Hi all,
inspired by this article on the net, 6LU8 Sweep-AMP i decided to build myself one, i have ordered about 700 pcs of these $1 tubes from Roy and Dale Rogalski of Vacuum Tubes Radio Tubes - 5,000 different tubes in stock - Over 10 million tubes! now it's time to put them to good use:
the 6LU8 is like a 6V6 and 1/2 of 12AT7 placed in s single 12 pin compactron envelope, i wanted to use the 21LR8 at first but then the novar sockets had issues, they were loose, i found out that they were intended for tubes like the PL504 which had thicker pins.....oh well.....here is the link for the 6LU8: http://frank.pocnet.net/sheets/123/6/6LU8.pdf
so i designed all the irons needed, the power transformers, filter choke and output transformers, the 2 output transformers used Edrel's RM20 cores which like his more expensive Z11's had the same 0.35mm thikness, Deeco Irons were then used for the power transformers and filter choke, deeco iron has a thickness of 0.5mm....
pics of the irons and some parts:
the power supply used the 3DG4 tube,http://frank.pocnet.net/sheets/093/3/3DG4.pdf it is likewise a hybrid rectifier using solid-state bridge, a toggle selector switch is used to select ss only rectification if desired.....the advntage of a hybrid is that being a full bridge rectifier transformer heating is way much lower than if staright full-wave is used using tube rectifier only......design and construction of the power transformer then becomes easier and cheaper....
construction pics:
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testing:
i used another set of speakers to test whether the polarity of the output transformer was correct, there is a 50-50 chance you will get it, but upon power up motorboating happened so i had to power down and reverse the plate lead connections to the right one.....after that, the amps was dead quiet, no hum, no hiss no noise.....i tested the amp and found out that the sensitivity was quite low, so i hooked up the 7N7 preamp to get a more decent volume.....later on i found out that i connected 470ohms feedback resistor instead of 4.7k so gain was really low....
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inspired by this article on the net, 6LU8 Sweep-AMP i decided to build myself one, i have ordered about 700 pcs of these $1 tubes from Roy and Dale Rogalski of Vacuum Tubes Radio Tubes - 5,000 different tubes in stock - Over 10 million tubes! now it's time to put them to good use:
the 6LU8 is like a 6V6 and 1/2 of 12AT7 placed in s single 12 pin compactron envelope, i wanted to use the 21LR8 at first but then the novar sockets had issues, they were loose, i found out that they were intended for tubes like the PL504 which had thicker pins.....oh well.....here is the link for the 6LU8: http://frank.pocnet.net/sheets/123/6/6LU8.pdf
so i designed all the irons needed, the power transformers, filter choke and output transformers, the 2 output transformers used Edrel's RM20 cores which like his more expensive Z11's had the same 0.35mm thikness, Deeco Irons were then used for the power transformers and filter choke, deeco iron has a thickness of 0.5mm....
pics of the irons and some parts:
the power supply used the 3DG4 tube,http://frank.pocnet.net/sheets/093/3/3DG4.pdf it is likewise a hybrid rectifier using solid-state bridge, a toggle selector switch is used to select ss only rectification if desired.....the advntage of a hybrid is that being a full bridge rectifier transformer heating is way much lower than if staright full-wave is used using tube rectifier only......design and construction of the power transformer then becomes easier and cheaper....
construction pics:
View attachment 620346
View attachment 620347
View attachment 620348
View attachment 620349
View attachment 620350
View attachment 620351
View attachment 620352
View attachment 620353
View attachment 620354
testing:
i used another set of speakers to test whether the polarity of the output transformer was correct, there is a 50-50 chance you will get it, but upon power up motorboating happened so i had to power down and reverse the plate lead connections to the right one.....after that, the amps was dead quiet, no hum, no hiss no noise.....i tested the amp and found out that the sensitivity was quite low, so i hooked up the 7N7 preamp to get a more decent volume.....later on i found out that i connected 470ohms feedback resistor instead of 4.7k so gain was really low....
View attachment 620355
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Very niceBy the looks of it you have quite some building experience.
thanks......i have quite extensive building experience with solid state amps....but it was a p-p 6EM5 that was my first tube build in the 70's.....i am back to building tube amps....
Cool project! Those TV tubes are nice; imagine that: a stereo PP amp with just four tubes. Even though it's usually not easy to find the output iron (I wasn't surprised to see you made custom designs), they're nice to tinker with.
But let me get this straight: you got 700 of these tubes? So we can expect a manufacturing output of another 174 of those amplifiers you showcase here?
But let me get this straight: you got 700 of these tubes? So we can expect a manufacturing output of another 174 of those amplifiers you showcase here?
Cool project! Those TV tubes are nice; imagine that: a stereo PP amp with just four tubes. Even though it's usually not easy to find the output iron (I wasn't surprised to see you made custom designs), they're nice to tinker with.
