Hi Everyone,
I'm looking around for the best way to use a couple of Output Transformers that I have.
Lundahl LL1679
gapped for 70mA
Primary has taps for 2.6k, 4.5k, and 9.7K
Seconday taps for 4,8, and 16ohm
Fairly flexible impedance-wise with all the taps, but limited in current.
What I am hoping for is to get about 20 watts @ 8ohms, somehow.
My current speakers are ~6 ohms and ~89db efficient.
The amp these OPTs are in currently is an SE EL34, and the 6 watts isn't enough for my listening habits.
The 70mA gap might be too low for going SE with big triodes like the 211, but could it be used with the "super" versions of the 300b like the EML 300b-XLS?
I might also entertain a PP build with them if the reduced Primary Inductance isn't a problem. The Data Sheet lists 40H (the pp version is 150H)
Any good ideas?
Thanks in advance for your input!
Regards,
John
I'm looking around for the best way to use a couple of Output Transformers that I have.
Lundahl LL1679
gapped for 70mA
Primary has taps for 2.6k, 4.5k, and 9.7K
Seconday taps for 4,8, and 16ohm
Fairly flexible impedance-wise with all the taps, but limited in current.
What I am hoping for is to get about 20 watts @ 8ohms, somehow.
My current speakers are ~6 ohms and ~89db efficient.
The amp these OPTs are in currently is an SE EL34, and the 6 watts isn't enough for my listening habits.
The 70mA gap might be too low for going SE with big triodes like the 211, but could it be used with the "super" versions of the 300b like the EML 300b-XLS?
I might also entertain a PP build with them if the reduced Primary Inductance isn't a problem. The Data Sheet lists 40H (the pp version is 150H)
Any good ideas?
Thanks in advance for your input!
Regards,
John
> about 20 watts
70mA times 9600 ohms is 672 Volts, 47 Watts dissipation. A pair of EL34 will stand that. Maybe one cheap or over-sized 6550-family tube. As Pentode, 47W Pdiss may be 18.8 Watts of audio output.
70mA times 9600 ohms is 672 Volts, 47 Watts dissipation. A pair of EL34 will stand that. Maybe one cheap or over-sized 6550-family tube. As Pentode, 47W Pdiss may be 18.8 Watts of audio output.
The following is just my opinion (food for thought)
40H is because of the medium air gap.
The air gap is needed so it can work SE and 70mA, right?
Using that 40H version to do push pull, will have an inductance of 10H per 1/2 of the primary (1/2 turns = 1/4 inductance).
If you do class A push pull, when both tubes have reasonable rp and are not near AB or near cut off, then both plates are woking
10H each, so in tandem they see 20H, as the other tube shares the load (that is as good as it gets for the 40H model when you decide to use it for push pull).
The 150H version is made for Push Pull, and the air gap is very small.
And . . . the plate currents must be almost exactly balanced, or the
transformer will saturate with even moderate signal level bass frequency music.
So the 40H model used in push pull mode can withstand a little more un-balanced plate current than the 150H model.
But the output tubes plates need to drive 20H total in class A, and 10H in class AB.
The right tool for the right job.
40H is because of the medium air gap.
The air gap is needed so it can work SE and 70mA, right?
Using that 40H version to do push pull, will have an inductance of 10H per 1/2 of the primary (1/2 turns = 1/4 inductance).
If you do class A push pull, when both tubes have reasonable rp and are not near AB or near cut off, then both plates are woking
10H each, so in tandem they see 20H, as the other tube shares the load (that is as good as it gets for the 40H model when you decide to use it for push pull).
The 150H version is made for Push Pull, and the air gap is very small.
And . . . the plate currents must be almost exactly balanced, or the
transformer will saturate with even moderate signal level bass frequency music.
So the 40H model used in push pull mode can withstand a little more un-balanced plate current than the 150H model.
But the output tubes plates need to drive 20H total in class A, and 10H in class AB.
The right tool for the right job.
