The high pass pole formed by C3 and R5 should be tuned to about 5 Hz. Therefore you can use a smaller value than 2.5 muF. FWIW, a PTFE part as C3 would be very transparent.
You can save weight and expense by replacing the loading choke and B+ decoupling filter on the 5687's plate with a CCS.
The 6 V. of bias for the 5687's grid is easily obtained from a stack of 3X red LEDs under the cathode. Using LEDs eliminates the bypass cap.
You can save weight and expense by replacing the loading choke and B+ decoupling filter on the 5687's plate with a CCS.
The 6 V. of bias for the 5687's grid is easily obtained from a stack of 3X red LEDs under the cathode. Using LEDs eliminates the bypass cap.
Looks fine, although you have more frequency response in C3 than you can possibly have in the OPT (face it, 2.5Hz transformers are notoriously hard to come by 
) and triode mode 6V6 will have real low power. Fine if ya got some horns or something though I s'pose.
Tim
) and triode mode 6V6 will have real low power. Fine if ya got some horns or something though I s'pose.Tim
I went 1.5 years with a EL84 SE amp in triode mode and it worked fine for me. My Fostex full rangers are about 96 dB 1w/1m. Two watts works really well with them. Thanks for the reply though.
Hi,
Gavin,
For best sonics I'd lower the value of C3 to 0.47µF which will still pass all the lows you'd ever need without the higher time constant of the big ******.
Instead of the MKP cathode bypasses you may want to try out Black Gates there instead, they'll take up less room and sound better too.
If you don't need the gain I'd even ommit C2 or at least give that a try. It should yield a little less distortion due to local degenerative feedback.
Cheers,😉
Gavin,
For best sonics I'd lower the value of C3 to 0.47µF which will still pass all the lows you'd ever need without the higher time constant of the big ******.
Instead of the MKP cathode bypasses you may want to try out Black Gates there instead, they'll take up less room and sound better too.
If you don't need the gain I'd even ommit C2 or at least give that a try. It should yield a little less distortion due to local degenerative feedback.
Cheers,😉
Thank you Frank, Sch3mat1c and Eli. I will do as you suggest Frank. With such a high plate load the cathode bypass on the 5687 isn't really needed is it?
Hi Gavin,
Not for the gain you want anyway...I'd actually overlooked the choke load but give it a shot just the same.
Cheers,😉
EDIT: Using Eli's LED bias scheme would even be better sounding still...CCS could be added later on as the proverbial icing on the cake if you like that approach.
Not for the gain you want anyway...I'd actually overlooked the choke load but give it a shot just the same.
Cheers,😉
EDIT: Using Eli's LED bias scheme would even be better sounding still...CCS could be added later on as the proverbial icing on the cake if you like that approach.
fdegrove said:
I've never tried LEDs a bias devices before. Why not. Tip of the hat to you Eli.
😀
After consulting with Mike LaFevre of Magnequest I have come up with this version that I will build one day. He suggested the coupling cap values that you see. I'm not sure why they need to be so large but I'm hardly going to argue with Mike about Parafeed coupling. I will post a PSU later. Cheers.
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