Toroids are fantastic for the power supply, or for push pull, but not for SE unless you use specific versions constructed for the use. For SE traditional types still present the best options.
Unless, you could to do a push pull triode connected version of the EL86, toroids will work well there. It isn't traditional, however, so you may want to do some testing there before you commit. You'll get an easy 5~8 watts there depending on your selection of voltages and operating points.
Sure Doug, as soon as I'll have anything to show I'll post it here.
Here is the sketch for that crazy idea with stepper motor which lifts the board with tubes:
I mean the stepper motor with lead screw similar to this:
Amazon.com: Iverntech NEMA 17 Stepper Motor with Integrated 210mm T8 Lead Screw for RepRap Prusa i3 3D Printers Z Axis or CNC Machine: Industrial & Scientific
Here is the sketch for that crazy idea with stepper motor which lifts the board with tubes:
I mean the stepper motor with lead screw similar to this:
Amazon.com: Iverntech NEMA 17 Stepper Motor with Integrated 210mm T8 Lead Screw for RepRap Prusa i3 3D Printers Z Axis or CNC Machine: Industrial & Scientific
The 12AX7 section into "12" W. O/P tube is the sort of thing found in low cost console amps. With the right parts, that sort of setup can be both "boombox" or HIFI, at your whim. Plug the right (high efficiency) good speakers in and your listening room is filled with 1st class sound.
Quite a bit can be "borrowed" from the Magnavox schematic I'm providing. "Maggotbox" used ultra-linear (UL) mode O/P tubes. We will use full pentode mode, for both technical and cosmetic reasons. Our power supply will be SS rectified, for reasons of cost and space. BTW, 6BQ5 = EL84.
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I have tried to summarize my understanding of two suggested amplifiers.
The listed pros and cons of those amps are just for my particular project.
pcan - Spud Amplifier with 6E5P Tube
Pros: very simple - only one tube (6E5P) per channel, only 4 resistors and 1 capacitor per channel, only one voltage for output stage (200V). The tube has nice glowing.
Cons: low wattage (about 1W). Large output transformers.
Price:
The tube 6E5P is about $5 on eBay
Output transformers ?
Power supply transformer ?
Total: ?
Eli Duttman - Magnavox type amp
Pros: only 2 tubes per channel. Small number of passive components - 7 resistors, 2 capacirtors per channel. Good wattage ~5W ?
Cons: requires two different voltages for two amplification stages (180V, 200V). That may need more complicated power supply/transformer.
Price:
The first amp stage (12AX7) is about $10 per tube on eBay
The output tube (6BQ5/EL84) is also about $10 on eBay
Output transformer (GXSE15-5K ?) is $43
Total: 10*2 + 10*2 + 43*2 = $106 + ?(power supply can be probably borrowed from Spud Amp if it's possible to use only 200V)
Right now I'm biased toward the Spud amp because of its simplicity.
I just need to clarify the cost of transformers.
The listed pros and cons of those amps are just for my particular project.
pcan - Spud Amplifier with 6E5P Tube
Pros: very simple - only one tube (6E5P) per channel, only 4 resistors and 1 capacitor per channel, only one voltage for output stage (200V). The tube has nice glowing.
Cons: low wattage (about 1W). Large output transformers.
Price:
The tube 6E5P is about $5 on eBay
Output transformers ?
Power supply transformer ?
Total: ?
Eli Duttman - Magnavox type amp
Pros: only 2 tubes per channel. Small number of passive components - 7 resistors, 2 capacirtors per channel. Good wattage ~5W ?
Cons: requires two different voltages for two amplification stages (180V, 200V). That may need more complicated power supply/transformer.
Price:
The first amp stage (12AX7) is about $10 per tube on eBay
The output tube (6BQ5/EL84) is also about $10 on eBay
Output transformer (GXSE15-5K ?) is $43
Total: 10*2 + 10*2 + 43*2 = $106 + ?(power supply can be probably borrowed from Spud Amp if it's possible to use only 200V)
Right now I'm biased toward the Spud amp because of its simplicity.
