Trouble with a Continental 816R-2B IPA re-fit

FM does it with frequency!
User avatar
Jim Sofonia
Posts: 158
Joined: Fri Jan 30, 2015 11:15 pm

Trouble with a Continental 816R-2B IPA re-fit

Post by Jim Sofonia »

We installed a Nautel VS1 into our 816 replacing the exciter and IPA and tested for the first time today. With some very touchy grid tuning we can get the tx up to full power (20kw). But the Nautel often sees a bad load and shuts down at startup. This transmitter has aways had a cold startup problem and we learned to leave the transmitter at lower power at startup and it will "drift" into proper tuning and climb to full power. But the Nautel isn't buying this startup condition. Hmmnn.. Anybody else re-fit a 816 like this?
User avatar
BroadcastDoc
Site Admin
Posts: 2743
Joined: Tue Nov 13, 2007 3:34 pm
Location: Milwaukee, WI
Contact:

Re: Trouble with a Continental 816R-2B IPA re-fit

Post by BroadcastDoc »

I actually have the same issue with my 816R-2B "drifting into tune" at startup. The Continental IPA will often show high (but not critical) VSWR until the transmitter has been on for a bit, then it settles in.

I can't recall - does the problem improve with leaving the filaments on for several minutes past the warm-up cycle?

As for me, my 816 retires into backup duty tomorrow. I'm turning up a new Nautel GV20. ;-)
Christopher "Doc" Tarr CSRE, DRB, AMD, CBNE
Help support the Virtual Engineer, use our 1&1 Affiliate link if you need good, cheap hosting.
Virtual Engineer. The Broadcast Engineering discussion forum
TPT
Posts: 1013
Joined: Mon Dec 03, 2007 3:18 pm
Location: St. Marys, WV

Re: Trouble with a Continental 816R-2B IPA re-fit

Post by TPT »

Suspect you will need a "dumb" IPA to keep the transmitter happy. Too much change in the match to satisfy a modern low power transmitter like the VS-300.

We were able to use a V-1 to drive a Harris HT-10, but had the same problem. No luck at all with a VS-300--would foldback too fast. Luckily, this was only temporary until the IPA was repaired.
User avatar
Dale H. Cook
Posts: 958
Joined: Thu Dec 20, 2007 9:08 am
Location: Roanoke/Lynchburg, VA
Contact:

Re: Trouble with a Continental 816R-2B IPA re-fit

Post by Dale H. Cook »

Did the 316R-2B previously have a solid state IPA or were you replacing a 4CX-250 IPA?
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html
User avatar
Jim Sofonia
Posts: 158
Joined: Fri Jan 30, 2015 11:15 pm

Re: Trouble with a Continental 816R-2B IPA re-fit

Post by Jim Sofonia »

Dale, it is a 816R-2B and had a SS IPA. This transmitter now about 26 years old has ate up a few IPAs over time including a recent failure that prompted us to try a new approach.
jammerdave
Posts: 129
Joined: Tue May 31, 2011 9:03 pm
Location: West Sacramento, CA

Re: Trouble with a Continental 816R-2B IPA re-fit

Post by jammerdave »

http://www.americanamptech.com/Grid%20M ... 0Kits.html
WTCM wrote:We installed a Nautel VS1 into our 816 replacing the exciter and IPA and tested for the first time today. With some very touchy grid tuning we can get the tx up to full power (20kw). But the Nautel often sees a bad load and shuts down at startup. This transmitter has aways had a cold startup problem and we learned to leave the transmitter at lower power at startup and it will "drift" into proper tuning and climb to full power. But the Nautel isn't buying this startup condition. Hmmnn.. Anybody else re-fit a 816 like this?
User avatar
Dale H. Cook
Posts: 958
Joined: Thu Dec 20, 2007 9:08 am
Location: Roanoke/Lynchburg, VA
Contact:

Re: Trouble with a Continental 816R-2B IPA re-fit

Post by Dale H. Cook »

WTCM wrote:... it is a 816R-2B ...
That's what I get for responding when I haven't finished my first cup of coffee.
WTCM wrote:... and had a SS IPA.
Is the swamping resistor still in place across the grid? Is it still 50 Ohms?
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html
Kelly
Posts: 559
Joined: Thu Aug 21, 2008 5:32 pm
Location: Washington D.C. Area

Re: Trouble with a Continental 816R-2B IPA re-fit

Post by Kelly »

As I remember doing a few of these conversions, the IPA reflected power/load issue is because PA grid and output tuning is set at operating temperature. The coupling between input and output on these transmitters are pretty tight anyway. From what I found, you find a sweet spot where the VSWR on the grid tuning isn't so bad during start and warm up that the IPA trips off. Guess Continental was counting on not having to start these transmitters with the solid state IPA conversions in really cold weather.
Skype:kellyalford Twitter: @KellyAlford
User avatar
Jim Sofonia
Posts: 158
Joined: Fri Jan 30, 2015 11:15 pm

Re: Trouble with a Continental 816R-2B IPA re-fit

Post by Jim Sofonia »

We found a broken cathode by-pass ceramic capicator under the tube socket and some burn marks on the cavity wall. Continental wants us to replace the finger stock on the shelf as well as the cap. before we go any further. They have been very helpful with this project.
I will check on the swamping resistor.
BigRed
Posts: 101
Joined: Tue Mar 27, 2012 8:59 am

Re: Trouble with a Continental 816R-2B IPA re-fit

Post by BigRed »

That tuning change on warm-up is a very common issue with that transmitter. I have one that I occasionally care for that does the exact same thing with the paralleled solid state driver situation. Everyone I've talked to about it, including Continental, concede that the problem exists.

