The AM Forum

Well figured it was time to start this behemoths own thread, Ive been rambling on other threads but the time has come ! Arrived via Fed-to-the-X today !

Stripping her down for cleaning and repair tonight ! Yes yes..... IT is ON !

Ok, turning down the volumn level no more exclamation marks. Front main dial coupling.....mangled and covered in a gob of silicon. I am a far better mechanic than electrical fiddle-farter so Ill takle that first after clean up.

I have notice a lot of out of place and new/oddball parts underneath the chassis. My first Viking, and I have yet to start tracing wiring, but there seems to be two added relays. PTT ???? anything else you guys see out of place or worth noting please speak up, ha.

(http://i300.photobucket.com/albums/nn7/CAVHOOAH/DSCN0593.jpg)

(http://i300.photobucket.com/albums/nn7/CAVHOOAH/DSCN0591.jpg)

(http://i300.photobucket.com/albums/nn7/CAVHOOAH/DSCN0590.jpg)

Fixed the coupling with two cotter pins, works great and has no rotational play. re-assembled and ran up on a variac with no 5R4 tubes installed. All seemed well ramping it up slowly, then.... I noticed the cherry red 6AL5. Flipping the anvil over, it appears these 15mf 450V caps might be a little dry...ha. Someone was definitely on a budget when the were messing with this thing.

So, the 6AL5 tube, got awefully red ! No fireworks though, just a really hot hot toooob.


Cleaned up the rig.
(http://i300.photobucket.com/albums/nn7/CAVHOOAH/DSCN0598.jpg)

Rebel caps in view.
(http://i300.photobucket.com/albums/nn7/CAVHOOAH/DSCN0599.jpg)

Dryer than a popcorn fart.
(http://i300.photobucket.com/albums/nn7/CAVHOOAH/DSCN0599.jpg)

I would invest in some electrolytic caps before the AC plug see a socket again.

Knee deep in that as I type.

While replacing the 15mf's I keep staring at this rectifier setup..and it doesn't make since to me. The diods are on pins 1&5 (  http://www.r-type.org/pdfs/6al5.pdf ) makes sense up to that point to me. Wonder why this thing came with a 6AL5 if it looks like they by-passed it with the diodes, I keep looking at the circuit and one other thing that's got me scratching my head is the have another OLD paper cap (3 way 30/30/20 all pos tied together) tagged on at the -75 output line....that then goes to some honkin relay... can someone explain what the heck Im looking at ?



Edit: yep PTT mod.

Alrighty, replaced the caps on the 6al5 circuit.....but that guy is still taking off ! Its fine for about 30 seconds of filament....then she suddenly turns cherry. Don't know how many more of these guys Ive got in the junk box. What could be causing that ? Oscillation ? Any ideas ?



Ya know, I told myself...I needed to get in here  and start communicating with you guys. I said, heck...I bet I can learn a lot ! Figured I would start a little thread or two to get some conversation started, all of them are basically dead air.... Is this the comraderie I hear about ? Dang, maybe this wasn't the start of a neat venture that Id thought it would be. Ill carry on as I always have with some neat projects....But if it hasn't felt like pulling teeth trying to get some kind of conversation going on around here.


Im either too young or too stupid for this place it seems...

 

Don't worry, it is summer and participation is always low.  If you have red plates then either the tube is bad or something is drawing a lot of current.  Disconnect the output wire from the tube and see what it does.  Did you put the capacitors in correctly?  This is the bias rectifier so the filters should have the positive to ground.  Any shorts near the tube socket.  Is L3 shorted in some fashion?

What condition is R15, 16 & 17?   Remove the lead at the connection of C 12 and R17 that goes to the rest of the transmitter after you check the proper installation of the filters and the all the other parts and try again.  You can use an ohm meter to look for lower than normal resistances but if you don't have experience in that method, I don't suggest you do that just yet.

If, by chance, you put the filters in wrong polarity then don't just reverse them, replace them they are bad.

Thanks Jim for the words of encouragement.

