Exciter – Transmitter suggestions

[KC9LKE]

I am building the 813’s x 813’s transmitter and am looking for a way to drive the 813 finals on the RF deck. They are in grounded cathode, with tuned grid input. I started thinking about building a separate Millen exciter to drive the RF deck and that quickly changed to an all in one RF deck, with band switching.

It looks like I’ll need about 12 watts of drive, but plan on 20 watts for overhead.

 A fellow ham offered a very stripped Ranger chassis with only the VFO and RF sections left. I’ve read that the Rangers didn’t have the greatest VFO but the problems could possibly be overcome. Also the Ranger VFO and RF section is very close to the Valiant, sans the three 6146’s, and it could be easily changed over if the valiant design offered better stability. If I remember my old valiant correctly the VFO was stable. If need be I could redesign the 6146 output for a smaller tube, but the Ranger has a drive level adjustment so I don’t believe that’s necessary. I would just have to match the 6146 plate to the 813 grids. The nice thing about the Ranger is that it has the wafer switches, coils, etc, and it’s free. But if it’s not a good starting point why use it.

Other option, pick a Collins PTO and scratch build, or build from QST or similar article. I would rather not go the microcontroller VFO route.

Again I would like to keep the “adjusting” to a minimum and build a 6 band RF deck.
Your thoughts, comments, and suggestions are greatly appreciated.

Thanks again

Ted / KC9LKE

[KB2WIG]

 “ A fellow ham offered a very stripped Ranger chassis with only the VFO and RF sections left. I’ve read that the Rangers didn’t have the greatest VFO but the problems could possibly be overcome. “

If it’s free, how can u say no???  ( read this http://amfone.net/Amforum/index.php?topic=25041.0)

 .  The Ranger vfo is ok; you want to replace the famous Chernobyl resistor…..

“
If need be I could redesign the 6146 output for a smaller tube, but the Ranger has a drive level adjustment so I don’t believe that’s necessary.   “

The drive level adjustment is a crappy way to go; I can’t think of why at the moment. You could plop in a 2E26 into the final. This baby will give you 20W at around 400V  (CCS rating).  You’ll have to make a few adjustments.


“  Other option, pick a Collins PTO and scratch build, or build from QST or similar article. I would rather not go the microcontroller VFO route. “

There are a few solid state VFO ckts in the handboo k that are nice and easy….  Gud luck

klc

[KC9LKE]

"The drive level adjustment is a crappy way to go; I can’t think of why at the moment. You could plop in a 2E26 into the final. This baby will give you 20W at around 400V  (CCS rating).  You’ll have to make a few adjustments."



Thanks

Ted

[ke7trp]

I have been through this. I now use a modern Transciever for the Exciter. I had an FT450 sitting around so I use it.  Any ham HF rig will do.  An old kenwood, yaesu or icom.  Just set the Rig on CW, Turn the variable power down and inch it up so you get the proper Grid Drive. This way, You have a very stable VFO, Simple to change Freqs and NO Drift.

Its also nice to put a cheap tuner between the Exciter and Class C amp Grids. This way you can fine tune the grid and make the Rig happy.  I use an old MFJ HF mobile tuner.

Build a relay in a box with multiple outputs.  One keys the Exciter, One mutes the RXer, One keys the Class C rig.

C

[KA1ZGC]

Its also nice to put a cheap tuner between the Exciter and Class C amp Grids. This way you can fine tune the grid and make the Rig happy.  I use an old MFJ HF mobile tuner.

I never understood the rationale behind this. Any tube amp, linear or non-linear, has a tunable input stage to transform 50 ohms to the grid input impedance at the operating frequency. The grid is either tuned, or it isn't. Adding a tuner to transform 50 ohms to 50 ohms (in other words, to accomplish nothing unless you're doing it all wrong to begin with), to then feed another tuned circuit to transform 50 ohms to some other impedance is like putting wheels on a bowling ball: time-consuming, and totally pointless.

It's even less useful if you're using a vacuum-tube exciter, since they already have tunable output stages. You're just giving yourself one more thing to tune for the sake of having one more thing to tune.

