Hi there,
I am looking for some schematics of an EL84 Single Ended amp.
If possible, without capacitors (or as few as possible) in the signal-path. Something really simple, like EABC80/EL84 or some ECC.../EL84 combo or, hopefully, something I haven't heard of yet.
I know, EL84 is not that exciting, but good to begin with...
Thanks, David
I am looking for some schematics of an EL84 Single Ended amp.
If possible, without capacitors (or as few as possible) in the signal-path. Something really simple, like EABC80/EL84 or some ECC.../EL84 combo or, hopefully, something I haven't heard of yet.
I know, EL84 is not that exciting, but good to begin with...
Thanks, David
RH design looks great
Suggested tweaks:
Change that EL84 cathode cap from electrolytic to either a motor run oil cap or a Solen polyproplyene. Same on the 10uF @ 350 v cap- polyproplyene. Change the 220uF filter cap to a pair of 100uF ARC oil cap (inexpensive on ePay). I can not impress enough the difference in sonics leaving electrolytics out of the circuit except for that capacitor at the rectifier.
Use the stellar sounding GE EL84 grey oval plate as it outperforms every EL84 I auditioned in my few amps plus a few owned by other audiophiles- all agreed, they kept the GE EL84 everytime.
I never heard a good sounding 12AT7 tube, it is a VHF/UHF RF amp tube used in older TV tuners, etc. Change that tube to a GE 5751 black plate or a RCA Command 5751 black plate. Change the 10K resistor at the B+ feed point to 22K, change the 22K plate resistor to 100K & the cathode resistor to 1700 ohm. The 12AX7 'family of tubes' allows plenty of NOS variations for tuning the sonics.
I used about every rectifier tube ever manufactured in quite a few different designs. Bump the transformer up to a range of 620VCT to 640 VCT & use a Sylvania 5R4GYB- inexpensive & plentiful. Even a Mullard 5AR4 or WE274 has nothing over the Sylvania sonically & a good rectifier tube makes for quite a difference in sonics.
The best coupling cap are Russian teflon. Parallel to get to .2uF or use nothing of less quality than AuriCap. AuriCap take about 200 hours to break-in.
I see no reason for two filament windings. Just bypass with a .1uF polyester type at the 12AX7 filament wires to ground.
My 2 cents.
edit= spelling error
Suggested tweaks:
Change that EL84 cathode cap from electrolytic to either a motor run oil cap or a Solen polyproplyene. Same on the 10uF @ 350 v cap- polyproplyene. Change the 220uF filter cap to a pair of 100uF ARC oil cap (inexpensive on ePay). I can not impress enough the difference in sonics leaving electrolytics out of the circuit except for that capacitor at the rectifier.
Use the stellar sounding GE EL84 grey oval plate as it outperforms every EL84 I auditioned in my few amps plus a few owned by other audiophiles- all agreed, they kept the GE EL84 everytime.
I never heard a good sounding 12AT7 tube, it is a VHF/UHF RF amp tube used in older TV tuners, etc. Change that tube to a GE 5751 black plate or a RCA Command 5751 black plate. Change the 10K resistor at the B+ feed point to 22K, change the 22K plate resistor to 100K & the cathode resistor to 1700 ohm. The 12AX7 'family of tubes' allows plenty of NOS variations for tuning the sonics.
I used about every rectifier tube ever manufactured in quite a few different designs. Bump the transformer up to a range of 620VCT to 640 VCT & use a Sylvania 5R4GYB- inexpensive & plentiful. Even a Mullard 5AR4 or WE274 has nothing over the Sylvania sonically & a good rectifier tube makes for quite a difference in sonics.
The best coupling cap are Russian teflon. Parallel to get to .2uF or use nothing of less quality than AuriCap. AuriCap take about 200 hours to break-in.
I see no reason for two filament windings. Just bypass with a .1uF polyester type at the 12AX7 filament wires to ground.
