Another Junkston Valiant Needs Help!***FIXED***GOT PIX NOW

[W3GMS]

Dave,
Like Pete said, with a scope I think you will zero right in on the problem.  There is a lot working on the rig so that leave little to check to gain operation on the higher bands.  If a doubler is not doubling, check the "L" and the "C" to make sure those values are still on.  With a scope use the formula F=1/T to determine what frequency your looking at.  I have seen people look at a scope and they think they are looking at the doubler frequency but they are looking at the fundamental!  Counters are good at measuring exact frequencies, but you can't beat a scope for trouble shooting a BA.  Its nice to see the amplitude and well as the waveform quality.   

I know a lot of guys using Valiant's and they have been on the air for years without any problems. 
 
Joe, W3GMS

[Dave K6XYZ]

For dang sure.....I've got a nice DX100 and 5100B I'm gonna do next and a ratted out terrible condition Ranger.
Funny thing....they all work....uhh...at least 20 years ago they did!
More projects....

Thanks Joe....that's exactly how I intend to do it.

[ashart]

This thought is general and not Valiant specific, but . . .

A friend bought a Valiant, and found inadequate output.

The problem was traced to improper bypass capacitors, but with a cute twist.

The parts list showed the use of CERAMIC capacitors for bypassing the plate RF choke.  The original owner had replaced the bypasses with tubular paper-dielectric capacitors which were enclosed in a, yes, ceramic, tube!

The original owner apparently didn't understand that the parts-list specification of ceramic capacitors was directed at the dielectric material and not the housing material!  The caps he had installed had a self-resonant frequency around 2 mHz, and of course got lousier (more inductive) as frequency increased.

Replacing the ceramic-housed paper caps with ceramic-dielectric disk caps, brought back full output to the Valiant.

I've seen many an error, and have myself made even more, but something about that one tickled me a bit!

73 de al h
w8vr

[Dave K6XYZ]

Thanks Al.....that's interesting. This rig has the original parts and I have substituted a few then replaced the originals if no improvement.
So far, it still dosen't work and am hoping for some help in the SW3 bandswitch area.

I scoped it and that just confirmed what I already knew....7.xxx from the VFO will not get through the 5763 and if course it won't multiply for the 20>10mtr bands.
I think there is something wrong with the b/s wiring but I havent found it yet.
Still no drive on 40>11mtrs.
160 and 80mtrs work ok but the driver log scale on the knob is at the wrong position for max grid drive as shown in the manual...yes, the knob is installed correctly.

Hopefully...I can find the problem before I get really pissed off and shove it over the side!

[Dave K6XYZ]

I'm still thrashing this thing.
I printed the construction manual and went through it checking the wiring.
I can't find any errors.

The tx has good output on 160 and 80mtrs.

No drive on the exciter at all on 40>11mtrs.....not that I care if it works on 11mtrs but that's the story.

I've done the resistance and voltage checks and scope/w counter observations and I still can't find it....cleaned the b/s and all other switches....removed the turret cap, disconnected the neutralizing cap....bla, bla....

I still believe there is something wrong in the exciter band switch/tuned ckts that prevents V4 from doubling and tripleing on 20>11mtrs. It isn't open...its non-resonant.

The VFO puts out 1.8xx and V4 doubles to 3.6xx and the tx works fine on 80mtrs.
BUT.....the exciter tune cap is wayyyy off the expected log position at the specified position.
Meaning that using the Table 4 'Typical Dial Settings' chart at 3.55 the exciter tune should peak the drive at about 38 on the dial. It peaks at 'zero' on the dial.....not good.

The 160mtr exciter dial position is very close to the expected position.

Change the b/s to 40mtrs and the VFO puts out 7.xxx like it should and should go straight through V4 without doubling...but it dosen't.

When the b/s is changed to any other higher band 20>11mtrs V4 does not double, triple etc. the 7.xxx VFO signal.
I get the same result using a 7125 and 7150mhz xtal....which totally eliminates the VFO.

Does anyone have any more ideas.....?

[WQ9E]

Dave,

Any chance connections to L6A have been reversed or it was installed backwards?  Do you know if this rig ever worked on 40 and up?  Was it kit built?

A grid dip meter would be handy but in lieu of that visually inspect.  For 160, all of L6A and L6B should be in circuit; most of the inductance will be switched in for 80 with correspondingly smaller amounts for the higher bands.  Reversed coil or tap wiring is consistent with working fine on 160 but problematic on other ranges.

