Asking Advice on Restarting Dormant Dx-100 and Valiant

[K4IMZ]

Any advice on using a variac to bring my old dx-100 and valiant back to 110v would be greatly appreciated.

I have been off air for around 10 years and now as the days grow shorter , I want to am as much as possible.

do I need to pull the finals during the reforming process ?? 

Again, Any Help appreciated... 

[ke7trp]

Open units and inspect and test all caps with cap checker. Test all tubes.  Replace as needed. OR:


Hook up dummy load,  Set all switches to correct postions.  Plug into variac, Turn power on transmitter on, Turn up slowly over 30 seconds. If you hear bacon frying, Cut it off.

The caps will accept a charge over a 5 to 10 second period, Then level out, More voltage in and they take more of a charge then level out ect..  Long periods of time at low voltage is not needed with the variac.  Just cut it up slow. If the caps are good, They will take it.

C

[Ed/KB1HYS]

for peace of mind just replace the existing Electrolytics with new bigger jobs.

move the 18K/2 watt "chernobyl" resistor out of the VFO compartment and replace with a Higher wattage resistor ( a standard 10 watt 20K WW will work FB and be much more reliable)

Finally, the turret-type "Special" loading cap is highly failure prone, replace it with some Door-knobs or transmitter-type fixed caps.

This will make the rig fairly reliable.  After that you can talk or tinker to your hearts content... 

[KC2IFR]

Dont forget about the last wafer on the band-switch. The contacts are very weak on 15 and 10 meters.
Also any of the padder caps used for loading should be replaced with larger ones.
I have 3 Valiants and it was possibly the worst AM transmitter Johnson ever built. 

[WQ9E]

It isn't worth chancing expensive iron on possibly bad electrolytic caps so just replace them; don't forget the bias caps.

But first, always loosen the set screws on the VFO coupler before turning the Valiant upside down or it will likely break.  It uses different input/output shaft sizes and is difficult to find so if you break it you will have to repair it.

Check the fuses to make sure they are the correct value.  I am not a fan of the dual fused line plug but if you insist on keeping it original I would suggest identifying the side that goes to the main power switch and fuse this with the stated 8 amp fuse.  Then put a 20 or 30 amp fuse in the neutral side so that is is unlikely to blow.  Finally, follow the old safety adage of the ground wire is the first to be connected and the last to be disconnected.  I prefer using a 3 wire line cord with the fuse properly installed in the hot or load side and I use an inline holder with the fuse installed under chassis so that I do not have to drill any new holes.

The Valiant benefits from inrush limiters for the LV and HV supplies and if you install these (cheap and available form Mouser and Digikey) you will not have nuisance fuse blowing from start up surges.

If you have the original 866A rectifiers, they must be run filament only for at least 10 minutes before applying HV for the first time.  This is to make sure any mercury in the solid form that is not where it should be gets vaporized before HV is applied.  After this initial startup then a minute or so is all that is needed unless the tubes are turned on their sides or upside down.  Either xenon or solid state is a better option for ease of use and reliability.

If it is an early production Valiant, the LV transformer winding that feeds the 866A cathodes will not be properly insulated.  Either replace or sleeve the wire from the LV transformer to the 866A cathodes to prevent breakdown and subsequent loss of the LV transformer.

As mentioned previously, replace the voltage dropping resistor in the VFO that feeds the VR tube.  Use the same resistance value but increase the wattage rating to 10 watts or greater.  This resistor can be replaced without taking the entire VFO apart.  You can access this resistor by removing the left side cover (your left looking from front to back) of the VFO.  The VFO will stabilize more rapidly if you put the resistor inside the VFO compartment like it was originally.

Early Valiants were built with a single 500 pf blocking/coupling cap and this is grossly insufficient on 160 and a bit low for 80 meters.  Later ones used dual 1000 pf or 1200 pf caps in parallel.  The original cap will result in low output on the lowest bands.

Kit built Valiants often had poorly cut metering shunts that are far from accurate.  Typically they are too long which at least was safe but led to low output.  If yours was kit built and the output is low at the correct plate current then check the actual plate current draw with another meter before spending a lot of time troubleshooting.  Typically, the problematic shunts are the ones for RF plate (actually cathode) and modulator current and you can buy replacements from Mouser.  The circuitry was changed slightly after the earliest Valiants to correct an issue where additional current was read by the final cathode current meter.  Johnson suggested two fixes: one was to load for higher current than stated in the manual and the other was to correct the circuitry.  I believe this information is on BAMA with the Valiant manual.

