Hi,
Need some input before I build one.
I recon this is nothing new, but I did not see threads in this forum in this.
While re-looking into EL84's datasheet, it looks promising to drive a EL84(output) in ultra linear mode with a trode connected mode EL84.
Also, read from somewhere that small pentode with a small Ra gives very pleasing results.
Why 5W? I happened to have a pair of hand wound 50mA max. 5.6k OPT with a 4.2k tap.
Has anyone tried this arrangement?
Please comment.
Need some input before I build one.
I recon this is nothing new, but I did not see threads in this forum in this.
While re-looking into EL84's datasheet, it looks promising to drive a EL84(output) in ultra linear mode with a trode connected mode EL84.
Also, read from somewhere that small pentode with a small Ra gives very pleasing results.
Why 5W? I happened to have a pair of hand wound 50mA max. 5.6k OPT with a 4.2k tap.
Has anyone tried this arrangement?
Please comment.
EL84 drive EL84
It seems to be redundancy, due to the same capacity tube drive the same tube, as we know, EL84 ( 6BQ5 ) is a sensitivity tube, the neg. bias only 7.2V. Do you need to have a million dollars to settle a thousand dollar bill ???
The correct way of driving an EL84 is to use a 12bh7 or similar power tube, excess driving power will bring you distortion. consider 12AU7, or 6FQ7 ---- etc.
If U use EL84 for driver, what loading will U use, and also the coupling method.
It seems to be redundancy, due to the same capacity tube drive the same tube, as we know, EL84 ( 6BQ5 ) is a sensitivity tube, the neg. bias only 7.2V. Do you need to have a million dollars to settle a thousand dollar bill ???
The correct way of driving an EL84 is to use a 12bh7 or similar power tube, excess driving power will bring you distortion. consider 12AU7, or 6FQ7 ---- etc.
If U use EL84 for driver, what loading will U use, and also the coupling method.
Hi 18thell,
Thanks for your respond.
I'm thinking of about -17.1~17.5V-ish bias for the power tube, so that that if 1Vrms Vin could use another EL84 set to ~15x gain to drive the output stage to near full power.
I would like to have fairly high cathode current (~10~20ma) on the driver.
Load wise, I haven't really decided yet, maybe I'll just relate to what the power tube want...
Could you elaborate on how distortion will be introduce to the power tube?
Cheers
Thanks for your respond.
I'm thinking of about -17.1~17.5V-ish bias for the power tube, so that that if 1Vrms Vin could use another EL84 set to ~15x gain to drive the output stage to near full power.
I would like to have fairly high cathode current (~10~20ma) on the driver.
Load wise, I haven't really decided yet, maybe I'll just relate to what the power tube want...
Could you elaborate on how distortion will be introduce to the power tube?
Cheers
If you use RC couple, that would be fine, but if you use direct couple, the voltage between the driver and output stage must be very high in order to satisfy the tube requirement.
If using trans. for inter coupling, the quality of the coupling trans. must be very high, otherwise poor sound reproduction U will get.
for EL84 plate loading, the ideal is 4.3K and for grid input is not less than 15K. How and where can U get such 4.3K: 15K ratio tranny. it would be a problem. The answer should be use RC couple, the C must be certain high in order to pass low frequency and enough driving current!!! consider this problem.
If using trans. for inter coupling, the quality of the coupling trans. must be very high, otherwise poor sound reproduction U will get.
for EL84 plate loading, the ideal is 4.3K and for grid input is not less than 15K. How and where can U get such 4.3K: 15K ratio tranny. it would be a problem. The answer should be use RC couple, the C must be certain high in order to pass low frequency and enough driving current!!! consider this problem.
Hi 18thell,
I agree that IT can be very expensive and frustrating when quality is not to the mark...
I like DC on paper, but when comes to really building one, I'll park lots of safty and hence slow down the prgress... It has always been a tempting ides....
Maybe we can monkey
Coupling caps is not a problem, I have quite a few to play around with.
The Mullard datasheet did shows 4.5k load for pentode and 3.5k for triode. But could you kindly elaborate how the 15k grid input is determined?
Woud love to hear some comments on choke loading the plate too.
BTW, need to make correction on the gai, theoritical gain of EL84 is 19x, so I don't think clipping the output tube is a big problem If we are careful with our volume pot.
Cheers
Simpleton,
Thanks for the link, but tht is for a pp amp, I'm more interested in a simple and good sounding SE amp.
Cheers
I agree that IT can be very expensive and frustrating when quality is not to the mark...
I like DC on paper, but when comes to really building one, I'll park lots of safty and hence slow down the prgress... It has always been a tempting ides....
Maybe we can monkey
Coupling caps is not a problem, I have quite a few to play around with.
The Mullard datasheet did shows 4.5k load for pentode and 3.5k for triode. But could you kindly elaborate how the 15k grid input is determined?
Woud love to hear some comments on choke loading the plate too.
