Few tears ago i saw on this site i think a tube amp project with a single television tube who didn't imply high voltage. Anybody remember this?
Low voltage (110 V B+) low power mini tubes:
5902 outputs, drivers: 5639 ,6021, 6111, 6112.
10K or more OT.
http://tubedata.milbert.com/sheets/141/5/5902.pdf
http://tubedata.milbert.com/sheets/137/5/5639.pdf
http://tubedata.milbert.com/sheets/141/6/6021.pdf
http://tubedata.milbert.com/sheets/049/6/6111.pdf
http://tubedata.milbert.com/sheets/137/6/6112.pdf
EDCOR - CXPP10-10K (10 Watt OT, 10K, $49)
EDCOR - XSM Series (2.5 Watt, 10K to 150 Ohm or 15K to 600 Ohm for headphones, $15)
There are even lower V tubes around. (28V)
http://tubedata.milbert.com/sheets/049/2/26A7GT.pdf
http://www.diyaudio.com/forums/tubes-valves/288807-low-b-voltage-amplifiers.html
Search on 26A7 to find some other low V threads.
Many of the big TV Sweep tubes (select ones with very square LV plate curve knees) will work at low voltage (and low Watts!). Also very low Ri type triodes will work for LV.
.
5902 outputs, drivers: 5639 ,6021, 6111, 6112.
10K or more OT.
http://tubedata.milbert.com/sheets/141/5/5902.pdf
http://tubedata.milbert.com/sheets/137/5/5639.pdf
http://tubedata.milbert.com/sheets/141/6/6021.pdf
http://tubedata.milbert.com/sheets/049/6/6111.pdf
http://tubedata.milbert.com/sheets/137/6/6112.pdf
EDCOR - CXPP10-10K (10 Watt OT, 10K, $49)
EDCOR - XSM Series (2.5 Watt, 10K to 150 Ohm or 15K to 600 Ohm for headphones, $15)
There are even lower V tubes around. (28V)
http://tubedata.milbert.com/sheets/049/2/26A7GT.pdf
http://www.diyaudio.com/forums/tubes-valves/288807-low-b-voltage-amplifiers.html
Search on 26A7 to find some other low V threads.
Many of the big TV Sweep tubes (select ones with very square LV plate curve knees) will work at low voltage (and low Watts!). Also very low Ri type triodes will work for LV.
.
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It used only one tube by channel, something like a 6EM7.
My idea was to build a small guitar amp with one tube.
My idea was to build a small guitar amp with one tube.
> a small guitar amp with one tube.
Taken literally- many modern amps are one tube and 999 transistors (half-dozen chips).
Depending how you define "guitar amplifier", a one-tube is a stretch. The 6EM7 and similar V-sweep tubes will need over 250mV on the first grid for the full Watt+ output; guitar amp sensitivity is usually closer to 20mV.
Yes, today guitarists run pedal-boards which include boosters so a 250mV sensitivity may be "useful". If you do not mind needing a pedal-board.
There are also stability concerns. Putting a 200V plate swing on the same bottle as a 20mV grid swing implies gain over 10,000, a LOT to put in an inch of space. It will be very difficult to avoid oscillation.
The simple/cheap cheat is to do a JFET first stage. Primary advantage is that tubes always hiss and usually crackle in their sockets, worse the smaller the signal. A soldered JFET has lower hiss and no socket tarnish. Run it with about 15V on the Drain and gain of 10 or 20, it won't clip guitar input, but will have some 2nd harmonic which is good.
Of course a little thought leads to a second JFET (for similar reasons) and then you can do some more serious single power bottles. 12FX5/60FX5 is a sweet sensitive 1-Watt. 25L6/50L6/6Y6 looks like a small 6L6 (it isn't!) and can be goosed to several Watts.
Recently I saw a triple-triode Duodecar idea, semi-push-pull but you "could" get the required gain in one jug (if you can tame the hi-gain instability) and a third-Watt output.
Taken literally- many modern amps are one tube and 999 transistors (half-dozen chips).
