Harris FM K5 Freq Change

FM does it with frequency!
TvRadioGuy
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Harris FM K5 Freq Change

Post by TvRadioGuy » Mon Jan 08, 2018 1:11 pm

We have a project that involve Changing A Harris FM 5K. We have the manual and we have the procedures for the Exciter But The manual does not explain the procedures nor it tell you what you need to do for a frequency change. It has The PA Tuning Procedure not frequency change. We called for support and it was mention it cost to much buy a new Transmitter as you by now no budget for new. Do any of you have any experience with this transmitter and is familiar with changing frequency on this model. This is a 3 Phase Unit any recommendation on phase converters.

Thanks

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RGORJANCE
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Re: Harris FM K5 Freq Change

Post by RGORJANCE » Mon Jan 08, 2018 2:12 pm

I need to have some specific information to provide the right info. Is this xmttr using a 4CX5000 final, and is it using a 4CX250 driver tube, and which exciter are you using?

What operating frequency is it on now, and what freq. will you be moving it to?

If this is the older box, sold up thru the 1980's, I think I have the info you require. I also may have a factory test data sheet either at the freq you are moving it to, or something pretty close. The test data sheets contain lots of measurement info you need to set the coarse tuning bar in the cavity, as well as other stuff.

As I recall, the Gates Air website should have some info available for download.

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TvRadioGuy
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Re: Harris FM K5 Freq Change

Post by TvRadioGuy » Mon Jan 08, 2018 5:32 pm

As per the book one tube is 4CX250B and the second is 4CX500A The Transmitters It siting now at 89.1 Lower to Higher end of the band 106.1. I Did find me info on the coarse tuning. It was buried in towards the end in the manual. But No Guide on what steps needed to properly Change to re tune to new frequency and adjust. for new frequency. A The MX 15 Manual has the steps.

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RGORJANCE
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Re: Harris FM K5 Freq Change

Post by RGORJANCE » Tue Jan 09, 2018 5:28 am

Attached is a pdf from the Harris data base that should detail everything you need to do the change. The one major problem you will run into is the availability of some special parts to do the change.
FM-5HK FREQ CHANGE.pdf
(497.3 KiB) Downloaded 32 times
If you have trouble opening the attached, se4nd me a pm with your email address----not the one on this site and I'll send it direct.

Good luck.

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TvRadioGuy
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Re: Harris FM K5 Freq Change

Post by TvRadioGuy » Tue Jan 09, 2018 11:35 am

Thanks for the Guide I am working with another Engineer that has not done a a frequency change on a Harris FM 5K. I am able to see the PDF. Do you have any recommendations on a Phase converter. Harris Gate suggested a Solid State unit. I was told a Rotary using works well.

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RGORJANCE
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Re: Harris FM K5 Freq Change

Post by RGORJANCE » Tue Jan 09, 2018 11:58 am

No current experience with rotary converters so I will leave that to those with recent experience.

I will, however, offer that way back when I was selling for Harris, there was a pretty good rotary converter out there and to the best of my memory it was a company in Indiana. Just found it in the archives.

Buffington and Payne
Hwy 17, RR #3
Plymouth, IN 46563

I don't have a phone number and I don't even know if they still are in business.

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Shane
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Re: Harris FM K5 Freq Change

Post by Shane » Wed Jan 10, 2018 12:49 pm

Gates/Harris would do well to respond half as quickly as you do, Bob.
Mike Shane, CBRE
---Omaha---

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RGORJANCE
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Re: Harris FM K5 Freq Change

Post by RGORJANCE » Wed Jan 10, 2018 2:53 pm

Thanks for the unsolicited endorsement.

(I'll buy the coffee next time we get together)

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Lee_Wheeler
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Re: Harris FM K5 Freq Change

Post by Lee_Wheeler » Wed Jan 10, 2018 9:33 pm

I can't recall if I've ever done a freq change on a 5K but I have done some 10Ks and 20Ks and their H3 variants. For sure on the 20K and I think the 10K the low pass filter had three different part numbers based on which segment of the band the operating frequency was. It was just dumb luck but on a couple of them I found other people that needed the segment that I was moving from and had the part for the segment I was going to - even swap and everyone went away happy.

