Does anyone have a factory test sheet(s) for a 2.5K FM? Frequency does not matter, it's the general range of readings I need. Will pay postage , copying, etc.
Please help! J Boyd
Please help! J Boyd
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Gates FM 2.5K, Factory test sheets?
- Thread starter jboydingram
- Start date
It would be a long shot but have you tried to call Harris? I needed a test sheet for a Harris 2.5k (same transmitter) and they actually had a sheet that would work. There was a charge but I seem to remember it was reasonable.
How soon do you need it? Have a test sheet from our 2.5 H (same transmitter, essentially) from when it was new in '1974; as well, I do believe, another test sheet for a 2.5K (not the one we have now, but the original one that is over in Indiana somewhere now). Have to travel tomorrow, but can get to it on Friday.
To start, our "H," before we turned it off, was running 910 ma plate current with 4050 volts on the plate for just under 2500 watts (which is about 68% efficiency--not great, but that's where it was happy). Don't remember the other readings, & we had disconnected the IPA to drive it directly with our FX-50 (took around 25~30 watts of drive for full output).
Did you find the frequency change/tune-up instructions from the Harris website? I believe I also have that PDF at the office.
To start, our "H," before we turned it off, was running 910 ma plate current with 4050 volts on the plate for just under 2500 watts (which is about 68% efficiency--not great, but that's where it was happy). Don't remember the other readings, & we had disconnected the IPA to drive it directly with our FX-50 (took around 25~30 watts of drive for full output).
Did you find the frequency change/tune-up instructions from the Harris website? I believe I also have that PDF at the office.
Hello...Thanks for the replies...I have the frequency change instructions, and pretty well know where the readings should be... I am heading from 105.3 to 106.9, and am changing from the "a" to "b" 5cx1500. Also, I am trying to replace the IPA section with a 50 watt exciter...to eliminate that stage...anybody ever tried that? I have no idea of the input impedance to the final, but my MFJ
impedance bridge says I am close....suggestions? Thanks...and my FAX is 662-563-9002 if someone wants to fax info...from the North of Mississippi, thanks....
J Boyd.
impedance bridge says I am close....suggestions? Thanks...and my FAX is 662-563-9002 if someone wants to fax info...from the North of Mississippi, thanks....
J Boyd.
About three years ago--New Year's day--transmitter failed (2.5H). Short in the IPA. At that time it was a 2 hour drive for me to the transmitter site. To get the transmitter back on, I connected the MX 15 (which was running at around 16 watts) directly into the final cavity. (In both the "H" and "K" the IPA is connected to the final by a short jumper into a BNC on the side of the PA cavity). Had to turn the exciter DOWN to get back to our (then) licensed TPO of 1100 watts.
So the short answer is yes, you can do this, and it works just fine. As I mention above, 25~30 watts seems to be what is needed to drive the final to full power. You will need to have an exciter that does not mind some reflected power when the transmitter (the PA) is cold, since the input impedance changes as the tube warms up. Otherwise, you may have problems getting back from a power failure. (I notice my Armstrong exciter,--on another transmitter, "fades up" from a power interruption; doesn't seem to bother the tube IPA in that box, a 10K, as it matches the time delay on restart).
To be safe, and to protect the exciter, you need to make a quarter wave shorted stub (piece of RG-8 trimmed for best VSWR, then soldered, works fine) which will protect the exciter in the odd case of a plate to grid short in the final. Stick a PL on it, and "T" it into the line from the exciter to the final. Then just tune the final grid for best match using the exciter's vswr meter.
We replaced our 2.5H3 ("3" for the original TE-3 exciter that it sold with) with a Nautel V-2 recently, but for the last couple of years we've used a 50 watt exciter driving the final 5CX1500B to get our (revised) TPO of 2450 watts. Originally a Continental 802A, then a BE FX-50--the FX-50 is now used to drive the Nautel.
The Nautel appears to need some more babying than the Harris--doesn't like hot weather at our un-air-conditioned site. But that's another thread.
So the short answer is yes, you can do this, and it works just fine. As I mention above, 25~30 watts seems to be what is needed to drive the final to full power. You will need to have an exciter that does not mind some reflected power when the transmitter (the PA) is cold, since the input impedance changes as the tube warms up. Otherwise, you may have problems getting back from a power failure. (I notice my Armstrong exciter,--on another transmitter, "fades up" from a power interruption; doesn't seem to bother the tube IPA in that box, a 10K, as it matches the time delay on restart).
To be safe, and to protect the exciter, you need to make a quarter wave shorted stub (piece of RG-8 trimmed for best VSWR, then soldered, works fine) which will protect the exciter in the odd case of a plate to grid short in the final. Stick a PL on it, and "T" it into the line from the exciter to the final. Then just tune the final grid for best match using the exciter's vswr meter.
We replaced our 2.5H3 ("3" for the original TE-3 exciter that it sold with) with a Nautel V-2 recently, but for the last couple of years we've used a 50 watt exciter driving the final 5CX1500B to get our (revised) TPO of 2450 watts. Originally a Continental 802A, then a BE FX-50--the FX-50 is now used to drive the Nautel.
The Nautel appears to need some more babying than the Harris--doesn't like hot weather at our un-air-conditioned site. But that's another thread.
Thanks, Tom, I would appreciate any info you can provide....J Boyd
I've read some info which was similar to what TomT posted in Radio World within the last year or so. I think they did a profile on a tube manufacturer (Richardson?) and their test exciter was feeding their final directly as well. Tom is right on target with the matching stub.
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