a.m. mode

[K5IIA]

got them changed.

gona try again tomm.

[KX5JT]

Hey Brandon,

Welcome to the best of ham radio!  You being in Pearl River and me south of Lafayette means we are at a great distance for awesome daytime 80 meter AM. 


Talk to you on the air,

73, John KX5JT

[K5IIA]

yep, i have heard you on a 3 foot piece of wire. hahahaha

[KA2DZT]

yep, i have heard you on a 3 foot piece of wire. hahahaha

Great on hearing John on the three footer,  just don't try to transmit back to him with it.  Your Valiant may experience another small fire followed by a minor explosion

Fred,  KA2DZT

[WQ9E]

Brandon,

Those replacement small mica caps are not going to stand up to typical AM transmissions, you might get away with them on CW if you keep the dashes very short   The original mica "turnstyle" cap had considerably more RF current capacity than these small receiving type replacements.  Unfortunately the turnstyle originals were very prone to failure like the one that was in your transmitter.

You are going to need some small transmitting type mica caps.  I imagine you also noted some changes in loading during transmission as these caps heat up and change capacity.

[K5IIA]

yes i did. i noticed my carrier got very small on scope. and my plate current was pegged. so i unkeyed.

after his transmission they must have cooled. i keyed back up. they lasted about 45 seconds or so and up in smoke.

only thing i have in the correct capacitance range is a big door knob cap i am going to put in there.

i am cutting some 8-32's down short enough now to bolt it in.

[W2VW]

Hi Brandon,

    Congratulations on choosing AM.

Your padder capacitors must be able to handle some R.F. current where they are located. Replacing the existing cooked ones with the same thing will yield the same result.

Whatcha gotta do is come up with the same capacitance value but a higher current rating. The solution depends on what parts you have on hand or can source.

If the caps are 1000pf the simple way would be to parallel smaller capicitance units and share the current. 10 X 100 pf or 5 X 200 pf would probably hang in there.

Obviously a series/parallel deal might work also.

There are a lot of prople here who know your tx inside and out.

Dave W2VW.

[K5IIA]

well i am back on the air untill i find another weak part of my station. 

[WQ9E]

Brandon,

If you cannot find some suitable vintage doorknob or large mica caps, take a look at the CDE MCM series RF chip caps.  They are SMD but you can add leads easily.  The price is not terrible and they have a decent RF current capability.  Mouser and Digikey are both stocking suppliers. 

[K5IIA]

I replaced the string of caps off the back of the band switch with a large doorknob. i think it will be ok.

i still have somethign heating up, after transmitting for a minute or so i have to re dip the plate.

i dont know if i should re investigate or just wait for the smoke signal of trouble again. hahaha

[K1JJ]

Hi Brandon,

Sounds like you know what you're doing there.  You'll get that station working FB in due time.

Try this technique to find the components that are heating up:  Take the rig outa the cabinet and load it up. Wait for the plate current (or whatever is changing) to occur, then spray suspected components with that cold spray stuff you can find at Radio Shark.  When you hit the right part the current will swing back to normal.

This does not apply to VFO/frequency sensitive components, as they will be affected big time even when good.

As an alternative, use a hair dryer and blow heat on the suspected areas to see the symptoms. Then the cold spray is your rifle shot to zero in. Be careful not to melt anything or overheat with the hair dryer. Alternating back and forth can kick bad components out on their asses fast.

