Gno -
Wow - kewl. The 14.9% 2nd order looks like it would be fat!! Could all this be applied to a triode power stage like the 6AS7 or does it need a Pentode? Could Germanium trasistors be used? Love their tone for guitar.
Gotta admit right now -- I am *way* outta my league here but it surrre looks exotic and cool.
Wow - kewl. The 14.9% 2nd order looks like it would be fat!! Could all this be applied to a triode power stage like the 6AS7 or does it need a Pentode? Could Germanium trasistors be used? Love their tone for guitar.
Gotta admit right now -- I am *way* outta my league here but it surrre looks exotic and cool.
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It should work the same way with a triode - the current mirror only senses the current flowing out of the cathode, and attempts to duplicate (and multiply) that. (So, with a pentode, the current mirror is actually trying to mirror screen+anode current, rather than anode current alone.)
Keep in mind I haven't built and tested this, so I don't know how well it works, or what unexpected problems might show up!
The problem I'm worried about is second-breakdown - if the transistor is run at the same B+ as the valve, then this problem may show up. Transistors tend to be unhappy when trying to cope with lots of voltage and lots of current at the same time.
If the transistor is run on a lower B+, that removes the second breakdown problem. But now you need an output transformer for the transistor, and you'll need one with a rather low primary impedance.
I think the idea can be extended to push-pull output stages, too...that might be really interesting.
But I think the most interesting thing that's come out of this thread is that a valve guitar amp can sound "valvey" without an output transformer.
And that makes me think about the possibility of a small (milliwatt power) valve guitar amp, using small-signal pentodes as "outputs", with a normal resistive anode load. Tap off the signal, feed it to a big solid-state power amp (P.A.?). It should still sound "tubey".
Maybe we can we do better than the old Garnet Herzog - that one used a 6V6 with an output transformer and a dummy load. After reading this thread, it looks as though we may not need the output transformer.
And if we don't need the output transformer, we may not need a high-power output valve, either - no worries about finding a 40k Raa transformer to go with a low-powered small signal pentode, just whack in a normal resistive anode load, and see if it still sounds "valvey" enough!
So I think this thread leads to all sorts of interesting new possibilities, from improved "Herzogs" to hybrid OTL (valve + transistor) amps.
-Gnobuddy
I think it deserves to be tried, with about 200V B+, and a PNP current mirror to get the signal out.
I was very excited about that idea for a while, before it dawned on me that a small-signal pentode easily produces 15% second harmonic distortion without having to play any tricks on it at all!
So that's the route I eventually went down. Rather than triodes with current mirrors, I experimented with a few small cheap RF small-signal pentodes to see what they sounded like.
To my ears, it's pretty easy to get lovely guitar clean tones out of them. IMO, don't put them at the input of the preamp, treat them like a tiny little output stage, and put them at the output end of the preamp.
Don't use the crazy maximum-voltage-gain approach with insanely high anode load resistors, either, just us normal anode loads around 50k or so. Low B+ around 150V seems to work well.
IMO, germanium power transistors are "three legged fuses" - best not to trust them for anything!
-Gnobuddy
I probe whit speakers of 600/800 ohms in first time because is very much esay adjust impedande and experiments whit it.
I probe speakers standar in some esperiments, and for guitar it is more normal and esay in config of 4x12 for example, whit its and 16 ohm or 32 ohm go at 64 ohm...or 128 ohm
I have serchs one solution real, in the middle position, or fabricate coils for this, whit 400 ohms or more its is ok.
Not produce the industry this high Z speakers, but if it increment the demand....
Other solution is build speakers of 600-1500 ohms in speakers big chasis for the diameter of the cable not too much big.
I not bulid for sales amps OTL and i can my amps whit speakers of 400 to 2000 ohms. But for how much time?, i not have response at thid
.
I probe speakers standar in some esperiments, and for guitar it is more normal and esay in config of 4x12 for example, whit its and 16 ohm or 32 ohm go at 64 ohm...or 128 ohm
I have serchs one solution real, in the middle position, or fabricate coils for this, whit 400 ohms or more its is ok.
Not produce the industry this high Z speakers, but if it increment the demand....
Other solution is build speakers of 600-1500 ohms in speakers big chasis for the diameter of the cable not too much big.
I not bulid for sales amps OTL and i can my amps whit speakers of 400 to 2000 ohms. But for how much time?, i not have response at thid
.Found some info about the high impedence speakers:
https://www.vintage-radio.com/repair-restore-information/valve_philips-speakers.html
https://www.vintage-radio.com/repair-restore-information/valve_philips-speakers.html
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If you use 6AS7Gs then 600 ohms is impractical- you would want a speaker with a much lower impedance!
With 8 6AS7Gs you can make 60-80 watts into an 8-ohm speaker fairly easily. In the amps I've built, I've put drivers in series for a higher impedance load like 32 ohms. That has made using 4 power tubes quite practical- and still getting about 50 watts.
