The AM Forum

I went to tune up the Viking and I noticed when I set the meter to bfr and started to tune there was no buffer current and the v6, 6aq5 tube was getting hot. I did check for low voltage and I was getting +320volts.
Any ideas.

check bottom for mods!

As a starting point, if the bias filter caps weren't replaced I would do so just to avoid other issues.

You don't have the plate voltage turned on do you?  Exciter tune-up should be accomplished with the HV off (plate switch off, PTT not pressed if you have added PTT).  The 6AQ5 naturally runs hot but it should only get very hot with the HV on and loss of excitation to the final.  It then earns its keep by drawing heavy current through the screen dropping resistor which protects the final (and power supply) from excessive current draw/heat.  In normal operation, grid bias developed with excitation keeps the 6AQ5 cut off.   Until you are able to achieve proper grid drive, DO NOT turn on the plate supply to the final.

Are you using VFO or crystal control?  If you are using crystal how does the oscillator current change between a socket with a crystal installed and one without (i.e. is your oscillator actually oscillating).  If VFO, can you hear the VFO oscillating in your receiver?  Are you sure the crystal switch knob is indexed properly so that you have truly selected VFO (someone may have reinstalled the knob improperly).

The buffer current is peaked by tuning the oscillator control and the grid current is peaked by tuning the buffer control.

If the two 10 uf cathode bypass caps in the low level audio stages have not been replaced I would suggest doing so.  Every older V1/V2 I have seen had bad caps here.  They were not shorted but capacity was low causing the cathode bias resistors to act as a negative feedback circuit greatly reducing gain and low frequency audio content.

You don't have the plate voltage turned on do you?  Exciter tune-up should be accomplished with the HV off (plate switch off, PTT not pressed if you have added PTT).  The 6AQ5 naturally runs hot but it should only get very hot with the HV on and loss of excitation to the final.  It then earns its keep by drawing heavy current through the screen dropping resistor which protects the final (and power supply) from excessive current draw/heat.  In normal operation, grid bias developed with excitation keeps the 6AQ5 cut off.   Until you are able to achieve proper grid drive, DO NOT turn on the plate supply to the final.

I haven't installed the PTT yet and I don't turn on the plate switch as the plate on the 6146 start to glow.
When I do a tune up on 40 meter as instructed per manual, the meter is on bfr and there is no meter reading.
Even if I bring up the Osc. I am running the VFO and I did check to see if the 0A2 does glow inside and I did measure 4 volts going to the VFO. I hooked up the HRO50 receiver and turned on my other transmitter to zero beat the receiver to the Yaesu frequency. Then I tuned the vfo to match the frequency and keyed the transmitter through my old brass key and I could not here anything in the HRO receiver.
There is plate voltage. I did a complete recap and yep I did make sure C12-13 were grounded to the + side of the caps.
Is there a schematic on the vic2 with voltage readouts on the tube pin numbers?


 

Do you have a FT-243 crystal you could borrow from another transmitter (or ham) for testing purposes so that you don't have to potentially troubleshoot the VFO and transmitter simultaneously?

I assume you are using the Johnson 122 VFO?  It can be set up for keying either via the transmitter keying line or the VFO can be keyed independently.  Unless you know how the previous owner set it up you will need to check the setup.  You will generally notice a very slight dimming of the VR tube when keyed.  If you don't hear it in your receiver, try plugging a key directly into the jack on the VFO.  Also, don't count too much on the VFO calibration as received so tune the VFO quite a distance either side of where your receiver is tuned.

The drive pot is a common failure item on a number of Johnson and Heathkit transmitters.  R25 serves both to control the screen current for V5 and as the bleeder resistor for the B+ supply.  As such it runs quite warm and is subject to failure.  If the pot opens up then depending upon where the break occurs you can end up with either no or very high screen voltage on the buffer tube.  Measure pin 6 of V5 and see what the voltage reading is with the drive control set about halfway through its rotation.  The transmitter needs to be on but does not need to be keyed for this measurement.

The Viking manual is pretty light on voltage data, some information is on page 21 and 22.

I assume you are using the Johnson 122 VFO?  It can be set up for keying either via the transmitter keying line or the VFO can be keyed independently.  Unless you know how the previous owner set it up you will need to check the setup.  You will generally notice a very slight dimming of the VR tube when keyed.  If you don't hear it in your receiver, try plugging a key directly into the jack on the VFO.  Also, don't count too much on the VFO calibration as received so tune the VFO quite a distance either side of where your receiver is tuned.

