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familar with a Gates FM-1G?

J

jboydingram

I have revived a 1-G to use as a standby, and it is running.
Do not have factory test sheet, and am not sure what the voltage/currents
should be.
Do you have a test sheet and/or can you fill me in...I don't won't to exceed
the specs but want to get every legitimate watt I can...Thanks
 
Well...that's good info...I have not exceeded 600 MA and my Ep is about 2500 volts...maybe I need to increase this,,,BUT, my emission may be down on the tube...SO...if anybody else has info, please input...and thanks a lot( i9f ever in North Mississippi, all engineering types are invited for catfish and hushpuppies at
WBLE, Batesville) I am not kidding, and have had several takers...
J Boyd Ingram
 
3 kV is the factory-specified plate voltage for the FM-1G at 1 kW output, and is controlled by adjusting the taps on the plate transformer, T2. Output (and current) will also be affected by adjustment of the bias voltage (front panel control) and screen voltage (front panel raise-lower switch). Bias should be set so that the final dissipates 0.2 A current with no drive (so that the final doesn't overload upon loss-of-excitation, as with an exciter failure). Bias is adjustable from 0 to -100 volts, and screen is adjustable from 0 to +270 volts. To test the emission of the 4CX1000A tube, use the transmitter itself as a tube-tester; if the filament-adjust acts like a power output adjust control, it's time for a new tube.
 
3KV at around 630ma is what I ran for years. I just retired a FM-1G in 2004.
I dont remember ever having a tube get weak but I sure had many to arc and make the plate choke explode and some even took out the plate current meter. I put a 1 amp fuse in the HV line where it went into the pa cavity. after this I never lost another plate current meter.
 
Thanks, that is a good report...I am running about 2500vdc on the plate, and will retap to get nearer 3KV...and how did the box sound when you were running it....any more comments on the 1G? Thanks
 
Assuming it's tuned up right, It'll sound as good as the exciter driving it... the "linearity" (or lack thereof) is of little concern with FM.

Aside from the output stages (remember youve got a grid-driven final amplifier, AND a grid-driven intermediate amplifier to worry about), you may also want to take a look at the grid tuning on both stages. The best way to do this is to tune for a null in AM noise, which compounds when you have two stages of amplification... Beg, borrow, or steal a mod. monitor that can make this measurement, and you're golden.

Hopefully, you're not using the original exciter (probably was a Gates Solid Statesman, but I may be wrong... All this equipment predates me by more than a decade). Even if it's just a standby, I'd hunt around for something more modern-day. If you've already done this, it probably wouldn't hurt to replace the electrolytic caps in the power supply and audio stages anyway.

In any case, it beats the heck outta being off the air!
 
The original exciter was all tubes. It would put out 10 watts to drive the 4CX1000 final. There was no IPA stage. Watch out for sudden plate current and power output changes when messing around with the grid tuning. On my FM1G the grid tune and the neuterlization adjustment interacted a lot. I have seen this transmitter do some crazy stuff while I was adjusting the grid tuning.
The station that had this transmitter use to sign off at midnight. It loved to wake the morning guy up (and me to) when he hit the plate on button. At least one or two times a month the plate choke would explode. Had very little trouble after the station went 24 hours.
 
I have multiple finals that have some emission if you want them leave a way to contact.
 
Oscillation? Time to re-neutralize. Especially if tuning the grid is too touchy.
The previous post regarding changing the electrolytic caps is also worth repeating.
These are often relied upon as >part< of the overall RF bypass filtering, and this capability often deteriorates while
they are still quite adequate for energy-storage/filtering at 60 and 120 hz.
You may try putting some HV .05s in parallel with these electrolytics, to see if high-frequency bypassing is improved.
If it is, change the 'lytics, and leave the .05s in there with the new filters. Good design should have them there anyway,
to avoid exactly this sort of problem. It is very common in old receivers.
 
Did not change frequency so felt like it was neautrilized...WRONG. Somebody must have diddled with it, as it was way off. Reaffirms the old adage When you assume, you make an a-- of u and me. This baby is off and running...next I will change frequency, and I guess neautralize again, and I am moving 5Mhz. Thanks everyone.
 
Yup, neutralize again. And every time you replace the final as well. If you can find the righ person in Quincy, Harris used to keep their tuning records. It's likely that they set and FM-1G up on whatever frequency you're headed for, and can give you a copy of all the dimensions and values for that frequency. Saves a LOT of time.
 
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