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Old 30th May 2012, 02:03 PM   #81
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Has anyone had any experience with vacuumtubes.net?
I have bought some tubes from them over the years. As with any vendor cleaning out their stock for cheap, expect some old boxes in good to fair condition and a few dead tubes. I did buy 1000 tubes from them about a month ago when the cheap tubes sale started. They looked OK, but I haven't had the time

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Might buy a handful. At $0.25 each, why not?
I got 500 tubes for $0.35 each. Where do you find tubes for $0.25 other than a hamfest?

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Question: what kind of power output would you be looking at in Push-Pull configuration?
I'll know for sure when I breadboard it up. It also depends on how hard you push the tubes. If you want a guess, I will assume class AB1 and say 8 to 10 watts with the 6GF7, 15 to 20 with the 6KY8, and maybe 25 to 30 with the 6LR8. More might be available in AB2 but that really complicates things with mosfets and negative voltages.
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Old 30th May 2012, 07:33 PM   #82
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Originally Posted by tubelab.com View Post
...If you want a guess, I will assume class AB1 and say 8 to 10 watts with the 6GF7, 15 to 20 with the 6KY8, and maybe 25 to 30 with the 6LR8. More might be available in AB2 but that really complicates things with mosfets and negative voltages.
If the complication is elegant and small, then sure, why not marry the new with the old for something unique.

A P-P with 20W on hand will be fine for my modest listening space. I have a Musical Fidelity A1 solid state integrated amp. It's rated for 20W per side. With my loudspeakers (Axiom M3's at 95 dB efficiency), volume at 10 o'clock is plenty to blow the room away...and cook eggs or boil water...that thing gets GD'd hot!!!

So, 10W plus is gravy if I were to go the P-P. How about the Spudd (the lower case D's are capital P's rotated 180 degrees) as a name? Ok, I'm putting the cart before the horse. Maybe I should finish my SSE first, before dreaming of my next dream.

I believe I am in for one SpudSE version as a kit as a Canada Day present (optimism).
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Old 31st May 2012, 02:34 AM   #83
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I know I have a few flavors of the LR8 variety in a box some place as well as a spare set of output transformers and if I look I bet I can come up with a power transformer. Sounds like something I may be building in the future as well.
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Old 31st May 2012, 04:59 PM   #84
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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.
Originally I was planning multiple filament windings on the same toroid, but it comes down to whether it's better (cost, hassle and weight wise) to do that or to just stick to the 6LR8. I'm thinking multiple power transformers (whether permanent or swappable) is probably going against the small and simple aspects of the amp, which is one of the things that I really like about it. That decision will be left until later down the track.

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Originally Posted by tubelab.com View Post
I have bought some tubes from them over the years. As with any vendor cleaning out their stock for cheap, expect some old boxes in good to fair condition and a few dead tubes. I did buy 1000 tubes from them about a month ago when the cheap tubes sale started. They looked OK, but I haven't had the time
Thanks.

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I got 500 tubes for $0.35 each. Where do you find tubes for $0.25 other than a hamfest?
Sorry, that was a typo, meant to say $0.75 a tube. Would be the same list you were looking at I believe (10+ @ $0.75 each, 100+ @ $0.50 each, 500+ @ $0.35 each)

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Originally Posted by tubelab.com View Post
I'll know for sure when I breadboard it up. It also depends on how hard you push the tubes. If you want a guess, I will assume class AB1 and say 8 to 10 watts with the 6GF7, 15 to 20 with the 6KY8, and maybe 25 to 30 with the 6LR8. More might be available in AB2 but that really complicates things with mosfets and negative voltages.
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So, 10W plus is gravy if I were to go the P-P.
My thoughts exactly. Especially if it looks even in the ballpark of 25 watts for 6LR8's in PP, that's more than enough for my needs. Also, for the sake of keeping the circuit a little simpler, I don't think going to AB2 is really necessary.
Besides, I'd be more than happy with the 5ish watts of the original SE design.
But I guess a lot of this comes down to long term interest in the design. Regardless of what I'm looking for from the amp, if moving toward a few more watts would be enough to get more people interested in the PCB's, then why not?
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Old 31st May 2012, 06:02 PM   #85
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I know I have a few flavors of the LR8 variety in a box some place
I will probably use a simple zener diode and mosfet regulator since it is universally available, and I have managed to blow the LR8 when used as a screen regulator. Granted I was playing my guitar through the amp, but I test all my amps with a guitar preamp since it is a worst case test...and I use the SSE and likely this board as a guitar amp.

