Title: Multi-Elmac AF-67 Battery Replacement Post by: W1KSZ on April 27, 2019, 02:48:30 PM Just picked up a rather clean AF-67 and Power Supply (caps all replaced in it !!).
As I figured, the 22.5 vdc Bias Battery is kaput (6.6 vdc). Which would folks prefer, replace the Battery (~$25) or do the Zener in the Cathode Mod. Is one better than the other ?? Tnx es 73, Dick, W1KSZ Title: Re: Multi-Elmac AF-67 Battery Replacement Post by: WA4WAX on April 27, 2019, 05:58:16 PM Have a look.
https://www.qsl.net/w/wb4kdi/Elmac/AF-67/CQFeb57.html Title: Re: Multi-Elmac AF-67 Battery Replacement Post by: ka1tdq on April 28, 2019, 08:17:36 AM I had one and as I remember, I did the following:
Removed the battery Grounded the center tap of that transformer it is connected to Lifted the cathode lead from ground for the modulator tubes and placed an electrolytic capacitor / paralleled resistor inline. Jon Title: Re: Multi-Elmac AF-67 Battery Replacement Post by: W2PFY on April 28, 2019, 04:36:32 PM Quote Lifted the cathode lead from ground for the modulator tubes and placed an electrolytic capacitor / paralleled resistor inline What were their values and watts? I though that you had a rather pristine AF-67 that was a keeper? Did you get rid of it? Did you have the PS or build a new one? Inquiring minds need to know Title: Re: Multi-Elmac AF-67 Battery Replacement Post by: ka1tdq on April 28, 2019, 04:50:54 PM I could only guess the values I used, but probably 100uf at 100vdc and a resistor of 500 ohms at 5 watts. Ballpark.
I got rid of it along with all my other tube stuff (amp included). The last few vestiges of my tube stock are being sold on various platforms as we speak. I'm getting rid of the stuff now while there's still a market. In a few years even the junk guy won't take it. I'm focusing on making my shack neat looking and solid state. My primary focus now is on my 24 FET transmitter. Jon Title: Re: Multi-Elmac AF-67 Battery Replacement Post by: wa1mtz on June 17, 2019, 12:42:20 PM I've used my af-67 mostly for mobile over the last 30 years,bought some zeners but never put them in, was much easier to put in 2 12v camera batts, abt half the size of an aa batt, in series of course, they will last 10 years. also, the elmac really likes 525v on the plate! load it to 115ma, plenty of mod!!
Title: Re: Multi-Elmac AF-67 Battery Replacement Post by: DMOD on June 25, 2019, 02:05:32 PM Just picked up a rather clean AF-67 and Power Supply (caps all replaced in it !!). As I figured, the 22.5 vdc Bias Battery is kaput (6.6 vdc). Which would folks prefer, replace the Battery (~$25) or do the Zener in the Cathode Mod. Is one better than the other ?? Tnx es 73, Dick, W1KSZ Here is one possible solution for the bias supply; Phil - AC0OB |