> winding physics is now way better.....but the iron hasn't changed........perhaps more exotic mixes.
Winding design was WELL understood in the 1930s and 1940s. Winding computations are summarized in RDH 3rd and derived in great detail in RDM 4th.
The actual winding is always limited by the wires and insulators you can get and what your winder wants to do. Poly varnish can be somewhat thinner and a LOT stronger than the old enamel. Fishpaper still has uses in hi-Z windings, but Kapton and Teflon tapes give better insulation in less space. Winding precision.... people still wind by hand, scramble or "neat", but even the neat wasn't too precise until the recent Swiss precision winders. Jensen used a very laborious quadfilar process until they got the Swiss machine, now they can do better by just laying the wires RIGHT where they need to be.
Iron has improved markedly in saturation, in both low-level and high-power flavors. I'm old, and when I saw the Gauss levels used in today's power transformers I was shocked. Permalloy of today will carry 6dB more than the old days.
Of course this is another case where better numbers do not assure better sound. Audio transformers never come close to saturation. Good audio iron almost has to be different from power iron: they work on opposite sides of the knee.
And ferrite used to be unthinkable, but now there are "ferrites" that will carry audio bass. (They have new fancy names... to me, if it ain't iron or air and is a powder-stuff then I call it Ferrite.)
Iron lamination insulation is another detail. We used to dip stampings in varnish. Now it is common practice to "rust" the iron. Laminations do not need 1,000 GigOhm insulation, eddy current impedance is OTOH an Ohm. Rust is thinner, more iron in the stack, but also rust has magnetic and electric properites which start to show far above the bass limit (i.e. in the critical midrange). Rupert Neve was a connoisseur of lam-rust.
> I don't understand why the ceased highly popular 6550A hasn't been re-introduced
Is the new "Tungsol"-brand 6550 anywhere near as good as the generic 6550s I bought in the 1970s, or just another 6L6 in new bottle?
But in general: making good sturdy tubes is hard work. Special metals and processing. When military and railroad contracts buy many thousand tubes a year, and the buyers track failure rates, the tubes have to be good and you can afford the work needed. When all your sales are pairs/quads to guitarists, who may not know a bad tube if it bites them, can't get a proper warranty, and certainly can't keep failure statistics, then you just build tubes "good enough".
Winding design was WELL understood in the 1930s and 1940s. Winding computations are summarized in RDH 3rd and derived in great detail in RDM 4th.
The actual winding is always limited by the wires and insulators you can get and what your winder wants to do. Poly varnish can be somewhat thinner and a LOT stronger than the old enamel. Fishpaper still has uses in hi-Z windings, but Kapton and Teflon tapes give better insulation in less space. Winding precision.... people still wind by hand, scramble or "neat", but even the neat wasn't too precise until the recent Swiss precision winders. Jensen used a very laborious quadfilar process until they got the Swiss machine, now they can do better by just laying the wires RIGHT where they need to be.
Iron has improved markedly in saturation, in both low-level and high-power flavors. I'm old, and when I saw the Gauss levels used in today's power transformers I was shocked. Permalloy of today will carry 6dB more than the old days.
Of course this is another case where better numbers do not assure better sound. Audio transformers never come close to saturation. Good audio iron almost has to be different from power iron: they work on opposite sides of the knee.
And ferrite used to be unthinkable, but now there are "ferrites" that will carry audio bass. (They have new fancy names... to me, if it ain't iron or air and is a powder-stuff then I call it Ferrite.)
Iron lamination insulation is another detail. We used to dip stampings in varnish. Now it is common practice to "rust" the iron. Laminations do not need 1,000 GigOhm insulation, eddy current impedance is OTOH an Ohm. Rust is thinner, more iron in the stack, but also rust has magnetic and electric properites which start to show far above the bass limit (i.e. in the critical midrange). Rupert Neve was a connoisseur of lam-rust.
> I don't understand why the ceased highly popular 6550A hasn't been re-introduced
Is the new "Tungsol"-brand 6550 anywhere near as good as the generic 6550s I bought in the 1970s, or just another 6L6 in new bottle?
