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Author Topic: My Valiant may be down for the count  (Read 33563 times)
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WQ9E
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« Reply #50 on: March 26, 2014, 12:00:44 PM »

Which series did you use?  The CD/CDV series from CD are traditional dipped mica caps and some of the "larger" series are specifically designated for "snubber" service since they will handle high peak current.  They  aren't like some of the caps purpose built for snubber service which may not work so well at RF.

I used to have a RF current guide for the 19 series but I can't  find it anymore.  But you can take a look at the data sheet for the next series smaller which has good RF current capability.  RF current capability generally increases with capacitance value and frequency.  What this means in practice for the Valiant is although RF current capability goes down for 160 meters this is also the band where you will typically have several of the large value coarse capacitors in circuit.  For the higher bands you will have smaller/less of the coarse loading caps in play but the current capability of the capacitor is also higher at these higher frequencies.

The 19 series in the 1KV (or greater) rating should be fine for the Valiant unless you are trying to load some very odd extremely high (voltage issue) or low (current issue) impedance load.  If you are  looking at very low impedance loads on 160 then use 1/2 or 1/3 value capacitors with two or three in parallel respectively.  If you are looking at really high impedance then get a tuner Smiley

The original valiant coarse loading caps carry a 1.2KV rating but that allowed for matching some pretty bizarre loads without using an antenna tuner.

Even the next smaller series should have no current issue except on 160.
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Rodger WQ9E
ka4koe
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« Reply #51 on: March 26, 2014, 01:12:07 PM »

I originally used the CDV16 series, but did not parallel the caps. So that may explain the failures on 80/40m.
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N8ETQ
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Mort


« Reply #52 on: March 26, 2014, 01:44:09 PM »


Phil Said:
" Any suggestions for these caps? Don't want to buy anything that is going to fry."


   Hey Phil,

        Thought I had suggested this before but...

  "Have your credit card ready and call Ameritron at 1-662-323-8211.
Ask for "Parts Department" and order 1 of each."  You won't need the
first few values but there handy for "Trimming".  They will be on your
porch by early next week and cost less than $30.

   These are what they use for loading padders in their AL-800 Amps.
You'll be set for life unless you do something foolish!

http://www.ameritron.com/Product.php?productid=AL-811



* Caps.gif (9.58 KB, 572x300 - viewed 514 times.)
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WQ9E
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« Reply #53 on: March 26, 2014, 03:10:12 PM »

Are the Ameritron caps made by Cornell Dubilier?  The numbering scheme seems to fit.  If so their DM15 parts would not be suitable for use in the Valiant since the fixed coarse loading capacitors carry the lion's share of the current in many situations.  The CD 15 series has even less current carrying capability than the 16 series he tried earlier.

Many amplifier designs use a large variable loading cap supplemented by fairly small padding caps for the lower  bands.  The Valiant uses a fairly small "fine tuning" variable for loading with the fixed capacitors providing most of the needed capacitance on the lower bands.  With a typical antenna on 80 meter AM the variable is providing around 300pf of loading capacitance while the fixed capacitors are providing from 2,100 to  2,7000 pf  causing most of the current to flow through the fixed capacitors.

Heath ran into similar issues with the fixed loading caps in the  DX-100 when owners tried to match unusual antennas and the DX-100B version moved from the fixed coarse plus fine loading combination to a mutli-section variable with all sections in parallel. A modification kit was also made for the earlier transmitter and many DX-100 transmitters were converted.  It lost some of the matching range but got away from the problem with fixed capacitors.  There really isn't room to do this in the Valiant without major modifications.
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Jim, W5JO
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« Reply #54 on: March 26, 2014, 04:43:26 PM »

I can't help but wonder what is happening in the case being discussed.

Heath ran into similar issues with the fixed loading caps in the  DX-100 when owners tried to match unusual antennas and the DX-100B version moved from the fixed coarse plus fine loading combination to a mutli-section variable with all sections in parallel.
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N8ETQ
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Mort


« Reply #55 on: March 26, 2014, 05:01:50 PM »


  LOL   It is provocative isn't it?

  Jim said:

"I can't help but wonder what is happening in the case being discussed."

   Right Rodger,

      The Load cap is about 800pf in the Amps.  He needs
to use the website to choose an Amp. They have doorknobs too
and  for about $65 he could re-create the Johnson "In House"
job with doorknobs.  I'm not sure who they get the caps
from.

      I haven't gone back and read this whole thread but
I thought he just lost the 1200pf chunk. A 1000pf DK and
a couple of silver mica's will bring that back. 

      I know Phil enjoys taking all those screws out
every couple of months anyway.

