6V6 Parafeed?

[G]

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?

[Eli Duttman]

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]

Originally posted by Eli Duttman
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?

[Eli Duttman]

DO you think a C4S will handle 15mA without a heatsink?

I really don't know. Ping VoltSecond on the Bottlehead "board".

[Sch3mat1c]

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

[G]

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.

[Sch3mat1c]

Alright, should work fine then.

[fdegrove]

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,

[G]

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?

[fdegrove]

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.