Yes, that is exactly what I did. Found that about 30 minutes ago. Since the start of the day, Ive ripped out the PTT additions, replaced caps and am now actually loading it up. Im just past the point of throwing the plate switch, and all is well there. I slightly loaded it to about 10 watts and halted to grab a beer and wipe the sweat off my forehead. By the book, all readings and adjustments are working as should. I will need to cross one more bridge shortly, and that is the missing tube that belongs in an added socket in the speech amp stages. 

Thanks again for the advice Jim, that is exactly what it was.

Grab some 1n4007 1A/1000V diodes from Mouser... $4.00 for 100. I generally use 1N5408 as they are rated for 3 Amps at 1KV.  $9.60 for 100.

http://www.mouser.com/

Looks like someone has been playing around the 6AL5

klc

Don't forget the infamous "chernobyl" resistor in the VFO.

I'd have kept the PTT stuff, unless it was very funky.

there needs to be negative bias on the 6AL5, check tube manual for values.
No negative bias, tube gets cherry red.
Check the cap that goes TO the grid, and the voltage on the grid wrt the cathode.

The magic smoke has left the building.

Some of it at least. All was going pretty good, just finished finding my first dip in the main dial when I turned to read the next step....a familiar smell wafted over to my nose. Appears the HV transformer has layed down on my, I shut it down fast but too late I fear. I pulled the 5R4's and lit it back up and carefully watched after applying the plate, and after about 15-20 seconds a whift of smoke again. Ive buttoned it back up for tonight, and will search for a replacement as soon as I get the wind back in my sails.

Im picking up a Ranger tomarrow, so my attention will be diverted and a better mood will ensue shortly after Im sure.

The bias caps were installed polarity backwards and all turned well with the 6AL5 tube.



Shut down shop, time for a cold refreshment and a Fender in my lap. Thanks again, I was wondering if I was here all alone for a while.

You are never alone,  It is just sometimes life gets in the way for all of us.  Sorry about the transformer.  If nothing surfaces you can have it rewound. it isn't cheap but is a solution. 

Be careful on the Ranger.  If it has not been serviced in a while, you will have the same set of circumstances.  Remember the polarity as you do the replacements.  One way is do them one at a time so you have something to compare, or use a digital camera to preserve the layout so you can look as you put it back together.  When you get to the audio circuits, pay partucilar attention to the layout because if you don't, you could build in problems as you go.  Have fun and keep plenty of beer available.

I would advise to keep the beer or any talk of it to a minimum when working on or pondering repair work with any of these vintage transmitters, especially for the first time. That's up to you of course.

HV can be deadly. There is a time and place for everything.

Al VE3AJM

  Get a hold of BRY, AF4K http://af4k.com/JOHNSON_VIKING_II_PARTS.htm he may have what your looking for. I too almost burned out T2 until I found a short in the PTT circuit someone installed needless to say I got rid of the PTT mess besides why do I need PTT? I'm still trying to find out why my unit will allow tune up in phone but, when switched to CW I get high plate current with no way to dip the plate it stuck at 230 ma.

73,Dave

Now Al, all that depends on when the beer is consumed, doesn't it?  No one advocates consuming any alcohol when doing the work.  By the way, I have seen people burned terribly from 48 volts or less with high current,  If we want to get into a safety discussion then he best remove all jewlery and metal objects from his person as well.

Got the Ranger today, really am pleased with it. Worked this evening replacing the last three old caps and throwing a antenna changeover together.

Hoping to dig back into the Vikingthis evening. I might have a transformer around here that will work, sure don't have 160 for a re-wind although that IS a good price.

    If your open to changing the original EF Johnson circuit design, consider replacing that transformer with a control transformer. Look for a 120V in with two secondary windings for either 240V (parallel) or 480V (series) connections. About a 350VA unit should do. Just go to Ebay and search for "Control Transformer 350VA", and several pop up..I see one for $8.00 used. Perhaps a 250VA unit would do.

   The idea would be to configure transformer as 120V in and 240V out, and use a full wave voltage doubler circuit with two diodes and two caps. The caps could each be something like 330uf @ 400V, and each diode a 1N5408. This will make just  under 600V DC at 500ma load.

   The idea would eliminate that HV oil capacitor, and the HV filter choke. The high capacitance would best be dealt with using a step-start relay with PTT B+ control.