Depending how you define "guitar amplifier", a one-tube is a stretch. The 6EM7 and similar V-sweep tubes will need over 250mV on the first grid for the full Watt+ output; guitar amp sensitivity is usually closer to 20mV.
Yes, today guitarists run pedal-boards which include boosters so a 250mV sensitivity may be "useful". If you do not mind needing a pedal-board.
There are also stability concerns. Putting a 200V plate swing on the same bottle as a 20mV grid swing implies gain over 10,000, a LOT to put in an inch of space. It will be very difficult to avoid oscillation.
The simple/cheap cheat is to do a JFET first stage. Primary advantage is that tubes always hiss and usually crackle in their sockets, worse the smaller the signal. A soldered JFET has lower hiss and no socket tarnish. Run it with about 15V on the Drain and gain of 10 or 20, it won't clip guitar input, but will have some 2nd harmonic which is good.
Of course a little thought leads to a second JFET (for similar reasons) and then you can do some more serious single power bottles. 12FX5/60FX5 is a sweet sensitive 1-Watt. 25L6/50L6/6Y6 looks like a small 6L6 (it isn't!) and can be goosed to several Watts.
Recently I saw a triple-triode Duodecar idea, semi-push-pull but you "could" get the required gain in one jug (if you can tame the hi-gain instability) and a third-Watt output.
The only one-bottle guitar amp I've run across (not low voltage by any stretch of the imagination) uses the 6AF11 Compactron. It has two triodes and a power pentode all in one bottle, which at first glance sounds like all you would need to create a Fender Champ or similar small SE amp.
Unfortunately, for the reasons PRR brought up, it seems to be very difficult to actually build a usable amp using all three sections (tubes) inside this Compactron. Usually, the result is extreme instability, though there are one or two self-documented claims of success on the 'Web. Google "Squirrel Monkey" or "Super Squirrel Monkey" or "6AF11 guitar amp".
On the sensitivity issue, the power amp section of my little 2-watt 6AK6 amp needs 10 Vpp on the input grids of the output valves to develop the full thundering two watts. 😉 Those are sensitive valves too, compared to the usual guitar-amp suspects.
Preceding those output valves with a MOSFET "source-o-dyne" phase splitter, and then a preamp valve, and some inter-stage attenuation for good clean tone, I found that plugging a guitar straight into this still produced no usable volume. Input sensitivity was maybe 1 Vpp at this point.
But inserting a Danelectro Fish-n-Chips graphic EQ/boost pedal into the chain made it into a usable clean-only amp for home use and jamming with acoustic guitars. I do not believe it ever reached full output power when used this way, however.
The Fish-n-Chips boost was set for its full voltage gain, 20 dB or x10. So 100 mV input sensitivity in combination with the amp. And that still wasn't enough to drive the amp to full output.
(By the way, that power amp was a build-in-progress at that point in time; it went on to receive a full valve preamp, with 2 gain stages in the clean channel, and 3 in the overdrive channel. Plenty of gain now!)
-Gnobuddy
Unfortunately, for the reasons PRR brought up, it seems to be very difficult to actually build a usable amp using all three sections (tubes) inside this Compactron. Usually, the result is extreme instability, though there are one or two self-documented claims of success on the 'Web. Google "Squirrel Monkey" or "Super Squirrel Monkey" or "6AF11 guitar amp".
On the sensitivity issue, the power amp section of my little 2-watt 6AK6 amp needs 10 Vpp on the input grids of the output valves to develop the full thundering two watts. 😉 Those are sensitive valves too, compared to the usual guitar-amp suspects.
Preceding those output valves with a MOSFET "source-o-dyne" phase splitter, and then a preamp valve, and some inter-stage attenuation for good clean tone, I found that plugging a guitar straight into this still produced no usable volume. Input sensitivity was maybe 1 Vpp at this point.
But inserting a Danelectro Fish-n-Chips graphic EQ/boost pedal into the chain made it into a usable clean-only amp for home use and jamming with acoustic guitars. I do not believe it ever reached full output power when used this way, however.