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Hi 6a3sUMMER,
Okay, let me see if I understand correctly. If the 40H gapped OPT is used for PP, just for ease we will say triode EL34 using the 4500pri and 8ohm sec taps (1:23.7 using nominal 6 ohm speaker impedance = 3375ohm primary impedance):
f3 will be:
f = Z/(2*Pi*L)
f=(15000||3375)/(6.283*20)
f=2755/125.66
f=21.92
f3 of 21.92= not so great, but maybe not so horrible (depending)?
Are my calculations somewhat right on this? Or have I completely botched it?
Okay, let me see if I understand correctly. If the 40H gapped OPT is used for PP, just for ease we will say triode EL34 using the 4500pri and 8ohm sec taps (1:23.7 using nominal 6 ohm speaker impedance = 3375ohm primary impedance):
f3 will be:
f = Z/(2*Pi*L)
f=(15000||3375)/(6.283*20)
f=2755/125.66
f=21.92
f3 of 21.92= not so great, but maybe not so horrible (depending)?
Are my calculations somewhat right on this? Or have I completely botched it?
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Hi PRR,
Sorry, I replied before thinking.
Of course you were referring to EL34 PSE, and 6550 SE (cheap-o because it may get worn out quickly, or KT120/150 because they have higher plate dissipation--if I read your inference right.)
Thanks for the responses!
Regards,
John
Sorry, I replied before thinking.
Of course you were referring to EL34 PSE, and 6550 SE (cheap-o because it may get worn out quickly, or KT120/150 because they have higher plate dissipation--if I read your inference right.)
Thanks for the responses!
Regards,
John
force of 1/2,
Push Pull:
Perhaps I am looking at it wrong, but here goes my approximations:
Pentode mode:
In class A push pull, each tube drives 1/2 of the primary turns (10H).
But the 15k of each EL34 plate is helping the other plate . . .
(effectively are in parallel, that is 7.5k driving 10H).
Just for illustration, with no load on the 8 Ohm output tap:
7500 = 2 x pi x f x L
7500/(2 x pi x L) = f
7500/( 2 x pi x 10) = f
f = 119.4 Hz
Depending on the loudspeaker woofer and enclosure design (for example closed box, or bass reflex): There are 1 or 2 bass frequency resonances, respectively.
Those resonances are often 16, 25, 40 Ohms at the resonance.
That means that at some bass frequencies that the 8 Ohm tap is essentially unloaded.
So, the - 3 dB can be as high as 119.4Hz.
Ultra Linear mode:
But if I remember, you are going to use Ultra Linear, so the plate impedance, rp, is much lower.
Suppose in UL, rp is half of what it is in pentode mode.
rp = 7500 Ohms, and effectively 2 parallel plates (class A) = 3750 Ohms
That puts the (unloaded 8 Ohm tap) - 3dB frequency at 59.7 Hz.
Now if your loudspeaker impedance at all bass frequencies is actually 8 Ohms, or actually 6 Ohms,
then your - 3 dB frequency will be much much lower than 59.7 Hz.
That is because of the 6 Ohm load on the secondary reflects 3375 Ohms on the transformer primary. And that 3375 Ohms is in parallel with the inductive reactance of the primary (of which that reactance varies with frequency).
An amplifier is part of a complete system, you have to include the loudspeaker in that system.
The loudspeaker is not an 8 Ohm load resistor, and it is not a 6 Ohm resistor.
Many people say that their amplifier is flat to 20 Hz (tested on a load resistor).
And then they complain that there is no bass on their loudspeaker.
But they know that with a high damping factor solid state amplifier, the loudspeaker has lots of bass.
Does that make sense?
To some extent, global negative feedback can improve this situation.
System, system, system.
That is just how I look at things.
Push Pull:
Perhaps I am looking at it wrong, but here goes my approximations:
Pentode mode:
In class A push pull, each tube drives 1/2 of the primary turns (10H).
But the 15k of each EL34 plate is helping the other plate . . .
