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Title: Restoring EFJ Desk KW. Suggestions on first steps? Post by: af6im on September 29, 2022, 08:38:32 PM Got a nice Desk KW complete, appears all original, but hasn’t operated in over 20 years. Reportedly working ok when retired. Any suggestions on where to start, what to test and known pitfalls for Desk KW newbies? Any assistance greatly appreciated.
Mark AF6IM Title: Re: Restoring EFJ Desk KW. Suggestions on first steps? Post by: K9MB on October 02, 2022, 08:39:35 PM Nobody has bit on this, so I will suggest that if you want suggestions, take pictures and if you can remove covers, do that and take more pictures.
I know very little about this transmitter, but I do not doubt that there are some on here who might know something about it and might make some suggestions. I will say, since you are a newbie, do not plug the thing in and remember that the voltages inside can kill you and you do not even need to touch high voltage- it can come for you. Every old geezer who has worked with high voltage, including this one fears and respects high voltage and a lot of us keep one hand in our back pocket even if we get close to it. Never assume that a cap is discharged- short it with a long probe to ground to be certain after it has time to discharge and power disconnected. Sorry if I underestimated your experience. I can not know it and there are no small mistakes in a kw tube transmitter. 73, Mike https://bama.edebris.com/download/johnson/deskkw/vik-kw.pdf Title: Re: Restoring EFJ Desk KW. Suggestions on first steps? Post by: DMOD on October 03, 2022, 06:26:02 PM Got a nice Desk KW complete, appears all original, but hasn’t operated in over 20 years. Reportedly working ok when retired. Any suggestions on where to start, what to test and known pitfalls for Desk KW newbies? Any assistance greatly appreciated. Mark AF6IM Well, this is certainly not a plug and play unit. It is 65 years old. What prior experience do you have with HV electronic circuits and AM circuits in particular? Don't assume: 1) Any of the tubes are operational, have them tested or have good replacements available; even if the filaments light, it doesn't necessarily mean they are up to the task, 2) Prior owners have NOT made changes or revisions to any of the circuits, 3) cabling and wiring have good insulation, 4) relays are clean and transformers are functional, 5) Bleeder resistors are operational; always use a shorting stick. See page 14 of this Brochure: http://www.radiomanual.info/schemi/Surplus_Radioamateur/EF_Johnson_catalog_957.pdf The Modulator may need an external audio Amplifier to drive it. Phil - AC0OB Title: Re: Restoring EFJ Desk KW. Suggestions on first steps? Post by: W3SLK on October 04, 2022, 11:32:31 AM AC0B said:
Quote The Modulator may need an external audio Amplifier to drive it. Memory serves me that was originally designed to be driven with the Ranger including using it as a speech amp to the 810 modulators.Title: Re: Restoring EFJ Desk KW. Suggestions on first steps? Post by: Detroit47 on October 04, 2022, 01:33:19 PM It is safe to assume all electrolytic caps are bad. If not bad leaky. Most if not all carbon resistors will have drifted up in value. As in all vintage equipment every component needs to be checked. It may run as is but never will be optimal.
Johnathan N8QPC Title: Re: Restoring EFJ Desk KW. Suggestions on first steps? Post by: K4NYW on October 05, 2022, 03:24:54 PM My Desk KW had HV wiring that had hardened and cracked - needed replacement. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Also be aware that this thing has the chassis tied to AC line neutral. So, for example, a 120vac relay is activated by grounding one lead while the other goes to one of the 240vac hot lines. That's why there is only one Key line from the Ranger to the Desk - the manual says if it doesn't key, then turn the Ranger AC plug over.... ---Things were different back then! |