  I attach a simulation from the Duncan PSU Designer II Cad program.

Jim
WD5JKO

Great tip !

Thanks, I hadn't thought one iota about that doubler idea. Ya know now that you mention it, Ive got a control transformer that may work in the garage.

Heres the specs...
http://livewiresupply.com/electrical-transformers/dongan-electric/50-0200-056.html

"POWER TRANSFORMER, CONTROL; POWER RATING 200 VA; PRIMARY VOLTAGE 600/575/550 VAC; SECONDARY VOLTAGE 120/115/110 VAC; 1 PHASE; 50/60 HZ; TEMPERATURE RISE 55 DEG C; UL, CSA"




That will put me slightly over 660VDC though...I think the formula is X 1.14 VAC for rectified cap filter PS right ? Anyone ever use a dropping resistor on a primary with success ?

No not quite dead air,,,,,,BUT do you have a schematic of this transmitter? Pictures of the underside and telling us about a glowing 6AL5 doesn't spark a reply and someone says , "Oh! the trouble is this or that". One member here might say that "Hammy Hambone" has been in it and it needs close inspection before plugging it in again. It sounds like that beast you bought from somewhere needs to be looked at carefully using the schematic to get it to working order. It looks like it had a very rough life, by someone who hasn't a clue about electronics. The transformer can be damaged by the bad overloads it is seeing now.
Someone replied to replace all electrolytic caps...And make sure the new ones are installed properly. Mouser or DigiKey are good places to by electrolytics.
Fred

It should work so long as you don't run a tone at 100% modulation too long. The lower VA rating will cause the B+ to droop more, and I'd bet the B+ would be around 700V key down which is fine using the 575V HV tap on transformer. This control transformer needs a bridge rectifier (not a doubler), and the caps need to be in series across the B+ and use equalizing resistors. You will want a lot of capacitance; like 330uf @ 450V X2...and a step-start relay.

Jim
WD5JKO

You will need a replacement plate transformer yes, but have you actually resolved why the original plate transformer smoked/opened/shorted? Was it just the transformer giving up the ghost on its own or another component in the HV line that has failed?

From what you've written on here and other threads, apparently there was no fusing/wrong value fuse there. So a transformer winding was acting as a fuse, which is never a good thing.

Al VE3AJM

I've found the following to be usefull when working with older equiptment.

http://amfone.net/Amforum/index.php?action=gallery;su=user;cat=53;u=714

Its really good for initial power up; the lamp limits the current, or becomes a fuse if there's a short somewhere. The switch is wired so that when thrown, it shorts out the bulb which will apply full voltage to the unit under test. You can even put a real screw in fuse to get higher values of pro tection.


klc

Yes, no fusing on the Hv x-frmr. I hate to admit this in the open airwaves, but I dont think I let it dry completely after its waterhose bath....think I still had some moisture in the HV iron. Been washing old nasty equipment like that this way for 20 years and this is the first catastrophe I can accredit to my scrub job.

Just got too excited I guess.

Ill strive to be calmn from here on out, ha ha.

That's a great old radio guy trick that I've been using for years. Many people have used this for warming up and reforming caps in older radios and it works pretty well, but of course the tube rectifiers don't start to conduct until the filaments get to a certain (unknown) temperature. I'm not big on trying to reform old caps since their later failure frequently takes something else with it.

I start with a small bulb, 15 or 25 watts and let things warm up for a day or so just to warm up and dry things out and then work my way up until I get to 100 watts.

In some ways it's better than a variac, since it's got built in current limiting. I suppose the best version would have both a variac and a bulb. I keep a voltmeter across the equipment side just to see what it's doing.

Well you gave it your best shot. This summer has not been hot enough to dry electronics. That piece could fit in an oven set for lowest temperature and left in there for four hours. Fusing these old soldiers is very critical.
Fred

What happened to you is not all that uncommon so don't fret.  Given the incident you would probably have had to fuse each winding, which is impractical.  The lesson here is be careful when replacing components, in this case one at a time so you would have a comparison.

Aha the price of experience, but don't let anyone discourage you.