But let me get this straight: you got 700 of these tubes? So we can expect a manufacturing output of another 174 of those amplifiers you showcase here?
thanks to YvesM, i used his design in winding the output transformer, it has around 10k primary anode to anode resistance to 6 ohms secondary....
those 700 tubes are not all same types, although i have around 40 or so 6LU8 and 21LR8 tubes to play around with......the rest are tv horizontal sweep tubes, damper diodes, and odd voltage double triodes, pentodes etc., etc..
i am not scared of non-6 volt tubes, i can make traffos for then as needed....
so far i have finished 2 albums listening to this amp, first is Beatles' "Rubber Soul" my all time favorite, and Norah Jones' "com away with me." .......very enjoyable listening....
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per CompactronTubesIndex.shtml:
...Every so often I hear talk of "9-pin Compactrons." Technically those don't exist; all Compactron tubes have 12 pins....However, in 1962 RCA introduced a line of tubes called Novar. These are all-glass tubes with nine .038" (1.2mm) pins on a base larger than that of the familiar 9-pin miniature. RCA introduced them for use in audio equipment, and the motivation may have been to create a larger base and bulb for greater power dissipation. Most of the Novars I've seen have been power pentodes like the 7868, or color TV rectifiers. There's something to careful of with Novar tubes. A very similar line was introduced in Europe at about the same time. These were called Magnoval tubes, and they have nine pins on the same diameter circle. However, and crucially, Magnoval tubes have larger pins, at .046" (1.27mm). If you plug a Magnoval tube into a Novar socket, the larger pins will damage the pin contacts on the socket. You can wreck the socket of a late-era tube tester by trying to test a Magnoval in the Novar socket. Before you test what you think is a Novar tube, put a mic or a digital caliper on those pins!
There were not as many Novar tubes as Compactrons, and they were never very popular. Sockets are more difficult to find, though I've seen them online. Sellers sometimes claim that a single socket will work for both Novar and Magnoval, but that's not true. The larger Magnoval pins will damage any socket designed for Novar tubes, and Novar tubes will rattle around in any socket designed for Magnoval pins.
...Every so often I hear talk of "9-pin Compactrons." Technically those don't exist; all Compactron tubes have 12 pins....However, in 1962 RCA introduced a line of tubes called Novar. These are all-glass tubes with nine .038" (1.2mm) pins on a base larger than that of the familiar 9-pin miniature. RCA introduced them for use in audio equipment, and the motivation may have been to create a larger base and bulb for greater power dissipation. Most of the Novars I've seen have been power pentodes like the 7868, or color TV rectifiers. There's something to careful of with Novar tubes. A very similar line was introduced in Europe at about the same time. These were called Magnoval tubes, and they have nine pins on the same diameter circle. However, and crucially, Magnoval tubes have larger pins, at .046" (1.27mm). If you plug a Magnoval tube into a Novar socket, the larger pins will damage the pin contacts on the socket. You can wreck the socket of a late-era tube tester by trying to test a Magnoval in the Novar socket. Before you test what you think is a Novar tube, put a mic or a digital caliper on those pins!
There were not as many Novar tubes as Compactrons, and they were never very popular. Sockets are more difficult to find, though I've seen them online. Sellers sometimes claim that a single socket will work for both Novar and Magnoval, but that's not true. The larger Magnoval pins will damage any socket designed for Novar tubes, and Novar tubes will rattle around in any socket designed for Magnoval pins.
yes, the 12pin compactrons are far better than the 9pins novars....those will be good with PL504 type tubes...
as i am aware of the issues with the chinese 9pin novar sockets, i still have to use them, i am looking for a crimping tool so i can rework the pins...using those as is makes for a very microphonic build....
I just fired up my Quad Spud'ed PP amp. I designed the PCB for cathode or adjustable fixed bias and chose adjustable fixed bias. The outputs could be configured as triode, UL or pentode mode, I chose pentode due to Bogen MX30A iron not having the UL taps and wanting higher output power.
I started this last July and finally finished the PCB design before Christmas. It took a while to get around to making the PCB by toner transfer and scrounging the components.
My initial impression after tweaking the GNFB is that I do not understand why this design concept is not more popular. It is a great little amp with good output iron.
I started this last July and finally finished the PCB design before Christmas. It took a while to get around to making the PCB by toner transfer and scrounging the components.
My initial impression after tweaking the GNFB is that I do not understand why this design concept is not more popular. It is a great little amp with good output iron.
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congrats, but ssshhhh! we do not want to let many people know
....it will bring up the cost of this tube.....yes, the triode is a beefy 12at7, and the pentode even stronger than the 6BQ5's, the 400volt plate rating is even nicer, what's not to like.....
my next build would be parallel push-pull using srpp input to an ltp stage and fixed biasing....
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