But in general: making good sturdy tubes is hard work. Special metals and processing. When military and railroad contracts buy many thousand tubes a year, and the buyers track failure rates, the tubes have to be good and you can afford the work needed. When all your sales are pairs/quads to guitarists, who may not know a bad tube if it bites them, can't get a proper warranty, and certainly can't keep failure statistics, then you just build tubes "good enough".
That $2850 is the price of the MQ-100 - not the ST-70 rebuild.
Joe hasn't gone woo woo.
I would suspect between Joe's boards and Uncle Ned's transformers, you could do a primo primo ST-70 for no more than 750-800 even without an old Dyna as a donor.
I did it for around $450 with a donor chassis and transformers, and am very happy with the results.
Joe hasn't gone woo woo.
I would suspect between Joe's boards and Uncle Ned's transformers, you could do a primo primo ST-70 for no more than 750-800 even without an old Dyna as a donor.
I did it for around $450 with a donor chassis and transformers, and am very happy with the results.
"I recall (a little dimly now) that the Audio Aero had an unusual topology, that they claimed someone had tried to do in the 1950s, and failed. Maybe wrong, but I think it was this amp that operates SET up to a certain watts, then switches automatically into pentode mode. " rick57
The "Capitloe / T.R.A.C." design appears to be a P-P triode class A / P-P pentode class AB implimentation of the Yundt composite amplifier. Published in the 80s.
for an explanation of composite amplifier operation see:
http://www.diyaudio.com/forums/showthread.php?postid=521505#post521505
The important point is that A2 (in diagram) is a current output amplifier, while A1 is a conventional voltage output amplifer. Hence, you will notice A2 implimented as pentode or MosFet (drain outputs) for high output impedance. A2 seeks to minimize current draw from A1 by the load.
They also have a P-P triode class A / MosFet class AB design, "Capitole TransTrac". This has the Mosfet amp (A2 in my diagram) connected to the secondary side of the transformer instead since it can handle the output current directly.
Marketing hype describes these designs as a "little local feedback" when in fact this topology is the premier case of elegant NFB. Nothing wrong with that however. This topology is the ultimate approach to low distortion impedance conversion, allowing a small class A amplifier to perform exquisitely into a light load, while producing high power output. Even the commercial solid state amplifiers haven't caught on to Yundt's topology yet.
Don
The "Capitloe / T.R.A.C." design appears to be a P-P triode class A / P-P pentode class AB implimentation of the Yundt composite amplifier. Published in the 80s.
for an explanation of composite amplifier operation see:
http://www.diyaudio.com/forums/showthread.php?postid=521505#post521505
The important point is that A2 (in diagram) is a current output amplifier, while A1 is a conventional voltage output amplifer. Hence, you will notice A2 implimented as pentode or MosFet (drain outputs) for high output impedance. A2 seeks to minimize current draw from A1 by the load.
They also have a P-P triode class A / MosFet class AB design, "Capitole TransTrac". This has the Mosfet amp (A2 in my diagram) connected to the secondary side of the transformer instead since it can handle the output current directly.
Marketing hype describes these designs as a "little local feedback" when in fact this topology is the premier case of elegant NFB. Nothing wrong with that however. This topology is the ultimate approach to low distortion impedance conversion, allowing a small class A amplifier to perform exquisitely into a light load, while producing high power output. Even the commercial solid state amplifiers haven't caught on to Yundt's topology yet.
Don
Attachments
SY:
Were you (“6DJ8 cascode diff amp with CCS and active regulation of the rails”) referring to the MQ-100 or the ST-70 rebuild?
There are many many (tube amp) fish in the sea ~ I just need to work out which one (in the confusing array) to fry.
At say 15 w, just for mids & bass, I’m leaning to SE, perhaps www.audiodesignguide.com/my/572se.html.
Need to be careful with the volts, but what do people think of the design overall.