(effectively are in parallel, that is 7.5k driving 10H).
Just for illustration, with no load on the 8 Ohm output tap:
7500 = 2 x pi x f x L
7500/(2 x pi x L) = f
7500/( 2 x pi x 10) = f
f = 119.4 Hz
Depending on the loudspeaker woofer and enclosure design (for example closed box, or bass reflex): There are 1 or 2 bass frequency resonances, respectively.
Those resonances are often 16, 25, 40 Ohms at the resonance.
That means that at some bass frequencies that the 8 Ohm tap is essentially unloaded.
So, the - 3 dB can be as high as 119.4Hz.
Ultra Linear mode:
But if I remember, you are going to use Ultra Linear, so the plate impedance, rp, is much lower.
Suppose in UL, rp is half of what it is in pentode mode.
rp = 7500 Ohms, and effectively 2 parallel plates (class A) = 3750 Ohms
That puts the (unloaded 8 Ohm tap) - 3dB frequency at 59.7 Hz.
Now if your loudspeaker impedance at all bass frequencies is actually 8 Ohms, or actually 6 Ohms,
then your - 3 dB frequency will be much much lower than 59.7 Hz.
That is because of the 6 Ohm load on the secondary reflects 3375 Ohms on the transformer primary. And that 3375 Ohms is in parallel with the inductive reactance of the primary (of which that reactance varies with frequency).
An amplifier is part of a complete system, you have to include the loudspeaker in that system.
The loudspeaker is not an 8 Ohm load resistor, and it is not a 6 Ohm resistor.
Many people say that their amplifier is flat to 20 Hz (tested on a load resistor).
And then they complain that there is no bass on their loudspeaker.
But they know that with a high damping factor solid state amplifier, the loudspeaker has lots of bass.
Does that make sense?
To some extent, global negative feedback can improve this situation.
System, system, system.
That is just how I look at things.
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force of 1/2,
A resistive load line at 1 kHz is not the same as:
The elliptical load of an output transformer at various frequencies,
which is effectively in parallel with:
The elliptical load of a loudspeaker at various frequencies.
Generally, push pull's ability to deal with an elliptical load is better than,
single ended's ability to deal with an elliptical load.
"All Generalizations Have Exceptions" - me
Just so you understand, I design and listen to single ended tube amplifiers and design and listen to push pull tube amplifiers.
I enjoy listening to both kinds.
A resistive load line at 1 kHz is not the same as:
The elliptical load of an output transformer at various frequencies,
which is effectively in parallel with:
The elliptical load of a loudspeaker at various frequencies.
Generally, push pull's ability to deal with an elliptical load is better than,
single ended's ability to deal with an elliptical load.
"All Generalizations Have Exceptions" - me
Just so you understand, I design and listen to single ended tube amplifiers and design and listen to push pull tube amplifiers.
I enjoy listening to both kinds.
Hi 6A3sUMMER,
Thanks again for your response!
Yes, I think I get it. I am definitely in the "just learning" stage (still).
I guess if I wanted to try PP with these, I would just have to try it and see if the bass dropped off too quickly due to drooping primary resistance at lower frequencies-- due to the reatcance, that is. (do I have that right?)
Of course, I have a nice pair of Mullard-style PP amps that I like quite a bit. Though, could be interesting to try a different topology.
As for SE, I would like to try an SE amp, again. I just need more wattage. I wonder if the smaller air-gap is going to be a serious impediment to that goal?
I will mull over PRR's suggestion of 6550 in pentode.
Thanks again for your response!
Yes, I think I get it. I am definitely in the "just learning" stage (still).
I guess if I wanted to try PP with these, I would just have to try it and see if the bass dropped off too quickly due to drooping primary resistance at lower frequencies-- due to the reatcance, that is. (do I have that right?)
Of course, I have a nice pair of Mullard-style PP amps that I like quite a bit. Though, could be interesting to try a different topology.
