I have a "true Mono" system in my office/parlor (Denon DL-102 cart > PhonoDude preamp) which uses a mono-block TubeLab Simple 45 rigged as a "flex-amp".
It uses a Heathkit IP-32 power supply, Fixed Bias, and a Pete Millett adjustable DC filament supply (w/ a nice Bourns 10-turn pot on top) and both 4 and 5 pin sockets, so I can easy switch between 45/46/2A3/300B tubes, as well as Tiny Triodes like 71A. The OPT connects to a Euro terminal block, so it can be switched-out quite easily.
Hydrostatic Pressure has been applied by the Chief Cook & Bottle Washer (CC&BW) to "get rid of those wires", as we have 3 toddler grandchildren (#4 coming soon), one of whom is an 18 mo old Daredevil.
Plus, it would be nice to have stereo available, even if we've well established that it's a SCAM.
The circuit is the last revision of the Simple 45, just before the 2SK2700 MOSFET was added to the power tube grid on the TubeLab SE. See the attachments.
The best OPT I've tried is the big EDCOR 25W 5K:8ohm (CSXE25-5K). It's pretty massive, but has a REALLY nice bottom end. My speakers are very efficient, so I'm not scraping the bottom of the barrel for that last watt.
I found the 45/Tiny Triode version superb, but just a little too "precious" for my tastes. This would be an excellent choice if I was listening to the proverbial "girl with a guitar" all the time. But, no.
The 46 was WAY better than I expected (esp. at borderline high Vp and dissipation) but was not quite a 45, and still too precious.
The 2A3 was, uh, just disappointing, like every 2A3 amp I've build.
For example, my TubeLab SSE with 6AV5s just blows away every 2A3 circuit I've built, across the board, and still only costs $7/tube.
If anybody knows how to make a 2A3 sound good, let me know.
HOWEVER, the 300B in this circuit was a revelation. Just Like Buttah, but "sturdy" at the same time. I suddenly realized that I've been chasing cheaper alternatives for a decade or two, but ended-up spending many more $$ than if I had bit the 300B bullet earlier.
So 300B it is.
Questions:
(a) my circuit uses 0.22 uF coupling caps (Russian PIOs) and NO MOSFET. Sounds terrific.
But I'm thinking I should make provisions to add-in the MOSFET (and change coupling cap of course). Y'all's thoughts on that?
(b) I am using an Electro Harmonix 300B, and running it pretty conservatively (400 V on the plate, -75V bias, about 75mA). Y'all's thoughts on this particular 300B and these operating points?
(c) IIRC, there's a 10 Ohm resistor/fuse on the 300B cathode. is this adequate run-away protection?
(d) I have a small cache of 5842s (and will probably scrounge some more), but I am leaving room for an octal socket just in case...y'all's thoughts?
The one time I tried the CCS on top of an octal tube (a 6SL7 into 6AV5s) it was really nice...I mean REALLY NICE.
(e) Simulated the power supply using the little Allied PST (6K56VG) which is 540VCT at 120mA. Using tube rectifier into a Heathkit potted chokes (10H, about 175 ohms) and a couple of RC stages after. Probably will use an indirect-heated rectifier tube for slower B+.
(f) For Bias supply, contemplating
(1) pulling off a PST HV (~270VAC)
(2) using a "back-bias" circuit, as shown for example in AikenAmps
What is Back-Biasing? -or-
(3) just adding a small bias transformer (I have room since there's no 5V fils transformer) and rectifier/volt divider circuit.
Any thoughts? I'm afraid that I've been spoiled by the IP-32 power supply.
(g) I always use star-grounding to one of the PST bolts (insuring electrical contact to the PST frame)...comments?
PS the Hammond chassis for the Nasty/Big Pete Millett Regulated Power Supply just arrived, so it'll be a minute before I start on the 300B project...
It uses a Heathkit IP-32 power supply, Fixed Bias, and a Pete Millett adjustable DC filament supply (w/ a nice Bourns 10-turn pot on top) and both 4 and 5 pin sockets, so I can easy switch between 45/46/2A3/300B tubes, as well as Tiny Triodes like 71A. The OPT connects to a Euro terminal block, so it can be switched-out quite easily.
Hydrostatic Pressure has been applied by the Chief Cook & Bottle Washer (CC&BW) to "get rid of those wires", as we have 3 toddler grandchildren (#4 coming soon), one of whom is an 18 mo old Daredevil.
Plus, it would be nice to have stereo available, even if we've well established that it's a SCAM.
The circuit is the last revision of the Simple 45, just before the 2SK2700 MOSFET was added to the power tube grid on the TubeLab SE. See the attachments.
The best OPT I've tried is the big EDCOR 25W 5K:8ohm (CSXE25-5K). It's pretty massive, but has a REALLY nice bottom end. My speakers are very efficient, so I'm not scraping the bottom of the barrel for that last watt.
