Hmm. After looking around for 6LU8 and 6LR8 tubes a bit more, they seem fairly comparable, so at least cost wise this is probably a moot point anyway.
That said, has anyone had any luck finding PCB mount Novar sockets? PCB mount 12 pin Compactron sockets are easy to find, and Magnoval too, but not Novar (only place I could find with Novar PCB mount sockets was charging $10 a pop)
Unless we wanted to go the route of manually crimping each pin in a Magnoval socket, we would need to find a decent supply of Novar sockets before putting this all together. Plus, as mentioned by squiffiness, as they don't seem to be in current production as far as I can tell, we'd probably need them before sending off the board to make sure the PCB holes for the socket are correct.
Was there a specific reason for going with the 6LR8 over the 6LU8? As far as I understand at, they're identical apart from the base, so it would seem as though going for the 6LU8 might simplify things?
EDIT: Just realised George explained the reasoning for choosing the 6LR8 back in post #5. It's quite late and I think my brain's checked out for the day
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Stan at ESRC has them. I saw him today at the hamfest, the sockets are there at his display, I had them in my hand. NO, I wasn't smart enough to ask the price, or measure the pin circle. This was the third day of standing in a huge asphalt parking lot in the 88 degree weather selling my warehouse junk. One more day to go. My brain was somewhat fried from the heat, 12 hour days, and lack of sleep and decent food.
I have however succeeded in converting one cubic Honda Element full of "stuff" into a bundle of cash. I will be stopping at ESRC next Saturday on my way home to drop off some tubes, and pick up some tubes.....and some Novar sockets.
I will check again for price and availiability of 6LU8 VS 6LR8. Availability is the main criteria. No point in designing an amp for a tube you can't get.
I am on hotel internet now. I probably won't be back to this forum until Monday evening. Any questions for Stan......post them here.
I'd be toast after the first day.
I'd probably prefer the spud over one of Pete's compactron amps, because George is funnier (sorry Pete
Even the stock DCPP amp has too much power for the desktop, but it does sound good.
jeff
I was referring to his "Jonokuchi" (dual triode) and his "Mighty Midget" (dual pentode).
The Midget appears to be a more involved design to stuff into a custom FrontPanel Express case unless you mod it somewhat.
The SimpleSpud (hoping...hoping) is much simpler in design from what I can see.
Earlier in the thread, George alluded to having something like a bunch of parts kits and gain matched tubes for the small board, but had not optimized his PCB design. Hopefully, the earlier post about small batch, inexpensive board houses in The Land of Mao will push this project over the top.
Another design (see neurochrome.com) used the functional twin of the 6LR8; the compactron 6LU8. The end product uses a 5AR4 in the P/S, a toroidal power transformer, UL and CFB and is a real looker in its wooden home.
It does look like George confirmed Novar PC mount socket availability, but wanted to confirm tube supply.
In the meantime, I have some time to burn, so I will keep trying to launch my own. If George beats me, I'll buy his board since he actually knows what he's doing.
My current plans are now to leave for Fort Lauderdale tomorrow morning. Drive the 1200 miles home over two days. Unload all the remaining hamfest stuff, load the trailer up with tubes and my old radio collection, turn around and drive 200+ miles back to Orlando to for an antique radio show Saturday morning. It happens to be in ESRC's parking lot, so I'll have some time to talk to Stan and maybe look around the warehouse. At last count it contained about 3 million tubes.
I would be willing to take a stab and say that bundle of cash is of a lot more use than a cubic Honda Element of tubes
Had a bit of a look around, and found vacuumtubes.net has 21LR8 tubes for US$0.75 each. Anyone have any experience with them? Although I'd need another heater tap on the PT, not a particularly expensive addition and it broadens the supply of *LR8 tubes I can use.
Also, were there any other voltage variants of the 6LR8 available? I've only been able to find the above two thus far.
If we can confirm pin circle, price and stock levels of those Novar PCB mount sockets would be handy. Assuming the PCB goes ahead, even if you don't do a full parts kit (a much bigger investment of both time and money) would you be willing to buy and ship the sockets with the board? Seeing as how scarce they are, and for those of us outside the US, would save some extra postage and running around.
I didn't sell as many tubes as I had thought I would. After I finally got a chance to go shopping I found someone selling NOS tubes for $0.25 each! He had a crowd. Yeah, I bought a few.
I sold "stuff" from my warehouse, old stereos (including a Fisher 400), test equipment, tube testers, transformers, and all sorts of stuff I didn't use.
I know there was a 21LR8 and a 31LR8. Not sure if there was a 16LR8.