With 8 6AS7Gs you can make 60-80 watts into an 8-ohm speaker fairly easily. In the amps I've built, I've put drivers in series for a higher impedance load like 32 ohms. That has made using 4 power tubes quite practical- and still getting about 50 watts.
atmasphere -
I am not a performing musician so lower power amps are better for me. I am looking to build a champ type amp to start with. Maybe a leadoff pentode into the 6AS7 triode power stage. I would like to try either a parallel (SE) or self-split power section first but push pull would be fine too if you have something handy to share. What I am most unsure of is the proper bias point for the 6as7 (never done loadlines on a triode) and the voltage swing it needs from the preamp, but I am no amp designer to be sure and will probably need more help as well. Could you suggest a starting place for a schematic? I'd be willing to try an OTL but again, I am more tone-driven than topology-driven. I would be happy to start a new thread so as not to offend the OTL folks.
I am not a performing musician so lower power amps are better for me. I am looking to build a champ type amp to start with. Maybe a leadoff pentode into the 6AS7 triode power stage. I would like to try either a parallel (SE) or self-split power section first but push pull would be fine too if you have something handy to share. What I am most unsure of is the proper bias point for the 6as7 (never done loadlines on a triode) and the voltage swing it needs from the preamp, but I am no amp designer to be sure and will probably need more help as well. Could you suggest a starting place for a schematic? I'd be willing to try an OTL but again, I am more tone-driven than topology-driven. I would be happy to start a new thread so as not to offend the OTL folks.
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@moonbird,
The issue with OTLs is that they loose efficiency at lower power levels. In fact the Holy Grail of OTLs is a low power amp, but really that's pretty tricky to say the least. One solution would be to build an array of smaller drivers so you can get the impedance up. For example if you wanted to use just one 6AS7G (which will still be a push-pull amp) the load impedance should probably be about 120 ohms for best results! You can see the practicality issue.
Now if you apply a lot of feedback to the amp, you can get the output impedance down, and while it won't make any serious power, at least you won't have heavy interaction with the impedance curve of the speaker. At that point you could make a 16 ohm load work as long as it was higher efficiency.
Either a Futterman or Circlotron circuit would work. I prefer the Circlotron as they are a bit easier to make IMO/IME.
The issue with OTLs is that they loose efficiency at lower power levels. In fact the Holy Grail of OTLs is a low power amp, but really that's pretty tricky to say the least. One solution would be to build an array of smaller drivers so you can get the impedance up. For example if you wanted to use just one 6AS7G (which will still be a push-pull amp) the load impedance should probably be about 120 ohms for best results! You can see the practicality issue.
Now if you apply a lot of feedback to the amp, you can get the output impedance down, and while it won't make any serious power, at least you won't have heavy interaction with the impedance curve of the speaker. At that point you could make a 16 ohm load work as long as it was higher efficiency.
Either a Futterman or Circlotron circuit would work. I prefer the Circlotron as they are a bit easier to make IMO/IME.
Yugo yes, my singles circuits are in this moment public for particular purposes only, in spain not apreciate the big work of this OTL.
But i publish all this.
I work years in this, for convert one complex amp in single amp for guitar, and posible and reality this whit my posibilities and small capacity of production.
And the response is...null in Spain, only some friend in front at one my OTL apreciate this.
Other people say: " this amp not is posible, or not is real or the saturation can be bad.?,
But it not is bad is more musicallity an utility.
Atmasphere and Moonbird-
All this is very interesting.
The explanied of philips bi-amp and speakers is real an very good, and I work in this all time. Good sound an very impresive the biamp circuit. Its is the "sant grial" for my, one single Amp in output "reality" and in low power (0,5 W and 4,5W) in style fender amp, and similar at fender champ, and others.
First scheme, one amp of 0,5 w for home...
Very very single and efective, for saturate whit pedals. Need one boster or more state in preamp) I have this whit only 1/2 ecc83 in preamp. But can put more eccXX or more power valve, my circuit have one only 12K5 valve/tube. The output is Z= 700 ohm aprox.and speaker z=700 ohm.
https://www.dropbox.com/s/5y89dg5w1tgkbbz/IMG_20161215_140858.JPG?dl=0
But i publish all this.
I work years in this, for convert one complex amp in single amp for guitar, and posible and reality this whit my posibilities and small capacity of production.
And the response is...null in Spain, only some friend in front at one my OTL apreciate this.
Other people say: " this amp not is posible, or not is real or the saturation can be bad.?,
But it not is bad is more musicallity an utility.
Atmasphere and Moonbird-
All this is very interesting.
The explanied of philips bi-amp and speakers is real an very good, and I work in this all time. Good sound an very impresive the biamp circuit. Its is the "sant grial" for my, one single Amp in output "reality" and in low power (0,5 W and 4,5W) in style fender amp, and similar at fender champ, and others.
First scheme, one amp of 0,5 w for home...