As for SE, I would like to try an SE amp, again. I just need more wattage. I wonder if the smaller air-gap is going to be a serious impediment to that goal?
I will mull over PRR's suggestion of 6550 in pentode.
If you want to use that transformer for push pull, but you do not want to use global negative feedback, the amp can be quite simple.
Suppose you want to use Pentodes like EL84, or EL34 output tubes.
Or suppose you want to use Beam Power tubes like 6BQ5, 7591, 6L6, KT66, or KT77.
Then, wire them in Triode mode (100 Ohm resistor from the screen to the plate).
In this mode, you will not, and can not use any UL tap.
Triode wired mode has less power, but it works quite well without global negative feedback.
The plate resistance in triode wired is from about 1300 to 1700 Ohms. In push pull Class A . . .
We get -3dB of from 10.3 Hz to 13.5 Hz without global feedback.
By the way, the 6550 is my least favorite tube. It has the most restrictive specification for maximum grid resistor of all those tubes. Therefore, it is one of the hardest tubes to drive with a simple driver circuit. (well I will not even consider using a KT120 or
KT 150. I am not a "High Power" tube man).
If you want to, you can build a push pull DHT (Direct Heated Triode) amp.
You can use 2A3, 6A3, or 300B tubes.
The rp of those tubes is 800, 800, and 700 Ohms respectively.
That can drive the 40H plate to plate inductance quite well.
300B push pull in Class A effectively gives 400 Ohms driving 10H inductance.
that is - 3dB at 6.4 Hz.
You will have a little more complexity, because the 2A3, 6A3, and 300B really should have their filaments powered by DC, not AC.
How much wattage do you really need?
Suppose you want to use Pentodes like EL84, or EL34 output tubes.
Or suppose you want to use Beam Power tubes like 6BQ5, 7591, 6L6, KT66, or KT77.
Then, wire them in Triode mode (100 Ohm resistor from the screen to the plate).
In this mode, you will not, and can not use any UL tap.
Triode wired mode has less power, but it works quite well without global negative feedback.
The plate resistance in triode wired is from about 1300 to 1700 Ohms. In push pull Class A . . .
We get -3dB of from 10.3 Hz to 13.5 Hz without global feedback.
By the way, the 6550 is my least favorite tube. It has the most restrictive specification for maximum grid resistor of all those tubes. Therefore, it is one of the hardest tubes to drive with a simple driver circuit. (well I will not even consider using a KT120 or
KT 150. I am not a "High Power" tube man).
If you want to, you can build a push pull DHT (Direct Heated Triode) amp.
You can use 2A3, 6A3, or 300B tubes.
The rp of those tubes is 800, 800, and 700 Ohms respectively.
That can drive the 40H plate to plate inductance quite well.
300B push pull in Class A effectively gives 400 Ohms driving 10H inductance.
that is - 3dB at 6.4 Hz.
You will have a little more complexity, because the 2A3, 6A3, and 300B really should have their filaments powered by DC, not AC.
How much wattage do you really need?
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Hi 6A3sUMMER,
Thanks again for responding.
How many watts? 10 seems to be too little. 20 seems plenty. 30 is generous. This is based on experience using EL34s.
SE UL EL34 making around 10 watts doesn't get me there with my current speakers. Even when I had Altec Valencias at about 96db/watt, I still liked more power.
El34 triode-strapped PP giving around 20 watts is plenty.
EL34 UL PP giving roughly 30 watts is a bit more fun, but that might have to do with the way I implemented the triode mode.
Spent the day yesterday tearing down an old amp and trying to do a fully scratch build using only what I had in the spare parts box. I have been a "constructor" for decades, building lots of amps, preamps, phono stages, but never really understood the circuits.
I made a UL SE EL34 with 6SN7 driver, fixed bias. Extremely basic. Just wanted to learn a bit through doing. Did all the equations myself. It works fine, but that is about the most I can say for it. (Ha ha)
Anyway, a 300B push-pull is really what I probably should build. I have looked over Lynn Olson's Karna schematic many times. What always stops me, aside from the cost of all the transformers, is the shear size! I don't have the room for two huge amp chassis plus two huge power supplies.