/Dan
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KB2WIG
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« Reply #56 on: March 27, 2014, 01:55:49 AM »

P,

Your friendly ePay has the following listing

Two  1000pF 6kV 40kVAR Doorknob K15Y-1

for

US $8.76
+$12.00 shipping


klc
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Ralph W3GL
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« Reply #57 on: March 27, 2014, 02:11:32 AM »

P,

Your friendly ePay has the following listing

Two  1000pF 6kV 40kVAR Doorknob K15Y-1

for

US $8.76
+$12.00 shipping


klc

Okay, make it easy for us lazy guys and publish the
ePay item number... That way we can "cut & paste"
right to the search line on eBay, thank you...
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73,  Ralph  W3GL 

"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other"     Ed Morrow
Pete, WA2CWA
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« Reply #58 on: March 27, 2014, 03:19:13 AM »

P,

Your friendly ePay has the following listing

Two  1000pF 6kV 40kVAR Doorknob K15Y-1

for

US $8.76
+$12.00 shipping


klc

Okay, make it easy for us lazy guys and publish the
ePay item number... That way we can "cut & paste"
right to the search line on eBay, thank you...


http://www.ebay.com/itm/2x-1000pF-6kV-40kVAR-Doorknob-Tesla-Capacitor-K15Y-1-/201046317152?pt=Vintage_Electronics_R2&hash=item2ecf4b5860
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Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
VE3AJM
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« Reply #59 on: March 27, 2014, 03:37:39 AM »

This thread is hilarious....

Al VE3AJM
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ka4koe
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« Reply #60 on: March 27, 2014, 08:40:04 AM »

"I know Phil(ip) enjoys taking all those screws out every couple of months anyway."

I consider it very bad luck to install more than one or two in the back.


We all have to start at the beginning. Everyone who loves old radios and works on them has a "first" that requires repair and restoration. I've just had more problems than most. My particular Valiant (The Beast) came to me after looking like it had been ridden hard and put up wet and was sort of working when I got it.

I started out with zero troubleshooting experience. But, I have learned so much! And, everyone has been so helpful and patient here.

I brag on the AM folks to my ham friends who don't do the mode. And, I still contend that AM folks are perhaps some of the nicer folks on the bands. We have our bad apples, but then again, who doesn't???


"This thread is hilarious...."

Let us all in on the joke so we can enjoy it!
 

Again, thanks!

Philip KA4KOE
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VE3AJM
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« Reply #61 on: March 27, 2014, 10:20:30 AM »

Just read some of the replies posted earlier. You may or may not get it. Good luck with all of it. Grin

Al VE3AJM
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KB2WIG
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« Reply #62 on: March 27, 2014, 11:47:52 AM »

"  I consider it very bad luck to install more than one or two in the back. "

There is a story of an AA in WW2 in GB.

It seems the RAF wanted to beef up bombers to increase the survival rate. So they had their boffins count holes and assess damage on the returning aircraft. Where there was the most damage, they were going to increase, or add armor to these areas.  One of the more senior designers took a drawing of the bomber improvements, and circled the areas that were not to be armored. He said something like "these aircraft came back shot up so we know the plane can fly with this damage. The planes shot down were probably hit in the other areas."

So, P is in good company not wanting to put the screws back in. I for one, utilize the same Ozona Bob methods with my VK2. I don't have any of the case attached ' caus I know things are gonna crap out......   ( I just got some Ruskie door knobs, and now its off the Ace Hardware  for some ' metric screws and then fingure out how to replace the fixed caps in the coupling.)

klc
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ka4koe
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« Reply #63 on: March 28, 2014, 11:10:29 PM »

Well, here we go again. Installed new snubbers, 1 KV, with three CDV16s paralleled at each position this time! Works fine as before .... UNTIL....

Are we excited yet?

Plate current need slams the right side of the meter.

Looked underneath. One of the jumper wires between the two rotary switches had come off one of its anchor points. Resoldered. Works fine again. I swear, is everything in this radio going to break before we're done??

Getting about 130 watts carrier, Coarse at 3, Fine at 10, 300 mA, 3.9 MHz.

OK, perhaps this will hold a couple of weeks. This time out, I learned the significance of ESR and what happens to caps when they get a leedle too hot.

PAN
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« Reply #64 on: March 29, 2014, 02:03:16 AM »

Philip,

Sorry you keep having so many problems with your Valiant.  But, looking at the other side, just think about all that you have learned working on the rig.  How much would a college course or courses cost you to learn this stuff?  Now add in all that all the readers of you posts have learned.

Don't give up,  you're finding every weak point in that xmtr.

Someday, as time permits, you'll be able to build up your own rig using your own design from everything you're learning.  You'll know what features to use and what methods  and circuits to not use, like fixed caps for loading, bad idea.

By studying the basic circuits you see in the vintage Handbooks, studying the circuits of the project xmtrs in these Handbooks and even the circuits in your Valiant you'll begin to learn that most of these xmtrs are just variations of the same circuits.

In time you'll be able to piece together your own xmtr design from parts you have or able to obtain.  It takes time, a lot of work and patience.  You've already proved that you have patience.

What I described above is probably the way most all of us OTs learned how to build xmtrs.  I doubt any of us went to xmtr building school.  I think I can speak for most of us OTs and say that we're eager to help.  We want to pass on to the next generation or even folks a decade younger whatever we think we know so it doesn't pass into history when we do.