I have one of those MFJ mobile tuners. They're useless, even by MFJ's standards. Pop off the cover, and you'll find the ends of the flimsy coil are jammed right up against the flimsy case on both the top and bottom. Set a coffee cup (or any other object) on top of one some day while you're transmitting and watch your VSWR soar as the coil changes value from the cover moving.

Tune the exciter into a dummy load (if you're using a vacuum-tube exciter), then drive the amp with it and use the input tuning cap to peak the grid. The exciter will see 50 ohms at that point, and both units will be tuned as well as they need to be. You can't get more resonant than resonant.

[W7SOE]

I am going to use a Millen 90800 to drive my 813 X 813 rig.  I don't see leaving 80m very often so that is OK.

Perhaps I could a a connection/switch for an external exciter and, as Clark suggested,  use my long dormant SS HF rig if I want to change bands.

Of course I would have to add taps to my tank coil for 40m and 20m and be able to tune the grid input on those bands as well.

Am I missing anything?

Rich

[K1JJ]

As Clark, I like using a modern solid state transceiver as an exciter for the class C plate modulated rigs. After being away from the rig for awhile, it's tough enough to remember how to tune up the big rig. It's nice to have a no-tune exciter that can instantly go from band to band without more tuning.  

I hate changing bands due to tuning, so this helps to encourage it.

In addition, I like the transceive mode for receiving cornvenience. I use the transceiver AND an SP-600 off the detector at the same time. There are times when PW stations can only be copied on the transceiver. (FT-1000D)

In the complex whirl of big AM tube rigs, simplifying tasks is a good thang. Add in a few more plate modulated rigs and things can quickly get out of hand...  (Help! My frickin memory is going!)

T

[ke7trp]

The tuner between the Transeiver is needed because they will not tolorate any SWR.  The modern rigs will yank the power right out.  On a Tube exciter it wont care if its 50 ohms. You can tune it to match the grids and get the required Drive.

The little MFJ works very well. It allows me to match exactly for all three low bands and thus the Solid state excite has to only put out 33 to 37 watts.  Remember, If its not right at 50 ohms, The rig will pull the power back and most little cheap rigs like this will start to run hot making 50 to 60 watts CW full bore for 10 minutes buzzard key down. Having it tuned perfectly is a must.

Its simple.  Turn off the HV, Key up, Tune the MFJ flat, set power for proper Grid, Unkey, Turn on HV and go.

C

[KA1ZGC]

The tuner between the Transeiver is needed because they will not tolorate any SWR.  The modern rigs will yank the power right out.  On a Tube exciter it wont care if its 50 ohms. You can tune it to match the grids and get the required Drive.

I hear ya, I'm just saying that the tuner shouldn't be necessary to achieve a 50-ohm resistive load at device input. Actually, the power foldback of a solid-state driver could be helpful, your grid current peak would just be that much more accentuated. It never shuts the power totally off or else it wouldn't be able to detect when the load is suitable once again.

In fact, if the grid peak and the exciter peak don't happen at the same point on the grid input cap, you know you have a reactive input on the second stage, and that's something to you'll want to address eventually (sooner than later if it were me). If the exciter sees a high SWR at the grid peak, then something is very wrong, and the tuner's only covering up a more serious problem.

True that a vacuum-tube exciter doesn't need to see 50 ohms per se, but if your impedance is too far removed from that, you start losing a lot of power in the transfer. The interconnecting cables are still 50 ohms. Just because you can get away with being sloppy in that situation doesn't mean you should. Best practice will always be to tune the exciter into a 50-ohm resistive load, then tune the input of the second stage to match the correctly-tuned exciter. I use a Ranger as a driver, and that method has always served me well without fail.

If you have a tuner at the antenna like I do, it also pays to tune that for the best match off the exciter as well, then everything is tuned for 50 ohms resistive, and switching between rigs is just a matter of turning them on or off.

If you can't run without the tuner, I'd be suspicious of the amp stage's input tank.

But to each his own, I guess.

