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Old 10th February 2009, 01:34 AM   #21
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korneluk's Avatar
Join Date: Jan 2005
Location: South Florida
Originally posted by sorenj07
Got the thing running. It's funny, absolutely black background, no hum, buzz or noise or ANYTHING. It freaked me out at first. Lucky eh? Makes for a very nice amp for my college dorm room. Sound gets as loud as I generally need with 88dB speakers...
What op points did you end up using? What is the plate current?


-- josť k.
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Old 10th February 2009, 02:33 AM   #22
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Join Date: Jul 2005
Location: West Virginia panhandle
Hi Tube Lab I in the proses of building PSE Amp with xxxx Tube was thinking D3a Driver-Inter-stage TX to Output Tube
Output TX 50% UL running the Amp 290 Volts 60mA by the way i Run the same Configuration with 300B sounds Excellent WAT YOU THINK
From what I have read the D3A and a driver transformer can be a good combination, but I can't say much from experience. The D3A is rare in the US, and I have never used them. I bought a pair from a seller in Germany, but haven't powered them up yet. I also do not use driver transformers in my designs. Not because you can't get a good one, but because you can't get a good one at a low cost. The D3A costs $15 to $20 each in the US, a good driver transformer much more. These may make sense with a 300B or other expensive tube, but the 6AV5 can still be found in the US for $3 or $4. I try to use the same cost structure for all the components in an amplifier.

Has anyone tried running this unnamed tube in pentode with partial feedback ala the RH807? Just curious....
I haven't, yet.

That's a nice looking tube (and amp). Checking out the datasheet for that ****, indicate a linear screen drive. Mmmm, future project idea.
Oh, yeah. I did a quick test amp a few years ago and got over 80 watts from a pair of the crummy slotted RCA's. I will have much more on this subject when my driver board is finished. Its at least 2 weeks away.

I have about 2 dozen 12AV7s and clones, and I expect that would work well with the CCS
I only have a few 12AV7's but I have a bunch of 5965, which is similar. My screen driven amp used the 5965, but it was resistively loaded. The new driver board can do resistor or CCS load. Both will get tested with a bunch of different tubes.

some Mullard 5751s, if I had to choose
Got 3 of those too.
Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
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Old 10th February 2009, 04:28 AM   #23
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Join Date: May 2006
Location: Berlin
Originally posted by korneluk

What op points did you end up using? What is the plate current?


-- josť k.
Plate current is ideally 63mA with a B+ of 320V or so. Bias is at 50V with an 800 ohm 10W cathode resistor. I'm expecting around 260V plate to cathode, when counting in OPT primary resistance.

I don't know what these specific variables have to do with the sound, though. It just looked like a nice operating point with the curves I could find.
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Old 11th February 2009, 04:56 AM   #24
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Join Date: Oct 2008
SorenJ: I'll post a pencil-whipped schema and some photos this weekend. Promise not to blanch[ this is about the 7th amp on this "chassis", which is a recycled Porter Cable power tool box.

Meantime I just bought a couple of Heathkit power supplies that need a laying-on of hands. Well, OK, they themselves could care less, but I need to open them up and look around in there. Nothing serious, it's JUST EXPLORATORY. Perhaps a Cap-ectomy?

After about 100 hours on The Tubes We Dare Not Name in a couple of different 2A3 er, 6B4G circuits, I finally got religion and did the Tubelab Glow Check with ALL the lights out in the shop.

Remember, I'm running The Tubes at a dissipation very close to Soren's, that is about 19.6W dissipation (in my case about 305 V plate and 65mA). Previously I hadn't seen anything out of the ordinary. This time, in pitch darkness, THAR SHE BLOWS so to speak: one thin (say 1/8" wide) red glowing line at ONE inside corner of the plates on each tube. I assume this is G2 under there?

At this op point, there's ~310V across the screen from the UL tap, which is a LITTLE higher than the data sheet recommends (somthing under 200V IIRC).

I have NO idea how to calculate the screen dissipation on a uL connection. Do I need a DCR number between the uL tap and the plate end of the OPT? I have no clue. In any case, I'm guessing I'm way over the data sheet value there too.

