I started to play with a tube headphone project for a little set of Merit universal output transformers and ended up with a PCB idea for a Quad SPUD in PP using 6LU8 tubes. I've used 6JN6 to 6LB6 tubes in other amps, this is my first SPUD amp.
I only have one SPUD, so for spacing trials I used a set of 6JN6 sweep tubes. The idea is to place the electrolytic caps on the back side of the PCB.
With the 6CG3 damper diode tube, it is just too crowded in the center of the PCB.
I like to use solid state diodes in the power supply but use a damper diode as a delay pass device for the B+. I don't have room for the 12 piner, are there any 7 or 9 pin diode tubes that can handle 200ma with 20 volts across them?
I found 6203 and 6AY3/6C19P as candidates, are there any better choices? I do not like to have the top cap, I would prefer to keep it simple.
I only have one SPUD, so for spacing trials I used a set of 6JN6 sweep tubes. The idea is to place the electrolytic caps on the back side of the PCB.
With the 6CG3 damper diode tube, it is just too crowded in the center of the PCB.
I like to use solid state diodes in the power supply but use a damper diode as a delay pass device for the B+. I don't have room for the 12 piner, are there any 7 or 9 pin diode tubes that can handle 200ma with 20 volts across them?
I found 6203 and 6AY3/6C19P as candidates, are there any better choices? I do not like to have the top cap, I would prefer to keep it simple.
Attachments
QUAD SPUD PP AMP
Finally did a toner transfer PCB and started stuffing.
I did a universal PCB to allow for playing with different combinations.
It is designed for cathode bias or adjustable fixed bias, I chose adjustable fixed bias.
Output configerations to choose from are triode, pentode and UL, I chose pentode with the G2 at 150V.
I have a set of 6.6K 40watt hammonds to try with it and a 600Vct 200ma tran for power. Still missing a few components, so another order is needed...
So for those who have played with the 6LU8, how much power have you squeezed out of the amps in what configuration?
Finally did a toner transfer PCB and started stuffing.
I did a universal PCB to allow for playing with different combinations.
It is designed for cathode bias or adjustable fixed bias, I chose adjustable fixed bias.
Output configerations to choose from are triode, pentode and UL, I chose pentode with the G2 at 150V.
I have a set of 6.6K 40watt hammonds to try with it and a 600Vct 200ma tran for power. Still missing a few components, so another order is needed...
So for those who have played with the 6LU8, how much power have you squeezed out of the amps in what configuration?
Attachments
QUAD SPUD PP AMP
Final components received today and the little quad spud is up and running. I had a Hammond 372-JX on the shelf from another project, it is a little overkill but works great. I ran out of CL80's and will need to order a few more. That should drop the voltages closer to the designed values. First stage output is running 20 volts higher that plan which raises the cathodyne from being centered. I can play with the bias or change the plate resistor.
I had some small 8K-8 outputs to use to fire it up. I've left the GNFB off of this combo.
I have a set of Bogen MX30A iron that I've cleaned up, just need to dust them off and lengthen the tube side wires. This trans has a built in feedback winding to play with instead of using GNFB.
It is configured now as an adjustable fix bias amp; running around -18 volts on the grid bias. Tubes are running at 385 Volts @ 45ma 17.3 watts. That is above their 14 watt rating, but no signs of stress and they are still an available inexpensive tube.
In cathode bias mode the raised cathode voltage to about 18V would reduce the tube dissipation to about 16 watts.
With the Bogen output iron (6.6kRa) I'm expecting performance to almost be on par with the KEG-EAR amp when running the 6P3S, 6P3S-E and 6L6 tubes (1650H output iron); also the little 6GV5 sweep tube amp with this same power iron.
Final components received today and the little quad spud is up and running. I had a Hammond 372-JX on the shelf from another project, it is a little overkill but works great. I ran out of CL80's and will need to order a few more. That should drop the voltages closer to the designed values. First stage output is running 20 volts higher that plan which raises the cathodyne from being centered. I can play with the bias or change the plate resistor.
I had some small 8K-8 outputs to use to fire it up. I've left the GNFB off of this combo.