[ashart]

Dave:

Here's a thought:

If you're a man of great trust, send the Valiant to me, and I'll try to repair it for you.  No charge, just for the challenge and the fun.  You pay shipping and insurance both ways.

I've a reasonably well-equipped lab, am a retired E.E., and have 60+ years experience as a technically-oriented ham.  See my website at www.w8vr.org for examples of workmanship.

I would do my best to fix it for you on your agreement that (a) I may fail and end up returning the thing to you unrepaired, and (b) My efforts may result in the need for parts, where you would pay for any parts needed, and you will be responsible for finding any special Valiant parts (eg., bandswitches, transformers, etc.), and (c) At worst, there's a long-shot chance that I might somehow destroy the thing, but for which I would not be liable.

If you're interested, let me know.

al hart, w8vr
farmington hills, mi

[w3jn]

Dave, where exactly are you losing the signal on the scope?

Scope the grid of V4 as you sweep the band switch up the bands.  If you're getting healthy signal there, and getting little or nothing on the plate of V4, I'd suspect that that multi-section/multi-tap coil in the plate circuit of V4 is wired incorrectly, or the switch wafer is 180 degrees out of phase.  Make sure that V4 is getting its proper screen and plate voltages in all bands.

See if C7 is at the far closed or far open end of its travel on 80.  If far closed, it's probably using the section of the coil meant for 40.  Sometimes the knobs get pulled and replaced in a haphazard manner so I wouldn't put a lot of stock in the knob calibration until you confirm 0 is actually full mesh closed.

[Dave K6XYZ]

I'll try to answer all questions.....
Rodger....L6A cannot be installed backwards due to it's original configuration.
The ceramic form has mounting holes on one end only.
It is not wired backwards either....although while checking this last week I DID discover that the 15mtr tap was on the 20mtr b/s contact and the 20mtr tap was never installed.
I corrected that and of course there was no change...nor did I expect a change.

Band switch SW3A rear is in contact only with contact 1 on the 160 band and as the b/s is rotated to higher bands, the b/s shorts out each L6A coil segment in turn starting from the top of L6A.
All b/s taps have continouity from L6A to their correct b/s contacts when the b/s is in the 160 mtr position. L6A is good end to end also.
The b/s is oriented correctly according to the pictorial....although the shaft index mark is 180 degrees from SW3B which is also installed correctly according to the pictorial.

Last week I also grid dipped the exciter on each band.....160 and 80 dips but there is no dip on any other band. I tried looking for a dip...any dip....nothing.
This thing is dipping ME!!!

As I mentioned previously....I have been through the entire construction manual for the exciter section and it is all wired correctly. (includes the ckt changes in the operators manual for softer keying)

Visually, I have been over this thing 10 times at least taking my time....10 days at least.

Johnny.....I'm not losing the signal on the scope.
VFO freq is on V4.8 AND V4.1.....That is the problem!!!
The exciter/mult plate ckt is not resonant on 40>11mtrs so V4 dosen't multiply.
I did a resistance and voltage check again today just to make sure....not only are the voltages pretty close to the manual but they are the same from band to band except for the plate and screen voltages that are a bit different because the tube is not operating on the bad bands.

C7 is flush closed when the exciter knob logging scale is at zero...per the book....first thang I did.
160 is about 10 points high at resonance but 80 resonates at zero....these measurements were done according to table something or other I previously mentioned.

That's it for the answers.....I guess the only thing to do is wholesale out the mica caps with decent parts.....unless C7 has some problem like an unsoldered rotor or something dumb like that.....meanwhile....I'm open to any further ideas.

[w3jn]

OK, if you're 100% sure the coils are in the right position on the bandswitches, and the coils have continuity thru the bandswitch, the other thing that will upset a resonant circuit is the capacitance.

Presuming the variable capacitor(s) haven't been replaced, I suspect perhaps one of the mica coupling caps has gone south and is either wrecking the Q of the circuit, or has changed value enough to affect the resonant frequency of the tank.   Also is C75 (the 10 pF from the bottom of L15 to the plate of V4) installed correctly?

If you have, or can borrow, a grid dip meter it'll be easy to check the resonant freq of the mult tank at each band position.  You can do this with a sig gen and a scope also (with the power OFF) and light coupling to the tank from the sig gen so you don't wreck the Q of the tank with the low impedance of the sig gen.