I just need to clarify the cost of transformers.
One thing you might consider with your stepper drive is that I've found some stepper drivers to be extremely noisy devices. Tube amplifiers are a high impedance circuit, so this could potentially cause some noise problems. I wouldn't let this discourage me from implementing it (it would make the whole project significantly cooler), but be aware that it could potentially be problematic.
My vote is for the Magnavox type amp- 1 watt is very small. Those would have to be crazy efficient speakers to get a reasonable SPL out of it.
No need to worry about the two voltages- one extra resistor and capacitor in the power supply and you're good to go.
If you're worried about the cost of the 6BQ5 tubes, the 6AQ5 is a slightly smaller (7-pin base) tube that is available for a few dollars each. They are electrically equivalent to a 6V6, and a SE 6BQ5 design could easily be modified to use 6AQ5s. If you can find some used output transformers for a 6V6 or 6BQ5 from an old console amp, you might be able to save some money over the Edcors. These seem to pop up on eBay all the time (or maybe it just seems that way to me since I'm never looking for them).
You only need one 12AX7, by the way, since they have two triodes in one tube- save 10 bucks.
This Antek Toroid would do for a power transformer. I've had good luck with Antek toroids in the past. They seem to be fairly conservatively rated and well shielded- good for a tube amp.
Also, I second the suggestion for a 0A2 or 0D3- they glow pretty colors.
My vote is for the Magnavox type amp- 1 watt is very small. Those would have to be crazy efficient speakers to get a reasonable SPL out of it.
No need to worry about the two voltages- one extra resistor and capacitor in the power supply and you're good to go.
If you're worried about the cost of the 6BQ5 tubes, the 6AQ5 is a slightly smaller (7-pin base) tube that is available for a few dollars each. They are electrically equivalent to a 6V6, and a SE 6BQ5 design could easily be modified to use 6AQ5s. If you can find some used output transformers for a 6V6 or 6BQ5 from an old console amp, you might be able to save some money over the Edcors. These seem to pop up on eBay all the time (or maybe it just seems that way to me since I'm never looking for them).
You only need one 12AX7, by the way, since they have two triodes in one tube- save 10 bucks.
This Antek Toroid would do for a power transformer. I've had good luck with Antek toroids in the past. They seem to be fairly conservatively rated and well shielded- good for a tube amp.
Also, I second the suggestion for a 0A2 or 0D3- they glow pretty colors.
I too looked at the AS-05T240. Unfortunately that item's rectifier winding is good for only 50 or so mA. of B+ and each of the "12" W. O/P tubes needs roughly 40 mA. 
$29.73 is the combined cost total for a Triad N-68X and a Triad VPS24-1000 and that's less than the cost of an AnTek model which will supply enough B+ current.
A total of 4 tubes: 1 12AX7, 1 0A2, and 2 "12" W. O/P tubes are needed for a "knockoff" of the Magnavox amp. Remember what I said about Russian 6Π15Π-EV stock. Less than $21 buys 4 tubes, which means you get a working set and a set of spares.
Matching is a non-issue in this SE/GNFB setup. Sockets correctly wired for the 6Π15Π accept EL84/6BQ5s, with zero changes. Should a good deal present itself down the road, it's a plug & play situation.
$29.73 is the combined cost total for a Triad N-68X and a Triad VPS24-1000 and that's less than the cost of an AnTek model which will supply enough B+ current.
A total of 4 tubes: 1 12AX7, 1 0A2, and 2 "12" W. O/P tubes are needed for a "knockoff" of the Magnavox amp. Remember what I said about Russian 6Π15Π-EV stock. Less than $21 buys 4 tubes, which means you get a working set and a set of spares.
Matching is a non-issue in this SE/GNFB setup. Sockets correctly wired for the 6Π15Π accept EL84/6BQ5s, with zero changes. Should a good deal present itself down the road, it's a plug & play situation.