The Fish-n-Chips boost was set for its full voltage gain, 20 dB or x10. So 100 mV input sensitivity in combination with the amp. And that still wasn't enough to drive the amp to full output.
(By the way, that power amp was a build-in-progress at that point in time; it went on to receive a full valve preamp, with 2 gain stages in the clean channel, and 3 in the overdrive channel. Plenty of gain now!)
-Gnobuddy
A small guitar amp with one tube.
There are some pentode triodes that could result in a cool little amp.
Like the ECL82, ËCL84, ECL86. They require some high voltage.
Here my lunchbox attempt
The higher voltage here obtained from the transformer makes it more on the clean side.
http://www.youtube.com/watch?v=WzEutOLRcD4
or my PCL84 amp using a MAX1771 SMPS, that works with a 12v wall wart
https://www.youtube.com/watch?v=GnCRv-u-dQ4&t=11s
I even found a japanese guy who built the squirrel monkey amp in the same enclosure:
https://marinesnow-jp.jimdo.com/%E7%9C%9F%E7%A9%BA%E7%AE%A1%E3%83%9F%E3%83%8B%E3%82%AE%E3%82%BF%E3%83%BC%E3%82%A2%E3%83%B3%E3%83%97/one-tube-mini-guitar-amp/
There are some compactrons that also have double pentodes, that could work like a champ
There are some pentode triodes that could result in a cool little amp.
Like the ECL82, ËCL84, ECL86. They require some high voltage.
Here my lunchbox attempt
The higher voltage here obtained from the transformer makes it more on the clean side.
http://www.youtube.com/watch?v=WzEutOLRcD4
or my PCL84 amp using a MAX1771 SMPS, that works with a 12v wall wart
https://www.youtube.com/watch?v=GnCRv-u-dQ4&t=11s
I even found a japanese guy who built the squirrel monkey amp in the same enclosure:
https://marinesnow-jp.jimdo.com/%E7%9C%9F%E7%A9%BA%E7%AE%A1%E3%83%9F%E3%83%8B%E3%82%AE%E3%82%BF%E3%83%BC%E3%82%A2%E3%83%B3%E3%83%97/one-tube-mini-guitar-amp/
There are some compactrons that also have double pentodes, that could work like a champ
Speaking of a pair of 25L6's (we were weren't we?), I limited them to 48V dc. Thinking about it running them in triode has some merit. Just a what iff experiment, never spent enough time on it to take the design seriously.
http://www.diyaudio.com/forums/inst...pired-amp-voltage-challenged-individuals.html
http://www.diyaudio.com/forums/inst...pired-amp-voltage-challenged-individuals.html
By pure coincidence, just yesterday I stumbled across a Youtube video featuring a Pine guitar amp (Canadian made, 2 watts, 50C5 output tube, which is a close relative to the 25L6).
These were made and sold at the very low-cost end of the market. The surprise for me is that they seem to produce quite a nice rock snarl once overdriven.
If you skip the first 1 minute and 30 seconds of waffling, and ignore the fact that the guitarist has obviously never sat down with a metronome in his life, you too might find you like the sound of this little amp: https://www.youtube.com/watch?v=C6HNX4AQVfY
I know I have something from the 50C5 family sitting around, mebbe a couple of 25C5's. Hmm!
-Gnobuddy
That link seems to be a mangled copy of an original write up by Joe Sousa, which I found on radiomuseum.org many years ago: Russian Subminiature Tubes
Fascinating little things, those rod "pentodes"!
-Gnobuddy
I got some of those subminis,
the 1ZH29B for output and the 1ZH24B for preamp.
There is some information about them in german. I found this schematic for a PP amp>
more info here:
Treffpunkt der Interessengemeinschaft :: Thema anzeigen - Russen-GT mit 200 mW
here a preamp that uses those tubes:
Gitarren-Vorverstärker mit russischen Batterieröhren 1SH29B - Michael Gaedtke
All working with 60v, and probably less than 500mA for the heaters.
