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Novar Spud :: A $200 sweep tube Spud with PCB

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Hi,

You can't go wrong with Tom's PCBs, the 6LR8 is a great sounding sweep tube.

I built my amp before I was aware of Tom's PCB being available, if I had known I would of bought a set to make my life easier.

I have attached a pic of mine for fun, great sounding amp.

BR,
Eric
 

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Thanks for your kind works. :)
The box was bought from an electrical wholesale company, it's designed to hold switchgear, relays, timers etc. I think it's made of PVC.
There's a steel plate fixed near the bottom of the box for mounting things to, keeping potentially "live" screws inside the box. If you have trouble finding one I can post one to you :) It's the perfect size for this board.
Originally I fitted the fan in an effort to keep dust out of the amp; the amp normally lives at my (very hot and dusty) workshop. I had fitted one of those little filters to the fan but found it doesn't stop much dust anyway. Need to find a better filter! The temperature at work often reaches 42c and the amp does lots if hours so I thought keeping things cool may help with longevity.
So.. Anyone else have one of these finished, or is this the only one in the Southern Hemisphere?
Kind regards from Australia. Pete.
 
Well... As Tubelab would say: "Transistors have specs, tubes have guidelines". :)

The max Vg2 of 150 V applies in pentode mode. Whether it's applicable in triode mode as well is anybody's guess. I haven't experienced any issues with it running at 300 V B+ in UL or triode mode. That said, I only tried four 6KY8 tubes, not a statistically representative sample size.

~Tom
 
Has anyone compared the sound differences between the 6GF7A, 6KY8 and 6LR8? I understand the power differences. Just wondering which you feel sounds best.

Heh, first you have to define "best". Considering that most of the cost is in the transformers, you could build 2 or 3 circuitboards configured for the different tubes and try the different combinations. I see that Tom has dropped the price of the bare PCB. Myself, I am part way down a different path: building a Novar Spud (triode) and also Tom's Modulus-86 to discover the differences between super low distortion solid state and single-ended triode. I think it will take me all year :)
 
I understand that "best" sound is subjective. I was just looking to see if anyone had compared the trio and would be willing to share their opinion.

I ordered two boards from Tom this weekend. The first build will be the 6GF7 since I have two nice pairs of those on hand. The second board will have the higher voltage power supply and will run 6KY8 and 6LR8. I have most of the parts on hand including one pair of Edcore transformers that came from a scrapped project. I plan on getting the metal work completed this summer but the bulk of the electronic work will be a winter project. I'm also putting together a Darling 1626/12SL7. I was hoping to get a board from Shannon Parks to speed along the assembly but it appears that he no longer sells boards. So it will be point to point instead. No big deal really. The hardest part is figuring out a grounding scheme.

Keep us updated on your findings. That sounds like a nice project as well.
 
Has anyone compared the sound differences between the 6GF7A, 6KY8 and 6LR8? I understand the power differences. Just wondering which you feel sounds best.

I have... :)

To me the 6GF7A sounds really sweet. I love the triode sound. With efficient speakers, I'd jump on that in a heartbeat, but you do need efficient speakers as with only about 1 W @ 3 % THD, you don't have a lot of oomph to work with.

The 6LR8 in triode mode sounds nice as well. It also provides more power than the 6GF7A so it isn't limiting your speaker selection as much. I seem to recall getting about 4.5 W that way.

To break the 5 W mark - even if only barely - connect the 6LR8 in UL mode. While it sounds pretty good in UL, I found I liked the triode connection better. The extra half watt or so isn't enough for me to desire the UL over the triode connection.

The 6KY8 provides slightly more power than the 6GF7A but not enough to care. For me, the choice is between the 6GF7A and the 6LR8.

The Novar Spud board supports all three tubes and both UL and triode connection for the pentodes by swapping out a few resistors, LEDs, and jumpers. The board is made with oversized pads for the components so it's easy to solder. Perhaps more importantly for the experimenter it is also easier to de-solder and re-solder without damaging the board. I designed the Novar Spud with the experimenter in mind and the design doc shows many combinations of biasing and connections of the three tubes supported by the board (6GF7A, 6KY8, and 6LR8).

Tom
 
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