BE FM25T Tube Change issue

FM does it with frequency!
fmrfman
Posts: 66
Joined: Sun Aug 17, 2014 1:43 am

BE FM25T Tube Change issue

Post by fmrfman » Thu Sep 01, 2016 10:48 am

Hmm. Ive got an BE FM25T. Did a tube change this week and I've had 2 complaints so far of reception issues. Anybody out there have experience tuning these up?

Mark

User avatar
NECRAT
Site Admin
Posts: 2932
Joined: Sat Nov 17, 2007 9:13 pm
Location: Taunton, MA
Contact:

Re: BE FM25T Tube Change issue

Post by NECRAT » Thu Sep 01, 2016 5:52 pm

Mark,

I separated your question from the other one, so it stands out, and will get more views that way.

-- Mike
http://www.necrat.us

"Arguing with an engineer is like mud wrestling with a pig. After a couple of hours, you realize the pig likes it"

Kelly
Posts: 480
Joined: Thu Aug 21, 2008 5:32 pm
Location: Washington D.C. Area

Re: Audio Issue

Post by Kelly » Thu Sep 01, 2016 5:58 pm

fmrfman wrote:Hmm. Ive got an BE FM25T. Did a tube change this week and I've had 2 complaints so far of reception issues. Anybody out there have experience tuning these up?

Mark
Hi Mark, Here's a start:

Like most transmitters the driver stages tune into the PA and interact with each other, so you will jockey back and forth between the IPA and PA tuning and loading controls until you reach peak output and dip in plate current. Once you reach peak tuning, then you should tune for minimum AM noise:

1. Turn off APC (automatic power control)
2. Throttle back transmitter output using the lower button (screen voltage) to around 90% forward power.
3. Slowly adjust Input tuning and loading for minimum reflected power. You will rock the tuning and loading controls back and forth until you see the minimum reflected. You should be in the green color.
4. Slowly rotate the PA tuning one direction and then the other for minimum plate current and peak output. Don't worry if it is less than the original 90% output.
5. Now slowly rotate the PA loading knob and you should see the TX output go up or down, depending on the direction of rotation. Adjust for peak output. If output starts to exceed 100%, lower power button to 100%.
6. Move back to the PA tuning control and repeat procedure in #4.
7, Move to the PA loading and repeat procedure in #5.
8. Move back to Input Tuning and Loading controls and repeat input tuning procedures on #3.
9. Repeat PA tuning and loading adjustments in the same order of 4 and 5.
10. If not 100% output, bump the raise button to 95% and repeat tuning procedures 3, 4, 5 until there is a clear needle peak output at around 102%, and PA plate current dips clearly. Your IPA input reflected power should still be in the green.
11. Using your local modulation monitor, switch to AM noise measurement.
gradually adjust your PA Loading control counter clockwise and watch the AM noise. As the PA output reduces closer to 100%, you will see a reduction in AM noise. If everything is tuned correctly, the target AM noise should be >-60dB. If not, then repeat the full list of tuning procedures until it gets closer.

There a lot of variables here too: If the tube is weak, you may have trouble reaching that AM noise figure or 102% output. Essentially what you're doing is tuning up the transmitter to operate efficiently at just slightly above 100%, then slowly un-loading or reducing the coupling to the antenna, reducing your AM noise. Remember sometimes low AM noise doesn't always equal perfect efficiency. That's why you tune for a higher power level first.

Good luck!
Skype:kellyalford Twitter: @KellyAlford

fmrfman
Posts: 66
Joined: Sun Aug 17, 2014 1:43 am

Re: BE FM25T Tube Change issue

Post by fmrfman » Fri Sep 02, 2016 1:48 pm

Thanks NECRAT. I was wondering where my post went. :-)

Kelly:

Big thanks. Exactly the detailed information I was looking for.

From step 11 you stated: "the target AM noise should be >-60dB". Do I interpret that that correctly to mean less than or equal to -60db?

Mark

User avatar
RGORJANCE
Posts: 1375
Joined: Mon Dec 31, 2007 7:48 am
Location: RACINE, WI

Re: BE FM25T Tube Change issue

Post by RGORJANCE » Fri Sep 02, 2016 2:58 pm

I have been thinking about this and am wondering if the replacement tube might be part of the issue.

Several days ago while re-tubing a QEI 5kw FM, an "offshore built tube" (triode) was inserted in the socket. Documentation provided with the tube showed it "good". As we fired up the rig, it didn't want to tune correctly. It started oscillating and it never made our small TPO of 3,400 watts, no matter how we tuned the rig. Yanked it out and plopped in a new Econco rebuilt. I had to stand on the "lower button" to keep the power down while fine tweaking the rig.

Second xmttr (FM-3.5K1) had been going flakey with not even a year on the "offshore" built jug. Popped in the Econco rebuilt (tetrode) and like magic, it tuned, had a ton of reserve. TPO also 3,400 watts.....no sweat.