The PA tuning is fairly straightforward but the usual problem are is getting the driver matched to the grid on the PA. On the 10 and 20 there is some "bend tuning" involved.

...Lee

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RGORJANCE
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Re: Harris FM K5 Freq Change

Post by RGORJANCE » Thu Jan 11, 2018 7:11 am

There are a couple items in the ipa/pa section that will require change....

1) coil in ipa section
2) the metal fixtures that connects the anode of the tub to the pa tuning tube.

These areas, I believe, are listed in the directions. I don' recall if dimensions are listed as I haven't looked at the instructions in quite a long time. Going strictly from (faulty) memory.

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RGORJANCE
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Re: Harris FM K5 Freq Change

Post by RGORJANCE » Thu Jan 11, 2018 7:55 am

TVRADIOGUY:

I have searched my test data sheets and am sorry to report I don't have factory test data sheets for an FM-5H/K series anywhere close to 106.1. Nearly all are for below 100 mhz.

The file I posted hopefully will contain enough info to get you close to where it needs to be for your new freq..

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Dale H. Cook
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Re: Harris FM K5 Freq Change

Post by Dale H. Cook » Thu Jan 11, 2018 9:12 am

Lee_Wheeler wrote:
Wed Jan 10, 2018 9:33 pm
The PA tuning is fairly straightforward but the usual problem are is getting the driver matched to the grid on the PA. On the 10 and 20 there is some "bend tuning" involved.
I was involved in the field retuning of a 20H3, which, IIRC, used the same cavity as the 20K. We had a Harris field tech come out who had factory experience adjusting the "bend tuning" of what he called, IIRC, "bastard L6." I don't know if the 5K uses the same matching network between IPA and PA.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

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RGORJANCE
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Re: Harris FM G thru K series

Post by RGORJANCE » Thu Jan 11, 2018 9:41 am

Just a bit of history on those boxes.

The FM-G, H, H2, H3 and K series all used the same half wave pa cavity design.....just different pipe diams as you got into the higher powers.

The big improvement came when a customer suffered severe damage in his FM-20G. He did some "on site mods" to get back on the air and noticed the efficiency was drastically different. It had gone waaaay up. He called the service department and the fellow helping him out realized what the customer had stumbled into. After a quick trip to the engineering department, and some experimenting, they could get the FM-20H (and later versions) up to 80%, or better PA efficiency----which they guaranteed to the customer on the purchase of the 20kw unit.

This change was, IIRC, placed in all xmttrs (FM-3H up to the 20KW rig). The improvement delivered greater stability, efficiency and most importantly substantially lower operating costs and significantly better PA tube life. Again, if memory serves----this took the three phase incoming current from around 100 amps per leg down to around 80 amps per leg on the 20kw box.

As Harris transitioned to the HT series, I think they went to a 1/4 wave cavity and did a relatively decent job of maintaining a decent (70% range) PA efficiency. I was long gone from the company by that period of time.

Hope this fills in some blanks, and sorry to divert from main topic.

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grich
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Re: Harris FM G thru K series

Post by grich » Thu Jan 11, 2018 9:59 am

RGORJANCE wrote:
Thu Jan 11, 2018 9:41 am
...As Harris transitioned to the HT series, I think they went to a 1/4 wave cavity and did a relatively decent job of maintaining a decent (70% range) PA efficiency...
Yep...my two HT-10's have a PA efficiency of 77-78%.

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kkiddkkidd
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Re: Harris FM G thru K series

Post by kkiddkkidd » Thu Jan 11, 2018 11:24 am

RGORJANCE wrote:
Thu Jan 11, 2018 9:41 am

The big improvement came when a customer suffered severe damage in his FM-20G. He did some "on site mods" to get back on the air and noticed the efficiency was drastically different. It had gone waaaay up.
So what was the snake-oil that he found?
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
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