However, I could make a much simpler 300B PP amp, and make it smaller. I think I would try for AC heaters on the output tubes if I did a DHT Push-Pull, as some of the hum would cancel, wouldn't it?
I have also been mulling over making a "Super" 300B SE amp, using EML or KR 300B-XLS. Those should give me almost 20 watts, if run at higher voltage. Though, these (I think) would require a larger air gap than 70mA. But I guess I could try it and see if they saturate. Core saturation would cause 'clipping' like distortion, no?
I have only recently started playing with DHTs, and only in preamps, but I really like them. Such intense clarity. So that is the route that has the most pull right now. Though, wrestling with noise is a real challenge in Directly Heated devices. At least I have a little experience under my belt, now.
Sorry for the long post with all the naive questions and statements.
Regards,
John
Thanks again for responding.
How many watts? 10 seems to be too little. 20 seems plenty. 30 is generous. This is based on experience using EL34s.
SE UL EL34 making around 10 watts doesn't get me there with my current speakers. Even when I had Altec Valencias at about 96db/watt, I still liked more power.
El34 triode-strapped PP giving around 20 watts is plenty.
EL34 UL PP giving roughly 30 watts is a bit more fun, but that might have to do with the way I implemented the triode mode.
Spent the day yesterday tearing down an old amp and trying to do a fully scratch build using only what I had in the spare parts box. I have been a "constructor" for decades, building lots of amps, preamps, phono stages, but never really understood the circuits.
I made a UL SE EL34 with 6SN7 driver, fixed bias. Extremely basic. Just wanted to learn a bit through doing. Did all the equations myself. It works fine, but that is about the most I can say for it. (Ha ha)
Anyway, a 300B push-pull is really what I probably should build. I have looked over Lynn Olson's Karna schematic many times. What always stops me, aside from the cost of all the transformers, is the shear size! I don't have the room for two huge amp chassis plus two huge power supplies.
However, I could make a much simpler 300B PP amp, and make it smaller. I think I would try for AC heaters on the output tubes if I did a DHT Push-Pull, as some of the hum would cancel, wouldn't it?
I have also been mulling over making a "Super" 300B SE amp, using EML or KR 300B-XLS. Those should give me almost 20 watts, if run at higher voltage. Though, these (I think) would require a larger air gap than 70mA. But I guess I could try it and see if they saturate. Core saturation would cause 'clipping' like distortion, no?
I have only recently started playing with DHTs, and only in preamps, but I really like them. Such intense clarity. So that is the route that has the most pull right now. Though, wrestling with noise is a real challenge in Directly Heated devices. At least I have a little experience under my belt, now.
Sorry for the long post with all the naive questions and statements.
Regards,
John
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I do not know if the Lundahl transformers you have includes UL taps. And I do not know what the UL tap percentage is (%). You need to consider that for push pull UL.
I will never build another single ended DHT or push pull DHT with AC powered filaments.
Instead I will use DC for DHT filaments.
Even if you get the hum to zero; you have another problem [hidden to some less knowledgeable persons].
The second and worse problem is that AC DHT filaments causes 2X mains power line frequency Intermodulation (50 Hz creates 100 Hz, and 60 Hz creates 120 Hz Intermodulation sidebands).
The problem is that those 2X Intermodulation sidebands appear on each and every musical note, and on each and every harmonic of those musical notes.
Imagine a flute playing a 440 Hz Concert-A note.
Ideally you get 440 Hz, and the second and third harmonics at 880 Hz, and 1320 Hz.
All is well. OK
But now, consider what happens with AC power to DHT filaments.
You have US power at 60 Hz, 2X is 120 Hz. The Intermodulation is - and + 120 Hz away from the original music note and its original harmonics.
