The AM Forum

We won't get into the details of my personal transmitter "Shakespearean Tragedy". Suffice it to say, I need more parts.

Purchased caps from Mouser. Those were bad as well. Got to buy 4 more, 22 uF electrolytic, 450V. Any brand recommendations as I think some of the Spragues aren't manufactured anymore. Made the bad assumption that if I got caps from Mouser, they would be good quality. WRONG.

Also, need a couple of 5V4's (one for my R388 and one for the transmitter) and a 6BY5GA. I'd rather not purchase off Ebay. Does anyone have a favorite vender? Unfortunately, no nearby hamfests anytime soon.

Thanks!

tubedepot.com has both tubes, plus a solid state plug in replacement for the 5V4

I get all my high voltage capacitors from Hayseed Hamfest  http://www.hayseedhamfest.com/ and http://www.justradios.com/capkits.html

I buy tubes from http://www.vacuumtubes.net/  or  http://antiqueradiotubes.com

I'll second the Hayseed Hamfest recommendation.  Fast service, friendly, and caps are his specialty.  Has many recapping kits for vintage xmtrs and receivers, too.

It's not like Mouser to sell bad parts. What was the part # and what was wrong with them so I can watch out myself? I use Mouser a lot.
Bill

My fault. They were Nichicons.

Nichicons are some of the best capacitors made. If they are bad, Mouser will replace them. Sprague has been out of business for years. They were purchased by Vishay.

By chance did you install them backwards?  Easy to do with the bias filters.

   Third for Hayseed....

http://hayseedhamfest.com/index.html



Second that!

Dooh!!!

/Dan

Found the problem.....?

The resistance from Pin 2 of the 5V4 to ground was only 300 ohms. After fiddling with it awhile, saw that the 300V line was connected to one of the wafers on the rear band switch, Pin 1. Cycled the band switch, counterclockwise and stopped just short of the 11m position. R goes back to around 15K ohms. AHA moment occurs. Decide to remove the band switch shield cover.  Resistance goes to 15K with switch in any valid band.

I think this intermittent connection may have been why I've been through 2 - 5V4's in no time flat. The 8 amp fuse was blowing regularly. One of the 22uf 450V filter caps associated with the 6BY5A blew as well. The last 5V4, when inserted, drives the resistance to ground from Pin to 60 Ohms, so its probably safe to say the tube was fried by the heavy current.

There is a terminal strip adjacent to C97/C98. There is a wire soldered to this strip and one end of an RFC L40. The switch shield was touching this small piece of wire where it was stripped, bent back on itself, and soldered.

Bent wire/terminal strip slightly. Still wants to short. Will figure out a way to insulate.

For awhile I had worried the LV tranny had shorted. It still may be. I also unscrewed the 1.5A fuse holder and discovered a 15 ampere fuse inside. OUCH. I hope this hasn't caused any damage. Never thought to check it as it never blew to begin with.

This may be a new one (shield short to ground).

Philip

Agreed on Hayseed Hamfest.  Good products.

For tubes:

hamtubes.com  and   vacuumtubes.com

I have dealt with both with good results.

Got the most recent Valiant damage repaired. New rectumfryer tubes for the bias and LV. New electrolytics. Replaced 15A fuse with correct rating 1.5A fuse. HOWEVER, 1.5A blew immediately on power up. Replaced with 3.0A size. Powers up fine. Not happy with this, but I am sure its better than the 15A I discovered in the fuse holder after the last failure.

Rig seems to be producing LOTS of grid drive now. Will set bias voltages tonight, reset clamper, etc. Quit around 11 PM last night so I could finish up relatively rested tonight.

What's the consensus on the 1.5A fuse size? Am I okay with a 3A? Or, do I have another problem lurking around somewhere waiting to bite me in my bee-hind?