[WD5JKO]

I once used a Yaesu FT-757 to drive a big KW input push pull triode final. It worked OK, but the drive level did drift a bit requiring periodic adjustment. I eventually switched over to a tube exciter for that reason. I did not want to key up and modulate when the grid drive was low. Maybe other SS rigs are more stable with the carrier control knob.

As for whether you need a tuner or not between a SS exciter, and a tube amp is certainly debatable. Sure the tube amp tuned grid input when at resonance will be a resistive load, but not necessarily 50 ohms. If you only need ~ 10 watts from a 100 watt SS exciter, I think the drive level will be touchy like I described above. So here is how you kill two birds with one solution; Instead of using a tuner on the exciter, use a 6 db pad. This accomplishes two things:

1.) Exciter will run 40w to get 10w 813 grid drive. This gets the carrier knob almost to midrange
2.) The exciter sees a maximum of a 2:1 SWR when the load is either "open" or a "short". Since the 813 input will be in between somewhere, the exciter will always see a reasonable SWR that shouldn't kick in the SWR based ALC.

I would somehow interlock the 813's to NOT BE MODULATED if the exciter drive was too low. Imagine switching it to SSB for exalted carrier reception, and then key up and talk when the drive was zero. Not good.

This idea means you need to build a power 6 db pad that can take the full exciter power. No big deal, but it is something else to do. In my opinion, it would be worth the effort.

My 2 cents,
Jim
WD5JKO

[KM1H]

Cheap and easy possibilities:

Pick up a DX-60 and HG-10B. Pull the audio tubes to reduce current.

Ive used a Meissner EX Signal Shifter to drive 813's in the past, a bit of work in the PS area brings the drive to whats needed.

A WRL Globe 90, the one covering 160-10M and matching VFO. The pair of 807's might need reducing to one.

If you just have to use a rice box go with a Kenwood hybrid. Nice power adjustments and no worry driving anything.

Carl

[KC9LKE]

W7SOE:
•   I am going to use a Millen 90800 to drive my 813 X 813 rig.

Very nice if you can find one. BTW good luck on Your Rig hope to hear it soon.

K1JJ:
•   In addition, I like the transceiver mode for receiving convenience. I use the transceiver AND an SP-600 off the detector at the same time.

A major point for using a transceiver, the receiver comes with for free, and is one less mouth to feed.

•   There are times when PW stations can only be copied on the transceiver. (FT-1000D)

You actually acknowledge them? 

KA1ZGC:
•   You're just giving yourself one more thing to tune for the sake of having one more thing to tune.

I agree, my main reason for building a band switching transmitter deck with the 6146 plate transformed to the 813 grids.

•   I use a Ranger as a driver,

Do you have any problems with instability or drift of the Ranger?


WD5JKO:

•   Instead of using a tuner on the exciter, use a 6 db pad.

•   I would somehow interlock the 813's to NOT BE MODULATED if the exciter drive was too low. Imagine  switching it to SSB for exalted carrier reception and then key up and talk when the drive was zero. Not good.

Very good points.

KM1H:

   Thanks for some more possibilities!

KE7TRP:

   I saw the picture of your transmitter, a FB job. I have the same cabinet on the way. Only empty. What type of iron did you use?

I have an Icom 746 PRO, its good for SSB but I severely dislike the sound of its AM. I may use it temporarily. KB2WIG mentioned that “The drive level adjustment is a crappy way to go” for the sake of learning, any one know why?

Thanks for the ideas so far. I really appreciate the groups input and the great AM site.

Ted / KC9LKE

[KL7OF]

It only takes 15 mils of drive to whip a pair of class C 813's into action..a single 807 driving a simple tuned input from the California handbook works for me...Good Luck....

[ke7trp]

The 746 pro is just fine.  Just sit down with a 9 volt battery, A 500k pot and make a voltage divider.  Run this to an RCA jack. NEGATIVE voltage to the center pin.  Pos to shield.  Plug this into the ALC jack.  Turn RF power on radio full bore, Adjust pot for what ever carrier you want. Turn audio up to what ever you want.  Now you will get the full power of SSB mode (100 watts) with any carrier you want. You dont even need to open the radio!