With AC filaments, you Also get Intermodulation distortion products at
320, 560, 760, 1000, 1200, and 1440 Hz.
That is not the original flute note and harmonics.
Well, now you know why I will never use AC on DHT filaments.
I will never build another single ended DHT or push pull DHT with AC powered filaments.
Instead I will use DC for DHT filaments.
Even if you get the hum to zero; you have another problem [hidden to some less knowledgeable persons].
The second and worse problem is that AC DHT filaments causes 2X mains power line frequency Intermodulation (50 Hz creates 100 Hz, and 60 Hz creates 120 Hz Intermodulation sidebands).
The problem is that those 2X Intermodulation sidebands appear on each and every musical note, and on each and every harmonic of those musical notes.
Imagine a flute playing a 440 Hz Concert-A note.
Ideally you get 440 Hz, and the second and third harmonics at 880 Hz, and 1320 Hz.
All is well. OK
But now, consider what happens with AC power to DHT filaments.
You have US power at 60 Hz, 2X is 120 Hz. The Intermodulation is - and + 120 Hz away from the original music note and its original harmonics.
With AC filaments, you Also get Intermodulation distortion products at
320, 560, 760, 1000, 1200, and 1440 Hz.
That is not the original flute note and harmonics.
Well, now you know why I will never use AC on DHT filaments.
Ah, yes. I have read about IMD with AC heated DHTs. Even so some (Lynn Olson) like AC heaters. It would be easy enough to try and go DC later.
DC is not a problem, of course, it just requires more chassis space for the extra transformers, rectifiers, smoothing caps and chokes.
DC is not a problem, of course, it just requires more chassis space for the extra transformers, rectifiers, smoothing caps and chokes.
You need to figure using filament transformers that are rated for 1.6 times the DC current of the filament.
A 300B 1.25 Amp 5V DC filament requires a filament transformer that is rated at
1.6 x 1.25 Amps = 2.0 Amps.
Use a 2.5 or 3 Amp secondary, and you will have a much cooler filament transformer.
The problem is the transient current I-squared x R losses in the secondary DCR, because
the supply uses solid state diodes, and charges a very large capacitance capacitor.
I have used brute force DC for DHT filaments.
Rectifier, Cap, series Power Resistor, Cap (CRC filter).
I always had 1mV (2 mV at most) ripple on those, low enough to make the Intermodulation distortion of the ripple so that it was way below the noise floor.
Chokes will spray magnetic fields, from the multi Amp transients. They are heavy, take up space, must be oriented, can not use steel chassis, and expensive to purchase. Just my opinion.
For a push pull output, always use either individual adjustable fixed bias, or individual self bias resistors and bypass caps.
Current balance is very important. Well, less so in your case since you have an Air Gapped version of the Lundahl transformer.
But if you ever replace it with a non air gapped transformer, you will need to update the bias circuits to Individual bias, so you can balance the plate currents.
Happy building!
Happy listening!
A 300B 1.25 Amp 5V DC filament requires a filament transformer that is rated at
1.6 x 1.25 Amps = 2.0 Amps.
Use a 2.5 or 3 Amp secondary, and you will have a much cooler filament transformer.
The problem is the transient current I-squared x R losses in the secondary DCR, because
the supply uses solid state diodes, and charges a very large capacitance capacitor.
I have used brute force DC for DHT filaments.
Rectifier, Cap, series Power Resistor, Cap (CRC filter).
I always had 1mV (2 mV at most) ripple on those, low enough to make the Intermodulation distortion of the ripple so that it was way below the noise floor.
Chokes will spray magnetic fields, from the multi Amp transients. They are heavy, take up space, must be oriented, can not use steel chassis, and expensive to purchase. Just my opinion.
For a push pull output, always use either individual adjustable fixed bias, or individual self bias resistors and bypass caps.
Current balance is very important. Well, less so in your case since you have an Air Gapped version of the Lundahl transformer.
But if you ever replace it with a non air gapped transformer, you will need to update the bias circuits to Individual bias, so you can balance the plate currents.