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Would be the same list you were looking at I believe
Yes. I got 100 25DN6's for a 50 watt sweep tube amp. 500 6HB6's for some new low cost projects, and 100 of each of the tubes that go in a little cheap guitar amp I made for the $100 amp challenge. The 6HB6's were a wide variety of brands, some in pretty worn boxes, but they were 35 cents. A few of the 25DN6's were old and in worn boxes. All of the other stuff looked good.

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I don't think going to AB2 is really necessary.
It isn't going to happen here. The idea here is for a cheap low cost amp. I should have some time tonight to fire up the 5 year old board and see what smokes. Then it's time to hack it up and see what I can make out of it.

I notified out warehouse landlord to apply our previously paid last months rent to June, so the clock is now ticking.....I have 30 days to get everything out.....This means I will be rather busy this month, leaving little time for tinkering.
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Old 31st May 2012, 08:46 PM   #86
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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?
I'm living in Tampa right now, I retire from my current job today and will be getting another one soon, so I'll end up either staying here in Tampa or moving to Dayton. About a 50% chance of either right now.
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Old 1st June 2012, 02:45 AM   #87
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I fired up the board after its 5 year sleep. It is still alive and works about the same as it did then. No testing was done with the 6GF7 since I don't have any left. Got to empty the warehouse, can't keep them all.

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Question: what kind of power output would you be looking at in Push-Pull configuration?
I wired the board up to regulated supplies for plate and screen and used a transformer as a phase inverter. My power output guestimates were pretty close. A screen regulator is needed for pentode operation. Otherwise too much negative bias is needed to keep the current down to a reasonable value.

The 6KY8A makes just over 20 watts when biased to the edge of dim redness in a totally dark room. 15 watts is probably a good number. B+ was 300 volts. Screen was 150 volts.

The 6LR8 hit 32 watts under the same conditions. B+ was 350 volts. Screen was 150 volts. They should be fine at 20 to 25 watts.

The 6KY8 is much smaller than the 6LR8 but the plate dissipation ratings are not too different. The 6LR8 requires much more drive than the 6KY8 and once I convert the input stages over to an LTP PI there might not be enough gain for full power from a CD player. I'll know more once I try it. Don't know when though.
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Old 1st June 2012, 04:50 AM   #88
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I don't know - I would bypass all this socket brouhaha and use chassis-mounted sockets that would take some abuse - the board would be mounted via spacers somewhat below the sockets with most of the components pointed down - the most sane arrangement, and I would string wires up from the PCB to the sockets. With the right arrangement of holes on the PCB, it wouldn't matter if you used a XLU8 or an XLR8, as long as there's some sort of table that tells one how to wire a socket for a particular tube to the board.
Stan has some XXLU8/LR8 tubes in his dollar list ( I forget which), so this approach could work. I don't usually buy kits/boards anyway, so I'm just mouthing off here...
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Old 1st June 2012, 12:19 PM   #89
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Originally Posted by tubelab.com View Post
I wired the board up to regulated supplies for plate and screen and used a transformer as a phase inverter. My power output guestimates were pretty close. A screen regulator is needed for pentode operation. Otherwise too much negative bias is needed to keep the current down to a reasonable value.
OK...so triode and UL; great. Looking over the SimplePP schematic from another thread leads to a question about a SpudPP. Do you foresee the phase inverter tranny for Push-Pull operation OR will the SpudPP schematic look fundamentally the same as the SimplePP?