Ok this is what I have now after doing some troubleshooting on the VFO, Yep it's a 122.
Now when I hit the brass key I do get cw noise on the receiver. So now the vfo does tune to 0 beat.
Back to the meter. When I turn the drive up to about 6 I do get some meter movement and when I key the transmitter the voltage or the meter moves up. Still nothing else. But getting closer. I think receivers are easier to work on. ::)

Not that I have seen.  Page 21 of the original manual shows some of the tube voltages.  And Figure 13 towards the back of the book shows the tube base diagrams.

Well, until SSB transmitters came out many hams would still build transmitters but few would build receivers :)

You are definitely making progress.  When you tune the oscillator control (with the key closed) does that cause a change in buffer current?  If so, leave the drive set to the mid point for now.  If you can peak the buffer current with the oscillator control then switch to the grid position and see if you can now peak the final grid current with the buffer control.  If the final grid current goes above 7 mils then decrease it immediately by reducing the drive control.   6146 tubes are easily damaged by excessive grid current.

There will be slight interaction effects in the exciter chain and after adjusting the buffer tune for maximum grid current leave the meter in the grid current position and adjust the oscillator tuning slightly and you will probably find that it can be tuned for slightly more grid current.   This isn't really important on the lower bands but on 10 meters, especially with a less active crystal that is being multiplied many times, this last adjustment will provide a bit more drive.

Be sure to test/adjust the clampler circuit once you get to the point of having sufficient grid drive to the final.  Follow the instructions and adjust the modulator idling current first as changing the resistor tap used to set modulator idling current also impacts the clamp tube setting.

Rodger, thanks for the replay.
I maybe found something but maybe you will know better. After reading the setup from the beginning, I found the oscillator was at 0 and it was open all the way . According to the manual 0 is fully meshed.
I went through all of the knob settings to make sure they are correct.

You are welcome and it sounds like you probably should check the other knobs also to make sure they are indexed correctly (to avoid future confusion).  If one was off the odds are good that the buffer control may also be indexed incorrectly.

If you haven't already done so, run the final tuning back and forth through its range a couple of times (plate switch off).  This will help to clean off the roller inductor so you don't have erratic tuning when you begin to tune the final.

Once you get the Viking 2 running properly it is one of the most trouble free transmitters available.

Well upon more investigation of this unit, I found out something that I should have looked at being around antique radios and what the homeowner will do. I looked at the osc circuit and started looking at the tubes and found a 6aq5 V6 where a 6AU6 should be. Made the trade and what do I get. Meter movement  for the oscillator and buffer.  Man you guys make really want to get to know these transmitters. Now to start the tune up and see if the thing is going to work. I did switch to plt and yep it is there.
I will keep you posted but now it's time to relax.

Good deal!  The little victories are nice and it will be a great feeling for you when you make your first contact with the transmitter.  It is also very wise to relax since working on this gear can certainly be deadly if you make a mistake while fatigued.

Given what you have found (knob installed wrong, wrong tube), I would check every other tube to make sure it is correct.  Also check the line fuse to see if it is the correct value.

Outside of the weight, the Viking II is not bad to work on since it has a pretty open chassis and doesn't crowd the parts like some other gear.  I am currently making some minor repairs to a newly acquired Davco DR-30 and I am working with very long needle nose pliers and a magnifying glass.

my viker2 has ptt and i have osc meter to the ping and buffer almost there but i use grid to load it up by putting in cw no plt switch on then when hit plt its all normal that's why i ask if it has mods mine has a 12ax7 speach amp and 12by7 driver going in 807's 6aq5 still there them tubes get bloody hot i have an audio amp in my nc-300 it bout cooked my skin on the glass but i don't mess with the v28 or v5 i know that tube get hot!

The most common role of a 6AQ5 tube is that of a class A audio output tube and in a receiver generally the two hottest tubes are the audio output and rectifier tubes.  It is normal for it to run quite hot.

In a modified Viking 2, if the 5R4 tubes have been replaced with SS substitutes and/or other games have been played that resulting in increased HV then the 6AQ5 will run a bit hotter.  But as long as the plate is staying black it is probably normal.