I would stay away from a voltage doubler. The L input full wave rectifier provides a much cleaner DC output and better regulation. If you must go with a capacitive input filter system at least use a full wave bridge. Having ripple on your DC don't make for beautiful audio.

John N8QPC

Got a final good bill of health on the Ranger I bought last weekend, I went ahead and replaced all the wax paper caps, so other than the micas...she should be good. Now Ill turn my attention back to the Viking II.

First things first, before I even worry about the transformer with a smoking habit, Ill be replacing the rest of the caps. Thanks for all the advice from all.

The lightbulb trick Ive seen in many a handbook but have yet to take the time to slap a board together. Bought a crate of 100 watters when there was talk of banning them.

 I managed to build a neat little TX/RX ant switch box yesterday too, no 120 VAC outside any cabinets now. Built it out of an old Wawwassee antenna switch box, threw in some neon bulbs, with jeweled lenses in a woodgrain case with the picture of a cat on the front. Only way it could get any more swaggier would be shag carpet on the top...

DOH!  There is no chernobyl resistor in the VFO, it's a Valiant II not a Viking Valiant II!!

 Sorry...


             dofus has left the building...

This must be a trick statement.



EF Johnson Viking Valiant II

(http://www.qsl.net/la5ki/org/vi/vali2.jpg)

That's a handsome rig ^^^^ I really like the white/grey colors on the Ranger II's.


Well, pulled the offending transformer out in the course of removing weight from the chassis to make it easier to work with. An odor emanates for sure in side the endbells. I might try it one more time with the light bulb and variac trick. Check out the pics.
(http://i300.photobucket.com/albums/nn7/CAVHOOAH/DSCN0655.jpg)

(http://i300.photobucket.com/albums/nn7/CAVHOOAH/DSCN0653.jpg)

(http://i300.photobucket.com/albums/nn7/CAVHOOAH/DSCN0654.jpg)


Ive dug out a slightly larger unit (it has filament, bias and control voltage windings) but it has NO center tap. Is there a way to use this transformer, I think I recall reading somewhere about working around that problem ?  

Heres a pic with the original transformer (sans endbell caps) and another dug out from the pit of despair.
(http://i300.photobucket.com/albums/nn7/CAVHOOAH/DSCN0656.jpg)

(http://i300.photobucket.com/albums/nn7/CAVHOOAH/DSCN0657.jpg)

Yes, Something about a 100 ohm wirewound slider tapped resistor across the secondaries and using the center slider as a center tap......

Anywhoo-doo da doo,

Found a slightly smaller transformer that will get me by for the time being. Installed it yesterday and finished wiring it up today. Also, stripped all the extra crap from the chassis and put it back to somewhat stock configuration on the speech amp sections. Also removed the half-butt attempt at a PTT setup, it was done fairly crappy.....so it had to go.


Now, it tunes to about 15 watts (Low indeed) and when in phone I have NO MOD current. Shouldn't I have current 50-60ma with the plate on ?

Do you have screen voltage on the modulator tubes? No screen no current.
Did you adjust R13? is R13 good? mine was found to have an open luckily I had an extra left over from a previous Ranger repair.
After adjusting R13 adjust the clamper.

73,Dave

That's a nice clean TX  Pete

Fixing to throw it back on the bench, spent the weekend over in Eastern KY with my son and ALOT of gunpowder...ALOT of gunpowder......

In the hopes of saving time and troubleshooting, the previous speech amp mods were gutted. The unit arrived in non-working condition with many "aftermarket" parts added by other owners, so the slate was really dirty when received. I turned back the clock in that section back to the original (?) radical-schematical (new word?).... so there has been a lot of tinkering with unknown results up to this point.

Saying this, just to see some activity from it is refreshing and a clue that I am at least heading in the right direction, HA.

Im really unfamiliar with this whole "modulator" setup, this be virgin grounds for this dummy, and I have yet to totally find all the voodoo stashed away in this thing. Wish me luck, Im reading the chicken bones on the bench right now !


They say "take another Advil, and rub your temples".... I comply.