I too looked at the AS-05T240. Unfortunately that item's rectifier winding is good for only 50 or so mA. of B+ and each of the "12" W. O/P tubes needs roughly 40 mA.
$29.73 is the combined cost total for a Triad N-68X and a Triad VPS24-1000 and that's less than the cost of an AnTek model which will supply enough B+ current.
My mistake- I thought that transformer had a pair of high voltage windings like some of their other transformers. Would have been perfect.
Before committing to the 6E5P design, I strongly suggest you to test if 1W is enough for your speakers. You may use one of those 1$ - 1W class-D chip amp boards from ebay; they distort the sound in a nasty way if overdriven, while the tube amp will not, but you will get the idea. The schematic proposed by Eli Duttman is a classic, proven circuit with more power and better power handling.
The schematic and a picture of the bottom of the 6e5p amplifier are attached to this post. You don't need matched tubes. Eli Duttman idea about the gas discharge regulator tube is excellent. I believe that on this amplifier you may use two 85A2 regulators in series; the recomended current trough this type of regulator is 6mA. The cathode current trough the 6e5p is about 30mA. Anode current and plate impedence are low, this means that the output transformer is not critical and you may use cheap toroidal transformers. The big transformers you see on my build were meant for KT88 tubes, but they turned out to be of subpar quality on the intended application. On this circuit they sound perfect. You may use much smaller transformers, such as the 3500 ohm version of the GXSE15 (I believe that the regular 5K version would also work, altough with lower output). A word of caution if you want to use cheap power toroidal transformers as output transformers: because this circuit is single ended, you need to oversize them a lot to avoid saturation. Try 100VA. Some are good for this application, other aren't, you may want to try out.
I build my smaller prototypes on clear plastic containers, they are easy to drill and placement of components is simplified. The L shaped aluminium bar on top is essential to avoid deformation due to the weight of the transformers.
The schematic and a picture of the bottom of the 6e5p amplifier are attached to this post. You don't need matched tubes. Eli Duttman idea about the gas discharge regulator tube is excellent. I believe that on this amplifier you may use two 85A2 regulators in series; the recomended current trough this type of regulator is 6mA. The cathode current trough the 6e5p is about 30mA. Anode current and plate impedence are low, this means that the output transformer is not critical and you may use cheap toroidal transformers. The big transformers you see on my build were meant for KT88 tubes, but they turned out to be of subpar quality on the intended application. On this circuit they sound perfect. You may use much smaller transformers, such as the 3500 ohm version of the GXSE15 (I believe that the regular 5K version would also work, altough with lower output). A word of caution if you want to use cheap power toroidal transformers as output transformers: because this circuit is single ended, you need to oversize them a lot to avoid saturation. Try 100VA. Some are good for this application, other aren't, you may want to try out.
I build my smaller prototypes on clear plastic containers, they are easy to drill and placement of components is simplified. The L shaped aluminium bar on top is essential to avoid deformation due to the weight of the transformers.
Attachments
Im very sorry to kind of hi-jack. I have often heard builders say they dislike pentode sound. Could you describe its sound and behaviour compared to UL and SE?
Also I have seen someone mention that a pentode poweramp is a transconductance amplifier. Is this true?Your proposal maybe something I would like to build for tweeter duty in an actively speaker. Thanks. And @ Rpi Best of luck with project
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I built a nice little guitar amp using a pair of 6gv8 tubes in push-pull. It makes about 10 watts in pentode with lots of good guitar distortion, but can be changed to a lower powered, low distortion triode mode by changing one component. The output uses an $11 Antek toroid transformer, a $10 switchmode power supply, and a 12v wall wart. Each channel is built on a 4" x 4" PCB and uses about $25 of components. 6F5P tubes can be substituted for 6GV8 to save a few dollars.
The circuit is Class "A"/single ended, as it must be using only 1 O/P tube per channel. Regulating g2 B+ at a fraction of anode B+ maximizes open loop linearity. In particular, highly annoying IM distortion is held down. Loop negative feedback of some kind is essential. Pentode O/P impedance is HIGH and that leads to an unacceptable damping factor. This setup employs a "simple" GNFB loop
If no NFB is "your thing", steer clear of full pentode mode O/P tubes. Perhaps the dislike mentioned is tied to the damping factor consideration.
