My Valiant may be down for the count

[KA2DZT]

Speaking of fuses.... a safety thang all youse old timers know; Be sure to connect the line cord directly to the END lug on the fuse holder.  This way if you space out and change the bad fuse with the plug still in, the hot end of the fuse is not touching your finger when you pull it out.   (maybe we should use a pair needle noze  just in case)

T

You're right, something that I forgot to mention, connect the hot line cord lead directly to the rear terminal of the fuse holder.  So, like you say, when you remove the blown fuse you not handling the hot lead since it's on the far end of the blown fuse.

Of course, all bets are off, if the blown fuse is not blown

Fred

[ka4koe]

I have an internally mounted inline holder. I didn't cut any holes in the chassis.

[ka4koe]

Short in the PTT relay line to ground. Plate iron okay!

[N3GTE]

Glad to hear it!!! On to the next problem!
Terry  N3GTE

[N8ETQ]

    Glad to Hear that Phil, I hope you have a bunch of
fresh doorknobs in waiting. I was wondering how you
made out with that.

     BTW I was a Harbor Fright today for some heat shrink
and actually picked up one of their "Good" DMM's, it was
on sale for 19.99 and I had a %20 coupon so it was like
$15. It has a freq counter and "uF" meter as well.  The
freq counter only goes to 20KC and the capacitance reading
takes a while but it does work. Their model #P37772. Also
has a temp range with internal sensor and came with a remote
sensor as well... Of course the "Harbor Fright Kludge" is
it only displays temps in centigrade.

/Dan

[ka4koe]

Not blowing fuses, screen voltage on transmit is around 205 volts. Loading is screwy on 80/40. Everywhere else is fine. Looks like the band switch and coarse loading are likely the causes again.

P

[KA2DZT]

Philip,

Just think of all the money you're now saving on fuses.  Glad you found the problem, never thought it was the plate iron.

That screen voltage looks about right,  6146s will run around 200 volts.  RCA manual says 150 volts but my 6146 always ran about 200 volts on the screen.

Keep us posted on the next problem.

Fred

[ka4koe]

....next problem.....

That has an ominous sound to it. Anyway, looks like I am going to have to reexamine the coarse loading and bandswitch networks again. Not doing its job on 80/40. The rest seem fine (10 is persnickety), with good current level and power outpoot (around 140W).

P

[N8ETQ]

   Sounds like that 1200pf section of the loading cap
"Stepped out for a Smoke". That's the way they do ya'.
If all is "Normal" above a "Course" loading position of
3 or 4 (where it is no longer used) assuming the switch
is good that's it.

    Still got those "Snubbers" in there?

/Dan

[ka4koe]

Yes I do. Replaced them all with snubbers, rated 1000V.

At the outpoot coupling, I paralleled 2-600s for the 1200, 2-450s for the 900, 2-300s for the 600, and 2-150s for the 300, to reduce heating. HOWEVER, knowing what I do now, this approach does nothing for the voltage rating. No visible scorching, but wonder if the top two could've been fried as they're only good to 1 KV. These are the CDV snubbers. Continuity across the contacts seems good, with around 1 ohm or less.

At the bandswitch, have 2 sets of 350s paralleled that are in series with each other, for a total of 350 at 2000V rating. At the next position, have a 6 KV 150pF doorknob (Commie-Cap brand).

Getting close. No screws in the back this time. The time for boldness is over.

[WQ9E]

Yes I do. Replaced them all with snubbers, rated 1000V.

At the outpoot coupling, I paralleled 2-600s for the 1200, 2-450s for the 900, 2-300s for the 600, and 2-150s for the 300, to reduce heating. HOWEVER, knowing what I do now, this approach does nothing for the voltage rating. No visible scorching, but wonder if the top two could've been fried as they're only good to 1 KV. These are the CDV snubbers. Continuity across the contacts seems good, with around 1 ohm or less.

Well the only way you will see anywhere close to 1KV on those output coarse coupling capacitors is if you have a nearby lightning strike.  Assuming the Valiant manages 600 watt PEP output at 100% modulation (that is a very healthy Valiant loaded to the gills) then with a 50 ohm antenna you will have a mere 174 peak volts appearing on the output side of the coupling network.    Lets say you try to load a badly mismatched antenna providing around 1000 ohms, this is not a smart thing to do but even with this ridiculous load you are still under 800 peak volts.  Take a look at the variable capacitor in the loading circuit, it clearly isn't designed for high voltage.  Legal limit amplifiers run into 50 ohm loads can use "receiver" spaced variables for the loading capacitor.