Fred
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ka4koe
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« Reply #65 on: March 30, 2014, 06:13:33 PM »

I haven't given up, Fred, and I appreciate the patience and encouragement. I've "buttoned" the Valiant up for now, with no screws inserted in the back.

Philip KA4KOE
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ka4koe
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« Reply #66 on: March 31, 2014, 08:35:40 AM »

In my particular case, the biggest weak points were the accessory plug (removed mine) and the band-loading switches and their associated caps.

Additionally, but not the biggest problem, the microphone jack was worn out as well.  When I say this TX was rode hard and put up wet, I meant it!

Here is a repair summary:

1. Removed/jumpered accessory jack.
2. Replaced microphone jack.
3. Replaced 866s with 866A RF Parts solid state equals.
4. Replaced modulator tubes and associated resistors after audio stage oscillated.
5. Replaced all electrolytics.....twice.
6. Replaced coarse loading caps three times.
7. Provided new tubes in the VFO compartment.
8. Replaced Chernobyl resistor in the VFO compartment.
9. Troubleshot multiple instances of fuse blowing.
10. Replaced power cord with 3 conductor type.
11. Provide line fuse on hot conductor (see item 10).
12. Cleaned topside of chassis and coils.
13. Put spaghetti over conductors where the pass thru holes to the various transformers.
14. Installed higher R shunt resistor at first audio stage.
15. Installed new clamper tube.
16. Installed new MV rectum-fryer tube twice.
17. Troubleshot overheating in MV circuit. Turned out to be a short underneath the internal metal shield over the band switch area.
18. Went through one can of Deoxit cleaning tube pins, sockets, and band switches.
19. Removed all tartar from rotary switches with toothbrush.
20. Provided new lamps throughout.
21. Cleaned big coils with Nevr-Dull.
22. Replaced 500 PF doorknob in loading circuit with 1000 PF doorknob.
23. Replaced HV bypass caps at B+ choke.
24. Repaired B+ choke.
25. Wired in a short cord for TR switching of Dow Key.
26. Set grid bias and modulator bias a couple times.
27. Troubleshot audio issues with oscilloscope.
28. Repaired lack of grid current on 40m and higher....this was a toughie.
29. Troubleshot excessive plate current at least three times.
30. Removed and thoroughly cleaned front panel, VFO eschutcheon, and knobs.

I'm sure I'm forgetting something.
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N8ETQ
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« Reply #67 on: March 31, 2014, 09:42:48 AM »



      Hey Phil,

          Did I miss it or did you not strap a pair of 1N4007's Back
to Back across that beautiful teardrop Meter?

/Dan





I'm sure I'm forgetting something.

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ka4koe
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« Reply #68 on: March 31, 2014, 09:49:50 AM »

Didn't hear about this one. Meter protection similar to that in Heathkit amplifiers in case the finals melt down, eg. grid to cathode short?
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N8ETQ
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Mort


« Reply #69 on: April 01, 2014, 07:55:08 AM »



   Yes, Any anomaly that would endanger the meter coil.

/Dan
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« Reply #70 on: April 01, 2014, 08:25:44 AM »

You are learning a lot.
Just think of the value in knowing how to keep 50 year old radios working!

All these radios are very old now, and most have had a lot of abuse or neglect.
The trick is to fix problems in advance with better then original parts, then a rig can be reliable.
Frequent use often keeps them that way, letting something sit unused is often bad for reliability.

My idea of fixing up a vintage ham rig is to remove all the parts inside and replace them all with ones twice as big, and you are good to go.

I dislike operating a bunch of old marginal parts in a bad design built to a price point, so went home brew a long time ago.
Its lots of fun trying to get the most/best out of the old radios though...and many looked very cool.

Two radios I had really good luck with are the 32V series, and the Gonset G76, both of which put up with a lot of abuse over a long time with no problems at all.
I think the 32v I have left has all its original parts in it except the rectifier tubes were changed to solid state and the modulator has been changed.





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« Reply #71 on: April 01, 2014, 02:33:01 PM »

Yes, you are learning a lot. And while these old rigs can be frustrating, there is a reason why so many are still being worked on and are still on the air. There's just something about these big old monsters that just won't die. Perfect, no. Good, yes. Improvable, most definitely.

Don't want to get too far off topic, but anyone know why the modulator resting current in my Valiant is too high (150 ma) when I first fire it up but drops to normal value (50-70 ma) after 15 minutes or so of casual transmitting? Modulator pot is backed all the way down. Leaky cap?

Also, anyone know of a source for the jeweled power and plate indicators on the Valiant?

Doug, WB5IRI
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« Reply #72 on: April 01, 2014, 03:17:44 PM »

WWW.tubesandmore sells some jewels.

Modulator resting current changes, look at the bias voltage (is it steady?) or the current through the modulator tubes is causing a cathode resistor to heat up.

Plate voltage will be steady, as will filiment voltage, but bias, screen and cathode resistance can change.

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ka4koe
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« Reply #73 on: April 02, 2014, 12:51:33 PM »

When I swapped out the D104 element for an original, the change in audio quality was staggering.
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