[WQ9E]

If you don't have a dip meter, set the Valiant to a blank crystal position and set it for the 40 meter band with the exciter tuning knob at 50.  Attach your signal generator through a DC blocking capacitor to the control grid of the multiplier tube and attach your scope with a 10X probe to the grid pin of one of the final tubes.

Set your signal generator to 7 mhz. and see if you can peak the scope display with the exciter tuning.  If not, set the exciter tuning knob back to 50 and sweep your signal generator while watching for a peak response on the scope to see where the plate circuit of the multiplier is actually tuned.

[W6TJK]

Here is a thought, or two:

in 160 and 80m position, SW3a has no effect.

in those positions, the plate for V3 buffer has then L5 + L15(choke) + L41 over to the keyer circuit

in examining the circuit, the bandswitch from 80 to 40 seems to have the effect of shorting across L15 ?!
this puts L41 in series with L5 (? my schematic is blurry on this part)

L41 (52uH) seems to be a fixed part, and  must show continuity for active 160/80 (needed to supply B+ to V3)

I am wondering, what with your earlier discussion of missing or misplaced taps, and of the dial indication being "way off", if now that you have the coil taps connected as desired, that the tuning of L5 is off ?

have you peaked it ?

normal technique is to peak starting from 10 meters and working on down.

I had some no-drive moments on my V-500, until I did the peaking correctly.

73
tom
w6tjk

[Dave K6XYZ]

Thanks to everyone for all your thoughtful suggestions....I have tried them all without success as well as some other things as well....and there is no improvement.

The damn thing DOES work on 80mtrs so perhaps I'll let you all sample the lousy audio.....
Actually, I think I'll start the same process with the DX-100 or the 5100B and see wha' happens.

So now...reluctantly...after 3 weeks.....I'm done...stick a fork in me....dawgmeat.
It's heading for the back burner...waaaaayy back.

Thanks Again

[Pete, WA2CWA]

Actually, you probably should have put it aside after the first week and then some back to it several weeks later with a fresh mindset. When I have a repair issue with a rig, I generally give myself 5 hours or less to find the problem(s). If I can't solve it within that time, I move on to something else. Weeks later I'll come back to it and generally something that I gloss over the first time will stand out as the culprit.

[WQ9E]

Like Pete said, put it aside for a bit and then come back to it.  Weird things happen to rigs and a fresh approach will often reveal  the true problem and solution.

I recently finished going through a Signal One CX-7A I picked up last fall.  After correcting some wiring errors and a couple of other faults I got the CX-7A running properly and made a few contacts.  Earlier I had picked up a nice looking Alpha 274 (twin 8874) amplifier and felt it would make a nice match for the Signal One.  With the Alpha in line the formerly nice audio from the transceiver was very distorted.  Since I had never used the Alpha before I assumed an amp problem and given the response of the plate current to the drive level from the CX-7A I assumed the problem was in the RF sense electronic bias switching section.  I found a couple of leaky electrolytic caps but replacement made no difference and when I defeated the interlocks and measured the bias system in operation it was performing perfectly dropping to intermediate bias when "keyed" and to operating level with a small amount of drive.  I then got smart and hooked the amp to a recently repaired Icom IC-751 and found the Alpha amp worked and sounded great with the Icom.  The real problem was the wrong size RF bypass cap installed on the Signal One microphone input allowing RF into the audio.

But then another problem!  While checking through the bias/control card for the Alpha amp I discovered several larger wattage carbon resistors out of spec so I replaced them with modern metal oxide resistors.  When I plugged the card back in the Alpha would no longer go into transmit.  I assumed I made an error so I rechecked all of my work and connections and found nothing wrong.  I put a shorting plug into the back of the Alpha to rule out a transceiver or cable problem.  After a bit more head scratching and measurement I found the problem was the RCA phono jack on the amplifier, the internal contact had failed coincidentally with my repair of the card.  Interestingly enough I had not even unplugged the T/R cable while repairing the card so it wasn't due to removing/reinserting the plug.  As they say S**T happens.

Good luck with your next project and come back to the Valiant soon!

[Dave K6XYZ]

Well.....here I am again!
BUT....this time I've got good news.
After a year and a half I think it's fixed.
It's been working for 6 months now and looks like it's gonna hang in there.

