Viking Valiant: overheating - out of tune

[n2awa]

Gents,

Do you think a Valiant (mine) could over-heat if it were out of tune? I normally leave the meter on "grid" current setting, and recall the needle started swinging (unusual) before I had time to shut everything down due to an over-heating smell in the shack. After the dust settled, I tuned-up the Valiant, and did another burn-in/heat test, with no untoward smells. I normally don't tune it up every time I use it, but maybe I should.

Layout...
top: Matchbox tuner <-- no real space between it and the Hallicrafters
middle: Hallicrafters S-40 <-- between Matchbox and Valiant (2" PVC spacers between it and the Valiant)
bottom position: Valiant

I have a Matchbox tuner sitting directly on the top of the Hallicrafters receiver, and it could have been the receiver over-heating. I'm not real sure. My sniffer is pretty good, but I can smell trace amounts of what ever it was in both transmitter and receiver (the receiver sits atop the transmitter - separated by PVC spacers).  See photo for reference. I'll plan to put some spacers between the receiver and the tuner so the S-40 can breathe.

[Pete, WA2CWA]

Out of tune (out of resonance), the final tank circuit can generate a lot of heat. Tubes are generating lots of RF energy and if out of resonance, the energy converts to heat in the tank circuit and puts a strain on all the components there. Every time you use any transmitter, you should always check to be sure it's tuned up properly. Makes the hard to get parts last a lot longer.

From the picture, the Valiant sides are blocked from good air flow,  the back has no vent holes, so the only place the heat can vent is from the top. With five 6146's, other tubes and transformers all generating heat, the air flow out the top should be unrestricted. I have two fans sitting on top of my Valiant to help expel the heat.  With the receiver sitting above it, the heat may also have some impact.

[flintstone mop]

Are we talking about a long transmission? Long key-down time? Those table-top TX's should be ok with an old buzzard of 6-7 minutes. Your shack air conditioned or at least a fan?
The old tube gear was always stressed to be in a small box, for convenience, and those days air conditioning was a luxury. You can imagine what a military comm center was like with racks and racks of tube gear making plenty of heat. My R-390A keeps the shack warm (slightly) during the winter.
And Pete brings up important issue....transmitter tuned properly? into a good load. Antenna?
If the TX is working properly and all of a sudden the meter readings take off and go bazerk; then you may have a failing tube or component failure. It's good you are watching the meters. The grid current should be steady. Maybe you should monitor the plate current? I'm not familiar with the metering for the Valiant.
Continual overloading in your transmitter will eventually cause a bigger problem.
Fred

[W3GMS]

Gents,

Do you think a Valiant (mine) could over-heat if it were out of tune? I normally leave the meter on "grid" current setting, and recall the needle started swinging (unusual) before I had time to shut everything down due to an over-heating smell in the shack. After the dust settled, I tuned-up the Valiant, and did another burn-in/heat test, with no untoward smells. I normally don't tune it up every time I use it, but maybe I should.

Layout...
top: Matchbox tuner <-- no real space between it and the Hallicrafters
middle: Hallicrafters S-40 <-- between Matchbox and Valiant (2" PVC spacers between it and the Valiant)
bottom position: Valiant

I have a Matchbox tuner sitting directly on the top of the Hallicrafters receiver, and it could have been the receiver over-heating. I'm not real sure. My sniffer is pretty good, but I can smell trace amounts of what ever it was in both transmitter and receiver (the receiver sits atop the transmitter - separated by PVC spacers).  See photo for reference. I'll plan to put some spacers between the receiver and the tuner so the S-40 can breathe.

Jeff,

Concerning your questions to me earlier, its very important that your resonate the tank circuit!  As others have said, off resonance is not good!  You mentioned you monitor the grid current.  I would check the grid current at tune up and then switch the meter switch to monitor the final plate current.  Remember also that the final plate current goes through your modulation transformer so its not only hard on the tubes but most of the iron in the rig as well. 

You have a very tidy looking shack but not the best from a thermal perspective.  I never put anything on top of a transmitter that requires ventilation.   I would go to a more horizontal flow rather than the stacked approach. 

As CE of your station, its important to tune it up right and monitor the parameters so you don't "cook" your gear  !   If you have any questions go visit Bob, 2ICQ and he can guide you through the process.  The manual is a good source of information as well. 

73,
Joe, GMS

[n2awa]

Try to answer two replies here. The shack is air conditioned, but last night it was cool (about 70 outside) so the windows were open. Top and side ventilation on the Valiant is good (contrary to the photo?), but the top could be better. Would like nothing more than to have you see the layout in person, but there is not much I can do in the way of spreading out horizontally. I hate stacking, but I have little choice at the moment. I'm trying to come up with a solution. I plan to put some spacers between the S-40 receiver and the Matchbox tonight and do some more testing. Should be around 7:00 p.m. or just after. A local ham said he would work with me.

