diytube.com

How do I change my Eiclone from fixed bias to cathode bias.

Hi Lee,

Sorry about your bias circuit woes. If you can email a nice selection of close up shots of the whole board that would be fantastic.

OK. To convert to a cathode biased Ike:
-Remove C18
-Remove R13 and R14. Either put them in R17 and R18 or use new resistors (same value).
-Remove R21 and R22 (the 10 ohm bias resistors)
-Add 560, 5W resistors to R23 and R24
-Add 100uF, 100V (can use higher) electrolytics to C5 & C6

You'll know the bias current by checking the voltage at the test points and dividing by 560.

Good luck. This will be a perfect match with these outputs (original HF87 iron).

Shannon

Shannon, the pictures are on their way. Did you get my email on the B+ for the HF87 OP transformers.

lth1 wrote:Shannon, the pictures are on their way. Did you get my email on the B+ for the HF87 OP transformers.

Yes, I re-read your transformer email - sorry I hadn't got that info to you:

J3-1 brown-yellow (plate)
J3-2 brown (screen)
J2-1 blue-yellow (plate)
J2-2 blue (screen)
J4-8 red (B+)

This is assuming that the Sams doc is correct. Just measure the impedance between all the taps and red for certainty.



Shannon