My 2 cents.
edit= spelling error
Did ya Google or try forum search?
I think everyone and their cat has made an EL84 SE at one time or another 😀
I think everyone and their cat has made an EL84 SE at one time or another 😀
Re: RH design looks great
Hi Amperex,
You are aware that this circuit uses shunt FB from the output stage plate? If so, you surely did the math and thus you know what load the poor 12AX7 (or its variants) will have to face 🙄
Yes, there is a reason why Mr. Kitic did chose the much higher gm 12AT7 at that place, indeed.
Tom
Hi Amperex,
You are aware that this circuit uses shunt FB from the output stage plate? If so, you surely did the math and thus you know what load the poor 12AX7 (or its variants) will have to face 🙄
Yes, there is a reason why Mr. Kitic did chose the much higher gm 12AT7 at that place, indeed.
Tom
Mine is pretty simple - second amp on my page. I used a toroid isolation transformer and added my own filament winding. Use a full wave bridge with 240V, doubler with 120V. There's no hum with 470 uF caps in the doubler, but it would need another stage of filtering for UL or triode wiring... My audio page
RH84
Build this amp. You will not regret. Simple and Cheap. Nice sounding, very high end. I play it with my Audio Note system. Thanks to Mr Kitic!
Build this amp. You will not regret. Simple and Cheap. Nice sounding, very high end. I play it with my Audio Note system. Thanks to Mr Kitic!
Hi,
no capacitors in the signal path? That is my speciality! 🙂
Maybe want to try this, I built it only yesterday (as a preamp):
If you're feeling groovy you can build it without electrolytics. It should be good for about 1.5 pure triode class A watts. Be sure to use a tube rectified power supply with CLCLC filtering. I recommend the EZ80 for this. You will be surprised how far those 1.5W will get you even on normal speakers!
Happy building
Michael
no capacitors in the signal path? That is my speciality! 🙂
Maybe want to try this, I built it only yesterday (as a preamp):
An externally hosted image should be here but it was not working when we last tested it.
If you're feeling groovy you can build it without electrolytics. It should be good for about 1.5 pure triode class A watts. Be sure to use a tube rectified power supply with CLCLC filtering. I recommend the EZ80 for this. You will be surprised how far those 1.5W will get you even on normal speakers!
Happy building
Michael
The RH84 looks awesome. That's the thing I've been looking for.
I done Google and the forum, but most EL84 Amps end up to be PP or "stuffed" with caps. After the Zenlite I want something as simple with tubes and as little caps as can be. Especially in the signal-path.
This thing will be small and beautiful. Thank you very much.
Dave
I done Google and the forum, but most EL84 Amps end up to be PP or "stuffed" with caps. After the Zenlite I want something as simple with tubes and as little caps as can be. Especially in the signal-path.
This thing will be small and beautiful. Thank you very much.
Dave
Wow, tubemaster, that thing looks awesome too, meine Fresse.
I think I wanna build em both.
The caps are all polypropylene and µ Farad, right? These must be big and expensive...
What exactly is meant with "4-5K" right above the Ausgangsübertrager?
Danke, Dave
I think I wanna build em both.
The caps are all polypropylene and µ Farad, right? These must be big and expensive...
What exactly is meant with "4-5K" right above the Ausgangsübertrager?
Danke, Dave
Servus Dave,
glad you like it. Yes the caps are µ Farad. The MKPs are not that expensive actually. You can get them at http://www.intertechnik.de. I use the Audyn Cap MKP QS 630V variety with good results.
The 4-5K above the OPT is the primary impedance meaning you can use anything from 4 to 5K here. One possibility is the HE-ET 40 Ausgangsübertrager from Welter: http://www.welter-electronic.de/bauteile/trafos/uebertrager/highend/highend_uebertrager.htm
Best regards
Michael aus München
glad you like it. Yes the caps are µ Farad. The MKPs are not that expensive actually. You can get them at http://www.intertechnik.de. I use the Audyn Cap MKP QS 630V variety with good results.