(Not that it matters but I’ve wondered for years if Andrea is an Italian male or female name. He/ she certainly has been productive).
Could someone explain what exactly is meant by a “fully transformer coupled system”. Coupled from x to y, to achieve z?
smoking-amp
Do you know if anyone get the Yundt composite amp working at the time? It seems a very good idea, for more work and parts.
Were you (“6DJ8 cascode diff amp with CCS and active regulation of the rails”) referring to the MQ-100 or the ST-70 rebuild?
There are many many (tube amp) fish in the sea ~ I just need to work out which one (in the confusing array) to fry.
At say 15 w, just for mids & bass, I’m leaning to SE, perhaps www.audiodesignguide.com/my/572se.html.
Need to be careful with the volts, but what do people think of the design overall.
(Not that it matters but I’ve wondered for years if Andrea is an Italian male or female name. He/ she certainly has been productive).
Could someone explain what exactly is meant by a “fully transformer coupled system”. Coupled from x to y, to achieve z?
smoking-amp
Do you know if anyone get the Yundt composite amp working at the time? It seems a very good idea, for more work and parts.
Fixing the link to the Andrea Ciuffoli SV572-3 SE amp:
http://www.audiodesignguide.com/my/572se.html
I think that the SV572-3 might be difficult to get considering Svetlana USA went belly-up and I don't think the the new owners still distribute them.
If you're thinking of an SE amp with a transmitter triode, something along the lines of a SE GM70 or SE triode-strapped 813 might be better. The valves likely will be cheaper, too.
The Ciufolli design is not fully transformer coupled:
RC coupling exists between the 6SN7 (input valve) and 6BX7 (driver valve)
Most all valve amps have a transformer coupled output stage because valves are intrinsically high impedance devices (high V, low I), and the transformer allows them to couple to speakers (which are low impedance). Some OTL (output transformer less) valve amps exist, but they are wacky in the extreme...
There are four main benefits of interstage transformer coupling:
The disadvantages include cost (a very major disadvantage), and the phase shifts that occur across interstage transformers which are more of a problem when designing a global feedback amplifier.
http://www.audiodesignguide.com/my/572se.html
rick57 said:
I think that the SV572-3 might be difficult to get considering Svetlana USA went belly-up and I don't think the the new owners still distribute them.
If you're thinking of an SE amp with a transmitter triode, something along the lines of a SE GM70 or SE triode-strapped 813 might be better. The valves likely will be cheaper, too.
rick57 said:
The Ciufolli design is not fully transformer coupled:
RC coupling exists between the 6SN7 (input valve) and 6BX7 (driver valve)
Most all valve amps have a transformer coupled output stage because valves are intrinsically high impedance devices (high V, low I), and the transformer allows them to couple to speakers (which are low impedance). Some OTL (output transformer less) valve amps exist, but they are wacky in the extreme...
There are four main benefits of interstage transformer coupling:
- The inductive load allows the driver valve to swing above the voltage rail, thus increasing the amount of voltage it can swing;
- It allows step-up/step-down ratios;
- A high impedance load is presented to the driver valve, thus increasing gain and reducing distortion (in triodes, anyway)
- The secondary of the transformer presents a low impedance to DC, allowing the output valve to stray into Class *2 operation on overload without causing 'blocking' distortion.
The disadvantages include cost (a very major disadvantage), and the phase shifts that occur across interstage transformers which are more of a problem when designing a global feedback amplifier.
Hi,
Wacky?
Nah, they're basically a wish to do away with all the conflicting demands of a good OPT and introducing their own set of problems by the same token.
For ordinary, medium to lowish efficiency speaker they're usually fine and among the best sounding amps of the PP variety when properly executed and interfaced.
Looking back and given that OPTs and chokes have greatly improved over the past twenty years or so, I could probably be quite happy without my OTL amps provided I'd change the speakers for more efficient, probably less linear units....
But OTLs whacky?
No, they can be absolutely fabulous despite their shortcomings....
Moreover, they're one kind of amp that's hardly been developed at all...Still mucho potential untapped there.