I would guess the latter case...but I suck at multiple choice exams.
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The 6KY8A makes just over 20 watts when biased to the edge of dim redness in a totally dark room. 15 watts is probably a good number. B+ was 300 volts. Screen was 150 volts.

The 6LR8 hit 32 watts under the same conditions. B+ was 350 volts. Screen was 150 volts. They should be fine at 20 to 25 watts.

The 6KY8 is much smaller than the 6LR8 but the plate dissipation ratings are not too different. The 6LR8 requires much more drive than the 6KY8 and once I convert the input stages over to an LTP PI there might not be enough gain for full power from a CD player. I'll know more once I try it. Don't know when though.
The power output ratings are quite encouraging. For anyone with efficient full-range, single driver speakers or two-ways, 20W should blow away even a medium sized room.
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I don't know - I would bypass all this socket brouhaha...
I tried a FreePCB layout to make a 3cm by 3cm adapter board that would hold the Duodecar socket and adapt it to the Novar. Alas, the pin circles are a bit too close to allow a circle within a circle that would avoid chassis mod and only require dropping the PCB down a few millimeters to drop in the adapter board. For any fans of the Wankel engine, I have noted that adopting a cardioid shape like the Wankel combustion chamber (i.e. two intersecting circles) with pins 4,5 on the Novar close to pins 1,12 on the Duodecar might just work. With Fenris' board service, you could procure 10 such adapter boards for $10, which would be nice and open the Tubelab Spud to the compactron twin of the 6LR8, depending on supply in your market. Even though I am spatially challenged, I will keep plugging away at that one. Keystone makes 0.040" round profile micropins that can be swaged into a board (no solder types I've seen). This could work...stay tuned.
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...and use chassis-mounted sockets that would take some abuse - the board would be mounted via spacers somewhat below the sockets...I don't usually buy kits/boards anyway...
From my perspective, a board addresses some of the things a novice like me would likely miss (stray signals intermingling, wire size, component placement issues, etc.) in a point-to-point layout. Knowing Tubelab would produce a design that has been prototyped, tweaked and generally ridden hard and put away wet before it's ever up for sale is a real bonus. This will reduce the chance for a loss of enthusiasm after the build by increasing the likelihood of success for DIY'ers.

And hey, with the current exchange rates US$ to CDN$, even though Canada just stopped minting pennies, at least my Maple Leaf 2 cents is about the same as two Lincoln's.
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Old 1st June 2012, 12:48 PM   #90
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I would guess the latter case...but I suck at multiple choice exams.
E) None of the above.

In order to maintain electrical compatibility with the dual SE option a single driver stage must remain connected to each output stage. There is exactly one way to do this. Currently there is a resistor and a capacitor to ground on the cathode of each input tube. You add a jumper so that the two cathodes can be tied together, then add a CCS to ground. This creates an LTP. For the SE version you place the R's and C's (or LED's) and leave out the CCS and jumper. For the P-P version you install the CCS and jumper, leave out the R's and C's. This also requires a capacitor in series with the input, which is replaced with a jumper in the SE version.

I have modified SSE boards in this manner to achieve 60+ watts, but it requires a bit more work since the CCS plate loads must be removed.

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I don't know - I would bypass all this socket brouhaha and use chassis-mounted sockets that would take some abuse
If I wanted to use chassis mounted sockets, then I would just PTP wire the entire amp. The circuit is pretty simple.

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a board addresses some of the things a novice like me would likely miss
That is really the only reason for doing this board. There have been several people succesfully build an SSE using PTP wiring from my schematic. There have been a few PTP SSE builds that didn't work including one guy in England who got rather annoyed when I couldn't help him fix the hum in an amp I didn't build, can not see, and had no clue how he laid it out or wired it.

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Keystone makes 0.040" round profile micropins that can be swaged into a board (no solder types I've seen).
I have made adapters before. You want pins that have to be staked into the board. If you rely on solder alone, the joint will eventually get brittle and go intermittent with repeated use.
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