I have not been in the habit of tuning up each and every time, but will make it a habit. Thanks for the comments, and maybe you will hear me on 3.840 tonight.

Bob ICQ said I may have toasted a loading cap in the pi network, but they are hard to access (in the "Christmas tree" he said). I have not had the Valiant opened in five years, so can't visualize it. He said to replace with military micas. Where would these be in the schematic - top right corner? Reference schematic link...

http://www.mbzponton.org/n2awa/radio_Johnson_Viking_Valiant_schematic.jpg

[n2awa]

Are we talking about a long transmission? Long key-down time? Those table-top TX's should be ok with an old buzzard of 6-7 minutes. Your shack air conditioned or at least a fan?
The old tube gear was always stressed to be in a small box, for convenience, and those days air conditioning was a luxury. You can imagine what a military comm center was like with racks and racks of tube gear making plenty of heat. My R-390A keeps the shack warm (slightly) during the winter.
And Pete brings up important issue....transmitter tuned properly? into a good load. Antenna?
If the TX is working properly and all of a sudden the meter readings take off and go bazerk; then you may have a failing tube or component failure. It's good you are watching the meters. The grid current should be steady. Maybe you should monitor the plate current? I'm not familiar with the metering for the Valiant.
Continual overloading in your transmitter will eventually cause a bigger problem.
Fred

Not long TX time. Antenna is tuned with the Johnson Matchbox. Have a 1.5:1 match. I'll monitor plate current. Thanks for the reply. Forgot to address these questions in my other reply.

[n2awa]

With the meter in "MOD" mode, I backed WAY off on the AUDIO knob.

I whistled into the mic., and set the AUDIO to full scale deflection. No more burning smell, no more raspy sounds in XMT, and the modulation meter is not getting pegged in that rude way.

I think what happened is I was over-driving the modulation transformer (T3) and may have scorched the two 22 ohm plate resistors. What is the power rating on those resistors? Not marked on the schematic.

[n2awa]

I talked to a couple AM stations who said my audio was very low. I cranked the audio pot all the way up, and there was no more transformer plate "talk-back" (raspy sound). I need to take this rig apart and see what's going on. Maybe one of the audio output tubes is bad? I'll bet the plate resistors are toasted too.

[DMOD]

The Modulator plate resistors are 22 ohm, 1/2 Watt according to the parts list.

The Viking Valiant Manual has the proper tune up procedures.

http://bama.edebris.com/manuals/johnson/valiant/

Phil - AC0OB

[flintstone mop]

you also need some way to monitor what you are doing in the RF world with a 'scope and see how much or little you are modulating. If tuning is drifting; then those caps you mentioned earlier are heating and changing value. Are the meter readings within specs? You are not over-revving the TX? Valiants are 100 W units? 125 maybe?
A dummy load is a good beginning to have a known load. Something in the antenna ckt might be getting hot and changing the tuning in the TX.
It reads here that you need to do a little preventive maintenance before the radio season begins.
Fred

[n2awa]

Found charring on one of the modulator plate resistor wires at terminal strip under the chassis. Photos show under side of chassis with choke (L45?) removed for easier access.

The primary of the mod. transformer has the same resistance on both sides (measured from plate resistor wire to ground), so the mod xfrmr seemed good. I have to wait until later today to test the 6146 tubes.

I may be looking for a new terminal strip. It is riveted in place. Anybody have a parts donor, or know of a reasonable facsimile?

Close-up of terminal strip...
http://www.mbzponton.org/n2awa/radio_Johnson_Viking_Valiant_06aug2013b.jpg

[n2awa]

Update: Sourced a NOS terminal strip and will attempt to replace it. No way to save the old, damaged one. Thanks for reading the thread and your comments/suggestions. If that does not solve the low modulation problem, I'll be writing more again soon. 

Hey Joe GMS - maybe talk to you on the Net on Sunday night!

[w8fax]

When I was redoing my Valiant I had three term strips that would arc. I also popped the resistor that went to the cap of the VR tubes, so  replaced both. (not the 866 tubes) I also replaced all the electro caps and checked all the tubes. VFO resistor also changed....good luck...AL

[W3GMS]

Update: Sourced a NOS terminal strip and will attempt to replace it. No way to save the old, damaged one. Thanks for reading the thread and your comments/suggestions. If that does not solve the low modulation problem, I'll be writing more again soon. 

Hey Joe GMS - maybe talk to you on the Net on Sunday night!

Hi Jeff,
I just talked to Bob, ICQ on the phone a few minutes ago and I understand he is sending you a new terminal strip.  Hopefully that will fix the problem.  One step at a time and a methodical approach is your best friend! 