Happy building!
Happy listening!
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Amplifier gain vs system gain structure
Hi,
I have read numerous places that the 300B single-ended needs about 180v peak to peak to reach full output.
The preamp I am planning on using with the amp has a voltage gain of about 6.
(Maybe this is the wrong way about it, but I actually measured this with a DMM using a 1V 1KHZ input signal. The preamp delivered a 6.7V signal on the output with the volume maxed.)
With this in mind, I was thinking that the amp should have an over all voltage gain of somewhere around 30.
Is this correct thinking?
I know I stated earlier that I needed 20 watts, but I brought home my office speakers which are ~92db sensitivity.
This is just enough for my SE EL34 to reach a decent volume, even in triode mode. These should make a good combo with an SE 300b.
I've never had a 300b amp, and I've never had an SE amp I liked that much. So I thought I would incorporate these two nevers into my design goals.
Thanks for in advance for your input.
Regards,
John
Hi,
I have read numerous places that the 300B single-ended needs about 180v peak to peak to reach full output.
The preamp I am planning on using with the amp has a voltage gain of about 6.
(Maybe this is the wrong way about it, but I actually measured this with a DMM using a 1V 1KHZ input signal. The preamp delivered a 6.7V signal on the output with the volume maxed.)
With this in mind, I was thinking that the amp should have an over all voltage gain of somewhere around 30.
Is this correct thinking?
I know I stated earlier that I needed 20 watts, but I brought home my office speakers which are ~92db sensitivity.
This is just enough for my SE EL34 to reach a decent volume, even in triode mode. These should make a good combo with an SE 300b.
I've never had a 300b amp, and I've never had an SE amp I liked that much. So I thought I would incorporate these two nevers into my design goals.
Thanks for in advance for your input.
Regards,
John
Correction!
I meant that the voltage-amp/driver would have a voltage-gain of 30, not the the overall amp including the finals.
I meant that the voltage-amp/driver would have a voltage-gain of 30, not the the overall amp including the finals.
If you designing amplifier for now existing pre-amplifier's output level, your amplifier only with this preamp working correctly.
Most of the DMMs measuring RMS, but cheaper ones are accurate at lower frequencies (I'm not sure, that at 1kHz these shows precise level, maybe at 100Hz).
180Vpp (2x 90V peek)= 63.64V RMS.
The "standard" sources output level approx. 2V RMS.
So the required "gain" is 31.82 approx. 32.
If you calculate with -at least- 3dB headroom, the ideal gain is 1.41 * 31.82 approx 45.
Most of the DMMs measuring RMS, but cheaper ones are accurate at lower frequencies (I'm not sure, that at 1kHz these shows precise level, maybe at 100Hz).
180Vpp (2x 90V peek)= 63.64V RMS.
The "standard" sources output level approx. 2V RMS.
So the required "gain" is 31.82 approx. 32.
If you calculate with -at least- 3dB headroom, the ideal gain is 1.41 * 31.82 approx 45.
Hi Euro21,
Thanks for the calculation correction!
That is the figure i will head for, then.
There are way too many ways to get there, though. It gets confusing.
I suppose I should just pick a topology and try it. Maybe start with something more traditional, and move on from there: single pentode, or Grounded-cathode medium mu triode+CF, or even cascaded triodes. (still too many choices!)
Out of curiosity, (on the topic of gain) what is a rough estimation of the gain of your D3a+2sk2700 driver stage?
Thanks again!
Regards,
John
Thanks for the calculation correction!
That is the figure i will head for, then.
There are way too many ways to get there, though. It gets confusing.
I suppose I should just pick a topology and try it. Maybe start with something more traditional, and move on from there: single pentode, or Grounded-cathode medium mu triode+CF, or even cascaded triodes. (still too many choices!)
Out of curiosity, (on the topic of gain) what is a rough estimation of the gain of your D3a+2sk2700 driver stage?
Thanks again!
Regards,
John