Comments for page: A New Look

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Posted by dak January 08, 2016 - 12:03 am
Hi Steve, on my amp there are several extra 6.3v filament taps, and if I need to have a bias supply I can reverse install a filament transformer to get 120 volts out. I guess I will break down and go with fixed bias for the outputs and try the EFB for the screens..Thank you for all your efforts. take care and have a prosperous new year

Posted by Steve L. January 07, 2016 - 06:52 pm
Hi Dak, Yes, all is well here. Having too much fun for a grown-up :) Thanks for asking. I see, about the amp. By the way, I had a thought about how you could develop a negative bias supply with the existing transformer. Since it doesn't require much current, you could capacitively couple from one of the HV windings to a rectifier, as shown in the sketch here: http://www.tronola.com/misc/Negative_bias_supply_concept.GIF.

Sorry that I can't sign up to work out the details but it should be amenable to experimenting. With the desired load on -Vb, C1 can be varied to adjust the DC voltage. Regulation might be a good idea to help get rid of hum and to keep the negative supply constant. C1 should be nonpolar. Just a thought. Best wishes, Steve

Posted by dak January 07, 2016 - 04:35 pm
hi Steve, I hope all is well with you and yours in this new year. I meant to thank you for the suggestion in the first place.
About my amp, I believe the Dynaco A420 output trannys were designed for cathode bias operation. According to the specs, the primary impedance is 6600 ohms into 8 and 16 ohm secondaries. It is the main reason I wanted to keep its operating conditions close to cathode bias and hoping to improve that with EFB. take care, Dak

Posted by Steve L. January 06, 2016 - 05:22 pm
Dak, I can't find it either. The Distributors link on the IR page doesn't work and I see that they say "Call factory." All that suggests that it might not be a viable part. You know, I didn't mean to butt-in here; I just wanted to correct that error. Sorry.

Posted by dak January 06, 2016 - 04:49 pm
Thank you for the correction. I checked, digikey and mouser for the OM7612ST, but that part is NLA. I also checked google but I did not find anything reasonable. Any suggestions? regards,

Posted by Steve L. January 06, 2016 - 03:10 pm
Dak, The regulator link you saw here was incorrect and has been fixed. (My mistake.) Please refresh the page in your browser to see the correction. (The wrong one was positive and EFB requires negative.)


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