Yes, I should be on the AWA PM/AM net this Sunday at 7PM on 3.840.

Joe, GMS

[W3NE]

IMHO: The Valiant runs too hot even under normal conditions. I installed two muffin fans in mine when I had it many years ago. One fan was directed on the final tubes, the other on the modulators. It doesn't take much air flow to cool all those envelopes and make a big difference in internal temperature. With appropriate fans noise was not objectionable.

Bob - NE

[Jim, W5JO]

The arcing between the two terminals you experienced is not all that uncommon.  I have seen those transmitters with glyptol on the terminals to prevent the arcing or with the putty that was for HV connections globbed on the terminals.

When you install the new strip be absolutely sure there are no sharp points on the solder connections especially pointing to the other terminal.  You have lots of high voltage on them and if things aren't just right they will arc over or to ground.  I suggest you use silver solder or sliver bearing solder on them along with being sure the solder connections are smooth and rounded everywhere.   If you have any insulated standoffs it wouldn't hurt to put the terminal strip on them slightly above the chassis.

Put the wires through the terminals and be sure they are tight.  Do not leave a strand sticking out in any direction.  While you are at it, reheat the solder on terminals where the meter shunts are.  The original shunt wire will not accept solder so all you can do is be sure the wire is tightly wound on the terminal then flow the solder to hold it in place.  I suggest you replace them with wirewound resistors and, again, be sure the solder is smoothly applied.  That transmitter generates a lot of heat and the 60/40 solder used to construct them will turn to little pebbles over the years.  If you see any like that anywhere in the set, reflow the solder to keep good connections.

It is a lot of work keeping a Valiant transmitting.  I suggest you remove it from the case once per year for a visual and smell test.  Then clean all the dust from the pi network and power supply then be sure everything is clean under the chassis, even a dust bunny can lead to the failure you experienced.  After thorough cleaning, do a performance test to be sure it works like it did when you first got it going.

Nothing like a little prevemaintenanceaintence.

[n2awa]

I am definitely not out of the woods, as you know how much finesse the next phase requires. Additionally, I may have to remove that large transformer from the top side - don't know yet - hope not. 

The terminal strip is riveted, so if my pop rivets are not the same size, I may have to drill out the holes (or get different size rivets), and the resulting metal flakes (from drilling) could cause problems. I don't want to drill, so I may just try to find smaller bolts to fit the existing holes.

Updating my web page (with this saga) reminded me of how many issues there have been since putting it on the air in 2007. Definitely not a trouble-free rig!

[WBear2GCR]

If you have an identically sized new solder lug strip, then you can excise the old one leaving the angled metal that formerly held up and was riveted to the phenolic strip. Now with minor effort and modification of the new one, you can solder the two together on those mounting legs.

That is, if you don't want to drill out the old.

[n2awa]

If you have an identically sized new solder lug strip, then you can excise the old one leaving the angled metal that formerly held up and was riveted to the phenolic strip. Now with minor effort and modification of the new one, you can solder the two together on those mounting legs.

That is, if you don't want to drill out the old.

Sorry, I don't quite get your wording. It's my fault. Are you saying the phenolic and metal parts of the strip can be separated?

I do plan to use an identical strip.

Here's another idea: Snip the metal tabs (including the soldered wires) off the existing strip, and tack-solder them onto the new strip - once the new strip is placed where the old one was.

Clipping, snipping and tacking would be less desirable than using my solder sucker to rid the strip of the old solder, and placing the new strip in place and putting fresh solder on the old wires. Now, if the insulation is brittle, it may be easier to clip the old strip terminals out and solder them to the new terminals.

This is all speculation at this point. Let me report back after I work on it a little (this weekend hopefully).

[WBear2GCR]

I think that is more or less what I said...

but you want more than a tack solder job. I'd want some metal to overlap.

Depends on the style of terminal strip ur working with how to do it.
Either way you need *heat* to do the job right.

[n2awa]

Got the repair finished tonight. Put the new terminal strip in, and got the wires soldered in place. It loads up, and has modulation, but have not tried it on the air yet. Maybe by Sunday night.

Does anyone have a spare white knob insert? One of mine went missing in all the commotion. See attached for reference.

[Pete, WA2CWA]

Buy a lollypop. Find one that has roughly the same stem diameter as the insert. Cut a short piece off. Spray it with clear spray. Let dry. Put a drop of glue on one end. Insert in hole. Done.

[n2awa]

Buy a lollypop. Find one that has roughly the same stem diameter as the insert. Cut a short piece off. Spray it with clear spray. Let dry. Put a drop of glue on one end. Insert in hole. Done.

Don't forget to eat the lollypop.