Very very single and efective, for saturate whit pedals. Need one boster or more state in preamp) I have this whit only 1/2 ecc83 in preamp. But can put more eccXX or more power valve, my circuit have one only 12K5 valve/tube. The output is Z= 700 ohm aprox.and speaker z=700 ohm.
https://www.dropbox.com/s/5y89dg5w1tgkbbz/IMG_20161215_140858.JPG?dl=0
All in only 12v whit one power tipe telephone movil, or power of guitar pedal or similar.
- Filaments in 12v
+B in 12v real, whithout infra power output
- AC to speaker, whit charge in 5v aprox.
- small weigth
- very single
- ideal beguinners ;-)
- otl face to face real whitout condensers.
- ideal for recicle and mantenence the natural globe.
-etc.
Preamp tipe fender , power tipe OTL.
The other in 4,5w is very esay, is preamp identical and power the bi-amp philips
And have 4,5w aprox.
- Filaments in 12v
+B in 12v real, whithout infra power output
- AC to speaker
, whit charge in 5v aprox.- small weigth
- very single
- ideal beguinners ;-)
- otl face to face real whitout condensers.
- ideal for recicle and mantenence the natural globe.
-etc.
Preamp tipe fender , power tipe OTL.
The other in 4,5w is very esay, is preamp identical and power the bi-amp philips
And have 4,5w aprox.
One big number of guitar sound ssmples of this OTL news.
Amplificadores de Válvulas OTL sin Transformador de Salída, Muestras de Sonido.
Amplificadores de Válvulas OTL sin Transformador de Salída, Muestras de Sonido.
If of course, I meant that it is always possible to reduce the maximum possible cable, and distances between components, the maximum simplicity, of course the circuit will have the minimum noise inherent to that valve or to which it is placed in the circuit.
The noise and humm can also be faced from various perspectives as we all know, I like LC filters. (Pi)
Although XCL82 itself can be noisier than other valves that do.
In guitar amplifiers that are going to be connected to pedals or pre-high gain the subject of noise and hum is somewhat delicate.
The noise and humm can also be faced from various perspectives as we all know, I like LC filters. (Pi)
Although XCL82 itself can be noisier than other valves that do.
In guitar amplifiers that are going to be connected to pedals or pre-high gain the subject of noise and hum is somewhat delicate.
These sound clips were from an OTL guitar amp? They sound great! Nice work!
For me, these clips you posted are clear evidence that an output transformer is not a requirement for great guitar amp sound.
-Gnobuddy
Yes, this is how you say.
all are samples of two OTL for Guitar, one of 0,6 watts and other of 5watts, whithout tonestack an whithout output transformers.
The first OTL amps for profesional guitar,whit one only valve in power at 12v, an other only 2 valves in power to 300v.
whit output 600 ohms speaker
Gnobudy i identical evidence in my head, bye bye output transformer and toestacks...
more of 3 years in total in this poyect, but big satisfaction by fin.
i work in other of 25 at 35 watts whit el34 and others.
very long time work it, in full funtion for probes and player guitar.
all are samples of two OTL for Guitar, one of 0,6 watts and other of 5watts, whithout tonestack an whithout output transformers.
The first OTL amps for profesional guitar,whit one only valve in power at 12v, an other only 2 valves in power to 300v.
whit output 600 ohms speaker
Gnobudy i identical evidence in my head, bye bye output transformer and toestacks...
more of 3 years in total in this poyect, but big satisfaction by fin.
i work in other of 25 at 35 watts whit el34 and others.
very long time work it, in full funtion for probes and player guitar.
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I contruct full clasic amp for guitar, and in this years OTL.
Other good notice, the clasic power part of philips OTL whit el86 is beautifull wit 800 ohms speakers an whit one preramp how the image of circit i put here. it is my OTL amp of 5 watts. and part of the samples there.
in hifi is identical, change 2 componets of pre amp for impedance and none more.
Other good notice, the clasic power part of philips OTL whit el86 is beautifull wit 800 ohms speakers an whit one preramp how the image of circit i put here. it is my OTL amp of 5 watts. and part of the samples there.
in hifi is identical, change 2 componets of pre amp for impedance and none more.
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What happens if you replace the speaker with an 800 ohm resistor, and then feed the signal into a powerful solid-state P.A. system or amplified speaker?
Not a valve OTL any more, I understand, but I'll bet that this hybrid approach will sound really, really good, and give you tremendous flexibility - sweet overdriven valve guitar amp sound at almost any volume.
That is very interesting, too. I have built a couple of guitar preamps with small-signal pentodes in them, and I also found less need for tone controls, and no need for a deep mid-scoop at all. (But a little treble boost above 1 kHz did sound better than completely flat.)
You got 600 mW of audio power - transformerless - using only a 12V power supply to the valve?
That requires about 45 mA (peak) current into a 600 ohm speaker. You were able to get 45 mA through the valve at only 12 volts B+? Amazing!
You earned that satisfaction. Congratulations!
-Gnobuddy
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