Ranger Blowing Fuse

[wb5kcm]

My Ranger is blowing the fuse. I have found that after it is used on AM for a while the modulator current is slowly climbing and eventually will go full scale and blow the fuse. It seems to do this as the modulator tubes gets hot with modulation. Does this sound like a gassy 1614? Any ideas to check on this will be most appreciated.
73, Randy, wb5kcm

[K1MVP]

My Ranger is blowing the fuse. I have found that after it is used on AM for a while the modulator current is slowly climbing and eventually will go full scale and blow the fuse. It seems to do this as the modulator tubes gets hot with modulation. Does this sound like a gassy 1614? Any ideas to check on this will be most appreciated.
73, Randy, wb5kcm

Try "pulling" both modulator tubes and see if the fuse still blows, and see if the rig is ok as a cw trans-
mitter.                                                   73, K1MVP

[Pete, WA2CWA]

One or both of the 1614's could be going soft and should be replaced. Also check to be sure the screen voltage on the modulators isn't increasing as your transmit. As Rene said, pulling both tubes will test to see if other areas might be causing the problem.

[wb5kcm]

Thanks, I will give this a try and also will look at the screen voltage.

[wb5kcm]

OK, this is what I have found. With the 1614's removed, I never show any MOD current at all, even after extended keydown. With the 1614's in and cold I show zero MOD current until I key then I show about 60 ma idle current. I notice after extended keydown and modulating the idle current will creep up to about 70 ma. The plate voltage is 600 vdc, the screen is 300 vdc keyed. The bias on the control grids is -43 vdc. One interesting note is that after keyed for extended period of time, when I release the key the screen voltage will remain at about 150 vdc even with the screen supply disconnected via the PTT keying relay! Where is the voltage coming from? It will gradually fall to a very low level slowly when the tubes cool down. I believe this is what is causing it to go into current runaway after a while and blowing the mains fuse. Also, I notice with the transmitter unkeyed the modulators are continuing to draw current (20 ma) and this gradually drops to zero after it cools. Sorry for being so long winded but hopefully from this someone has had the same symptoms. Thanks, Randy, wb5kcm

[K1MVP]

Randy,
I guess my question would be,--with the modulator tubes removed, does the rig load up on cw
and provide the rated output of 45 to 50 watts, in CW ONLY with the key down?
Am trying to verify that the problem is/ is not in the modulator.
If the rig is ok as a cw rig,--then I would try another pair of modulator tubes,(6L6`s or 5881`s)
as I recall.--Its been a while since I have worked on a Ranger.
Most of the rigs I am familiar with are the DX-40,--DX-60 and the Eico 720 in which I use an
outboard modulator.
I am not sure how they develop the screen voltage(for the modulator) in the Ranger,--if its through a screen dropping resistor or is it a "fixed" screen supply.
Some other guys who own Rangers might be more familiar with how they develop the screen voltage.

                                                      73, Rene, K1MVP

[wb5kcm]

Hey Rene, thanks for the info. I did try the Ranger on CW and it seemed to put out normal output. Mostly, I keyed it in the Phone mode by sliding the locking bar up on the D104. I held it keyed for one time about 20 minutes with about 40 to 45 watts output. During this time without the 1614's in, I never saw any MOD currentt at all. After this I put the 1614's back in and did some more testing. This is when I found the screen voltage there after unkeying. The screen voltage is applied through the PTT keying relay and is connected to the low voltage power supply @ 300 volts. What is weird is that there is this gradually decreasing screen voltage there even when the 300 volts is disconnected. I feel like this is due to a bad 1614 one or both. Just not sure about that. I am going to try and pick up a set of 1614's or 6L6 this weekend to try them. If anyone has any ideas, I am open to try. Thanks, Randy, WB5KCM

[K1MVP]

Ok,--so it looks like the "basic cw" portion is ok,--and your problem is in the modulator.
I would definitely try another set of modulator tubes, before anything else.