I already have all the parts for building the PC board itself. I was planning to do a "small parts kit" like I currently have for the Simple P-P. It contains all of the parts that you solder into the board. No tubes or transformers. I have about 100 of the 6LR8's too. I even tested them and sorted them by power output for a fixed input voltage to assure evenly matched channels.
I sold some tubes to Stan at the hamfest. He owes me some money, so i will pick up a bunch of sockets Saturday.
Currently in a hotel room about halfway home.
Tubelab 6LR8 Spud Schematic
I have noted in the schematic for the Simple ProtoSpud ultralinear mode is used by not CFB like in the SSE.
Was there some design reason for avoiding CFB with the 6LR8?
A couple of other amps out there in DIY'land use various forms of feedback. The power hungry spudders all use UL for boost and some CFB for THD.
Could/Should the ProtoSpud Mark II consider CFB as part of the equation since a feedback cap would replace the bypass cap to ground on the pentode?
Second, since the first ProtoSpud underwent some cathode bias surgery on the triode section ("yellow" diode in for cap/resistor combo), will the design go traditional Cap/Res or move forward with the yellow diode to get the voltage drop consistent?
Continue to hope ProtoSpud will come to life as a PCB some time in the future.
I have noted in the schematic for the Simple ProtoSpud ultralinear mode is used by not CFB like in the SSE.
Was there some design reason for avoiding CFB with the 6LR8?
A couple of other amps out there in DIY'land use various forms of feedback. The power hungry spudders all use UL for boost and some CFB for THD.
Could/Should the ProtoSpud Mark II consider CFB as part of the equation since a feedback cap would replace the bypass cap to ground on the pentode?
Second, since the first ProtoSpud underwent some cathode bias surgery on the triode section ("yellow" diode in for cap/resistor combo), will the design go traditional Cap/Res or move forward with the yellow diode to get the voltage drop consistent?
Continue to hope ProtoSpud will come to life as a PCB some time in the future.
George, I missed you today at ESRC, I got there a little late and almost everyone had left. I did however pick up a pair of 21LR8 tubes and sockets from Stan.
To test if the PCB production house was still good, I had a set of small PCBs made from Seeed Studio. I ordered on the 13th, they were produced and shipped on the 18th, and arrived today the 26th. Turn around was less than two weeks, although this could vary. The PCBs are very nice, with no flaws that I can see.
I played around the other night and made a PCB design for the spud that fits on a 10 x 10 cm board, including a regulated power supply. It probably still needs alot of tweaking and may not fit if I use larger components, but a better 10 x 15 cm board can be done as well.
To test if the PCB production house was still good, I had a set of small PCBs made from Seeed Studio. I ordered on the 13th, they were produced and shipped on the 18th, and arrived today the 26th. Turn around was less than two weeks, although this could vary. The PCBs are very nice, with no flaws that I can see.
I played around the other night and made a PCB design for the spud that fits on a 10 x 10 cm board, including a regulated power supply. It probably still needs alot of tweaking and may not fit if I use larger components, but a better 10 x 15 cm board can be done as well.
Sorry, I didn't know you were coming. I had a collection of old radios so Sherri and I dragged them all up to the Florida Antique Wireless Guild swap meet in Stans parking lot. Sherri sold all of them by 9:30 and we had to drive back to Fort Lauderdale, so we left. We have friends in the Orlando area so we will be back up there in a few weeks. Are you local to that area?
One of the swap meet vendors was selling tubes for $0.25 each. I found an old RCA 2A3 in the box so I bought it. Odds of it working......about the same as the lottery.
Stan bought a bunch of tubes from me at the Dayton hamfest so I had a store credit to spend. I now have plenty of sockets for the board and some tubes to experiment on.
Tube amp boards, especially ones to be assembled by builders of varying experience levels should be a bit bigger than they need to be, and use oversized pads for all the parts to avoid pads lifting from the PC board when changing parts. I made mine 4 X 6 inches, so 10 X 15 cm is just a few seconds with a belt sander
I dug out the old board, and found the layout on my PC, then I started thinking.......how could I change the design to make it appeal to a larger audience.....what would I change so that I would want one.
I have several SE amps, but only two ever get used. I have a Tubelab SE with 45's in it. It makes about 2 watts but they are the nicest 2 watts I have! I have an SSE that can out power this board, so why to I need this board, or what could I do to it to make it useful to me?
First off, your requests were for THIS design, so this design will be on the PC board. CFB? Maybe. I tried it on the original board and it didn't do much, but that might have been because some Schade feedback is already applied in the design. I have been thinking about additions that could be selected at build time, or with jumpers.
The original design would be implemented as shown in the schematic.
It can use the 6GF7 in triode mode (it is a dual triode) without any changes. The original board was tested with 6GF7's.