I have a set of Bogen MX30A iron that I've cleaned up, just need to dust them off and lengthen the tube side wires. This trans has a built in feedback winding to play with instead of using GNFB.
It is configured now as an adjustable fix bias amp; running around -18 volts on the grid bias. Tubes are running at 385 Volts @ 45ma 17.3 watts. That is above their 14 watt rating, but no signs of stress and they are still an available inexpensive tube.
In cathode bias mode the raised cathode voltage to about 18V would reduce the tube dissipation to about 16 watts.
With the Bogen output iron (6.6kRa) I'm expecting performance to almost be on par with the KEG-EAR amp when running the 6P3S, 6P3S-E and 6L6 tubes (1650H output iron); also the little 6GV5 sweep tube amp with this same power iron.
Attachments
interesting....SPUD means by my definition, that only one tube stage is used. This means no cascading. The first tube does the whole job.
Thomas shows one with the 6HS5 here: VinylSavor: Tube of the Month: The 6HS5
Here is one with the 6С45П: 6s45pe Eintaktverstaerker
Thomas shows one with the 6HS5 here: VinylSavor: Tube of the Month: The 6HS5
Here is one with the 6С45П: 6s45pe Eintaktverstaerker
"SPUD" means a single tube (or "tuber") per channel. The only was to practically do it was with a SE dissimilar triode or pentode tube, and the sweep tubes are the most logical ones to use. While technically no longer a single tube (per channel) amp, your amp uses the traditional Spud tubes. I did something vaguely similar with a 13DE7 and I've thought about using a pair of compactron sweep tubes for a PP guitar amp, but haven't left the design stage.
Based on the consensus, I would have to reclassify my amp to a Quad Spud TUBED PP Amp, or Quad SPUD'd PP Amp or just a Quad 6LU8 PP Amp for those who wish to leave all in one tube=complete amp stage.
There is another sin in the design, I used sand, for a zener G2 160V reference and in the power supply.....
I'll find out this weekend with the Bogen iron what it sounds like, the end may justify the means....
There is another sin in the design, I used sand, for a zener G2 160V reference and in the power supply.....
I'll find out this weekend with the Bogen iron what it sounds like, the end may justify the means....
Its both side toner transfer, the top side is harder for me to do. Seems like it does not like to transfer to the glass side... a coat of clear to protect it and the Dremel tool drilling marathon.
I use testor's modeling enamel paint to touch up the areas that did not transfer correctly or were a little weak. When I run out blue I have 9 other colors to use..
When I iron the silkscreen top on I don't always get it lined up, or it moves when I start with the iron. It helps when stuffing it.
So if this is a combination of different design ideas does it become a "Spud Casserole Amp"?
I use testor's modeling enamel paint to touch up the areas that did not transfer correctly or were a little weak. When I run out blue I have 9 other colors to use..
When I iron the silkscreen top on I don't always get it lined up, or it moves when I start with the iron. It helps when stuffing it.
So if this is a combination of different design ideas does it become a "Spud Casserole Amp"?
Attachments
Bogen iron initial impression, very good... It took a little playing with feedback, I tried the built in feedback winding first but ended up with a resistor and little 100pf cap feed back from the output as GNFB. I have the 6LU8's configured in Pentode mode with 160V on G2, no UL taps on the Bogen iron. I have an older set of Hammond 1650H (6.6KRaa) to try also, but I expect about the same performance. With the zener string, I have a 53V reference for raising the heater ground to minimize the stress on the cathodyne's stage heater to cathode voltage differential. By theory this should also assist in minimizing noise coupling to the cathodes.
I was pleasantly surprised by the performance of this little PP amp. I'm pushing the tubes over their ratings by a couple watts without any visual signs of an issue, no smoke, red plating, etc... I can substitute a 50ohm resistor 5watt or add another choke for the damper diode's 10 volt drop for a simpler design and lower load heater on the transformer. I don't understand why this combination is not more popular.
I was pleasantly surprised by the performance of this little PP amp. I'm pushing the tubes over their ratings by a couple watts without any visual signs of an issue, no smoke, red plating, etc... I can substitute a 50ohm resistor 5watt or add another choke for the damper diode's 10 volt drop for a simpler design and lower load heater on the transformer. I don't understand why this combination is not more popular.
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