Ok on the PTT,--problem there is, it seems like everyone who incorporates PTT has a different way
of doing it, and most times there is no "info" or documentation as to how the guy did it.
I like doing my mods "externally",--I added PTT in a DX-60, with an external box(real easy on a DX-60)
so that when I sell the rig,--it remains original and I keep my PTT for any other rig that I may
want to keep.

There are advantages to having a rig with built in VFO, modulator, etc, but I prefer separate units,
like my Eico 720 with an external modulator, VFO, etc,--for "maintainability" cause if my VFO
"craps out",--I got a spare, and if my modulator goes,--I have another spare, and can still remain
on the air and fix the "problem child"  when I feel like it.

Good luck with the problem,--If "push comes to shove",--you could always cathode modulate
the rig externally(with the 6L6`s out of the circuit" if the problem turns out to be a "pain".
                                             
                                             73`s, K1MVP

[wb5kcm]

OK, today, I was able to pick up a couple 1614 tubes from Nortex Electronics here in Fort Worth. After some extended testing it looks like they have done the trick. My modulator current looks to be much more stable and have been unable to blow the fuse. Just having trouble getting someone to answer my CQ on 3885 today. Will keep trying. Looks like one of the original 1614's had an intermittnt short. Both of them had date codes showing 1954. Thanks for all the input and suggestions. 73, Randy, wb5kcm

[K1MVP]

OK, today, I was able to pick up a couple 1614 tubes from Nortex Electronics here in Fort Worth. After some extended testing it looks like they have done the trick. My modulator current looks to be much more stable and have been unable to blow the fuse. Just having trouble getting someone to answer my CQ on 3885 today. Will keep trying. Looks like one of the original 1614's had an intermittnt short. Both of them had date codes showing 1954. Thanks for all the input and suggestions. 73, Randy, wb5kcm

Randy,
Great,--glad to hear the rig is now working,--as far as getting out on 3885, I am not sure what your
band conditions are down there in Texas, but up here in the Northeast, its can be a real "pain"
to run 50 watts on am on 75 especially at night with all the "tall ships".

You miight want to try getting on 40 meters(am) on or about 7290 to 7295 on weekends during the
day, and you may have a lot more luck being heard.
I have found that 40 meters during the day is much more favorable if you are running only 50 watts.

                                                  73`s and good luck, Rene, K1MVP
   

[Jim, W5JO]

Randy, if you didn't get an answer, don't forget there are a lot of us on 3.885 every morning from about 9 AM until nearly 11 in many cases.  In the afternoon around 4-5 there is a bunch on too.   I can hear 35 watts from the metroplex here very well.  I will be listening for you.

[wb5kcm]

Thanks Jim and Rene, I will give 40 meters a try during the day. I heard someone say they were working some AM on 7160, I will give that a try maybe tomorrow. I did work Ken, KA5RHK in DeQueen, Ar this evening and got a good signal report. Sounds like the little Ranger is doing its thing. I will look for you Jim on 75 meters.
73, Randy, WB5KCM

[WA1HZK]

One thing I have done on my Ranger mods is to ground the screen of the modulator and the final on standby. This eliminates the tubes taking off on their own and cuts back on the heat inside the cabinet. These mods are posted on the site. I also build a real adjustable bias supply so I can tame whatever modulator tubes I'm running. Worth it.
Keith
WA1HZK

[wb5kcm]

Hey Keith,

Yes I have used some of your mods. I appreciate the info you have on the web site. It helped me in getting a lot of this done to my Ranger. I have posted a lot of photos of my Ranger and HQ-170 projects on my Flickr site
http://www.flickr.com/photos/wb5kcm/sets/72157594523189590/
Both are now working like a champ.
I used Ranger mod info from you and WA1HLR and W3AM, AD5X, W8JI. I really liked your regulating the LV supply with the two OD3 tubes, it works great.
73 de Randy, WB5KCM

[Steve - WB3HUZ]

That's a great combo, the Ranger and HQ-170. Nice looking tower you have too. Wish I had one of those. Hope to hear you on the air.