There was a hilarious story in an issue of Radio and Television News where a technician was called out to repair an expensive hifi/TV combo in time for a party.   The technician arrived at a very nice house and was escorted by the maid to the room containing the broken entertainment device, a very formal room with expensive carpeting.  He carefully put down a thick layer of newspaper to protect the carpet and as he was doing this the woman of the house came in to check on him.  As he was testing he noticed a slight scorched odor and assumed some food was being prepared for the party.  After finding and fixing the trouble he was preparing to put the chassis back in the cabinet and to his horror discovered the newspaper had slipped and the output tubes had left two perfect scorched circles on the expensive carpet.  The wife was horrified with the party coming up but he asked to borrow a pair of tweezers and some glue.  He then carefully pulled out matching little tufts of carpet from the carpet in the closet and glued them back in for a perfect match.  In the end he did such a nice job the owners refused to have him pay for a carpet person to do the repair-but he said he was sweating bullets the entire carpet repair time :) 

I imagine more than one technician has left perfect scorched circles on an arm by letting it briefly rest on an output tube or rectifier during servicing.

There was a Doctor here many years ago, he was a very active ham and one day during the summer he decided  to do some work on the amplifier with out a shirt on and he leaned over to check out what was going on the inside and keyed the mike. He did have a big funeral.
It pays to be extra careful.
 

I was going through the clamper adjustment according to the manual and the transmitter will not go below 350 ma. I did check the tubes and all is good. At one point the transmitter did come alive and put out about 10 watts. So I am thinking there is no bias but I was getting 81 volts. the plates of the 6146 does get a red sopt on it after about 15 sec of plate. I did adjust the r13 for 2'' from the back and did check the r30 for operation and set it to full ccw. Is there something I am missing?

What are you reading for grid bias directly at pin 5 of the 6146 tubes (plate switch off, CW mode with key open, no drive to the final)?  With drive the tube will also develop additional bias so this measurement must be made with no excitation to the final. 

Check bias voltage at the junction of L3/R17 with the HV off and on, it should not vary appreciably.  There are a few circuit faults which could cause bias loss with HV but that would be unusual.

Clamp adjustment is set with the transmitter set to an empty crystal position and you should be able to drop the plate current to near 0 since the clamp tube will pull the screen voltage down to near 0.  I generally make the final clamp adjustment with the final loaded to normal output with normal drive and set the clamp adjustment to just the point where it begins to reduce plate current.

What are you reading for grid bias directly at pin 5 of the 6146 tubes (plate switch off, CW mode with key open, no drive to the final)?  With drive the tube will also develop additional bias so this measurement must be made with no excitation to the final.
The voltage was tested at -83 volts.

Check bias voltage at the junction of L3/R17 with the HV off and on, it should not vary appreciably.  There are a few circuit faults which could cause bias loss with HV but that would be unusual.
This is what the test came out at.  Off -83 volts- On -65/8 volts. During the test the 5 amp fuse blew. Replaced the fuse and it seems ok now.

On -65/8 volts?  I am not sure what this means?

Two more measurements (be very careful since these will be checked with HV on).

Before starting make sure that R-30 is set to its full clockwise position.

1.  Start with plate switch off.

2.  Make sure you are in CW mode with key plugged in but open (no excitation to final).

3.  Since the final is drawing excessive current, turn the HV on very briefly (just long enough to take a reading) while making the measurement at the tube pins from below the chassis..

4.  voltage at pin 5 (control grid)?

5.  voltage at pin 3 (screen grid)?

here are the voltages readings,

4.  voltage at pin 5 (control grid)? -81vdc

5.  voltage at pin 3 (screen grid)? 450vdc

With the screen at 450, the clamp circuit isn't doing its job. 

Have you tried a different 6AQ5?  You could temporarily swap the 6AQ5 out of the V5 position if you don't have a known good spare.

Other possibilities:

R13 is prone to failure and is easily damaged, make sure you have positive voltage (I believe it should be between 170-200 volts with HV on) on the end of R29 connected to the tap on R13.   

Also make sure R29 isn't open and is somewhere close to its 470K value.

With normal grid drive the clamp tube is cut off (not conducting) but without drive the 6AQ5 should conduct heavily drawing significant current through R28 greatly reducing the screen voltage.  Variable pot R-30 forms part of a voltage "mixing" circuit and is adjusted so the HV sample via the tap on R13 and reduced by R29 offsets the standing negative bias taken from the R24 L6 connecting point.  Under this condition the 6AQ5 is conducting but as the final is driven additional grid bias is developed and the additional negative voltage now overcomes the positive voltage introduced to R30 increasing negative grid bias on the clamp tube and cutting it off. 