Going back to the topic, some months ago I was reading some scanned version of old magazines and did found some interesting stuff, like a guitar amplifier with only one tube. Interesting that they provided plans for a simple chassis too.
Found it, thanks to the guys over cigarboxnation:
http://api.ning.com/files/ctVGzmtSoN9Zk8WL9uQqTFt9YU9JPkz4DT0hl15bSes9DtsB5lRczY9h7x2CzFKfHiEgSiasdCOme2TmTnCrjo778K9T6VaX/OneTubeCigarBoxAmplifier1955.pdf
it does requires an isolation transformer, but that would be easy to add. Even the box pictured in the article looks big enough for an extra transformer.
the 1ZH29B for output and the 1ZH24B for preamp.
There is some information about them in german. I found this schematic for a PP amp>
more info here:
Treffpunkt der Interessengemeinschaft :: Thema anzeigen - Russen-GT mit 200 mW
here a preamp that uses those tubes:
Gitarren-Vorverstärker mit russischen Batterieröhren 1SH29B - Michael Gaedtke
All working with 60v, and probably less than 500mA for the heaters.
Going back to the topic, some months ago I was reading some scanned version of old magazines and did found some interesting stuff, like a guitar amplifier with only one tube. Interesting that they provided plans for a simple chassis too.
Found it, thanks to the guys over cigarboxnation:
http://api.ning.com/files/ctVGzmtSoN9Zk8WL9uQqTFt9YU9JPkz4DT0hl15bSes9DtsB5lRczY9h7x2CzFKfHiEgSiasdCOme2TmTnCrjo778K9T6VaX/OneTubeCigarBoxAmplifier1955.pdf
it does requires an isolation transformer, but that would be easy to add. Even the box pictured in the article looks big enough for an extra transformer.
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The 60 volt operation sounds interesting, particularly for people who are scared off by (entirely legitimate) concern about building and working with circuitry containing 300 V - 500 V.
The tube is unusual, and may be hard to find. However it amounts to a single pentode for amplification, and a (valve) diode for rectification, both in the same bottle.
I will eat my hat if that single pentode is capable of enough voltage gain to provide anything other than the cleanest of clean guitar sounds. 😀
Also, 120V is low by valve standards, but still high compared to the voltages untrained people should be dealing with. In the USA, a variety of safety regulations kick in for anything above 50V, which is one reason why there is so much industrial stuff operating at 48 V DC.
IMO, today it would make more sense to use a 1N4007 (silicon) rectifier. If we are also willing to forego (safe) low-voltage operation, that would allow use of a triode-pentode valve, and then you could get enough gain for a broader variety of guitar sounds.
One interesting possibility is a 6LY8 - from the data sheets, it contains a triode which appears to be half of a 12AX7, along with a 5W high-transconductance pentode (20,000 umho). At a glance, the pentode will only need about 4 Vpp at the control grid to drive it to full output (maybe 2W single-ended). The half-12AX7 should easily manage the usual voltage gain of 40 - 60 times, so it should be possible to achieve something around 80 mVpp input sensitivity, as long as lossy tone control circuits are avoided.
80 mVpp input sensitivity will be enough to get some crunch and overdrive out of many electric guitars.
I stumbled across this valve when ESRC had them on their dollar list. Never built anything with one, though.
-Gnobuddy
> a guitar amplifier with only one tube.
Does not say "guitar". It needs over 3.5V input to make the mighty 0.85 Watt output; guitar wants 0.02V-0.05V. Yes, some guitars can go near 1V, but you don't want to wang that hard on every note, may as well play acoustic.
The usual use of that tube is a battery beach radio of 0.1W output on 90V battery, but also a wall-plug for home use w/o battery and with greater volume. It has also been seen in intercoms, though with a hot carbon mike and hefty step-up transformer or some other extra gain.
117L7 may be a trace scarce, but 117N7 and 117P7 are super similar and the N7 is $8 at TheTubeStore, so won't be hard to get.
