Using a sweet tube that I'd really rather not make any more famous than it is. It's the square plate version made by GE, supposedly the most rugged and able to take well over 18-20W. I have all the parts except for the OPT's, which will come any day now. No boutique parts, but low-impedance Nichicon etc.
Here are the schematics. I should note that the OPT's I'm using are Edcor GXSE15-16-8K's run as 4K:8, which have a tap for ultra-linear.
What do you guys think?
I am open to the possibility of using a noval pentode or something in the place of the SRPP, maybe in E-linear a la PakProtector
Here are the schematics. I should note that the OPT's I'm using are Edcor GXSE15-16-8K's run as 4K:8, which have a tap for ultra-linear.
What do you guys think?
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I am open to the possibility of using a noval pentode or something in the place of the SRPP, maybe in E-linear a la PakProtector
Really? How do you figure? I'm getting a gain of 36 with the 5965 SRPP, and the output tubes are biased at -50V, so that means I need almost 1.4V to max them out. Seems like I'm cutting it a bit close as it stands...
I'm interested in the pentode driver option though. Could you possibly link me to an example of a schematic where they implement something like that?
I'm interested in the pentode driver option though. Could you possibly link me to an example of a schematic where they implement something like that?
Most everyone knows what I think about the **** (number withheld to protect the currently reasonable price), although I believe the must rugged of the breed are the Sylvania's (no glow at 25 watts). I was driving them with a CCS loaded 5842 buffered by a mosfet follower (PowerDrive) which gives a gain of about 40 (hacked Tubelab SE board). This is just barely enough, although I was running the **** a bit hotter which required a higher bias voltage allowing more drive. These tubes respond well to cathode feedback especially with the Edcor OPT's.
I have found some GE 6BQ6GA's that have the same guts inside them. They behave the same way as the **** except for the plate cap and pinout. The pinout is the same as the 6L6 except for the plate cap, so they can be stuffed into a 6L6 circuit with some serious rebiasing and a plate cap wired to pin 3. I put some of the AES 98 cent tubes into a Simple SE board which uses a CCS loaded 1/2 of a 12AT7 for a driver and cathode bias for the output tube. Plenty of gain, sounds great, 98 cents for the output tubes! Not all GE 6BQ6GA's have **** guts inside though.
I have found some GE 6BQ6GA's that have the same guts inside them. They behave the same way as the **** except for the plate cap and pinout. The pinout is the same as the 6L6 except for the plate cap, so they can be stuffed into a 6L6 circuit with some serious rebiasing and a plate cap wired to pin 3. I put some of the AES 98 cent tubes into a Simple SE board which uses a CCS loaded 1/2 of a 12AT7 for a driver and cathode bias for the output tube. Plenty of gain, sounds great, 98 cents for the output tubes! Not all GE 6BQ6GA's have **** guts inside though.
The datasheet mentions this pesky screen grid maximum rating of 175 volts. If we believed in datasheets these tubes would never work in triode or UL. Every tube that I tried will work to 275 volts and some will go to 350. When cranked this hard, you need lots of negative bias, and therefore lots of drive.
When you are misapplying a tube, you just "crank them up till they glow, then back up a little". Some serious experimenting is often required to find the sweet spot. Many tubes don't like it, but some do. My favorite sweep tube has a max screen rating of 275 volts and a plate dissipation rating of 40 watts. The right ones will work just fine at 450+ volts and 90+ watts in triode mode. Need about 100 volts of bias and a big bunch of drive though.
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...
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Hi your SET AMP looks very nice well done.
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
Thanks
Rudi
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
Thanks
Rudi
6**5GA [the tube we dare not speak its number] SE with 6SL7s
Inspired by George aka tubelab I have been hacking around with the tube that shall remain nameless, trying different operating points & drivers, naturally searching for Nameless Tube Nirvana.
I am using Edcor 5K:8 OPTS, always wired ultralinear.
I seem to have settled on a "slightly hot" operating point, with B+ around 360-370V with bypassed cathode resistors of about 920 ohms. This gives about 59-60V at the cathode, for about 65 mA plate current and 19.6 watts plate dissipation. My Nameless Tubes are Sylvanias, and they don't show any signs of distress here at all.
I like SorenJ07's 12AV7 SRPP implementation (esp all them Henries in the P/S; that's heavy iron after my own heart), but I wanted to try the IXYS CCS chip.
I have about 2 dozen 12AV7s and clones, and I expect that would work well with the CCS (sort of a sand variation on the Soren SRPP), but the tube that fell to hand was an old 6SL7WGB.