Cheers, 😉
Wacky?
Nah, they're basically a wish to do away with all the conflicting demands of a good OPT and introducing their own set of problems by the same token.
For ordinary, medium to lowish efficiency speaker they're usually fine and among the best sounding amps of the PP variety when properly executed and interfaced.
Looking back and given that OPTs and chokes have greatly improved over the past twenty years or so, I could probably be quite happy without my OTL amps provided I'd change the speakers for more efficient, probably less linear units....
But OTLs whacky?
No, they can be absolutely fabulous despite their shortcomings....
Moreover, they're one kind of amp that's hardly been developed at all...Still mucho potential untapped there.
Cheers, 😉
"Do you know if anyone get the Yundt composite amp working at the time? It seems a very good idea, for more work and parts." rick57
There is a wide spectrum of design possibilities for the Yundt VI composite amplifier depending mainly on gain in the A2 current amplifier. I should clarify that Yundt wrote the 1st comprehensive treatise on the 4 main types of composite amplifiers, but I think most of them were known in some form well before that.
If the gain of the A2 current amplifier is low, then it simply shares current with the voltage amplifier in some ratio, set by the loop gain. Examples of this type are the Quad Current Dumping Amplifier and I'm pretty sure the RDH4 handbook mentions a class A triode / class B pentode parallel amplifier. I have included an example of this in the diagram attached. The Sziklai complementary feedback pair, used in many SS amplifiers could also be considered a simple example of this. (diagram bottom left corner) A hybrid composite amplifier is easy to do as well (top of diagram).
Yundt, in his MIT thesis and his more well known IEEE paper, develops a composite amplifier using high gain in the A2 current amplifier so that the A1 voltage amplifier is essentially unloaded.
Performance results were published as well. (distortion results can be better than either of the A1 or A2 amps individual specs!) Using high gains in the A2 loop makes feedback stability more tricky and is probably the reason few (if any) commercial designs have explored this type. (military/missile use is a different story) Therefore, I usually think of the high gain A2 current amp version as the Yundt type design.
Using high gain in the A2 current amplifier loop makes possible the design of a hybrid (SS, MosFet for A2) impedance converter for tube amps that would not need an output transformer for the tubes. The higher the A2 gain, the more the A1 voltage amp is unloaded. Remenber, the A1 voltage amplifier sets the output voltage, A2 just carves out the load current it sees. A1 then effectively sees a high load impedance. So a hybrid design of this type will accurately sound like the A1 tube amplifier with a light load. An added benefit is that the voltage amplifier does not even see reflected inductive currents from the speaker either (SOME people feel this is important for global NFB amps). The A1 voltage amplifier can be most any kind of tube amp, NFB or no NFB, SE or PP.
Don
There is a wide spectrum of design possibilities for the Yundt VI composite amplifier depending mainly on gain in the A2 current amplifier. I should clarify that Yundt wrote the 1st comprehensive treatise on the 4 main types of composite amplifiers, but I think most of them were known in some form well before that.
If the gain of the A2 current amplifier is low, then it simply shares current with the voltage amplifier in some ratio, set by the loop gain. Examples of this type are the Quad Current Dumping Amplifier and I'm pretty sure the RDH4 handbook mentions a class A triode / class B pentode parallel amplifier. I have included an example of this in the diagram attached. The Sziklai complementary feedback pair, used in many SS amplifiers could also be considered a simple example of this. (diagram bottom left corner) A hybrid composite amplifier is easy to do as well (top of diagram).
Yundt, in his MIT thesis and his more well known IEEE paper, develops a composite amplifier using high gain in the A2 current amplifier so that the A1 voltage amplifier is essentially unloaded.
Performance results were published as well. (distortion results can be better than either of the A1 or A2 amps individual specs!) Using high gains in the A2 loop makes feedback stability more tricky and is probably the reason few (if any) commercial designs have explored this type. (military/missile use is a different story) Therefore, I usually think of the high gain A2 current amp version as the Yundt type design.