Rodger, You have been a good teacher. To bad I couldn't take a class from you.
This is what I found.
R28 is open and I thought I had checked this but I guess not.
I will have to wait until Monday to get one if there is any in town. After I get this rig going I might have a slim idea of what is going on here. I did overhaul the National HRO50 receiver and it is running great. Transmitters are just a little elusive for me yet. Some day It will click. I understand how receivers work but transmitters?
I guess it's the idea that you can take a signal off the plate and sent it into a antenna that mechanically shorted and make it work. To many years working on the antique radios I guess.
BTW R28 is a 20k ohm but it looks like to be a 25 watt?

Thanks, these days I would rather teach vintage radio repair than business courses  :)   After 26 years of teaching college courses either I am getting more cynical or more students are too busy looking for short cuts (probably a little of both).

Are you sure R28 is open? That would remove all screen voltage from the finals since it is in series.  Did you mean R13?

Rodger WQ9E

Yep R28. R13 does check out ok.
I pulled it out of the circuit and rechecked the resistor and it is open.
During setup, Johnson wants you to adjust R13 so the slide is at 1 1/2'' or 2 '' from the back of the radio.
Do you know what they are looking for in ohms during setup of the clamp circuit?
If you going to learn the right way, sometimes you have to take the long and hard way.

The most important thing the tap sets is the screen voltage (and thus idle current) for the 807 modulator tubes.  As I recall that will be reached with the tap about 1/3 of the way up from the grounded end of R13 (well slightly above ground end since there is a very low resistance meter shunt in series with ground).   Once you set up the modulator screen voltage then the clamp adjust control is adjusted.  So for the final clamp adjustment you will need to first make sure the modulator tubes are drawing rated idle current and adjust the tap as needed.

R13 uses fine wire that is extremely fragile so exercise great care when moving the tap.

Every transmitter gets a little easier - until you tackle a really involved phasing rig like a Johnson Pacemaker :)

Check C45 and C28 also to make sure neither is shorted since that would cause the replacement resistor to burn out.  I would be suspicious that one of these may have shorted taking out your first fuse and damaging R28.

Revise, r28 open and I rechecked r13, this time I removed all wiring and it is also open.
Where can I get a new one?
This thing is like chasing a rabbit around a hole.
I checked the resistor with a magnifying glass and yep broken wire.

Unless you are lucky enough to have a big parts store in the area you won't be able to find the resistor locally.  For the 20 K fixed resistor Mouser does have them and they aren't expensive at $2.29:  http://www.mouser.com/ProductDetail/Vishay-Dale/HL02506Z20K00JJ/?qs=sGAEpiMZZMtbXrIkmrvidMSY%252b1GTbUwvMoAjHCWlPas%3d

You can also get the 20K adjustable from them and this needs to be a 50 watt unit, adjustable WW units are a bit more expensive:  http://www.mouser.com/ProductDetail/Ohmite/D50K20KE/?qs=sGAEpiMZZMtbXrIkmrvidB8tHLcYn%252bvCO0C403mjYL4%3d

Mouser has no minimum order but if your order is only for a couple of resistors then choose USPS instead of default UPS shipping.  Of course now would be a good time to stock up on other standard passive components you need and if so consider ordering sufficient stock of common items for future repairs since there is generally a significant quantity discount.


But with both of these resistors failed, definitely check the screen bypass caps.  R13 is a pretty common failure item due to wear/fragile nature.  With the final not drawing a lot of current and the bleeder (R13) open, HV would soar since without critical load the power supply filter would operate as a capacitor input filter instead of choke input  and that might have taken out a screen bypass cap in the process.

Thanks for so much info and the tremendous amount of help. Time to go shopping, and I just got a shipment of parts in.
Oh well. I also decided to go through the Johnson T/R switch and replaced the electrolytic cap and low and behold a .005 cap flashed to the case at one point. This cap is common to both transmit and receive.
That was all I need is to have this do something else to the transmitter.
Stay tuned for more after I get the parts installed. I just hope everything goes well. At least is talking now to get it yelling.

Rodger, I received the new resistors from Mouser, Installed them, found a couple of other problems and this dog hunts. ;D
115watts out in ruff tuning. Now off to button up the bottom and start adjustment of the clamper circuit and put it out on the air. Rebuilt the T/R switch and when I plug it in for the receiver I do get a substantial bump in receive signal. Well maybe not to much but the little needle did wiggle a little more.  The 122 vfo is working correctly and zero beat into the HRO501T.
Checked alignment on the receiver and all is good.
I want to thank you for all of the help and others who contributed to the current thread. I may have other questions but for now it is time to kick this pig and make it squeal.  :D 

Always good to have a happy ending  :)

Congratulations on getting it running again!