Philip
KA4KOE

Phillip,

The 1.5 amp fuse must be a "slow blow" fuse, a regular one will open from the inrush current.  You could probably use a 1.5 amp regular fuse if used in conjunction with an inrush current limiter. 

I have inrush limiters in my Valiant and Valiant II transmitters but I have never tried a regular fuse in the 1.5 amp position because I am running the original fuses having never had one blow.

Rodger....

Your last statement makes me, and I'm sure a lot of others, feel very insecure and inadequate!

PAN

Well, I did have one as my novice rig so I have had a LOT of experience with them :)

I did blow one of the main line fuses courtesy of a stuck plate relay leading to the loss of an 866A.  Since then I have been MV free.

1.5 amp seems a little light for most any supply in a xmtr.  You should be fine with the 3amp fuse.

Rodger is right about the slo-blow fuse.  You need that at the very least in a 1.5amp fuse.

Fred

I agree with Fred.  What kind of xmtr is this?  I must've missed a turn somewhere. An EICO 720 uses a 3 amp SB

Al

OK, it's a Valient.  The LV supply takes a 1.5 and I bet it's a SB.  The HV takes much bigger but the print is to foggy for me - Looks like a 5 or 8 amp

 OK OK, it's an 8 amp fuse

Yes, I'm fixing it again so I can soon enjoy the perfume of billowing magic smoke clouds AGAIN.

:)

New shack??


"      enjoy the perfume of billowing magic smoke "


klc

Didn't burn down the house, so no new shack. Not that bad....update

Valiant is working. Plate current is unstable on 40m, but I think this is a result of the band switch loading caps heating up. Those caps were iffy to begin with. Just finished talking with Terry W2PFY @ 7290 KC in NY state and he said it sounded good. Terry was using a BC610. I have stopped using the F word when referring to "successful" work on the Valiant (5 letters, starts with an F and ends with a D). Let's say we addressed the previous failures and replaced components from whom the magic smoke was released. I ended the QSO when the plate current started bouncing all over the place. No sense in tempting the lightning that lurketh in the components thereof.

Voltages look good. Bias' look good. Could not achieve neutralization on 20m. Needs more C per the manual. I had the cap fully meshed and couldn't add more C.

In other good news...whatever I did solved the oddball unequal sidebands on 40m issue.

OK, replaced the old style Atoms with 85 deg C, 22 UF, Nichicons.

Also replaced all caps around the bandswitch with RF "snubber" caps as recommended by Rodger WQ9E. Used two in each position to lower current in each 2-300 for 600pf, etc. So now have 300 PF, 600 PF, 900 PF, and 1200 PF replaced.

Installed a 150 pF 5 KV Russian doorknob at one of the loading spots. Looks like there is another batch of 4 -350 in S/P that will also need replacement. Looks messy. Pin 4 of SW3B, front.

We're getting there.

Got a lot done today. Feel good about it. Thinking about my Dad.

Philip

Had the Beast on the air for several hours last night on 75M 3885 KHz. Good audio reports for a bone stock Valiant. Very stable. Good grid current. Good power output. I exhibited a rash streak and actually put the chassis in its case and put in four, count 'em, FOUR screws.

Here is a photo.

Philip

Again, had the Valiant on-line last night on 75M AM for over three hours. My plate current was set at 330 mA. Later last evening,  I noticed Ip would go up to 340, then down to 330, etc. etc. Then I realized the wind was really whipping it up outside with 40 mph gusts, thereby causing the fiberglass fishing pole antenna (military AT-1011/U) to flop around in close proximity to the foliage out back.....no problem after all!

Keeping our fingers crossed!!!

Looks really nice!
Now you just need a mod monitor or scope.

Terry must be a fixture on 40 meters, I worked him also!

Got it covered. Scope is on the floor between the 388 and the Valiant.

Phil You sound good here in Rimersburg ,PA other night!

    KB3RDT Carl

Good to know at least something is working correctly. Oops. I done jinxed it. Another failure may be imminent.