Using high gain in the A2 current amplifier loop makes possible the design of a hybrid (SS, MosFet for A2) impedance converter for tube amps that would not need an output transformer for the tubes. The higher the A2 gain, the more the A1 voltage amp is unloaded. Remenber, the A1 voltage amplifier sets the output voltage, A2 just carves out the load current it sees. A1 then effectively sees a high load impedance. So a hybrid design of this type will accurately sound like the A1 tube amplifier with a light load. An added benefit is that the voltage amplifier does not even see reflected inductive currents from the speaker either (SOME people feel this is important for global NFB amps). The A1 voltage amplifier can be most any kind of tube amp, NFB or no NFB, SE or PP.
Don
Attachments
Thanks smoking man, it’s good to finally get a reference on those and a basic understanding; I hope to be able to follow up with these more involved approaches with (much) more experience. .
For my first tube amp and limited time I’ll go for a kit. I’ve formed this shortlist so far:
- Welborne, maybe the DRD www.welbornelabs.com/drd45.htm
- Audio Note, say the Kit 2 http://audionotekits.espyderweb.net/
- OTL T16 OTL www.transcendentsound.com/T16OTL.htm
- Hagerman (one vote already for the Cymbal) http://www.hagtech.com/cymbal.html
- DRD: http://www.bottlehead.com/et/et.html
- Ladyday 300B SET Mono Block www.diyhifisupply.com/diyhs_ladyday.htm
I’ve read most raves about at the Audio Asylum about OTLs eg www.audioasylum.com/forums/otl/messages/668.html and
“after listening to a push/pull made by the same manufacturer. After 4 hrs of p/pull i was not prepared for the sonic onslaught of OTLs. I noted a transparency that was as clear as water itself and the soundstage had real depth and clarity far beyond other types of amps. OTLs are true giant killers..... "
Can the asylum folk be trusted? 😉
Although some commercial OTLS are outrageous $, the 15 watt T16 OTL kit is $1149, apparently including everything but the lid.
I know they can run very hot, I can live that, but is there a real catch to OTLs? Tubes burn out quicker? Or is it the ovrlooked shortcut to nirvana?
For my first tube amp and limited time I’ll go for a kit. I’ve formed this shortlist so far:
- Welborne, maybe the DRD www.welbornelabs.com/drd45.htm
- Audio Note, say the Kit 2 http://audionotekits.espyderweb.net/
- OTL T16 OTL www.transcendentsound.com/T16OTL.htm
- Hagerman (one vote already for the Cymbal) http://www.hagtech.com/cymbal.html
- DRD: http://www.bottlehead.com/et/et.html
- Ladyday 300B SET Mono Block www.diyhifisupply.com/diyhs_ladyday.htm
I’ve read most raves about at the Audio Asylum about OTLs eg www.audioasylum.com/forums/otl/messages/668.html and
“after listening to a push/pull made by the same manufacturer. After 4 hrs of p/pull i was not prepared for the sonic onslaught of OTLs. I noted a transparency that was as clear as water itself and the soundstage had real depth and clarity far beyond other types of amps. OTLs are true giant killers..... "
Can the asylum folk be trusted? 😉
Although some commercial OTLS are outrageous $, the 15 watt T16 OTL kit is $1149, apparently including everything but the lid.
I know they can run very hot, I can live that, but is there a real catch to OTLs? Tubes burn out quicker? Or is it the ovrlooked shortcut to nirvana?
OTLs are the sort of amp that will dictate your choice of speaker. Low impedances, large impedance swings, and low efficiency designs will make OTLs crumple and die. They generate a LOT of heat and tend to need a lot of maintainence. And frequent tube changes.
Getting rid of the output transformer is a worthy goal that extracts a cruel price.
Getting rid of the output transformer is a worthy goal that extracts a cruel price.
Hi,
Rick,
Before answering your questions about what kit to choose I'd like to hear more about the kind of speakers you intend to hook the amp up to.
Efficiency, size of listening room, ease of drive, nominal impedance, are the units impedance corrected, colour of your underwear, etc.......
