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my 300B SET project

Nice job with my favorite little tubes!

Now here's something to think about if you ever get the urge to tinker some more. I just did some upgrades to my Supratek tube preamp, which uses the 7193 tubes (since I converted it from 6SN7s) as output tubes.

First I replaced the cathode resistor and bypass cap on the 7193 tubes with 4 Cree SiC Schottky diodes in series to get 3.45V fixed cathode bias; this resulted in greater clarity of the sound and improved bass performance (both depth and texture improved greatly). Each Cree is good for ~0.85V at 11mA and cost $0.93 each at Digikey.

Secondly, I replaced the plate resistor with an IXYS IXCP10M45S constant current source chip along with a Vishay Spectrol 500ohm pot (to adjust the current supplied to 11mA). HOLY MOLY! What an improvement! The CCS give the tubes a horizontal load line, and also result in about 30-40% more gain. I couldn't believe what I was hearing - voices were startlingly real, sound was powerful, detailed and crystal clear. The chips are ~$2.00 each at Digikey.
I'm waiting for more of the chips to do a cascoded CCS (two chips connected in series), which is supposed to be even better, but even just the chip/resistor is a huge improvement over a plate resistor. Once I have the current dialed in to my satisfaction I'll replace the pot with a Mills 5W resistor.

If you don't mind a little sand in the amp, I heartily recommend the above setup for the 7193s.

Oh yeah, those are GREAT looking amps - nice job!
 
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KGBMAN said:
Can I ask how much $$ you have into these?
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About $1200. or so for the set, That's a guess as I really didn't keep track of what I spent.

Thanks also to MAX for the tips on driving the 7193's. These amps already really make you feel like the performer is standing in the room with you. I might just build a pre amp using those tubes! SET12 also likes to use diodes for better dynamics.
 
Dave:

Those look incredible. Like works of art.

I really like that they are mirror images of each other. Makes them look all the better.


:thmbsp::thmbsp::thmbsp::thmbsp::thmbsp::thmbsp:
:thmbsp::thmbsp::thmbsp::thmbsp::thmbsp::thmbsp:

Enjoy the music!

Shelly_D

BTW: Once operational have you done any changes to the design to get the sound right?

Would you be willing to post the schematic?

Thanks

Shelly_D
 
Shelly d I changed 1 resistor and 1 capacitor on the bench before I started using them.

The cathode resistor on the first tube was doubled in value to bring the voltage up a bit and I went from a .22uf to a .33uf capacitor in the 300B circuit. Other than that they are as built. I need to draw up a power supply schematic yet and I don't want to post anything until that's done.
 
that is one good amp for sure... makes me think think about what to do with the trannies from my 2nd 1000a, i feel a build coming.
 
Perchdog, You could use those 1000A trannies and build an upgrade of the 1000A circuit . I still like the 7591 tube, I might work on an amp with that tube this winter.
 
Hi Dave,

Wow! Stunning! I'm happy to hear that they meet your sound expectations. Thanks for the link.

Regards,
SixCats!
 
Thanks SixCats, and 1mor, I had the neighbors over tonight and had to turn them on for them. They are not audiophile people at all but it sure was fun watching their jaws drop when the music started. The lady looked at me and said it sounded simply magnificent. Her husband said he never heard anything even close. That was a pretty nice compliment!
 
Dumb question from a non-tuber. Is it common for there to be so little (component wise) in a tube amp? If so, are the parts rediculously high priced? If not, why don't we all have them?
 
Elwood, Building a tube amp is a lot different than working with sand amps. Speakers have to be very sensitive so the higher priced stuff is what you look at, you want 95db or better as a rule (some exceptions). The amps will sound the best with the fewest components, this is true of all types of amps. The best amp would simply be a piece of wire with gain, however we all know that's not possible. The more components you use the more noise you get, cover that up with filters (even more parts) and you loose what you set out to gain. My amps are 7 watts each using only the 3 tubes and a handful of resistors and capacitors. If I can engineer less parts into any future amps I build I would keep that as a top priority. Back to the 7 watts of power, With my speakers I can drive people out of the room with volume. So those 7 watts properly used with good speakers do just fine. Single ended tube amp design gives such pure beautiful sound once you listen to a good one you will understand why many of us think sand amps sound so thin.
 
Very well stated Dave. Couldn't have asked for a better explanation. Know of any decent tube amp kits. Thanks for the reply.
 
elwood127 said:
Very well stated Dave. Couldn't have asked for a better explanation. Know of any decent tube amp kits. Thanks for the reply.
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There are a number of good tube amp kits out there. But first you need to decide how many watts you need (you can get 30 watts for a push pull amp), what your budget is, and what level of sophitication you are looking for.
 
Elwood, djnagle said it well, do a search for tube amp kits and you'll find many. At this point I feel I can be a scratch builder. These guys on the forums can figure out anything I can't!
 
What is your budget?

How much power do you need?

What type of music do you listen too?

What speakers are you driving?

How big is your room?

If you can give us some answers to these questions, we can help more better.
 
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