We have noticed strange issues with the tubes and suspect that the internal characteristics are quite different than USA built jugs. I would be curious to know if the new jug put into the FM25T might be other than an Econco rebuilt. Did it tune gracefully without any difficulties?

Fossil

Kelly
Posts: 480
Joined: Thu Aug 21, 2008 5:32 pm
Location: Washington D.C. Area

Re: BE FM25T Tube Change issue

Post by Kelly » Fri Sep 02, 2016 4:36 pm

fmrfman wrote:Thanks NECRAT. I was wondering where my post went. :-)

Kelly:

Big thanks. Exactly the detailed information I was looking for.

From step 11 you stated: "the target AM noise should be >-60dB". Do I interpret that that correctly to mean less than or equal to -60db?

Mark
Mark your AM noise should be a greater number than -60dB. You'll see the lowest AM noise if everything is near perfect at somewhere near -65dB.
Regarding the discussion of rebuilt or new tubes: I ALWAYS prefer installing new. I've found that you'll spend 50% for used, but it will only last about 30% as long as a new tube will. And the tuneup and performance of a new tube will be much better. This is especially true for optimum tuning for low AM noise.
Econco rebuilt tubes are sketchy, to say the least.
Skype:kellyalford Twitter: @KellyAlford

Kelly
Posts: 480
Joined: Thu Aug 21, 2008 5:32 pm
Location: Washington D.C. Area

Re: BE FM25T Tube Change issue

Post by Kelly » Fri Sep 02, 2016 4:39 pm

RGORJANCE wrote:I have been thinking about this and am wondering if the replacement tube might be part of the issue.

Several days ago while re-tubing a QEI 5kw FM, an "offshore built tube" (triode) was inserted in the socket. Documentation provided with the tube showed it "good". As we fired up the rig, it didn't want to tune correctly. It started oscillating and it never made our small TPO of 3,400 watts, no matter how we tuned the rig. Yanked it out and plopped in a new Econco rebuilt. I had to stand on the "lower button" to keep the power down while fine tweaking the rig.

Second xmttr (FM-3.5K1) had been going flakey with not even a year on the "offshore" built jug. Popped in the Econco rebuilt (tetrode) and like magic, it tuned, had a ton of reserve. TPO also 3,400 watts.....no sweat.

We have noticed strange issues with the tubes and suspect that the internal characteristics are quite different than USA built jugs. I would be curious to know if the new jug put into the FM25T might be other than an Econco rebuilt. Did it tune gracefully without any difficulties?

Fossil
I made the mistake of trying one of those Svetlana Russian made tubes in a QEI 30kW rig. What a disaster! Unbeknownst to me, when I finally got it to tune up, the stupid transmitter started throwing a spur right on TV Channel 6, causing angry OTA TV viewers. Replaced the tube with a new one, and problem solved. Although to be fair, that transmitter was a total hunk of junk.
Skype:kellyalford Twitter: @KellyAlford

User avatar
RGORJANCE
Posts: 1375
Joined: Mon Dec 31, 2007 7:48 am
Location: RACINE, WI

Re: Svetlana Russian made tubes

Post by RGORJANCE » Sat Sep 03, 2016 12:10 pm

Ours were Nationals made in China.

This tube issue is hauntingly similar to the Eimac issue back in the 70's when they had problem with the 5CX1500 jugs. Yuck!

Fossil

User avatar
kkiddkkidd
Posts: 501
Joined: Mon Dec 03, 2007 11:13 am
Location: Lawrenceburg, TN

Re: BE FM25T Tube Change issue

Post by kkiddkkidd » Sat Sep 03, 2016 5:02 pm

Kelly wrote:
fmrfman wrote:Thanks NECRAT. I was wondering where my post went. :-)

Kelly:

Big thanks. Exactly the detailed information I was looking for.

From step 11 you stated: "the target AM noise should be >-60dB". Do I interpret that that correctly to mean less than or equal to -60db?

Mark
Econco rebuilt tubes are sketchy, to say the least.
I have all but given up on Econco rebuilds. I have a EO ECO22 that seems to like the National tubes. 2 of them have lasted longer than 3 or 4 Econcos. The main problem that I have with them is that they seem to be nickle plated rather than silver. I have had 4CX-5CX Nationals damage the grid connections.

All tubes are junk... I just put a Econco 4CX3500 in a tx and am holding my breath. It tuned up nicely at least.