Do be careful not to run excessive grid current which will damage the 6146 tubes.  Johnson included a warning from RCA with one run of manuals because the originally stated current was too high.  8 mils is plenty of grid excitation.

If the drive control for the Valiant goes out, the same basic circuit used with the DX-100 (uses a standard carbon pot and a TV HOT) can be used with the Valiant.

Finally,  note that for minimum (actually no audio clipping) turn the clipper control FULLY CLOCKWISE.  This is counter intuitive but this defeats all audio clipping action.  If you turn it fully CCW it is running at about 30 db of clipping and will sound truly horrible.

My original novice rig was a Valiant back in 1974 and I got back into vintage operation with a Valiant that I purchased in 1994.  I bought another one at a hamfest 5 years ago because it looked nice and was $50.  Both of these had the caps replaced and the HV supply converted to SS.  The only failure since then was one plate relay stuck and was replaced.  So replace the old parts that need it and tune it properly and you will have a good reliable transmitter with enough power to work well on the low bands.  I just bought a Valiant 2 to match my SSB adapter so I will soon have a 3 Valiant household.

Rodger WQ9E

[Jim, W5JO]

I don't suggest you use a variac to bring up any piece of equipment.  To get the HV to conduct you will need at least 90 volts on the primary which means you will have near the spec voltage on the filters.

Change all electrolytic caps first then check for shorts by pulling the rectifier tubes and checking for the proper
AC voltage at the rectifier sockets.  If OK, the plug the rectifier tubes back in and turn it on, watching everything.

I suggest you sell the Valiant without doing anything to it.  It has several flaws that are difficult to fix as Rodger mentioned.  Plus after you have it going, then you have to be careful of SWR or wrong antenna, either could cost you a bandswitch wafer.

Later Johnson stuff is just to finicky to fool with for my money.

[Ed/KB1HYS]

I have 3 Valiants and it was possibly the worst AM transmitter Johnson ever built. 

Am I the only one that sees the Irony...

[KC2IFR]

Hi Ed,
As much as I have had problems with the Valiant, I like the freeken thing. I modified the shi% out of them, modulated them with backward connected Hammond transformers and finally they sounded great.
Long story........

Bill

[Ed/KB1HYS]

Hey Bill!
No offense, I just saw some humor...

Yea the Valiant is not a great rig, but it is good for learning the art and if someone want's to drill, blast and experiment there's no fear of ruining some "collectible" rig as there are plenty available at reasonable cost.

All I'll say is that mine has taught me quiet abit over the years, maybe that's it's greatest value.

Oh and so as to not totally hijack the thread,  another component that is a bit weak and could be replaced is the encapsulated choke at the base of the plate choke.   Replace with a standard size out of the mouser catalog. 

Other things I've done to mine:

Removed the 9-pin accessory jack and just hardwired everything together.
Removed the SSB Input jack and used that hole for a fuse holder on the hot line.
Removed the "crystal socket" relay socket and replaced it with two mini banna-pin sockets (way easier than making a plug from an old crystal case).
SStated the 866 due to wiring deficiencies in the filament wires and shorts to case causing bad stuff to happen.
Bypassed the clipper and "audio-filter" parts and tweaked the audio chain with recomendations from Tim-tron.

Still using the 6146 mod tubes, but need to adjust the bias slightly as the B+ is higher after SStating the rectifiers.(I think). 

Works ok and I no longer get audio reports that say, "sounds ok for a Valiant".

[K4IMZ]

WOW !

 Thanks everyone for the great input.. and the Quick Welcome to the board..I feel right at home..

ok :
KE7TRP : that's what my plan was to variac slowly up from 30 to around 90vac,

Ed/KB1HYS : yes ha!  the ka-boom in the valiant vfo.. more on the val later on it may have been replace by the previous owner   

KC2IFR: I agree that EFJ Must have created the valiant as an afterthought...and threw in the great audio as a bonus..

WQ9E: goofing up and taking out the "iron" is what I was concerned about.. and the fused 2 prong plug now gives me pause . now the 866's ... well ok I admit .. I love  merc/vap rectifiers...  yea I'm sick...