Gary WZ1M enjoys a good reputation:

http://members.tripod.com/tubes_tubes_tubes/transformerrewindingservice/id28.html

Unless you are going to have this transmitter as a parts, I'd recommend investing in fixing the transformer.  It would be a shame to jury rig something else that might not do the trick

Al

Thanks for the link again AL, But it still is not feasible. I have ALOT of priorities (young father in a crap economy) ahead of this gal. Besides, I found a suitable transformer, I realize now that update never made it to print. 600VAC CT at almost the same physical size... slighty smaller (IE about 10 plates less thickness). Don't know the current rating, but this should be sufficient to bide my time to line everything else out until I can find a OE replacement.

Just measured the screen voltage, its reading almost 300V with the plate switch flipped and does not change in either phone or CW. This voltage should be ALOT lower correct ?

Not mine. I got rid of my Valiant II years ago at Dayton for around $90. Didn't look as good; probably didn't work as good; and was a constant annoying piece of equipment. Don't miss it at all.

OOOOOla,  After following the threads about the Viking II i felt I must interject.
 The HV plate transformer in the Viking1&II is a piece of crap. It has porr voltage regulation and runs hot. I have a number of Viking II plate transformers that I will never use. If you are interested I could part with one. There are better pieces.
            -----------------Overview--Viking I & II -----------------

