Viking 1 no Grid Current on meter

[AB5OR]

I need some help finding out where to look.  I am new at my Viking 1 we just got working (sort of).   In tuning, it was discovered that the grid current isn't working in the meter.  It is generating grid current as we were able to get it tuned somewhat  and watching it produce output on a watt meter.   Anyhow, I am wondering where to look first at why I am not showing grid current.   All the other meter settings are fine.   First thing I know we'll do is clean the contacts, and especially on the ceramic switch below the meter.   I am wondering if a resistor or something simple could be the culprit.    I definitely want my grid current to be accurate !

Thanks for any help in advance to this newbie.   

Joe

[WQ9E]

Joe,

Is it producing near normal output?  If so then you can safely assume you have  enough drive and the problem is definitely in the metering circuit.

The meter shunt itself must be intact because otherwise you would pin the meter even with minimal grid current AND when not in the grid metering position the final would have no bias and would be very upset.

It could be the switch but since it works on other ranges I would suspect one of the wires from the switch to the shunt.  As a quick check, identify the leads from the grid shunt to the meter switch and then with the switch in any position other than grid check for continuity between those leads and the resistance should be very low.  If you do get this low reading then suspect the switch, otherwise it is probably a bad connection or broken wire.

While you are in there, make sure that the 5R4 tube bases and sockets are clean or they will build up carbon tracks.

[AB5OR]

Yes, I should've provided more info.   Yes, it seems to be producing just fine.   I am using the VFO, and using a service monitor, it is calibrating and seems very stable.   So, then we moved over to tuning.   The OSC and BUFFER currents are just fine, plate is fine, everything seems fine, except zero reading on the grid meter.  Yes, tomorrow, everything is getting cleaned up.  Everything seems mostly ok, so I'll move on from there.    So that you'll definitely know that I am a newbie, what exactly does the buffer do?    Thanks... Joe

[WQ9E]

Hi Joe,

It sounds like you have a healthy transmitter with a minor problem.

The buffer amplifies the signal and multiplies the frequency (for most bands) and serves to isolate the oscillator stage to prevent it from being shifted in frequency by the load of the final.  This last function is what gives the buffer its name.

Welcome to AMfone!

[AB5OR]

Healthy transmitter, minor problem!   That sounds great!   Kind of what we were thinking.    It appears this box has been modified to what I've heard called a 1.5 or 1 to 2 conversion.   The finals are 6146's and someone added a 1/2 amp fuse in line with the 6146's that I blew yesterday when I had no idea what was going on, and we weren't close to resonant.   Afterwards, we didn't have that problem gain.    Buffer makes perfect sense.   Really appreciate the info.   I hope it's just fine.   One other problem.... I found a D-104 mic in great shape.   It has the 4 pin connector.   How might I go about interfacing to the Viking standard jack.   I am really not sure what that jac is called exactly.  I've heard there is an adapter for this, but I don't know.

Joe

[WQ9E]

Your Viking 1 probably has PTT added.  What does the current mic jack look like on the transmitter?  If modified for PTT then the most commonly used connector was the 2 pin style that Johnson used on later equipment.  This was also the connector used on a lot of Heathkit and Hallicrafters gear. 

If it is the original (not modified for PTT) then it is a single conductor with the contact right in the center of the connector.  This style was common to many transmitters and cheap test gear of the era.

[AB5OR]

Definitely the original.   It doesn't have PTT added.   

[WQ9E]

If you are planning to dedicate a mic to the Viking then the easiest approach is to remove the current connector and put a matching one on for the Viking.  But, if you think you will want to add PTT in the future then it would be best to go ahead and put a different connector on the Viking 1 but if the front panel is nice you don't want to mess it up. 

So, If you are going with PTT I think I would go for a connector that will fit in the existing hole and I don't think a 4 pin will fit.  I would choose a style (at least 2 conductors plus ground, possibly a headphone style jack) and put a matching plug on the mic.

If you aren't interested in PTT and are will to dedicate the mic to the Viking try to find the matching connector and install that on your microphone.  If you can't locate one it is possible to modify a standard PL-259 coax connector to work with this existing connector.

If the mic will be used for multiple rigs then you could wire up an adapter with a female 4 pin to whatever male connector is used on the Viking.