Just to refresh the memories without reading the whole gnarly thread again......
This transmitter had never worked...ever...from 40mtrs on up.
It worked fine on 160/80mtrs.

I determined that the multiplier was not multiplying the VFO signal for 40mtrs on up.
Just to jump to the chase and leave out all the crap that I did......here's the deal.....

L15 is mounted on TS6. This inductor is shorted by SW3-A from 40mtrs and up. I determined through very close visual inspection that L15 was installed too close to the other lugs on TS6. In fact, one of the other lugs was bent slightly and was touching the L41 end of L15.
This did not affect the multiplier on 160/80mtrs because the multiplier does not multiply on those bands.
BUT....this condition obviously detuned the multiplier enough to throw it completely out of resonance for 40mtrs and up.
I had previously grid-dipped it and it was nowhere resonant on any of the bands other than 160/80mtrs.
When I corrected that lug the tx worked on all bands for the first time in more than 50 years since it was built.

SO.....that's the rest of the story....and the end of the story!

Thanks to all for your help.

73

[w3jn]

Congrats on nailing that tough dog problem, Dave!

[W3GMS]

Dave,
Doesn't it feel good when you nail the problem!  Then when you find it you say, "why did I not see that earlier".  All of this stuff is a humbling experience!

Congrats on sticking with it. Folks with less character would have flipped it on E Bay! 

Joe, W3GMS 

[Dave K6XYZ]

Here is a thought, or two:
in examining the circuit, the bandswitch from 80 to 40 seems to have the effect of shorting across L15 ?!
this puts L41 in series with L5 (? my schematic is blurry on this part)
L41 (52uH) seems to be a fixed part, and  must show continuity for active 160/80 (needed to supply B+ to V3)
tom
w6tjk

Johnny and Joe....thanks for your nice comments!
I had set it aside and let it smell bad for about a year until I discovered that the bench was getting weak.
In that time I had taken to heart what Tom had said in the quote.
I looked over the schiz closely and put the maloit on that dadgum choke and spotted the problem almost immediately....like 20 seconds or less. This problem was virtually invisible so I'm not surprized that it had not been found.
Having retired from AT&T and NORTEL, I have a long history of finding componant level ckt problems like this....I can tell you though that I was getting a bit desperate.

Thanks

73

[Knightt150]

If this transmitter was a KIT you can expect anything, something tell's me it never did work on the higher bands. And that maybe the reason it was never used much.

John W9BFO

[ke7trp]

We got one a few years back that did not work on AM.  Opened the rig up to find there was NO modulator installed. Ever.  Nothing. empty holes. I guess the builder was CW only

C

[Dave K6XYZ]

If this transmitter was a KIT you can expect anything, something tell's me it never did work on the higher bands. And that maybe the reason it was never used much.

John W9BFO

I had already told you several times that it was a KIT and that it had never worked on the higher bands.
This is not a POS radio....whoever assembled it did a great job....but made a slight mistake.

[Dave K6XYZ]

Well.....here I am again!
BUT....this time I've got good news.
After a year and a half I think it's fixed.
It's been working for 6 months now and looks like it's gonna hang in there.

Just to refresh the memories without reading the whole gnarly thread again......
This transmitter had never worked...ever...from 40mtrs on up.
It worked fine on 160/80mtrs.

I determined that the multiplier was not multiplying the VFO signal for 40mtrs on up.
Just to jump to the chase and leave out all the crap that I did......here's the deal.....

L15 is mounted on TS6. This inductor is shorted by SW3-A from 40mtrs and up. I determined through very close visual inspection that L15 was installed too close to the other lugs on TS6. In fact, one of the other lugs was bent slightly and was touching the L41 end of L15.
This did not affect the multiplier on 160/80mtrs because the multiplier does not multiply on those bands.
BUT....this condition obviously detuned the multiplier enough to throw it completely out of resonance for 40mtrs and up.
I had previously grid-dipped it and it was nowhere resonant on any of the bands other than 160/80mtrs.
When I corrected that lug the tx worked on all bands for the first time in more than 50 years since it was built.

SO.....that's the rest of the story....and the end of the story!

Thanks to all for your help.

73

This was a hidden problem so while I have the rig out of the cabinet again I thought I would post a picture or two of what and where the problem was.
This rig worked only on 160 and 80mtrs....the rest of the bands had no drive because the multiplier was not working. Please read the details above and compare to the pictures. the nasty looking black choke is L15.