The board can use the 6LR8 in triode, UL and pentode. All modes were tested with the original board. The 6LU8 has a 300 volt screen grid rating, which I routinely violated without issue in my original testing.
My thoughts on possible additions:
A mosfet screen voltage regulator would allow the use of the 6KY8 which is a triode - pentode combination tube slightly smaller than the 6LR8. It has a 150 volt screen grid rating requiring the regulator. A regulator would allow operation of the 6LR8 at a lower screen voltages. This might be useful for higher plate voltages without wasting excessive voltage across the cathode resistor. The regulator would be very simple and either jumper selectable, or left off at build time if not needed.
The board is currently configured for operation as a two channel SE amp. It is possible to design the board such that it can be built as a stereo SE amp, or as a single channel P-P amp. This would not be a jumper selection. It would be a different set of parts installed at build time and of course one P-P OPT instead of two SE OPT's. This would mean that there would be two different parts lists, and not every part on the board would be populated for either configuration.
Thoughts?
I have several SE amps, but only two ever get used. I have a Tubelab SE with 45's in it. It makes about 2 watts but they are the nicest 2 watts I have! I have an SSE that can out power this board, so why to I need this board, or what could I do to it to make it useful to me?
First off, your requests were for THIS design, so this design will be on the PC board. CFB? Maybe. I tried it on the original board and it didn't do much, but that might have been because some Schade feedback is already applied in the design. I have been thinking about additions that could be selected at build time, or with jumpers.
The original design would be implemented as shown in the schematic.
It can use the 6GF7 in triode mode (it is a dual triode) without any changes. The original board was tested with 6GF7's.
The board can use the 6LR8 in triode, UL and pentode. All modes were tested with the original board. The 6LU8 has a 300 volt screen grid rating, which I routinely violated without issue in my original testing.
My thoughts on possible additions:
A mosfet screen voltage regulator would allow the use of the 6KY8 which is a triode - pentode combination tube slightly smaller than the 6LR8. It has a 150 volt screen grid rating requiring the regulator. A regulator would allow operation of the 6LR8 at a lower screen voltages. This might be useful for higher plate voltages without wasting excessive voltage across the cathode resistor. The regulator would be very simple and either jumper selectable, or left off at build time if not needed.
The board is currently configured for operation as a two channel SE amp. It is possible to design the board such that it can be built as a stereo SE amp, or as a single channel P-P amp. This would not be a jumper selection. It would be a different set of parts installed at build time and of course one P-P OPT instead of two SE OPT's. This would mean that there would be two different parts lists, and not every part on the board would be populated for either configuration.
Thoughts?
George,
Options are good. It will probably add to your support work load though. No matter how well you explain the options, someone will still be confused...This amp will appeal to newbies since it will seem pretty simple.
Hopefully we can help you out here on the forum.
FWIW...I'm in for 2 boards... for sure
Dave Ganzer
Options are good. It will probably add to your support work load though. No matter how well you explain the options, someone will still be confused...This amp will appeal to newbies since it will seem pretty simple.
Hopefully we can help you out here on the forum.
FWIW...I'm in for 2 boards... for sure
Dave Ganzer
Gets my vote as the starting point. Simple...for folks like me starting out.
Didn't realize that was what R14/24 were doing on your original schematic. Hey, I learned something new today.
Agree with earlier...options are good to mod later for something a little different or new. De-soldering practice is a good skill to know for mod surgery.
That's pretty cool and sounds like an interesting challenge to set up a PCB that is so flexible.
It would indeed be a conversation piece to have a pair of monoblock 6LR8 P-P amps for more power/less THD...call it "Miller Lite" or use the DuoDecar sockets with 6LU8's and call the P-P version the Tubelab SimPPle ComPPactron.
Question: what kind of power output would you be looking at in Push-Pull configuration?
Did a bit more hunting and I've found plenty of 21LR8's and 31LR8's, but doesn't look like there ever was a 16LR8. Might buy a handful. At $0.25 each, why not?
Has anyone had any experience with vacuumtubes.net?
Well, at least it's something. The stereos, test equipment and the like would be good to get out the door, help empty out those warehouses.
Excellent. Makes the project that little bit easier at the builder's end.
I like the sound of this actually. I happen to have several 5kohm PP OPT's sitting around, saves on iron. Besides, who can say no to more power?
I'll put myself down for 4 boards/kits if the PP part of it comes to fruition, otherwise just the 2 I originally put myself down for.
I know you'd mentioned how you might get the 21V for the filaments of the 21LR8. Are you considering small, separate filament transformers (like the small Antek's that spit out 20-40V) to do the job? That might make the job of using the tubes you've discovered useful in the NovarSpud.