T

[KB2WIG]

...also, if ya use the spray, be carefull Not to let the cooling spray go UP the tube sockets..... the tubes do not like this and they will say so quickely. Ask me how I know.....


klc

[K5IIA]

thanks for the comments and help.

it did this one antenna nad dummy load.

also when i loaded up on the high bands where the aux is bypassed it did not do it.

i isolated the aux coupling and got pf readings on each setting.

for right now i seriesed two .005 1200v old mica's big block ones.

because that is within 150pf of where it was at. i think i will be able to get the rest with the air variable.

this valiant used a small cap with 4 lugs on it. another valiant i have uses 4 individual old mica's

so i really think this was the weak link and i am going to try to gather parts to get the aux switch back 100 percnet with better componets.

thanks again for the warm welcome..
brandon kf5iia

[K5UJ]

I have some mica tx caps; maybe I can send you some--they are the brown sangamo jobs that are about an inch long, half inch thick, and 3/4 inch wide.  let me know the cap value, and voltage, but I don't know much at all about the Valiant so I don't know for sure if these are what belong in there.

[WQ9E]

Be extremely careful inside an operating Valiant.  There is exposed HV at many points with plenty of current available and it is an "accident rich" environment.  Say for example, you accidentally spray and shatter a tube as noted by the previous poster.  You will probably jerk your hand back in surprise and hopefully not come in contact with a voltage source.  Many years ago I read a GE publication where they detailed accidents involving TV/radio repairmen and one of the more common accidents involved servicemen hurt by an imploding picture tube after they received a fairly minor shock and hit the fragile neck of the tube while jerking back from the shock.

I would first visually check for capacitors in the RF path not suitable for RF, if small dipped micas like those in your photo are present in the loading circuit they are simply not going to handle the RF current from the Valiant.  This includes the coupling cap C37 which should be at least 1000 pf for operation on 80 and preferably larger.  The later Valiants and Valiant II were built with a 2,000 pf cap which is suitable for proper operation on 80 and 160.  If the proper caps are in place, run the Valiant into a dummy load to make sure that the issue is not in your antenna system.  If the grid drive drops, this is likely from the coupling caps to the final grid which fail fairly often.  Try the Valiant on a higher band (10 or 15) at which point you should typically have the auxiliary coupling caps out of the circuit when fully loaded.  Visually inspect both the band switch and coarse loading switch contacts for heat damage and also the solder connection to the RF out SO-239.

 

[K5IIA]

the grid current stays the same.

also acts same on dummyload or dipole.

i did notice the contact was black on the aux coupling.

i am going to take it back down tomm. and i guess bypass the aux switch and see if that helps.

i may also try to get some of that spray.

[ke7trp]

Brandon.  Next time you are inside the valiant.  Take a tooth brush and some contact cleaner such as deoxit and clean the band and loading switches. Turn the switch and scrub the contacts and wafer clean.  If you look close, There are small rivits and you will likely seen carbon traces from the rivits to the contacts.  These arc and then blow out the caps or worse, Torches the switch.  Very common problem and an easy solution.

C

[KX5JT]

Nice working you right now on 3890 AM Brandon!  The Valiant with the 811A's modulating sounds great!  You're doing great!

John KX5JT

[ke7trp]

I can barely hear you guys.   Not enough to talk, to much noise.. But I heard your voice JT.

C

[KX5JT]

Hey Clark cool!  WW9W came in after (now on with him about to sign)... he's on his BC610 near Dallas.

Hey Brandon and anyone else....

Don't forget the AMI west coast net that you can listen and watch on

http://stickam.com/wj6w

  Around 2:30 utc people start gathering.. Net starts officially at 03:00 utc

(that's 8pm Pacific, 10pm Central and 11pm Eastern ... DOES it run on Collins night?)

[K5IIA]

yes in deed very cool... I'm having a great time. Good talking with you john. you were putting a great quality signal over here. i'm about to go back in the shack and listen some more.

[K6IC]

JT,

  ...  "DOES it run on Collins night?) "

YES,  EVERY  Wednesday night.

Brandon,  Welcome here and to AM.  Congratulations.  Have Fun,  Vic

[K5IIA]

JT,

  ...  "DOES it run on Collins night?) "

YES,  EVERY  Wednesday night.

Brandon,  Welcome here and to AM.  Congratulations.  Have Fun,  Vic

Thanks i am having a great time...