Point is, these kits all vary in power output and topology...
OTLs are about the least efficient of all amps but, yes they have that magic with the right kind of speakers and no, the guys at the asylum can't be trusted....😀
Another point; Bruce Rozenblit, the designer of the range of OTL kits is too busy taking care of his dying uncle right now that he prefers not to bother with business for a while.
Other than that, a well thought out OTL is no more complicated or frightening than any other plain vanilla amp.
They do like to see an easy load as they don't have an OPT to separate the output tubes from the speaker load.
I wouldn't bother with a cap coupled output as you're likely to lose most of the benefits of the OTL.
Cheers, 😉
Rick,
Before answering your questions about what kit to choose I'd like to hear more about the kind of speakers you intend to hook the amp up to.
Efficiency, size of listening room, ease of drive, nominal impedance, are the units impedance corrected, colour of your underwear, etc.......
Point is, these kits all vary in power output and topology...
OTLs are about the least efficient of all amps but, yes they have that magic with the right kind of speakers and no, the guys at the asylum can't be trusted....😀
Another point; Bruce Rozenblit, the designer of the range of OTL kits is too busy taking care of his dying uncle right now that he prefers not to bother with business for a while.
Other than that, a well thought out OTL is no more complicated or frightening than any other plain vanilla amp.
They do like to see an easy load as they don't have an OPT to separate the output tubes from the speaker load.
I wouldn't bother with a cap coupled output as you're likely to lose most of the benefits of the OTL.
Cheers, 😉
SY
What sort of maintenance, bias adjustments?
And frequent tube changes - 22 tubes is a lot: the outputs tubes (16*6C19PI), or the drivers etc (2*12AX7, 2*12AT7 & 2*12AU7)? I have no idea of their cost?? 
Frank
> I'd like to hear more about the kind of speakers:
My three way, so far basically designed & drivers bought, but not yet built (finsihing another speaker).
With < 160 Hz: an H frame dipole woofer, active with a high watt SS amp.
And to be driven by the tube amp to be identified:
- 160 – 1200: Hz a JBL 2202 nominal 8 ohms, 100 dB
- > 1200: Aurum Cantus G1, nominal 8 ohms (actual 7), 100 dB.
(Dispersion patterns could match better, but no design is perfect). Output impedance of the T16 OTL is 1.0 ohm.
I imagine that the JBL &G1 would be a modest load (maybe with a zobel), that shouldn’t rule out many amps. Listening room is 5.3*6.7 *3 m (16*21*9 feet).
Yes these kits deliberately vary in topology, but power is 8 – 15 watts.
In part the question is what is the best topology for the above speaker, in part it’s which kits execute things better. (btw, what is a cap coupled output)?
Anyone
Cheers,
What sort of maintenance, bias adjustments?
And frequent tube changes - 22 tubes is a lot: the outputs tubes (16*6C19PI), or the drivers etc (2*12AX7, 2*12AT7 & 2*12AU7)? I have no idea of their cost?? Frank
> I'd like to hear more about the kind of speakers:
My three way, so far basically designed & drivers bought, but not yet built (finsihing another speaker).
With < 160 Hz: an H frame dipole woofer, active with a high watt SS amp.
And to be driven by the tube amp to be identified:
- 160 – 1200: Hz a JBL 2202 nominal 8 ohms, 100 dB
- > 1200: Aurum Cantus G1, nominal 8 ohms (actual 7), 100 dB.
(Dispersion patterns could match better, but no design is perfect). Output impedance of the T16 OTL is 1.0 ohm.
I imagine that the JBL &G1 would be a modest load (maybe with a zobel), that shouldn’t rule out many amps. Listening room is 5.3*6.7 *3 m (16*21*9 feet).
Yes these kits deliberately vary in topology, but power is 8 – 15 watts.
In part the question is what is the best topology for the above speaker, in part it’s which kits execute things better. (btw, what is a cap coupled output)?
Anyone
Cheers,
OTL NFB no problem?