Watch this video YouTube
If you need cheap OT, here are some: Transformer - Output, 8 W, Single Ended | Antique Electronic Supply
If you need cheap OT, here are some: Transformer - Output, 8 W, Single Ended | Antique Electronic Supply
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H713, I'm still not sure if I'll implement that idea with stepper motor. Though it definitely adds a wow factor to the project The idea was to start the motor right after the player startup and move the board with tubes back during the shutdown procedure. So the motor shouldn't interfere with a playback. The drivers for stepper motors have a sleep mode like in this one: Amazon.com: Adafruit (PID 3297) DRV8833 DC/Stepper Motor Driver Breakout Board: Computers & Accessories
I have a spare pair of these speakers (3") which I could use for the project: Amazon.com: DROK15W Mini 3'' HiFi Full Range Speaker 4 Ohm Anti-magnetic Audio 2.0/2.1 Home Stereo Woofer Loudspeaker 90dB High Sensitivity for DIY Boombox Satellites Speaker: Electronics I believe 4" is maximum size which I can afford taking into account the available space. So if you could recommend any good full range efficient speakers of size 4" or less, please let me know.
Fenris, could you show the schematics of your amp and how it looks like? Thanks in advance!
Eli Duttman, you gave so many ideas... It's just tough for me to imaging the final schematics for the amp which you mean. Again I've never built tube amps before. As usual - one image would worth thousand words. It looks like the Magnavox type amp is the preferable option among posters here. I just need to come up with the final schematics and parts list.
electrix, thank you for one more option! It just adds more uncertainty to the making of the final decision
It looks like power transformer and output transformers need a lot of space. Is it possible to keep them separately from the rest of the amp? How far they can be placed? Will that considerably affect the sound (EM interference etc)?
I'm going to use some voltage converter for Nixie IN-9 tubes for VU Meter similar to this one: MC34063 High Voltage DC DC Converter Boost Electronic Tube Power Supply Module | eBay Is it possible to use something like that for the amp?H713, I'm still not sure if I'll implement that idea with stepper motor. Though it definitely adds a wow factor to the project The idea was to start the motor right after the player startup and move the board with tubes back during the shutdown procedure. So the motor shouldn't interfere with a playback. The drivers for stepper motors have a sleep mode like in this one: Amazon.com: Adafruit (PID 3297) DRV8833 DC/Stepper Motor Driver Breakout Board: Computers & Accessories
I have a spare pair of these speakers (3") which I could use for the project: Amazon.com: DROK15W Mini 3'' HiFi Full Range Speaker 4 Ohm Anti-magnetic Audio 2.0/2.1 Home Stereo Woofer Loudspeaker 90dB High Sensitivity for DIY Boombox Satellites Speaker: Electronics I believe 4" is maximum size which I can afford taking into account the available space. So if you could recommend any good full range efficient speakers of size 4" or less, please let me know.
Fenris, could you show the schematics of your amp and how it looks like? Thanks in advance!
Eli Duttman, you gave so many ideas... It's just tough for me to imaging the final schematics for the amp which you mean. Again I've never built tube amps before. As usual - one image would worth thousand words. It looks like the Magnavox type amp is the preferable option among posters here. I just need to come up with the final schematics and parts list.
electrix, thank you for one more option! It just adds more uncertainty to the making of the final decision
It looks like power transformer and output transformers need a lot of space. Is it possible to keep them separately from the rest of the amp? How far they can be placed? Will that considerably affect the sound (EM interference etc)?
I'm going to use some voltage converter for Nixie IN-9 tubes for VU Meter similar to this one: MC34063 High Voltage DC DC Converter Boost Electronic Tube Power Supply Module | eBay Is it possible to use something like that for the amp?
