 22k will
definatly put you better at say 6.5 - 7ma for the both.
So I see why your's works well, I think mine needs a bit more "boost"
(I've got to try some more LED's as well here)
Again more experimenting to follow, thanks for the info.
Later,
Keg
Did you see the big box full of tubes with the sign that said:
"Free Tubes, be a ham and take a couple, don't be a pig and take them all."
I found a 6GF7 and a 6EM7 in that box. I also found a few big sweep tubes at the "every tube is $3" table. Stan has at least one medium size sweep tube in his $1 list. I don't have the number here at work, but I got some to "test".
I did the prototype PC board about the same time that I did the Simple P-P PC board. The email about the Simple P-P was about 10 times as much as the spud board, so the Simple P-P board has been sent out to the board shop. Once I get the instruction manual written (I can't take the pictures until I have the boards) I will another board. The spud board didn't seem to create much attention, and the universal driver board is already generating email. It doesn't even exist yet.
The spud amp is pretty simple, it could be built with point to point wiring, or even.......clip leads (just kidding).
By the time I saw the box of 'take a few' tubes, it was down to about 20 tubes and I didn't recognize anything.
The 'everything is $3' table was a goldmine. A very pretty 5Z4, half a dozen NOS 12AT7, two pairs of 6GF7(a) from matching manuf., two matching pairs of 6LR8, etc. I even left a few tubes behind because I started feeling greedy...
I skipped Stan and the other Orlando tube dealer. I figured they'd still be here after the hamfest. My last vendor was shocked, simply shocked that anyone would buy (metal) 6L6 tubes, so I took all four of them for $5 ea along with a matched pair of used 6L6GC (more than $5), a small collection of tube rectifiers and some $6 JAN Philips 12AT7 parts. I suppose I'll have to build my second S SE board with a lower B+ voltage to make a home for the lower dissipation tubes (or some Russian 6p3s-e tubes, or 6V6, or ... )
I fully understand the board priority situation. I'm already considering the idea of building a single channel via p2p from the discussion in this thread. Even I wasn't very curious about the Spud board before I found a few tubes that would fit it... I think it's a commercially dead product without a better/known supply of appropriate parts.
Overall, it was a fun afternoon. I didn't even glance at any ham radio items. I think I'll still renew my license this year because everyrone I meet is instantly impressed to meet a real Am Extra.
Rick
The 'everything is $3' table was a goldmine. A very pretty 5Z4, half a dozen NOS 12AT7, two pairs of 6GF7(a) from matching manuf., two matching pairs of 6LR8, etc. I even left a few tubes behind because I started feeling greedy...
I skipped Stan and the other Orlando tube dealer. I figured they'd still be here after the hamfest. My last vendor was shocked, simply shocked that anyone would buy (metal) 6L6 tubes, so I took all four of them for $5 ea along with a matched pair of used 6L6GC (more than $5), a small collection of tube rectifiers and some $6 JAN Philips 12AT7 parts. I suppose I'll have to build my second S SE board with a lower B+ voltage to make a home for the lower dissipation tubes (or some Russian 6p3s-e tubes, or 6V6, or ...
)I fully understand the board priority situation. I'm already considering the idea of building a single channel via p2p from the discussion in this thread. Even I wasn't very curious about the Spud board before I found a few tubes that would fit it... I think it's a commercially dead product without a better/known supply of appropriate parts.
Overall, it was a fun afternoon. I didn't even glance at any ham radio items. I think I'll still renew my license this year because everyrone I meet is instantly impressed to meet a real Am Extra.
Rick
I found that one about 3 PM on Friday. The box was nearly full. I always do a hamfest backwards. I got there at 1:30 on Friday, went to the back of the tailgate area and started making a quick pass towards the front, looking for obvious goodies. I check out the back building first and didn't get to the commercial stuff until after dark. I didn't look at radio stuff until Saturday.
I stopped at Stans place on the way to the hamfest to drop off a truckload of tubes. I dropped off my shopping list and he brought the tubes and sockets to the hamfest on Saturday.
I was thinking that the only way it would work was to offer a complete kit, and it would need to be price competitive with some of the other cheap amp kits out there. Once Sherri gets back we may revisit the idea of offering parts kits.
I didn't stop to really check out all of the tubes she had until Saturday. There were some good tubes there that I can get cheaper from Stan. An example is the 6LU8. It is the same tube as a 6LR8 except in a 12 pin base. Stan has them on the $1 list. Other goodies on his $1 list, the 6EZ5 is an octal sweep tube similar to the 6W6, works in a Simple SE with a lower supply voltage. The 6GV5 is the $1 sweep tube whose number I couldn't remember. Don't know what it will do, but for $1 I'm going to find out.
I got a tech plus license about 25 years ago. I lost a battle with the local code enforcement nazis over my antennas, and lost interest about 20 years ago. I renewed my license twice just in case I ever wanted to tinker with radios again.
I am thinking about designing a ham SDR so I upgraded to an Extra and purchased a multi band wire antenna. I design two way radio equipment for a living, so I might cook up something cool if I ever find time for it.
Finally Britain did something right, so I now have a 'Full' license for life. There only was one technical grade when I did it, that was 'damn difficult'. I mean, you're about to embark on Her Majesty's Airwaves, old boy. What!
They got rid of the morse requirement, too.
w
Citizen's Band? The cheek of it. Next thing they'll all want communicators like Star Trek.
73 de Mike zerO Romeo Oscar November
They got rid of the morse requirement, too.
w
Citizen's Band? The cheek of it. Next thing they'll all want communicators like Star Trek.
73 de Mike zerO Romeo Oscar November
I made the first prototype for this amp almost a year ago. It was about the same time that I did the prototype for the Simple P-P. The Spud SE generated about 5 emails while the Simple P-P overflowed my in basket. The Simple P-P boards should be in house in about 2 weeks. I will then be busy writing the assembly manual.
Interestingly I got more email requesting a bigger Simple P-P than I got about the Spud SE, although interest in the Spud amp has picked up in recent weeks. I will get back to it as time permits, but I can't say when right now with all of the stuff going on in my life right now.
I have the Eagle schematic, and I can post it but there are no component values on it. I put the board in a safe place, so when I remember where that safe place is I can find out what parts are actually on the board.
Notice. Diodes D7 and D8 are only used if a full wave NON _CT power transformer is used. They are not needed with the typical power transformer.
Interestingly I got more email requesting a bigger Simple P-P than I got about the Spud SE, although interest in the Spud amp has picked up in recent weeks. I will get back to it as time permits, but I can't say when right now with all of the stuff going on in my life right now.
I have the Eagle schematic, and I can post it but there are no component values on it. I put the board in a safe place, so when I remember where that safe place is I can find out what parts are actually on the board.
Notice. Diodes D7 and D8 are only used if a full wave NON _CT power transformer is used. They are not needed with the typical power transformer.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.