If you don't get any traction with solving, or at least minimizing that IPA VSWR on warm-up issue you can always stick an isolator between the new IPA and the final. That way most of the reflected power will be absorbed by the load in the isolator and the Naughty-tel's VSWR protection circuitry will be none the wiser (or use a circulator with an out-board load) Just make sure in ether case that the components are sized to handle the power and that you have enough reserve power to overcome the insertion loss of the isolator. Probably not a cheap solution, to be sure, but a workable one.

Here's a link to an example device but there are other companies that make them as well.

http://www.rec-usa.com/Data%20Sheets/3A ... _Radio.pdf
User avatar
Jim Sofonia
Posts: 158
Joined: Fri Jan 30, 2015 11:15 pm

Re: Trouble with a Continental 816R-2B IPA re-fit

Post by Jim Sofonia »

UPDATE: 1st As asked by Dale the grid swamping resistor is still in there and measures 50 ohms. Continental had us remove some other power resistors from the cathode circuit as they said they weren't needed. We got the grid circuit tuned well enough last Friday that the Nautel would power up without faulting out while we wait for the tube to warm up with VSWR bouncing from 25 to 46 watts. But tuning was still a bit unstable. My assistant Eric discovered the TX ran better with the IPA directional coupler removed. Upon examination we found the N connector center pin burned on both mating surfaces. Now when we power up the reflected power to the Nautel starts at 26 watts and after 5 minutes slides down to 1 watt. We are now happy with the upgrade and the 816 may live on for many years. Thanks for the advice from you guys as well as Richard at Continental to get this going.
User avatar
KPJL FM
Posts: 613
Joined: Fri Nov 16, 2007 9:28 am
Location: planet Earth, 3rd rock from sun

Re: Trouble with a Continental 816R-2B IPA re-fit

Post by KPJL FM »

WTCM wrote:My assistant Eric discovered the TX ran better with the IPA directional coupler removed. Upon examination we found the N connector center pin burned on both mating surfaces.
That was going to be my suggestion, really :o The harris rigs I've had will do that too.

Now you just need to find reliable rebuilds for that tube....
Trim to fit, paint to match, tune for minimum smoke.
User avatar
Jim Sofonia
Posts: 158
Joined: Fri Jan 30, 2015 11:15 pm

Re: Trouble with a Continental 816R-2B IPA re-fit

Post by Jim Sofonia »

KPJL FM wrote:Now you just need to find reliable rebuilds for that tube....
This is true. We are concerned about the future availability of good tubes. For years I used Econco, then moved to Freeland with very good rebuilds, now back to Econco and take what we can get.
maarkotech
Posts: 20
Joined: Sun Aug 11, 2013 4:39 am
Contact:

Re: Trouble with a Continental 816R-2B IPA re-fit

Post by maarkotech »

pls can some body help with me, continental fm tx 21.5kw,
When Tx was powered, the exciter started working fine, but the forward
power of the tx remain at zero.
-No warning light, all the green lights are ON, but still the final
ouput is zero watt. below are the readings taken while the tx was
running:

P.A
PA SCREEN CURRENT:Oma
PA SCREEN VOLTAGE:80VOLT
PA GRID CURRENT: 2ma
plate voltage: 2kv
plate current: 0.2A
EXCITER
FORWaRD PWR; 2.5W
REFLECTED:00.0W
AMP VOLTAGE;4.1VOLT
AMP CURRENT:0.81
IPA
Ec: 45V
Ic:8A
FWD PWR:80W
reflectd pwr; 10W
Normal power supply on all phases present;
I noticed when i increased the exciter output the IPA output remain
unchanged it seems the IPA is not amplifying, to confirm this i may
have to desolder the RF transistors to test.
initially when i installed the exciter, the transmitter will want to start, but the PA SCREEN OVLD light, will come on and it will shut out.

I have been troubleshooting all night long, but still yet to detect the
remaining fault.
User avatar
Dale H. Cook
Posts: 958
Joined: Thu Dec 20, 2007 9:08 am
Location: Roanoke/Lynchburg, VA
Contact:

Re: Trouble with a Continental 816R-2B IPA re-fit

Post by Dale H. Cook »

maarkotech wrote:... it seems the IPA is not amplifying, to confirm this i may have to desolder the RF transistors to test.
The way to check the IPA is to terminate it in a metered dummy load (Bird or similar) or an unmetered dummy load behind an inline meter (Bird, Dielectric, or simlilar) and measure the IPA output power. There is no sense in unsoldering transistors when this simple test will tell you if the IPA is working.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html
Post Reply