I really like the stability of a modern VFO on the exciter.  THe ranger Drifts like a Drunk down the highway. You can also change bands and you dont have to tune it.

As for the tuner, You dont need it if you make a perfect input network. Otherwise, The Solid state rig really wants to see 5o ohms. So its a cheap and easy fix. The MFJ was Free and it has simple knob for inductance.  33 watts provides 30MA of Grid to the 4-400s. A bit more on 40 meters, About 45 watts. 

The Transmitter I have is in two bud cases. One deep case for the modulator and one standard case for the RF deck.  The iron, robert put in the unit. Its Iron from a Collins 20V2 mostly. 

C

W7SOE:
•   I am going to use a Millen 90800 to drive my 813 X 813 rig.

Very nice if you can find one. BTW good luck on Your Rig hope to hear it soon.

K1JJ:
•   In addition, I like the transceiver mode for receiving convenience. I use the transceiver AND an SP-600 off the detector at the same time.

A major point for using a transceiver, the receiver comes with for free, and is one less mouth to feed.

•   There are times when PW stations can only be copied on the transceiver. (FT-1000D)

You actually acknowledge them? 

KA1ZGC:
•   You're just giving yourself one more thing to tune for the sake of having one more thing to tune.

I agree, my main reason for building a band switching transmitter deck with the 6146 plate transformed to the 813 grids.

•   I use a Ranger as a driver,

Do you have any problems with instability or drift of the Ranger?


WD5JKO:

•   Instead of using a tuner on the exciter, use a 6 db pad.

•   I would somehow interlock the 813's to NOT BE MODULATED if the exciter drive was too low. Imagine  switching it to SSB for exalted carrier reception and then key up and talk when the drive was zero. Not good.

Very good points.

KM1H:

   Thanks for some more possibilities!

KE7TRP:

   I saw the picture of your transmitter, a FB job. I have the same cabinet on the way. Only empty. What type of iron did you use?

I have an Icom 746 PRO, its good for SSB but I severely dislike the sound of its AM. I may use it temporarily. KB2WIG mentioned that “The drive level adjustment is a crappy way to go” for the sake of learning, any one know why?

Thanks for the ideas so far. I really appreciate the groups input and the great AM site.

Ted / KC9LKE

[KA1ZGC]

Do you have any problems with instability or drift of the Ranger?

It drifts a bit at first. "Problem" is in the eye of the beholder. Over the first 20 minutes or so of operation, it may drift a grand total of 2-3 kHz if I don't occasionally correct it, then it settles down and stays put. I just periodically re-zero someone of known-fixed frequency three or four times during that period. After a while I can just leave it be.

It would probably be a pain to operate CW from a cold start, but for AM purposes, I'm quite happy with it.

Of course, if you get your hands on some crystals, drift just becomes something that happens to other people. 

Bear in mind that this rig has had (an unusual set of) Timtron mods, most notably the low-power mod. I use it almost exclusively at the 15W level to drive a 4-250. Tim was re-thinking some of his Ranger mods a few years back, and mine was the guinea pig. The low-power mod is common, though. If you're looking for 12W nominal and 20W just-in-case, a Ranger with the low-power mod could be a good start. You probably won't get 20W in the low-power position, but you could milk 17-18W anyway.

Good luck with the project!

[Detroit47]

I have been through this. I now use a modern Transciever for the Exciter. I had an FT450 sitting around so I use it.  Any ham HF rig will do.  An old kenwood, yaesu

Why would you want to hook up some rice box to your homebrew American made rig?

73 N8QPC

[ke7trp]

Its superior 

C

[Detroit47]

Then why use tubes when you can use fet's ? To each his own.

John

[Bill, KD0HG]

Rangers are perfectly stable VFOs.

The big issue with the Ranger and Valiant I is a resistor inside the VFO box has a tendency to overheat and fail, replace it with a 5 or 10 watt wirewound.

While you're in there, clean the wiper contacts on the VFO main tuning capacitor and lube the planetary gear.

I use a Ranger I for an exciter and once warmed up, it doesn't budge.