[AB5OR]

Ok.   I think I'll just dedicate the 104 to this box. ...   So, I'll just get that connector.  I think that 4 pin is pretty common.

Thanks again....  I'll post what I find tomorrow with the meter.   Very, very exciting!

[KA2DZT]

Thanks again....  I'll post what I find tomorrow with the meter.   Very, very exciting!

Hi Joe,

Glad you're excited!!

But, pay attention to what you're doing with the rig.  We don't want you to electroplate yourself.  Lots of high voltages in a xmtr.

Welcome to the AM Forum.

If you have any more questions just let us know.  There are plenty of folks on this board with the answers.

Fred

[AB5OR]

Thanks a lot for the comment.   Yes, you are very correct.   It is amazing how much DC voltage IS inside a xmtr.   I am working with two guys that have been doing radio work since the 60's, one commercially for a long time (70s to 90 or so 2 way radio, then paging, etc)  That would be my dad.   He still has his old tube caddy from earlier years (and several working tubes).  I grew up around radio, but never got the bug to work on them and really understand them until lately.    I am asking basic questions because I want to learn somewhat on my own, but under the watchful eye of the pros so to speak.   I watched them both very gently handle the radio, and testing voltages yesterday, hooking up from a distance, carefully making sure caps had discharged, etc.   Only takes one time to kill you.   I'm VERY cautious messing around....   

[WQ9E]

Excellent comments on safety.  My father was a civilian supervisor in an Air Force precision measurements electronics lab and they were strict about safety standards.  He also did calibration and repair of test gear in his home shop so I grew up with safety standards deeply ingrained.  Some of the basics were no rings or jewelry to be worn around equipment (decreases effective body resistance and can turn a minor shock into an electrocution event), always wear insulating shoes, make power on measurements only when necessary and keep left hand in pocket while doing so. 

To me the most important additional rules are never continue to work when tired/stressed because this is when the accidents occur and Never let familiarity breed contempt.    A lot of severe and/or fatal accidents are two part events, for example the old time TV technician who received a minor shock and jerked suddenly hitting and breaking the fragile neck of a CRT causing it to implode or the radio tech who jerks his arm away from a hot tube and into exposed high voltage.


Keep in mind that a lot of very smart people, like amateur radio operator and early television experimenter Ross Hull, were electrocuted doing building and repair work.  With some hobbies if you do something really dumb it will just cost you money (and embarrassment) but with amateur radio the only good outcome from stupidity is for the Batesville casket company.

[AB5OR]

I am still working on this.  I have found the one lead off the meter goes directly to the 6al5 rectifier tube, but that tube is actually an oc2.    Don't know if that's a Problem, but that's where I am.    Anyone know?   

[WQ9E]

Hmmm, there is no voltage regulator tube in a stock Viking 1 or 2 so your transmitter has been significantly modified.  The 6AL5 (bias rectifier) function has probably been replaced by solid state diodes and the modifier may have regulated the bias since the 0C2 is designed to regulate at 75 volts which is what should also appear at the output of the bias rectifier.

The 5.1 ohm shunt (SH-4, final grid current) is located between the main output of the bias supply and the junction of R24/R27.  The wiring sounds correct if the tube is being used to regulate the bias voltage.

[AB5OR]

So, I got grid current finally!

1.   Vfo had a solder joint come off the center of the coax that was sometimes touching the terminal, and sometimes not, and sometimes ground.   Result was a weak or no rf output, thus nothing to drive, or wildly erratic.

2.   Didn't know you don't see any grid current until a fairly tight window on the buffer....  Is this correct?  New here.

3.   Got grid current to 8 ma (6146 tubes)...

4.   Flipped plate on, but meter pegged until I backed off the drive a bit.  Cut plate off as I didn't want to fry the 6146s.

5.  Oscillator knob shaft is needing some work and doesn't always turn....  Not exactly sure how to set this.   I see the peak, then drop, then peak as the manual mentions... Where should I set this?

[WQ9E]

So, I got grid current finally!


2.   Didn't know you don't see any grid current until a fairly tight window on the buffer....  Is this correct?  New here.

3.   Got grid current to 8 ma (6146 tubes)...

4.   Flipped plate on, but meter pegged until I backed off the drive a bit.  Cut plate off as I didn't want to fry the 6146s.