W5JO: although I had no pause of not un-boxing my riceboxs and throwing the juice to them wfo, with the iron I was going to slowly bring up to 90vac (standby of course) and then restart at line voltage..

as for selling the valiant, that may be the answer , I will open it up and see what mods the previous owner( a good friend , K4HU S/K )  performed , if any,,
 it worked like a valiant years ago but still sounded like a valiant.. ha

I wont even get into my other projects except to say , i no longer possess the motor skills to complete them..

so it looks like the dx-100 is the target xmtr for now , if it passes the smoke test.!   

now what the hey did i do with my mic's ?

ed/KB1HYS : you got that right about the experimental composition of the valiant... and there is no such thing as hijacking a thread... the more info shared the better... and I have read the tim-tron tweaking and that looks promising.. 

but why dump the 866's   except for the shorting...ha  I lost a couple years each time an old 8008 went south .. we replaced some with "christmas trees" s/s..

Thank you all again , keep posting ,



 

[WQ9E]

One quick note on the DX-100.  The original one had a wide range output matching network with switched fixed padding caps similar to the Valiant.  The DX-100B substituted a bigger variable load cap and dropped the switched fixed loading caps.  Many DX-100's were upgraded to the B circuit since it was more reliable.  So if you have a DX-100 but find the changed loading circuit, don't be surprised or worried-it's a good thing.

Rodger WQ9E

[Ed/KB1HYS]

You don't have to change the 866's.  I would have left mine in but a series of blown fuses and other things led me to believe I had issues there so I solid stated them. (they are now in my HB Power supply deck though).  Later I found that the filament line had burned through to the chasis in one point tucked behind a cable bundle.  It would touch intermittently and if I was keyed up - Zap!  It was in a tough place that I wouldn't have noticed had I not done some other work.

I think this same problem had lead the original owner to mount the two fuze holders in the front panel for easier access.

[WQ9E]

Ed,

You are lucky you didn't lose the LV transformer!  The filament lines to the 866A tubes are a common failure if you have an early production Valiant. 

I like the looks of the 866 tubes but I replaced my last set in a Valiant when the plate relay stuck on and applied HV immediately when I turned on the main power switch.  That damaged one 866a and I decided not to chance taking out the plate transformer if something similar happened again.

My Hallicrafters HT-19 is the only rig I am currently running with MV rectifiers and mostly because it gets very little use.  It is a combination CW/NBFM rig with provisions for external plate modulation of the 4-65 final.  I have a homebrew modulator that I plan to rebuild to use with the HT-19 and at that point I will probably lose those MV rectifiers.  They are pretty however.

Rodger WQ9E

[N3DRB The Derb]

I think this same problem had lead the original owner to mount the two fuze holders in the front panel for easier access.

why do so many hams seemingly always take the road to stupidville when they get a problem? fuses blow? mount the holders on the front panel so I can get to them faster. Yeah, thats the ticket. or put 30 amp jobs in there......or add some aluminum foil....

but dont ever get to the cause of the problem. Just treat the symptoms. 

[Jim, W5JO]

Reforming old capacitors by any method is an exercise in futility.  Even though they do reform, they will fail shortly if they are of old manufacture.  I have reformed caps with a cap checker in the past only to have the paste dry in less than a year causing excessive leakage current that can be fatal to a component if they are left in circuit or short. 

Those HV caps in a DX 100, if they have not been changed, are old and will fail quickly.  You risk a choke in this case and, most probably, the top cap in the string will be the one with the highest leakage.  With the scarcity of parts for these things, why do we risk catastrophic failure?   Excessive leakage in capacitors is also a major source of heat in these old transmitters and receivers.  I am with you Derb.

[KB2WIG]

 " Cowards die many times before their deaths. The valiant never taste of death but once "

W.S.



klc

[K4IMZ]

Reforming old capacitors by any method is an exercise in futility.  Even though they do reform, they will fail shortly if they are of old manufacture. With the scarcity of parts for these things, why do we risk catastrophic failure? 

Armed with a load of excellent information, I'm really not in that big a hurry to fire up the dx-100 , so recapping is in order...

valiant will have to wait or will be in back of truck at h/fest .. ha

have found a lot of mods/updates for dx-100s...

any recommendations ?

no I can't junk it, .. ha     

it's a legacy hand down from my old engineer,

 

[Jim, W5JO]

have found a lot of mods/updates for dx-100s...
any recommendations ?
it's a legacy hand down from my old engineer, 

Yes there are a lot of modifications, but I would only change the coupling caps in the audio section for a bit better audio.  Not a lot, but some.  I will leave the bandwidth up to you but, all in all, it is a functional, reliable design.  If you mess with it too much, it can become a problem child.  Have fun with it.