Hi Frank
You said previously re distortion that ~ how it is spreads and what it contains that seems to matter. http://www.diyaudio.com/forums/showthread.php?s=&postid=397970&highlight=#post397970
“Applying this to OTL design can be done as the NFB loop acts in a different way than if it would entail OPTs but it sure isn't all that easy.”
Are you saying that while there apparently is substantial NFB in OTLs 🙄 eg in particular, the OTL T16 OTL, that the normal disadvantages of NFB have often been avoided?
Cheers
Hi Frank
You said previously re distortion that ~ how it is spreads and what it contains that seems to matter. http://www.diyaudio.com/forums/showthread.php?s=&postid=397970&highlight=#post397970
“Applying this to OTL design can be done as the NFB loop acts in a different way than if it would entail OPTs but it sure isn't all that easy.”
Are you saying that while there apparently is substantial NFB in OTLs 🙄 eg in particular, the OTL T16 OTL, that the normal disadvantages of NFB have often been avoided?
Cheers
Output tube replacements are frequent. So are spectacular failures taking out a few parts; an odd oscillation (inadvertent cable problem for example) can turn catastrophic. Bias, balance, offset all need frequent adjustment. In the Futterman amps, there were a slew of pots trimming various internal voltages all of which needed to be tweaked regularly.
Direct couple your outputs (the best way to go for performance) and the question is when you'll lose a speaker, not if. OTLs are unwelcome in my house just for that reason.
Frank will no doubt have a different view!
Direct couple your outputs (the best way to go for performance) and the question is when you'll lose a speaker, not if. OTLs are unwelcome in my house just for that reason.
Frank will no doubt have a different view!
Frank
The case against?
What life in hours use is likely from the 16 6C19PI output tubes in the OTL T16 OTL? 😕 Can you protect from the odd oscillation (eg speaker protection kit help?)? 😕
SY/ Frank
> Bias, balance, offset all need frequent adjustment
How frequent is frequent?
😕
Thanks
The case against?
What life in hours use is likely from the 16 6C19PI output tubes in the OTL T16 OTL? 😕 Can you protect from the odd oscillation (eg speaker protection kit help?)? 😕
SY/ Frank
> Bias, balance, offset all need frequent adjustment
How frequent is frequent?
😕
Thanks
Confusion reigns!
[br]
Dear Rick57,
These fanatic toob-o-holics have filled your head with too much!!
Let's keep this butt simple.
Your road to instant audio nirvana is not coming through ANY pentode/beam tetrode tube, kit or not.
You want a P-P 300B amplifier to start your toobe journey with.
The good part is that you can build such a thing from scratch without breaking the bank, without much technical ability and with a DVM, soldering iron and a hand drill.
People have built perfectly good amps on cake pans and wood boards for goodness sake!
Now, in your part of the globe, you ought to be able to get Chinese 300Bs pretty inexpensively, and chinese iron (transformers) cheap, cheap. You are going to HK? There are TONS of pretty decent, inexpensive (VERY) amps being made in China. Buy a pair. Fed Ex them back.
In HK, the place must be swamped with iron, and tubes!!
Even a fairly weak example of a 300b PP amp will be pretty darn good.
Imho you *ought* to be able to find a complete p-p 300B China made amp there for <$300US per channel, no problem. You might have to do a little investigating to get past the hustlers and con artists, but they are available I am pretty confident.
What to look for? Simply the rated bandwidth - the wider (higher top end extension) the more likely the iron is well wound. (yeah they could be lying... but so what)
You can then dork with the circuit and the components once you get them home... that is enough to start you off...
Worst case scenario? You buy a pair of replacement output transformers when you get home (maybe from James in Taiwan?) and swap out the ones in the cheapo unit, IF they aren't all they need to be.
Alternatively, just look at a whole bunch of online p-p amp schematics and build the one that you can get most of the parts for most easily!
ANY amp you build is better than NO AMP!! It doesn't MATTER if the iron is any good, or if it sounds great the first time out!