[KA1ZGC]

Yep. Actually, to give you some comparison, my Ranger drifts a whole lot less in its first 20 minutes of operation than my HQ-129X does. The 129 can drift 6 or 7 kHz over that period. I spend more time touching up that VFO than I do touching up the Ranger's.

Also, the drift exhibited by my Ranger is not typical of the line. Tim's Ranger II might have drifted all of 700-800 Hz in the same period my Ranger would drift 2-3 kHz. It's more drift than a typical Ranger, but still not enough to justify tearing into the VFO compartment, which is a bit of a pain.

The Chernobyl resistor has been replaced in my VFO, so I can't necessarily blame that, unless the tolerance of the replacement is slacker than it claims.

So yes, a Ranger makes a fine exciter for a big rig, and it was designed specifically so you could do that. The accessory plug on the back gives you easy access to the output of the mod tubes, making it simple to switch between internally-modulated standalone service and unmodulated exciter service with an audio output plenty loud for most big transmitters. I built a switch box for mine which allows me to easily flip from standalone Ranger to driving the Junkyard Dawg.

In your case, since you have (or at least have been offered) a Ranger chassis with the RF and VFO sections still intact, you've got all you need for a dedicated driver. Just swap out the Chernobyl resistor, and various other touch-ups mentioned, and you'll have yourself a dandy little exciter.

[KM1H]

Yep. Actually, to give you some comparison, my Ranger drifts a whole lot less in its first 20 minutes of operation than my HQ-129X does. The 129 can drift 6 or 7 kHz over that period. I spend more time touching up that VFO than I do touching up the Ranger's.

On what band? My 129X drifts about a 5th of that on 80/40M after rebuilding and bucking the AC line down to 112V. For the higher bands I replaced the oscillator trimmers with submini Johnson variables which really settled things down. I use them inmany radios.

Carl

[KA1ZGC]

Yep. Actually, to give you some comparison, my Ranger drifts a whole lot less in its first 20 minutes of operation than my HQ-129X does. The 129 can drift 6 or 7 kHz over that period. I spend more time touching up that VFO than I do touching up the Ranger's.

On what band?

When I fire it up, it's usually on 75. If I go to 40, it's usually mid-day after giving up on 75, so everything's warmed up. Ditto 160 in the evening. Haven't done much on the higher bands because a 200' flat-top has really goofy patterns anywhere above 20, and even there it's kinda funny-lookin'.

My 129X drifts about a 5th of that on 80/40M after rebuilding and bucking the AC line down to 112V.

Yep, another one of those things on my "been meaning to get to list". Hell, I haven't even replaced the filter caps yet, which I'm pretty sure are leaky.

For the higher bands I replaced the oscillator trimmers with submini Johnson variables which really settled things down. I use them inmany radios.

Now that's a good idea. Another entry on the list, thanks!

[ke7trp]

Now I have heard it all..    A Johnson ranger being stable.  KAWMAWN!!!!   

[ke7trp]

Hmmm..  First time talking over an hour on 75 to ww9w,the big Rig had a new problem came up with the exciter.  The FT450 has a system of lowering power as the fan is turned up to cool the radio.  This is obviously dangerous for a class C amp.

If you start out at 36 watts CW to excite the 4-400s at 30ma, You get about a half hour of back and forth use. Then when the rig heats up it turns the fan on and the power goes to 15 watts!    Then, If you keep going and you did not notice the now low Grid Drive, The Rig cuts power OFF, NOT good on a Class C.  Luck for me, I have a breaker in the HV so trip.. But it sill put a good 2 seconds of full slam plate current on the rig before that Tripped.

So Scratch the FT450 as being a good exciter.. There is a menu in the FT450 service list that allows you to adjust this. Then you probably blow the rig up though.. 

Time to move the Rig off the top of the Transmitter and over to the desk across the room. This might fix the problem but its still dangerous.



C

[The Slab Bacon]

Why dont you split your final grid biass to partial fixed and then make up the rest with grid leak. This way if you lose drive, you will still have some protective biass to limit the plate current down to a safe level.