The Viking I and II is the best thought out in the RF department. It is almost general coverage as it is. Yep! 17 and 12 meters on AM . The rest of the transmitter is in great need of fixing:
    Power supplies. Solid stating of ALL supplies is a must. Why screw with lossy heat producing vacuuuuuuum tube rectifiers. Biass supply: Get rid of the 6AL5. Use two 1kv PIV diodes . Go choke inpoot filter. ( Eliminate the first cap at rectifier anodes. Use existing filter reactor. Use at least a 100Mfd 150 volt cap for filtering the Biass. The outpoot voltage will be in the order of -80 -90 volts or so.This is fine. Next, the LV supply; Solid state this one as well. Use 3Kv worth of diode per leg. Set this one up for choke inpoot as well. If left cap inpoot ,the B+ will end up being about 370 volts,A bit much! Going choke inpoot will drop the voltage to the order of 250 volts. This will be a lot easier on various components and circuit considerations. A low drive issue may be on 10 and 15 meters if operation there is contemplated. I used a 6BF5 instead of a 6AQ5. The pin out is the same. It is a drop in. The filter cap should be at least 200Mfd@450 volts used in the low voltage supply. The HV supply must be solid stated as well a pair of K2AW type diodes ,at least 6-8Kv PIV rating to be used or two strings of 1Kv diodes mounted on a terminal board works well too. With the stock plate transformer the outpoot voltage will be about 700VDC. The 8MFD oil cap is barely sufficient for the job . Jim WD5JKOs suggestion to use a pair of 330 Mfd caps in series is the best way to go. In terms of plate voltage anything from 500-800 volts will work. Obviously the 800 volt level will make about 125 watts outpoot. Whereas 500 volts will make about 75-80 watts out. In the grand scheme of things the difference in outpoot power will be hard to notice at the other end. A machine tool transformer as suggested will work well . A 480 volt secondary with a bridge rectifier and cap inpoot filter will deliver about 625-650 volts under load. I noticed a discussion of a transformer that was rated @ 575 volts. This would deliver 500 volts under load choke inpoot bridge rectified.
You have many options here. ---------------AUDIO--------------------
Probably the weakest part of the Viking I & II is the modulator. The speech amp has barely enough gain when using a  good D-10-4 microphonium. The audio quality is like that of two dixie cups and a string. There are many modification articles to fix the problems more or less. Problem is they all involve drilling and blasting and replacement of at least the driver transformer.
The mod transformer can be a weak link as well. The existing circuit can be improved by doing the following : K.i.s.s. mod.( Keep It Simple Stupid) If you are using a preamp /EQ and good microphonium . Low gain of the system is not an issue. Replace the carbon resistors used on first stage of audio,6AU6, After 60 years or so the values can change radically. Use at least a .2Mfd screen bypass cap. Use at least a .01 cap for the coupling cap to microphonium gain pot. The cathode bypass cap should be at least 25 Mfd@ 10 volts or so . Don't forget the plate de-coupling cap. A.1 mfd cap is used. This should be changed to at least a 10 MFD 450 volt cap. Change the second 6AU6 to a 6AQ5. The pinout is very similar. The cathode pin of the 6AQ5 is what was the suppressor grid pin on the 6AU6. The cathode pin of the 6AU6 is one of the two pins used for the grid of the 6AQ5. This makes it simple. The cathode resistor can be of the same value but a two watt rating for safety. Use at least a 50Mfd 25 volt bypass cap. The 6AQ5 is triode connected by connecting the screen to the plate through a 4.7K resistor,value very non critical.  This will at least open up the audio response of the speech amp without getting too carried away.
Not so K.i.s.s.  mod. If more gain is needed to use a D-10-4 microphonium do the following: Follow instructions for the upgrade of the first 6AU6 but change the 1Meg grid resistor to at least a 10 meg resistor. This change should be done to ANY transmitter when a D-10-4 or other peizo-electric microphonium is used. Relocate the goose tube(6AQ5) from where it is located to the tube socket vacated by the 6AL5. Place another 6AQ5 in the socket and wire it according to the K.I.S.S mod. The second 6AU6 becomes a resistance coupled stage. Simply use a 47K 1watt resistor from the LV B+ to the plate of the 6AU6. The 22K screen resistor is connected to the plate. A .01-.05 cap connects the plate of the second 6AU6  to the grid of the 6AQ5 audio driver. A 100K resistor is connected from the plate of the 6AQ5 to the plate of the second 6AU6. This is a loop of negative feedback around the audio driver. The cathode resistor of the second 6AU6 should be 1K unbypassed. This can be a point to wrap a loop of negative feedback around the modulator. This mod with negative feedback around the modulator still has plenty of gain with a D10-4 microphonium. --- Modulator addendum---
It is important to place a 10-15K 1 watt resistor in parallel with the secondary of the driver transformer. This provides a much steadier load impedance presented to the audio driver. When the grid voltage swing does not drive the mod tubes into grid current the driver transformer is looking into an infinite impedance. Some audio clipping distortion will be noticeable as one leans into to audio. There are also phase shifts that take place near the ultrasonic audio range that will cause the modulator go into parasitic oscillation when negative feedback is placed around the modulator. I introduced negative feedback with two 470K 2 watt resistors directly from the secondary of the mod transformer to the cathode of the second 6AU6. Adding negative feedback is the very last step to be considered before calling it done. If the modulator takes off reverse the modulator tube plate caps. This is what happens with positive feedback.  The biass and screen voltages are very poorly regulated in the Viking I & II. This must be fixed. First of all deal with the screen voltage. In one Viking II I did up 20 years ago I used the choke inpooted low voltage supply(250 volts) through a set of relay contacts as part of the  PTT circuit I installed. This voltage also feeds the screen of the goose tube. This required a biass voltage of about -24 volts or so. I used a string of 6 Volt radio shack zener diodes. I also placed a 100 Mfd or so 50 volt cap across the zener string. The only disconcerting thing to someone that does this mod it will be noticed that the PA plate current indication will take a negative swing. THIS IS NOT REALLY HAPPENING. Being that the modulator cathode return is tied to the HV B- rail and the meter shunt for the PA stage is from chassis ground to the B- rail. The screen current drawn from the modulator tubes is referenced to chassis ground . This varying current is in opposition to the current flow through the PA plate shunt and there fore causes the meter to swing in a negative direction. To anally retentive people this is a problem. For those that understand it is a non-issue. The usual 20K 50 watt bleeder with the slider tap has always been a failure point in the Viking I & II transmitters. A good stiff voltage source for the screens of the modulators is just as important as a stiff biass supply. There is an alternative. In my collection of gear I have a practically mint Viking II CDC . I was very hesitant to do any rip tear mods. The 20K bleeder was in perfect shape. I simply placed a pair of VR150s in the sockets vacated by the 5R4s I did not even have to reset the tap, It worked perfectly. One thing though. A 10 MFD 450 volt cap must be place across the VR tubes.A 500 ohm 2 watt resistor is placed in series with the VR tubes to prevent the possibility of any relaxation oscillation effect that can occur with gaseous regulator tubes. Zener diodes are free from this effect. See AM Window- Valiant mods I authored.
 In the case of your Viking II ,you are free to make some bigger changes. Move the modulator tubes to the socket holes used by the 5R4s This opens up space for a much larger and better modulation transformer, IE Stancor A 3894 etc. -------------------------PA Stage---------------------------
The  6146s are not neccessarily operating in class C.  The biass voltage from the biass divider string goes through a low value resistor to the grid RF choke The value should be 4.7-5.6K to provide more grid leak biass. This improves modulation linearity. The screen dropping resistance is 20K .This should be 30-35K depending on plate voltage. If the replacement plate transformer delivers 500 volts,20 K is OK. If a DX 100 plate transformer is used.(800+volts) 35-40K is needed. The disc ceramic bypass caps used at the base of the plate FR choke are .01. This really impacts high audio frequency response. They should be pared down to 1000-3000Pf 3Kv units.
---------------------------Addendum-------------PTT----------------
 A PTT circuit is very useful. There are a number of different schemes.  4 poles of relay should be contemplated. One pole to key the exciter, another for the plate transformer and Keyed AC for antenna changeover relay. Another pole for modulator screen voltage and the last pole for auxillary equipment control. RX muting etc. With the solid stating of the power supplies this leave two 5 v philament windings. Seriesing up of these windings  and use of a bride rectifier with 4700MFD filter cap will give you 12-14 volts DC for 12V relays. If a higher voltage keying system is contemplated. The biass supply will work well. A 240 AC coil relay should pull in @ 70-90 volts DC . A pair of 120 DC coil relays with the coils in series should work. If somewhat more voltage is needed simply hang two more 1Kv diodes off of the Biass taps on the LV xfmr and 100 or so 200 volt cap will provide 130-150 volts or so.
In most locations the AC line voltage is around120--125 volts. This results in higer than 6.3V philamnet voltage. This causes the transformer to run hotter than usual along with reduced life expectancy of the tubes. The LV transformer is wound for 115 VAC. I wired the two unused seriesed 5 volt philament windings in series with the primary of the LV transformer. This dropped the philament voltage to 6.1 or so. In the end ,you will have a reliable transmitter that will have respectable audio with full modulation and minimal distortion. The Viking II will give many hours of pleasurable operation in it's modified state.
I realize I made a real old buzzard transmission here but when I see someone in a sand trap I thought I would help out. To others who have a Viking I or II who are contemplating modification please consider what is said here. Hmmmmm I smell another Henrynellar modification article Unless Steve HX edits it and put it up on AMFONE -----------------------------------FINI-
Tim WA1HnyLR