I used a bunch of the Svetlana 833 tubes and they far exceeded the life of any other recent 833. Based on that, I ordered a Svetlana for an FM TX (3CX15000?) and OMG... What a pain. The tuning was miles off and had to adjust the course tune to make it work. It had good life but when I tried to reorder, was told it would be months before a new tube would be available. Thankfully I had marked the original course tune locations and got it back close in just a few minutes.
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

User avatar
kkiddkkidd
Posts: 501
Joined: Mon Dec 03, 2007 11:13 am
Location: Lawrenceburg, TN

Re: Svetlana Russian made tubes

Post by kkiddkkidd » Sat Sep 03, 2016 5:41 pm

RGORJANCE wrote:Ours were Nationals made in China.

This tube issue is hauntingly similar to the Eimac issue back in the 70's when they had problem with the 5CX1500 jugs. Yuck!

Fossil
And in the 90's when they forgot how to build YU148's (3CX6000). I forgot how many I put in a CCA FM10000g but it was something like 7 in 12 weeks. About 200hrs was the average before the ceramic fractured. Rebuilt YU148's were awful.
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

W2XJ
Posts: 77
Joined: Mon Dec 03, 2007 12:15 pm

Re: BE FM25T Tube Change issue

Post by W2XJ » Sat Sep 03, 2016 10:59 pm

I have found that most FM amplifier cavities require consistent parameters. With new tubes you can't switch brands without making major changes to the tuning which includes the shelf adjustment where possible. As far as rebuilds go, I always got my own tubes rebuilt once I knew they were 'good' tubes rather than use rebuilt tubes from strangers. When you start using 'whatever' bad things happen and they always have.

User avatar
kkiddkkidd
Posts: 501
Joined: Mon Dec 03, 2007 11:13 am
Location: Lawrenceburg, TN

Re: BE FM25T Tube Change issue

Post by kkiddkkidd » Tue Sep 06, 2016 9:14 am

W2XJ wrote:As far as rebuilds go, I always got my own tubes rebuilt once I knew they were 'good' tubes rather than use rebuilt tubes from strangers. When you start using 'whatever' bad things happen and they always have.
That is a practice that I have encouraged my clients to do but have had little success. I have a 3CX3000 Econco in an old CCA FM3000 (might be a CSI) TX right now that has given pretty good service and I am going to make sure that we send it back for rebuild instead of a swap. Otherwise, I have exactly 4 FM clients with tube mains smaller than 10kw, 1ea 10kw, 1ea 22kw. 3 of the 5's are about to become backups to Nautel's and am strongly encouraging that clients replace the Eco22 and CCA FM10000g with SS units.

The one CCA 3000 will be on the air until it collapses onto itself from metal fatigue. Just like it's sister AM CCA AM1000 will. Just like their little brother FM using a CCA FM500 (on top of a mountain) will. Of course, this station still plays CDs and commercials from MD on the main FM.
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

fmrfman
Posts: 66
Joined: Sun Aug 17, 2014 1:43 am

Re: BE FM25T Tube Change issue

Post by fmrfman » Tue Sep 06, 2016 10:23 am

The solid state transition can't happen fast enough for me (of course this takes all the fun out of it 'eh?). Give me a Nautel now! ;-)
Seriously at $1, 500 to $7,000 a pop for a tube solid state is a no brainer if you are buying a new transmitter.

RGORJANCE:

I attempted the rebuilt Econco 3 times. First 2 attempts I tuned and ran her up to 100%. Sometime after 30 to 40 minutes there would be a loud pop and we would be off the air. Third attempt to bring her up I tuned and only ran her at 70%. She ran about 8 hours with another loud pop and a "something burned smell".

Ordered a new Eimac from Richardson, popped her in and re-tuned. That was last Tuesday and she's been humming along ever since.

The Econco rebuild was one I had on hand that was in a factory sealed box. BE factory does not recommend rebuilt. I was trying to save our organization money since we are "no to low" budget.

Kelly
Posts: 480
Joined: Thu Aug 21, 2008 5:32 pm
Location: Washington D.C. Area

Re: Svetlana Russian made tubes

Post by Kelly » Tue Sep 06, 2016 10:24 am

kkiddkkidd wrote:
And in the 90's when they forgot how to build YU148's (3CX6000). I forgot how many I put in a CCA FM10000g but it was something like 7 in 12 weeks. About 200hrs was the average before the ceramic fractured. Rebuilt YU148's were awful.
I frequently thought they should have renamed those tubes: Y-ME148.
Skype:kellyalford Twitter: @KellyAlford

jammerdave
Posts: 117
Joined: Tue May 31, 2011 9:03 pm
Location: West Sacramento, CA

Re: BE FM25T Tube Change issue

Post by jammerdave » Tue Sep 06, 2016 11:49 am

Are you running HD? I recently went through a lot of crap with the same rig... If so, I will fill you in on my findings... Have you seen it on a spectrum analyzer?

df

fmrfman wrote:Hmm. Ive got an BE FM25T. Did a tube change this week and I've had 2 complaints so far of reception issues. Anybody out there have experience tuning these up?

Mark

Post Reply