I found the 45/Tiny Triode version superb, but just a little too "precious" for my tastes. This would be an excellent choice if I was listening to the proverbial "girl with a guitar" all the time. But, no.
The 46 was WAY better than I expected (esp. at borderline high Vp and dissipation) but was not quite a 45, and still too precious.
The 2A3 was, uh, just disappointing, like every 2A3 amp I've build.
For example, my TubeLab SSE with 6AV5s just blows away every 2A3 circuit I've built, across the board, and still only costs $7/tube.
If anybody knows how to make a 2A3 sound good, let me know.
HOWEVER, the 300B in this circuit was a revelation. Just Like Buttah, but "sturdy" at the same time. I suddenly realized that I've been chasing cheaper alternatives for a decade or two, but ended-up spending many more $$ than if I had bit the 300B bullet earlier.
So 300B it is.
Questions:
(a) my circuit uses 0.22 uF coupling caps (Russian PIOs) and NO MOSFET. Sounds terrific.
But I'm thinking I should make provisions to add-in the MOSFET (and change coupling cap of course). Y'all's thoughts on that?
(b) I am using an Electro Harmonix 300B, and running it pretty conservatively (400 V on the plate, -75V bias, about 75mA). Y'all's thoughts on this particular 300B and these operating points?
(c) IIRC, there's a 10 Ohm resistor/fuse on the 300B cathode. is this adequate run-away protection?
(d) I have a small cache of 5842s (and will probably scrounge some more), but I am leaving room for an octal socket just in case...y'all's thoughts?
The one time I tried the CCS on top of an octal tube (a 6SL7 into 6AV5s) it was really nice...I mean REALLY NICE.
(e) Simulated the power supply using the little Allied PST (6K56VG) which is 540VCT at 120mA. Using tube rectifier into a Heathkit potted chokes (10H, about 175 ohms) and a couple of RC stages after. Probably will use an indirect-heated rectifier tube for slower B+.
(f) For Bias supply, contemplating
(1) pulling off a PST HV (~270VAC)
(2) using a "back-bias" circuit, as shown for example in AikenAmps
What is Back-Biasing? -or-
(3) just adding a small bias transformer (I have room since there's no 5V fils transformer) and rectifier/volt divider circuit.
Any thoughts? I'm afraid that I've been spoiled by the IP-32 power supply.
(g) I always use star-grounding to one of the PST bolts (insuring electrical contact to the PST frame)...comments?
PS the Hammond chassis for the Nasty/Big Pete Millett Regulated Power Supply just arrived, so it'll be a minute before I start on the 300B project...
Attachments
Another thing...
How about ~constant current biasing on the driver?
I've previously used NiMH batteries (with and without fine-tuning "helper resistors) on 12**7s and 6**7s to good effect.
Others have built circuit VERY similar to the Simple 45 using LED bias on the driver; see Post #50 in this thread: https://www.diyaudio.com/forums/tub...-schematic-recommendations-5.html#post5852504
I haven't used LED cathode loading, but I've seen lots of discussion about "harshness", whatever that means.
How about ~constant current biasing on the driver?
I've previously used NiMH batteries (with and without fine-tuning "helper resistors) on 12**7s and 6**7s to good effect.
Others have built circuit VERY similar to the Simple 45 using LED bias on the driver; see Post #50 in this thread: https://www.diyaudio.com/forums/tub...-schematic-recommendations-5.html#post5852504
I haven't used LED cathode loading, but I've seen lots of discussion about "harshness", whatever that means.
If I keep talking to myself, I’m gonna need a Social Worker
Continued study answered A couple of my questions:
Re: constant current biasing of 5842
TubeLab George earlier wrote:
“ I set the current source to 12 mA (with a current meter connected in place of the 5842, plate to cathode). Then I set the plate voltage (with the 5842 installed) to 175 volts by adjusting the cathode resistor. My batch of 5842's seems to have a wide variation from tube to tube, so the cathode voltage will wind up anywhere from 1.75 to 2.5 volts. This unfortunately rules out LED bias without trying a lot of LEDs.”
Re: Bias circuit
The now-defunct TubeLab SE bias circuit looks straightforward enuf, and half-wave rectified to boot...
Continued study answered A couple of my questions:
Re: constant current biasing of 5842
TubeLab George earlier wrote:
“ I set the current source to 12 mA (with a current meter connected in place of the 5842, plate to cathode). Then I set the plate voltage (with the 5842 installed) to 175 volts by adjusting the cathode resistor. My batch of 5842's seems to have a wide variation from tube to tube, so the cathode voltage will wind up anywhere from 1.75 to 2.5 volts. This unfortunately rules out LED bias without trying a lot of LEDs.”
Re: Bias circuit
The now-defunct TubeLab SE bias circuit looks straightforward enuf, and half-wave rectified to boot...