The 4-5K above the OPT is the primary impedance meaning you can use anything from 4 to 5K here. One possibility is the HE-ET 40 Ausgangsübertrager from Welter: http://www.welter-electronic.de/bauteile/trafos/uebertrager/highend/highend_uebertrager.htm
Best regards
Michael aus München
Good point
My error. Remove the shunt feedback resistor & the low performing 12AT7. That feedback is unnecessary in Class A operation. Everything else I stated makes for a superior amp.
My error. Remove the shunt feedback resistor & the low performing 12AT7. That feedback is unnecessary in Class A operation. Everything else I stated makes for a superior amp.
Hi GG,
That is a pentode. Nice work on the 50EH5 amplifier!
It is not in the primary signal path as I like to call it. Still of course it affects the sound but it is indispensable in this position.
One advantage of this circuit is that the cathode bypass resistor is quite large which enables you to use a smaller size bypassing cap (about half the size than in a non dc coupled circuit) so it is possible to use an MKP like SCR or Audyn Cap.
Michael
That is a pentode. Nice work on the 50EH5 amplifier!
It is not in the primary signal path as I like to call it. Still of course it affects the sound but it is indispensable in this position.
One advantage of this circuit is that the cathode bypass resistor is quite large which enables you to use a smaller size bypassing cap (about half the size than in a non dc coupled circuit) so it is possible to use an MKP like SCR or Audyn Cap.
Michael
tubemaster said:
I thought it was a pentode. Now looking at the schematic that I posted in comparison to yours, they both look very similar, so what it the difference that makes your schematic a triode?
Hi,
The screen grid (grid 2) is tied directly to the anode. This way you can operate any pentode as a triode. In case HF oscillation occurs you can use a 100 ohm resistor in between.
Michael
The screen grid (grid 2) is tied directly to the anode. This way you can operate any pentode as a triode. In case HF oscillation occurs you can use a 100 ohm resistor in between.
Michael
tubemaster said:
Sorry Michael, I just want to be certain I am following correctly. For an SE Pentode EL84, a simple application is shown in schematics I showed.
Now for a SET EL84 (Triode), the screen grid (pin 9) is connected to the plate (pin 7).
The Pentode gives more power, but what is the sound quality difference between the two?
Hi GG,
Yes exactly.
The Pentode produces more odd order and higher order distortion which is more unpleasant to the ear. Compared to the triode the pentode sounds "harsh" whereas the triode sounds "smooth". These differences are more obvious in a single ended amplifier. Pentodes also tend to be more nonlinear than triodes which is the reason you often find them used with negative feedback.
Michael
Yes exactly.
The Pentode produces more odd order and higher order distortion which is more unpleasant to the ear. Compared to the triode the pentode sounds "harsh" whereas the triode sounds "smooth". These differences are more obvious in a single ended amplifier. Pentodes also tend to be more nonlinear than triodes which is the reason you often find them used with negative feedback.
Michael
Tubemaster.
Rather intrigued with your el84 DC design.
I've been using a little Mullard 3/3 DC amp for around 8 years with no failures or problems.
I may well give your design a go as it uses no feedback unlike the 3/3.
I take it that resistor values are critical and are there any set up problems.
I have a number of valves awaiting projects and I had thought of building a small SE amp using a nice pair of MO KT66's.
Any thoughts on a DC circuit using these valves would be very much appreciated.
STU.
Rather intrigued with your el84 DC design.
I've been using a little Mullard 3/3 DC amp for around 8 years with no failures or problems.
I may well give your design a go as it uses no feedback unlike the 3/3.
I take it that resistor values are critical and are there any set up problems.
I have a number of valves awaiting projects and I had thought of building a small SE amp using a nice pair of MO KT66's.
Any thoughts on a DC circuit using these valves would be very much appreciated.
STU.
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