5.  Oscillator knob shaft is needing some work and doesn't always turn....  Not exactly sure how to set this.   I see the peak, then drop, then peak as the manual mentions... Where should I set this?

2.  Buffer tuning does have to be precise, sharply tuned circuits are necessary for clean output.

3.  6 ma is plenty of grid current for a pair of 6146 tubes in class C, I wouldn't go any higher.

4. (also 5).  First make sure the oscillator and buffer knobs are properly indexed to their respective capacitors (5.b. and d. on page 3 of the manual).  Then follow the curves in the charts on pages 15 and 16 of the manual to get the rough settings of the oscillator and buffer controls. 

Note that for 20 and 15 meters the oscillator is tuned in the 7 Mhz range while the buffer is tuned in the 14 and 21 mhz range respectively.  For 10 meters the oscillator tuning is set in the 14 Mhz. range while the buffer tuning is in the 28 mhz. range.  On 160, 80, and 40 the oscillator and buffer are both tuned to the output  frequency.  You will find it handy to make up an index card with the settings for quick tuning when changing bands.

Curve 1 on page 15 provides the same information for the final tuning.


When tuning up, preset the oscillator, buffer, and final to the proper setting according to the curves (or the chart you make up).   Check the manual for the proper starting point for coarse and fine coupling which is based upon the band you use.  With the oscillator and buffer controls at their preset positions only a slight touch up will be needed.  With the final tune and coupling set at the proper starting positions you will avoid excessive plate current and tune up will be faster.  You will generally need to advance coupling beyond the initial position to load the final to its rated input.  You will also find that grid drive drops a bit as coupling is increased so you will likely need to increase it slightly at the completion of tune up.  But do not go beyond 6 mils for a pair of 6146 tubes as excessive grid drive will damage the tubes.

If your oscillator shaft is binding, try a drop of oil where the shaft goes through a bushing at the front of the capacitor.  I use lightweight synthetic (0W20 motor oil works fine).  For stubborn cases, heat the bushing a bit with a soldering iron and then apply a couple of drops of oil from a syringe.  The oil will be drawn into the bushing as it cools.

[AB5OR]

Once again, thanks for the help.   That response on tuning could very well be a stand along HOWTO.   The manual is good, but it's great to hear a real world procedure.   I have to replace the sleeve between the knob shaft and the shaft of the variable capacitor.   The plastic is worn, screws stripped, etc.   I'll get that done this morning... 

Then I'll let you know what is happening.

[w1vtp]

Yeah, the manual says that 8 ma is dancing on the precipice of a 6146 meltdown (4 ma per tube).  Also, the manual says to not key the rig when drive is at 6 ma with the plate supply off as that will exceed the screen power ratings.  That last one has me scratching my head.  I'm at work so I can't refer to the manual.  Just a head's up

Al

[KM1H]

3.  6 ma is plenty of grid current for a pair of 6146 tubes in class C, I wouldn't go any higher.

Even that is pushing it and 8ma will fry a pair of tubes in no time. With good tubes 5ma is fine and dont be tempted to increase it to improve the audio which pretty much sucks out of the box. 
See the other V II thread running about the fixes for that.

My own is a V II CDC model with a rebuilt audio section and I'll be doing it to the V I next which has some other audio mods Im not thrilled about.

[KA2DZT]

At 600 volts on the plate in AM service, the grid current for a 6146 is shown to be 3.4ma in the RCA tube manual.  Not sure what the grid current for a 6146B would be, maybe the same amount.

Fred

[KM1H]

And the manual is a recipe for disaster. RCA later came out with a change that became a Johnson bulletin.

When in doubt search for all the info.

[KA2DZT]

Thanks for letting me know about the change in grid current specs.

In my HB 6146B xmtr I usually run 3-3.5ma grid current with about 650v.  Doesn't seem to bother the tube, its been in the rig about 10 yrs and it was used then.

[AB5OR]

I got it working by playing around using tuning help above.    Putting out 115 watts, around 4 ma grid current!    Anyhow, tell me about the 6146b tubes.      What is required for their use?

[WQ9E]

If your rig was modified to be similar to the Viking 2 they should work just fine.  I use 6146 B and W suffix tubes in all of my Johnson and Heath gear without ill effects.