The idea was to start the motor right after the player startup and move the board with tubes back during the shutdown procedure. So the motor shouldn't interfere with a playback. The drivers for stepper motors have a sleep mode like in this one: Amazon.com: Adafruit (PID 3297) DRV8833 DC/Stepper Motor Driver Breakout Board: Computers & Accessories I have a spare pair of these speakers (3") which I could use for the project: Amazon.com: DROK15W Mini 3'' HiFi Full Range Speaker 4 Ohm Anti-magnetic Audio 2.0/2.1 Home Stereo Woofer Loudspeaker 90dB High Sensitivity for DIY Boombox Satellites Speaker: Electronics I believe 4" is maximum size which I can afford taking into account the available space. So if you could recommend any good full range efficient speakers of size 4" or less, please let me know.
Fenris, could you show the schematics of your amp and how it looks like? Thanks in advance!
Eli Duttman, you gave so many ideas... It's just tough for me to imaging the final schematics for the amp which you mean. Again I've never built tube amps before. As usual - one image would worth thousand words. It looks like the Magnavox type amp is the preferable option among posters here. I just need to come up with the final schematics and parts list.
electrix, thank you for one more option! It just adds more uncertainty to the making of the final decision
It looks like power transformer and output transformers need a lot of space. Is it possible to keep them separately from the rest of the amp? How far they can be placed? Will that considerably affect the sound (EM interference etc)?
I'm going to use some voltage converter for Nixie IN-9 tubes for VU Meter similar to this one: MC34063 High Voltage DC DC Converter Boost Electronic Tube Power Supply Module | eBay Is it possible to use something like that for the amp?H713, I'm still not sure if I'll implement that idea with stepper motor. Though it definitely adds a wow factor to the project
The idea was to start the motor right after the player startup and move the board with tubes back during the shutdown procedure. So the motor shouldn't interfere with a playback. The drivers for stepper motors have a sleep mode like in this one: Amazon.com: Adafruit (PID 3297) DRV8833 DC/Stepper Motor Driver Breakout Board: Computers & Accessories I have a spare pair of these speakers (3") which I could use for the project: Amazon.com: DROK15W Mini 3'' HiFi Full Range Speaker 4 Ohm Anti-magnetic Audio 2.0/2.1 Home Stereo Woofer Loudspeaker 90dB High Sensitivity for DIY Boombox Satellites Speaker: Electronics I believe 4" is maximum size which I can afford taking into account the available space. So if you could recommend any good full range efficient speakers of size 4" or less, please let me know.
Fenris, could you show the schematics of your amp and how it looks like? Thanks in advance!
Eli Duttman, you gave so many ideas... It's just tough for me to imaging the final schematics for the amp which you mean. Again I've never built tube amps before. As usual - one image would worth thousand words. It looks like the Magnavox type amp is the preferable option among posters here. I just need to come up with the final schematics and parts list.
electrix, thank you for one more option! It just adds more uncertainty to the making of the final decision
It looks like power transformer and output transformers need a lot of space. Is it possible to keep them separately from the rest of the amp? How far they can be placed? Will that considerably affect the sound (EM interference etc)?
I'm going to use some voltage converter for Nixie IN-9 tubes for VU Meter similar to this one: MC34063 High Voltage DC DC Converter Boost Electronic Tube Power Supply Module | eBay Is it possible to use something like that for the amp?
Let me see what I can do with MS Paint. I do "hen scratch" schematics and my scanner is currently inoperative.
Also, an aging man's twitchy hands don't help.In the meantime, focus on the differences in pin out between the 6Π15Π and the 6BQ5. The key fact is that 1 type connects the suppressor grid (g3) to the cathode internally and the 2nd type brings g3 out to the base, where it has to be "jumpered" to the cathode. Sockets wired for the 6Π15Π accept 6BQ5s, but not the other way around.