The 6sl7 chart revealed what appeared to be a VERY linear area around 2mA and -2.0V grid. (It turns out that Horizontal Load Lines are really easy to eye-ball!) Wasn't sure that the IXYS chip would work well at such a low current, but it looked worth a try.
I "biased" the chip with 1.8K (with the 1K "snubber" that George recommends), and used LITHIUM AA cells for battery bias.
Dropped the B+ to around 250V to feed the CCS and let her rip.
I had never used Lithium cells before, and the ones I used were NOT fully charged; figured I would let the bias current do the charging for me. HOWEVER, while charging they sounded like they were "leaking" (scratchy, like a loose connection). Neither NiMH nor NiCad cells do that. For a second I thought I had made a huge mistake, but after ~15 minutes they cleaned-up completely.
Without getting too hyperbolic about it, this set-up works great.
Plate current is a little higher than I wanted (2.15 and 2.13 mA measured at the pins, with the tube out), and the Lithium cells bias up right about 1.73V...If I do it again, I may use a slightly higher value to bias the CCS chip, say 1900 or 2K ohm.
Obviously, the 6SL7 is pretty darned linear to begin with, but now there's PLENTY of driver gain (the chart says a real 70, although i haven't measured) and between constant current on the plate and ~constant voltage on the cathode, this thing is EXTRA clean.
I'm not sure about "the octal sound" that some DHT folks talk about (psychoacoustics?), but this foundling 6SL7 in this circuit is at least as clean and open as the best of my 9 pins (some Mullard 5751s, if I had to choose).
I'm using the Tubelab local bypass cap (1500uF, IIRC) on the Nameless tube, and on some pieces (e.g. Folsom Prison Blues), I think I need to pad it down with a pot as the bass is overwhelming. Great stuff. Easy, simple, cheap. I'm going to have to replicate this one on a "keeper" (aka High WAF) chassis.
I'll post photos and a schema if there's any interest.
hareynolds
Inspired by George aka tubelab I have been hacking around with the tube that shall remain nameless, trying different operating points & drivers, naturally searching for Nameless Tube Nirvana.
I am using Edcor 5K:8 OPTS, always wired ultralinear.
I seem to have settled on a "slightly hot" operating point, with B+ around 360-370V with bypassed cathode resistors of about 920 ohms. This gives about 59-60V at the cathode, for about 65 mA plate current and 19.6 watts plate dissipation. My Nameless Tubes are Sylvanias, and they don't show any signs of distress here at all.
I like SorenJ07's 12AV7 SRPP implementation (esp all them Henries in the P/S; that's heavy iron after my own heart), but I wanted to try the IXYS CCS chip.
I have about 2 dozen 12AV7s and clones, and I expect that would work well with the CCS (sort of a sand variation on the Soren SRPP), but the tube that fell to hand was an old 6SL7WGB.
The 6sl7 chart revealed what appeared to be a VERY linear area around 2mA and -2.0V grid. (It turns out that Horizontal Load Lines are really easy to eye-ball!) Wasn't sure that the IXYS chip would work well at such a low current, but it looked worth a try.
I "biased" the chip with 1.8K (with the 1K "snubber" that George recommends), and used LITHIUM AA cells for battery bias.
Dropped the B+ to around 250V to feed the CCS and let her rip.
I had never used Lithium cells before, and the ones I used were NOT fully charged; figured I would let the bias current do the charging for me. HOWEVER, while charging they sounded like they were "leaking" (scratchy, like a loose connection). Neither NiMH nor NiCad cells do that. For a second I thought I had made a huge mistake, but after ~15 minutes they cleaned-up completely.
Without getting too hyperbolic about it, this set-up works great.
Plate current is a little higher than I wanted (2.15 and 2.13 mA measured at the pins, with the tube out), and the Lithium cells bias up right about 1.73V...If I do it again, I may use a slightly higher value to bias the CCS chip, say 1900 or 2K ohm.
Obviously, the 6SL7 is pretty darned linear to begin with, but now there's PLENTY of driver gain (the chart says a real 70, although i haven't measured) and between constant current on the plate and ~constant voltage on the cathode, this thing is EXTRA clean.
I'm not sure about "the octal sound" that some DHT folks talk about (psychoacoustics?), but this foundling 6SL7 in this circuit is at least as clean and open as the best of my 9 pins (some Mullard 5751s, if I had to choose).
I'm using the Tubelab local bypass cap (1500uF, IIRC) on the Nameless tube, and on some pieces (e.g. Folsom Prison Blues), I think I need to pad it down with a pot as the bass is overwhelming. Great stuff. Easy, simple, cheap. I'm going to have to replicate this one on a "keeper" (aka High WAF) chassis.
I'll post photos and a schema if there's any interest.
hareynolds
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