Does not say "guitar". It needs over 3.5V input to make the mighty 0.85 Watt output; guitar wants 0.02V-0.05V. Yes, some guitars can go near 1V, but you don't want to wang that hard on every note, may as well play acoustic.
The usual use of that tube is a battery beach radio of 0.1W output on 90V battery, but also a wall-plug for home use w/o battery and with greater volume. It has also been seen in intercoms, though with a hot carbon mike and hefty step-up transformer or some other extra gain.
117L7 may be a trace scarce, but 117N7 and 117P7 are super similar and the N7 is $8 at TheTubeStore, so won't be hard to get.
I've played a lot of acoustic guitar lately, and one of my bigger concerns is that it is easy to become heavy-handed and learn to use excessive force when you play a lot of acoustic guitar.
Then you go back to an electric with a 0.009" high E, and find you are pulling the strings sharp every time you form a chord, because your left hand has lost its light touch. Oh, and you're much slower than you used to be, because heavy and forceful doesn't go that well with fast. (Al De Meola and Frank Gambale notwithstanding.)
Mebbe a starting point for 0.1W of distorted guitar? Nice that you don't need an unobtainable primary inductance (and impedance) for the output transformer.
I briefly looked at the 50C5 and its relatives for the same reason. They should work well even with low-inductance 70V line transformers.
0.1 W of distorted guitar can actually be too loud in some home environments, when combined with a typical guitar speaker.
-Gnobuddy
> starting point for 0.1W
A usual beach-radio "power" tube was 3V4. Wants 10K load at 10mA for 0.27W out. There was a smaller (battery thrifty) "power" tube but I dis-remember the name. 1S4 was similar (same?) but the data goes to low volt/power (whopping 0.065W at 12%THD and 45V).
Common Miniature 7pin (B7G) Battery tubes (valves)
While adequate on a beach blanket, these radios were lame in a house. To broaden the appeal, makers added a 117V power stage more-like a 50C5, like any other kitchen radio. A rectifier was included. The 117V rectifier also powered the filaments, switched from parallel to series. (I've had a 6550 working 30V on G2 for sub-Watt output.)
You know that since you will not be working battery or transformerless, *any* of the 50C5 types can be worked from 110VDC down to 30VDC on the plate to hit your power target. If the heater voltage is awkward, 6Y6 is 6V though massively fat for the job. And of course 6V6 EL84 can be worked at low B+ if you accept/want low power.
A usual beach-radio "power" tube was 3V4. Wants 10K load at 10mA for 0.27W out. There was a smaller (battery thrifty) "power" tube but I dis-remember the name. 1S4 was similar (same?) but the data goes to low volt/power (whopping 0.065W at 12%THD and 45V).
Common Miniature 7pin (B7G) Battery tubes (valves)
While adequate on a beach blanket, these radios were lame in a house. To broaden the appeal, makers added a 117V power stage more-like a 50C5, like any other kitchen radio. A rectifier was included. The 117V rectifier also powered the filaments, switched from parallel to series. (I've had a 6550 working 30V on G2 for sub-Watt output.)
You know that since you will not be working battery or transformerless, *any* of the 50C5 types can be worked from 110VDC down to 30VDC on the plate to hit your power target. If the heater voltage is awkward, 6Y6 is 6V though massively fat for the job. And of course 6V6 EL84 can be worked at low B+ if you accept/want low power.
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What are good conditions for el84 at lower voltage.
I have one running at 218v on the plate and 88% dissipation. The OT is 7k 16 ohm but it appears to be a better match when using an 8 ohm speaker.
I'm wondering if I can get close to 100% dissipation if I use a -5v bias from say 85r bias resistor.
There is not much headroom though.
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I have one running at 218v on the plate and 88% dissipation. The OT is 7k 16 ohm but it appears to be a better match when using an 8 ohm speaker.
I'm wondering if I can get close to 100% dissipation if I use a -5v bias from say 85r bias resistor.
There is not much headroom though.
Sent from my iPhone using Tapatalk
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