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6V6 Parafeed?

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G

Member
Joined 2002
Hi All,

Been playing around with a Parafeed design for a 6V6 SE amp. Anyone familiar with this topology? Do any gross mistakes stand out?
 

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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.
 

G

Member
Joined 2002
Eli Duttman said:
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.

Hi Eli. DO you think a C4S will handle 15mA without a heatsink?
 
diyAudio Senior Member
Joined 2002
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,;)
 
diyAudio Senior Member
Joined 2002
Hi Gavin,

With such a high plate load the cathode bypass on the 5687 isn't really needed is it?

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.
 

G

Member
Joined 2002
fdegrove said:
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.

I've never tried LEDs a bias devices before. Why not. Tip of the hat to you Eli.
:D
 

G

Member
Joined 2002
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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