[K4IMZ]

Yes there are a lot of modifications, but I would only change the coupling caps in the audio section for a bit better audio.  Not a lot, but some.  I will leave the bandwidth up to you but, all in all, it is a functional, reliable design.  If you mess with it too much, it can become a problem child.  Have fun with it.
[/quote]

You read my mind!
That is about what I decided on after I got this article.


(( Coupling Caps
Change out the 510pf caps to 0.01, 0.02 or 0.05mf caps. What determines the value of coupling cap is the value of the resistor it looking into (the ratio of the two values). For example, in the DX100 second stage the grid leak resistor is a 500 kOhm potentiometer. Five hundred kOhms (500k) and 0.01 uF is good ratio for low
end response. Change the cathode resistor and bypass capacitor to 2.7 - 4.7 kOhm and 100mF/50V
respectively.  excerpt from Tim's article ))

I also want to beef up the filter caps.

Thank you again for the comments and please continue ,

[Jim, W5JO]

It will be ok to beef up the filter caps, just don't go overboard.  You have a choke input filter on the HV but the LV is cap input.  If you to too high on the LV you can cause trouble on the transformer.  I would leave the first cap in the LV at the suggested value and, if you wish, increase the one after the choke by no more than 5% or so.

Actually since these things never had trouble with hum or other maladies, I would just put back what you find.  You will have to go up in value for the HV but there are computer style that will do the job fine.  You can get those clamp brackets that have two screw eyelets that will match the mounting holes in the chassis.  Then just clamp a couple of 150 uf, 450 volt/525 volt surge caps in there.

[ke7trp]

I agree with this.  Dont go to much over the original values.  I have made this mistake in the past.  On choke Power supplys, dont go to much over just as mentioned.  In other areas, You can double them.  For example, The VFO input can benefit from a larger cap to stabilize the VFO under mod. I think there where alot of areas where larger caps would have been used if they existed and the cost was inline with the product.

As far as doing the audio mods,  I suggest you get the rig up and running at 100% factory specs and enjoy it. Then, As you have spare time, You can change things around and test what has been changed.  I have learned not to "fork Lift" radios where you modify everything at once. Its tempting, But many times causes more trouble then the mod is worth.

Number one rule.. Post here if you are thinking about changing something. These guys have helped me so many times, I lost count.



C

[WD5JKO]

It's hard to follow all this great advice, so I will only try to agree with Jim, Clark, and others.

In general, for those contemplating increasing the low frequency response of an audio amplifier, doing so by increasing coupling capacitor values really ALSO needs to be done with increasing B+ bypass capaciticance values as well as any cathode bypass capacitors. We can get in trouble with instability (motor-boating might be one consequence) if we just change the coupling capacitors to a higher value. Another area of concern is with magnetic core saturation with any transformers in the audio path. Therefore I agree 100% with Jim, Clark, and others about bringing up the rig stock, or near stock first before attempting any major modifications.

Jim
WD5JKO



 

[K4IMZ]

Therefore I agree 100% with Jim, Clark, and others about bringing up the rig stock, or near stock first before attempting any major modifications.
Jim
WD5JKO

I agree,, the caps look like sin,.. correction .. firecrackers....
glad I did not Juice it...
can't believe how heavy it has grown (/sarc) ..
and a water based lacquer coat on the copper plated chassis ?

oh well, just take my time and get some caps on the way..

Thanks again to everyone for the support...

ps... oh yea.. Gotta take my main ricebox in for repairs... oh boy!!

just like a car,, when they set idle, the gaskets dry out ...

[K4IMZ]

I Did not give up... been without power, phone/net for over a week. even twisted pair land line down.. too much snow - ice.. 

as gump says " I know all about feeding a gas generator at 3am "

Question :::  what do you recommend to clean dirty switches and contacts..

I looked up blue-shower and almost fainted.. It's triple priced..  ( I'm Old)

thanks again

rc / k4imz

[N2DTS]

Deoxit gold?

A long time ago, I did up a $10.00 dx100.
I eliminated that dumb center tap off the back to back high voltage electrolytics, solid stated the power supplies, used big regulator tubes in the old rectifier sockets to get regulated screen voltage, trashed the teeny weenie driver transformer and put in KT88 tubes in AB1, after trashing all the original audio section.

It was a lot of fun.

Brett