BTW, need to make correction on the gai, theoritical gain of EL84 is 19x, so I don't think clipping the output tube is a big problem If we are careful with our volume pot.
Cheers
Simpleton,
Thanks for the link, but tht is for a pp amp, I'm more interested in a simple and good sounding SE amp.
Cheers
It has been observed that this amp should sound very SE in characture. This is because it forgoes the error correction of a normal PP amp.
It could also be argued that it could easily be cheaper to build than an SE amp as PP transformers are cheaper and sound better pound for pound than SE transformers. You also get improved bottom end and more watts to boot.
Worth considering at least. If you do - make shore and use the CCS.
Shoog
Indeed, after building mine all I can say it that it sounds great with excellent bass and detail. So I second Shoog's opinion.
Again concerning this circuit, please note the in this self-split configuration, the grid is polarized at aproximately the same level as of a regular SE EL84 stage (7~8V), which again is a good basis of study/inspiration for a SE EL84-EL84 drive-like-drive topology.
Again concerning this circuit, please note the in this self-split configuration, the grid is polarized at aproximately the same level as of a regular SE EL84 stage (7~8V), which again is a good basis of study/inspiration for a SE EL84-EL84 drive-like-drive topology.
Audio_idiot said:
For the music industrial equipment, they will set the output impedance to 600ohms, and the input impedance of the power amp is 15k.
Usually the input impedance of a power amp. if too high, noise is large, reverse is small, but if set the input impedance too low, it will damp down the output of the preamp. cause not enough drive voltage, cannot achieve max. output power.
For preamp, the output impedance is 600ohm, thus it can drive tenth of power amp. without low down the output voltage, because the input Z of the power amp is considerable high.
To set the input impedance is by setting the ground grid loading, one is by resistor, the other is transformer, transformer divided into AF, and RF, as U said, choke loading is a kind of method.
In AM transmitter, the AF modulation either by ! : ! transformer ratio or using choke coil. these method widely used on plate modulation.
Plate load could be anything, resistance, inductance, resonance cct.
depends on the application.
Hi guys,
Was away for work, sorry for the late respond.
18thell,
Thanks for you clear explinations.
Simpleton, Shoog,
Thanks for you pointers. I really like the idea of the compact PP amp. I'd actually built 2 power amps with the same topology, an EL84 to the dot (DIYPARADISE'S CIRCUIT) and a RU32 with CCS which I fiddle around with the design. They actually sounded very much like SE.
RDF,
I was warned about the microphonics... but I was also told that EL84 can actually sing very well! that's why I was keen to have a go at it. Did you like what your hear? i.e. if we can just forgo the microphonics?
Cheers
Was away for work, sorry for the late respond.
18thell,
Thanks for you clear explinations.
Simpleton, Shoog,
Thanks for you pointers. I really like the idea of the compact PP amp. I'd actually built 2 power amps with the same topology, an EL84 to the dot (DIYPARADISE'S CIRCUIT) and a RU32 with CCS which I fiddle around with the design. They actually sounded very much like SE.
RDF,
I was warned about the microphonics... but I was also told that EL84 can actually sing very well! that's why I was keen to have a go at it. Did you like what your hear? i.e. if we can just forgo the microphonics?
Cheers
Hello,
as coincidence would have it, I designed such an amp recently.
I have built several amps with an EL84 as driver, even an IT coupled LCR RIAA phono preamp.
The EL84 is a great driver tube and gives a fantastic sound.
Here is the schematic:
I do not recommend ultralinear mode.
Feel free to ask any questions you might have.
Best Regards
Michael
www.tubemaster.de
as coincidence would have it, I designed such an amp recently.
I have built several amps with an EL84 as driver, even an IT coupled LCR RIAA phono preamp.
The EL84 is a great driver tube and gives a fantastic sound.
Here is the schematic:
An externally hosted image should be here but it was not working when we last tested it.
I do not recommend ultralinear mode.
Feel free to ask any questions you might have.
Best Regards
Michael
www.tubemaster.de
Bas Horneman said:
Hello Bas,
no it's not that bad
I like the pentode on the output a lot but for input I prefer a triode.The pentode/triode switch on this amp changes the sound character considerably. While triode mode is more neutral, pentode mode is more tuby, maybe even better than real.
Best regards
Michael
Hi simpleton,
I built the EL84 first by following the circuit to the dot, after which I canabilised the OPT for the 832. will post some pix sine your are interested. I actually regreted this as I really prefer to listen to the Simple EL84. BUT I left it as it was because 832 has that cool look
Tubemaster,
Thanks for sharing your design.
Why not UL?
I read that pentode with small load could sound great, is this the case here?
Cheers
I built the EL84 first by following the circuit to the dot, after which I canabilised the OPT for the 832. will post some pix sine your are interested. I actually regreted this as I really prefer to listen to the Simple EL84. BUT I left it as it was because 832 has that cool look
Tubemaster,
Thanks for sharing your design.
Why not UL?
I read that pentode with small load could sound great, is this the case here?
Cheers
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