[N8ETQ]

   Right on Rodger, Low voltage and relatively high
peak current. Thats why I question "Snubbers". Just
what the H*ll is a Snubber, It's a network of either
R/C or L/C, heck some even have diodes in em. I think
there intended purpose (Transient suppression) would
make them Iffy for all but the lowest  continuous
RF currents.

    The "C" may be the predominant component but
he's not alone, from what I read.

   Anything can take 500A for a cycle or 2.

   Maybe Phill can provide the part number of these "Snubbers"?

/Dan

[WQ9E]

Dan,

I am with you on RF current rating.  I believe some of the "snubber caps" were aimed at wide market and may carry a decent RF current rating but I doubt if that goes for all of them.

I nearly got figuratively AND literally burned by some Ceramite doorknob caps.  Although they look like a regular RF doorknob they certainly don't act like one in terms of current capability.

[W3GMS]

Anytime I have used snubbers that were either in switch mode power supply design in the primary of the switched converter stage or networks to suppress arcing on relays. 

From an RF standpoint, especially in the loading circuit you want the lowest possible series inductance along with low ESR.  As mentioned, its not a voltage rating issue but with the technology of the cap, how well it can handle the RF current.

Joe, GMS     

[ka4koe]

Search CDV on Mouser, 1000V, Cornell Dublier. Can't seem to find affordable doorknobs in the right values. Grabbing at straws here. Any suggestions for these caps? Don't want to buy anything that is going to fry.

[WQ9E]

Data sheet here for CDV series: http://www.cde.com/catalogs/5.024-5.027.pdf

Side note:  used "DuckDuckGo" search engine to get away from Google adding all of their garbage to the HTML when copying address.  Another reason I despise google

[W2VW]

The Class E guys get away with chip caps at plenty of I @ 50 ohms.

[W3GMS]

I have always used silver mica caps as loading caps up to 100W or so.  Over 20 years with them without any problems.  I try and get the 1KV parts. 

Joe, GMS

[K1JJ]

The Class E guys get away with chip caps at plenty of I @ 50 ohms.

As they say, $20 and a handful of chip caps will build ya an e-rig....

[ka4koe]

Looks like those snubbers didn't make it. Paralleled a good doorknob via jumpers and it works fine. Loading switch is fine.

[ka4koe]

Tried some 3 KV Ceramite ceramics. Also, used a temperature probe. I paralleled three 470 pF at the 1200 pF coarse loading position. Needless to say, they heat up fast. I think they are rated 85 degrees C. Back to the drawing board. But hey, it loads up pretty as you please!!

Philip

[WD5JKO]

Phillip,

   You won't blow these guys:

https://www.atceramics.com/UserFiles/trans_cap_equiv.pdf

Explore their web sight, they have all sorts of stuff.

The ATC stuff is the Cadillac in RF capacitors. We use various ATC's in a SMT package at the 3KW level at work. They never fail. They won't be inexpensive though.

Why your caps get hot:
http://www.atceramics.com/Userfiles/esrlosses_appnote.pdf


Jim
WD5JKO

[ka4koe]

Dern, Jim, you made me laugh.

[WQ9E]

Tried some 3 KV Ceramite ceramics. Also, used a temperature probe. I paralleled three 470 pF at the 1200 pF coarse loading position. Needless to say, they heat up fast.

Philip

I warned you about those Ceramite caps which behave more like thermite when in the presence of RF   I remember one of the commercial manufacturers tried to use similar caps for awhile in one of their amps as padders on 160 and the power would drop during an extended dash as the capacitor rapidly changed value from heat.

[ka4koe]

I think you warned someone else but I read your post ex post facto. It was fun, however, watching that digital thermometer climb and climb and how FAST it did so! Anyway, they were cheap as dirt so no biggie.

However, I did note that you liked the CDV snubbers. Mine went, so I'm wondering if I needed to reconfigure them differently. Did you parallel some of lower value to split up current and therefore reduce heating? The CDVs come in 1 KV, I think, so would you also need to do a series/parallel setup to reduce heating and reduce voltage across each?