Reminds me of George Washington's hatchet.  The handle has been replaced five times and the head twice!  ;)

Wowzer ! That's a wonderfully informative post Tim !!!!

To start, Ive read  more than a handful of your writings already and especially enjoyed the Plate Xformer to Mod Xformer article.....just up my ally with all the junk laying around here. Researching around, I found an article somewhere in a internets-spacewarp about your mountain and was intrigued. To shorten the story here, I am enjoying the archives of your Broadcashhhh . Its nice to find something I can listen to, sit back and be truly entertained for the evening ....with a few cold ones of course.


Thanks for pitching it back to me Tim, Id bet your a busy fella and it too some time to write all that.

It was an Ebay buy, and had quite the layer of funk amongst it. There has been an extra hole punched in the audio section, and many odd-ball resistor (gonna-get-me-by) combos. I guess from what Im gathering is my fine specimen is not really that fine and I should just cut loose on it.


I did find the big tapped resistor in the bottom open due to rust forming under the slider. That's the stopping point of current progress right now. I found it going through the voltage charts in the manual.

I will re-read your post a few more times to fully grasp ahold, otherwise Im liable to say something completely stupid.


I really appreciate the extra gust of wind in my sails, its going to be a good challenge for me.

replacement tapped resistor ordered ! MAN ! Some of this stuff is getting harder to find !

In the meantime I am in step one of Tims advice....SS the power supplies.

Im not a fool to disregard good reading for sure.