5cx1500a

[jboydingram]

Seeking new or usable 5cx1500a as a spare for standby transmitter. What have you? JBI

 

[TomT]

Get a 5cx1500B. Lasts longer. The "a" in our 2.5k would run around a year at the most. Would get two years or better on a "B."

 

[jboydingram]

OK,,,thanks...will take either if someone has...Don't want to be down on the main and standby....jbi

 

[BobOnTheJob]

This is slightly off the original topic, but if you have any Econco rebuilt tube that's new in the box & you won't be needing it, Econco will buy it from you at a better price than you'll ever get on Ebay. In my recent case, I had a 3CX15000A7 that I sent to them that cost $1525 in 1997. They tested it & a check for $991.25 (65% of it's 1997 purchase price) arrived yesterday. Might have gotten a couple hundred bucks on Ebay. This only works if it's not used & their tests reveals that it's good--mine passed. When buying a used transmitter, ask that the spare tubes be included. They may have substantial value. Debbie Storz is the contact at Econco. 1 800 532 6626 Ext 126.

 

[jboydingram]

I have a tube...thanks, all.....J Boyd

 

[RolfTaylor]

JB

If this IS a B note that that you will need to retune the cavity slightly as part of installation.

I have a tube...thanks, all.....J Boyd

 

[jboydingram]

Thanks...I need all the help I can get. J Boyd

 

[mr_elbows]

'retune slighty' ????

both times that I've changed an A to a B (in FM-2.5K's) it was a MAJOR re-tuning chore, due to major internal differences

 

[jboydingram]

OK...what direction should I go...up or down on the tuning stub...or is there a rule? Tnx J Boyd Ingram

 

[TomT]

We went from an "A" to a "B" in a 2.5H (basically the same as a "K"). Don't remember major problems. May be frequency dependent.

 

[greg.hahn]

OK...what direction should I go...up or down on the tuning stub...or is there a rule? Tnx J Boyd Ingram

Uh, yeah. The shelf position inside my Continental transmitter is marked for A or B. But I don't remember which one is higher. I think there was about a half inch difference. If you have a Continental 2.5KW transmitter and you want to know, send me an email. If you have something else, you'll just have to play with it.

 

[RolfTaylor]

I could easily be wrong, but I have the distinct recollection of raising the shelf about 1/2 to 1" when installing the B in the old Collins/Rockwell/Continental 1.25kW rig the first time.

This was operating at 91.1 mHz

The B's were only marginally better in this rig. We instituted filament voltage management and lifetime ranged from about 14 months all the way up to nealry 3 years. Never could figure out what the difference was - very odd. The last one we used happened to be a Svetlana and it was well over 2 years when the rig was retired, but we'd had varians last long before so go figure.

Good luck

OK...what direction should I go...up or down on the tuning stub...or is there a rule? Tnx J Boyd Ingram

Uh, yeah. The shelf position inside my Continental transmitter is marked for A or B. But I don't remember which one is higher. I think there was about a half inch difference. If you have a Continental 2.5KW transmitter and you want to know, send me an email. If you have something else, you'll just have to play with it.

 

[Jim Graham]

Slightly off the subject again, but, regarding filament voltage. I had a Harris MW5 in the '80s and the 4CX3000 modulator had TERRIBLE tube life until I actually measured the filament voltage on it. WAYYYY to high when the front panel meter indicated normal. After lowering the voltage to slightly below nominal, I never had to change the tube again. - JG

 

[greg.hahn]

I went and looked at my transmitter for J Boyd. The B mark was 3/4 of an inch lower than the mark for the A. (My rig is at 103.1)

Of course, the marks were just a starting point. Often you had to change it by a couple of millimeters to achieve resonance. I have always had SUBSTANTIALLY better life from a 1500B than a 1500A. (I'm surprised there are still 1500As out there.)


On the filament voltage: That is an excellent point. I've seen transmitter filament voltage meters that were substantially off as well. A true RMS reading voltmeter should be used to establish what your true filament voltage is.

On the other hand, you can go by your front panel meter if you disregard the number and just use it for reference. Lower the filament voltage by .1 volt increments until you see plate current start to fall off. Then raise it a bit above that point.

 

[BobOnTheJob]

On the other hand, you can go by your front panel meter if you disregard the number and just use it for reference. Lower the filament voltage by .1 volt increments until you see plate current start to fall off. Then raise it a bit above that point.

That's my preferred method. Have you noticed that various rebuilds require different filament voltages to hit that sweet spot? I've seen them vary by as much as 0.5 volts with no apparent penalty in tube life.

Good job on the new WQNU...gets out well. Heard it in the car in Paoli the other day. I was the contract engineer at the Versailles,In station that moved from 103.1 as part of this huge chess game. That station moved to 102.9 about 30 miles farther NW and is running 500W horizontal only on a 50' tower behind somebody's farm house. I guess that it's just a place holder until someone buys it & actually uses it. Strange how these things play out. That's the third one of my stations that were impacted by similar circumstances...I built WQKC 93.7 Seymour,IN back in 1992 & that's now on 93.9 in Louisville and WIFE 100.3 Connersville,IN was transplanted & is now WMOJ in Cincinnati. I took care of that one since 1987 until it left. They came & they go...there's never a shortage of work for an RF guy...

 

[greg.hahn]

That's my preferred method. Have you noticed that various rebuilds require different filament voltages to hit that sweet spot? I've seen them vary by as much as 0.5 volts with no apparent penalty in tube life.

Good job on the new WQNU...gets out well. Heard it in the car in Paoli the other day. I was the contract engineer at the Versailles,In station that moved from 103.1 as part of this huge chess game. That station moved to 102.9 about 30 miles farther NW and is running 500W horizontal only on a 50' tower behind somebody's farm house. I guess that it's just a place holder until someone buys it & actually uses it. Strange how these things play out. That's the third one of my stations that were impacted by similar circumstances...I built WQKC 93.7 Seymour,IN back in 1992 & that's now on 93.9 in Louisville and WIFE 100.3 Connersville,IN was transplanted & is now WMOJ in Cincinnati. I took care of that one since 1987 until it left. They came & they go...there's never a shortage of work for an RF guy...

Thanks, Bob. That was a chess game I didn't think we would win.

Some consultant picked the site, which must be the real key to the success of it. All I did was pick the antennas and do a pattern study. It's not supposed to radiate so well to the north.....