Gas discharge tubes are roughly analogous to Zener diodes. A current limiting resistor is wired in series with the tube and connected to the driving voltage source. The little "150" V. 0A2 mates perfectly with 2X 6Π15Π "finals". While this document focuses on Octal gas regulator types, the key features are well explained. In particular, look at the 0D3, which is quite similar (electrically) to the 0A2.
>>> make steampunk model.
>> stepper motor which lifts the board with tubes:
> I've found some stepper drivers to be extremely noisy
How is it SteamPunk without STEAM??
No steppers in steam days.
Steam is electrically silent.
Put bolt-on power resistors on a small metal box. Add pop-off valve from a pressure cooker. Fill box with water. Apply electricity to resistor (use math). Eventually the water boils.
You can buy syringes (not needles). You can buy large syringes for glue. Huge syringe for washing a cow's ear(?).
WEST SYSTEM Syringe for Epoxy Resin | West Marine
Plumb the steam-box to the syringes. Nail tube-board to syringes. Tubes rise.
>> stepper motor which lifts the board with tubes:
> I've found some stepper drivers to be extremely noisy
How is it SteamPunk without STEAM??
No steppers in steam days.
Steam is electrically silent.
Put bolt-on power resistors on a small metal box. Add pop-off valve from a pressure cooker. Fill box with water. Apply electricity to resistor (use math). Eventually the water boils.
You can buy syringes (not needles). You can buy large syringes for glue. Huge syringe for washing a cow's ear(?).
WEST SYSTEM Syringe for Epoxy Resin | West Marine
Plumb the steam-box to the syringes. Nail tube-board to syringes. Tubes rise.
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Mr. Gillespie knows his stuff. However, I'll pick a few small nits. The 470 Kohm grid to ground resistance at the I/P will adversely interact with the voltage amplifier triode's high CMiller to cause HF info loss. IMO, 100 Kohms is a better choice for that job. The 'X7 triode exhibits low transconductance (gm) and presents a minimal risk for parasitic oscillation. IMO, the 10 Kohm grid stopper is overkill and a 100 Ω carbon composition (CC) part is quite sufficient. Where I would like a 10 Kohm or even larger CC grid stopper is on the O/P tube's control grid, where the drawings show none. While parasitic oscillation is always a matter of concern in a DIY project, a substantial value in this position also aids in the blocking distortion dept.
Assuming a 100 Kohm I/P grid to ground resistance, insert a 0.082 μF. cap., like this, in the line between the RCA jack's center pin and the grid to ground resistor. A high pass filter that "corners" at 19.4 Hz. is formed that provides protection against infrasonic noise driven O/P "iron" core saturation.
Pentode plate current is much more influenced by screen grid (g2) voltage than it is by plate voltage. We are going to 0A2 regulate g2 voltage at 150 V. Wherever the voltage doubler B+ supply comes in, it will be OK. O/P tube control grid bias will be adjusted to ensure that plate dissipation does not exceed a safe 11.5 W.
The Zobel network on the O/P transformer secondary and the 300 pF. phase compensation cap. are "iron" specific. The Edcor trafo may or may not need a Zobel network. Exact setting of the phase compensation part's value requires a square wave generator and an o'scope. If necessary a brute force method of phase compensation is available.
Assuming a 100 Kohm I/P grid to ground resistance, insert a 0.082 μF. cap., like this, in the line between the RCA jack's center pin and the grid to ground resistor. A high pass filter that "corners" at 19.4 Hz. is formed that provides protection against infrasonic noise driven O/P "iron" core saturation.
Pentode plate current is much more influenced by screen grid (g2) voltage than it is by plate voltage. We are going to 0A2 regulate g2 voltage at 150 V. Wherever the voltage doubler B+ supply comes in, it will be OK. O/P tube control grid bias will be adjusted to ensure that plate dissipation does not exceed a safe 11.5 W.
The Zobel network on the O/P transformer secondary and the 300 pF. phase compensation cap. are "iron" specific. The Edcor trafo may or may not need a Zobel network. Exact setting of the phase compensation part's value requires a square wave generator and an o'scope. If necessary a brute force method of phase compensation is available.
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