Find an old tube receiver at a yard sale, pawn shop or online and canibalize it for the output transformers, the power transformer and build up a DHT (directly heated triode) amp!! Almost FREE! :- )
The good part of that is that most of the 35-60 watt old receivers had pretty good output iron! (just check to make sure you're not canibalizing a highly collectable piece first!)
And yes many people will tell you to build an SE amp. Don't on your first time out. Three reasons: not enough power, more stringent ouput tranny requirements, harder to keep the hum level down - ie. it's a more difficult project!
The main reason that many newcomers to audio DIY build tube amps is that they are really simple, easy to build, few parts, and relatively free of disasterous melt down (compared to solid state). Oh, and they happen to sound very good.
_-_-bear
PS. any line up with 6SN7/6SL7/300B (or 2A3/6A3 or similar) is likely to automatically sound quite good. 😀
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Dear Rick57,
These fanatic toob-o-holics have filled your head with too much!!
Let's keep this butt simple.
Your road to instant audio nirvana is not coming through ANY pentode/beam tetrode tube, kit or not.
You want a P-P 300B amplifier to start your toobe journey with.
The good part is that you can build such a thing from scratch without breaking the bank, without much technical ability and with a DVM, soldering iron and a hand drill.
People have built perfectly good amps on cake pans and wood boards for goodness sake!
Now, in your part of the globe, you ought to be able to get Chinese 300Bs pretty inexpensively, and chinese iron (transformers) cheap, cheap. You are going to HK? There are TONS of pretty decent, inexpensive (VERY) amps being made in China. Buy a pair. Fed Ex them back.
In HK, the place must be swamped with iron, and tubes!!
Even a fairly weak example of a 300b PP amp will be pretty darn good.
Imho you *ought* to be able to find a complete p-p 300B China made amp there for <$300US per channel, no problem. You might have to do a little investigating to get past the hustlers and con artists, but they are available I am pretty confident.
What to look for? Simply the rated bandwidth - the wider (higher top end extension) the more likely the iron is well wound. (yeah they could be lying... but so what)
You can then dork with the circuit and the components once you get them home... that is enough to start you off...
Worst case scenario? You buy a pair of replacement output transformers when you get home (maybe from James in Taiwan?) and swap out the ones in the cheapo unit, IF they aren't all they need to be.
Alternatively, just look at a whole bunch of online p-p amp schematics and build the one that you can get most of the parts for most easily!
ANY amp you build is better than NO AMP!! It doesn't MATTER if the iron is any good, or if it sounds great the first time out!
Find an old tube receiver at a yard sale, pawn shop or online and canibalize it for the output transformers, the power transformer and build up a DHT (directly heated triode) amp!! Almost FREE! :- )
The good part of that is that most of the 35-60 watt old receivers had pretty good output iron! (just check to make sure you're not canibalizing a highly collectable piece first!)
And yes many people will tell you to build an SE amp. Don't on your first time out. Three reasons: not enough power, more stringent ouput tranny requirements, harder to keep the hum level down - ie. it's a more difficult project!
The main reason that many newcomers to audio DIY build tube amps is that they are really simple, easy to build, few parts, and relatively free of disasterous melt down (compared to solid state). Oh, and they happen to sound very good.
_-_-bear
PS. any line up with 6SN7/6SL7/300B (or 2A3/6A3 or similar) is likely to automatically sound quite good. 😀
I have no direct experience of OTL T16 OTL but I seriously doubt that it suffers from the problems SY described.
My own direct experience from OTLs is from the one I built for myself and the 3 copies of that one that I have built for some friends, my own OTL use the same 6C33C tubes from the beginning, now almost five years without any failure or noticeable drift. An amplifier that oscillates when connected to any normal load be it cables, ESL speakers or even without load is a incompetent design and has nothing to do with OTL as such, I would be very surprised if that was the case with OTL T16 design.
It is quite easy to design protection circuits so that even a drastic failure, (that is unlikely to happen in a good design) will not give any risk for the speakers.
Regards Hans
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