Nevertheless, my PLAN is NOT to change the op point, as The Tubes sound so good here (and cost $3 each), but instead I think I'll look around for a cheap surplus 120V hour meter and put it into a utility box with a plug, and see how many hours I get out of these tubes at this op point. This is my preferred shop amp, so I put 30-40 hours on it most weeks. I know, I should get out more.

Anybody care to pick an Over-Under? Let the bidding start at 1000 hours.

PS I just WAY over-paid for a pair of NOS 6BQ6GA Sylvanias ($2.50 each). Let that be a lesson to y'all; a little loose chatter and the price of these tubes has gone up 250% in a little over a month!
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Old 13th February 2009, 06:38 AM   #25
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Default The Nameless Tube w/6SL7WGB driver

Here's the schematic for the my cobbled-together 6**5GA amp with the 6SL7WGB driver with IXYS CCS on the plate and Lithium AA cells on the cathodes.

I've been looking at the Sylvania 6SL7WGBs on eBay the last couple of days, and I think the driver tube is the single most valuable part of this amp (including the OPTs(!)). I guess that makes it the Casting Pearls Before Swine amp.

I'll post of photo of the Underbelly in a separate post.

In another note, my "new" Heathkit !P-32 power supply had a pair of excellent branded Daystrom "by GE" 6L6GCs in it, so I ripped them out and plunked them into one of my Simple SEs, where they sound EXCELLENT. Even the Wifely Unit complimented the "new sound".

I replaced the GEs with a pair of new JJ 6L6GCs, but I was wondering whether I can use "straight" 6L6s as specified on the schematic, as opposed to the 6L6GCs that came with (and are in all the other ones I've seen). Did Heathkit make a boo-boo on the schema, or maybe change the tubes to GCs when the 6L6s didn't last?

I measured the plate voltage directly at >600V (that is, the potential between plate and cathode pins) with NO current, which falls to about 176V at 400 volt supply voltage. These op points look dubious for a straight 6L6 to me.

I was thinking that this would be a good application (READ: excuse to buy) some of those coin-base Russkie 6P3S-E tubies, hope I got that number right, you know the ones they advertise on eBay as being equivalent to 6L6GBs, 5881s, 6L6GCs, and a '59 Cadillac Coupe DeVille. I see reports from GEE-Tar folks that they can be pushed to 600V plate. Opinions?
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Old 13th February 2009, 06:38 AM   #26
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Join Date: Oct 2008
Default 6**5 SE Amp Underbelly

Here's a look at the underside of the 6SL7WGB driver for the Nameless Tube SE Amp, showing the AA cell holder and the CCS board nailed up in the corner (actually on a 1/2" standoff).

Note the green Russian Paper-In-Oil caps; these have great bang-for the buck; I've used about 20 so far without any duds. Ordered a bunch more, so we'll see if the quality holds up. I haven't done a head-to-head comparison with Auricaps or Jensens, but for about $1 each in quantity, including shipping, I think these are definitely a screaming bargain. Provided of course I don't run into a bad batch.

The "chassis" is an old Porter Cable toolbox lid which has hosted a lot of amps. The white bit is sign-makers aluminum sheet (22 gauge, I think) painted both sides. I just cut a rectangle of the sign material, punch holes in it, and bolt it over the opening in the "chassis".

More-or-less an intermediate step between clip-lead spaghetti and a bona-fide high WAF job. Note that most of the wires have crooks in the ends and are tacked in place for easy rearrangement. The AA cells have resistors on the negative end which I was using to raise the bias voltage to around 2.0V; I tacked jumpers around them when I decided I liked the sound better at around 1.75V

I have had TWO noisy lithium cells that wouldn't quiet down after a charge, which I attribute to old age (I found them lying around, they're probably at least 3-4 years old). By contrast, I've used all manner of NiCad AA cells without a single noisy one. Cheapest NiCads I've found are at Harbor Freight on sale for about $1 each.

I need to do further research on Lithium cells to see what might be causing this scratchy noise.
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