Ranger Grid drive problem

[n2ry]

Howdy all,

First time poster - long time reader.

I've read thru everything here that I could find about Rangers.
I'm still working on a problem with mine and grid drive.

160 has at most 3.5ma
75 has no more than 2ma
40 is maybe 1.5
20,15 maybe 1.0 - 1.5
10 has 2.ma

power output is no more than 20 -25 watts max, some lower.

replaced the 6cl6s - still no joy

checked R7 & R8 - both with tolerance (from a previous post)


I have used this on 160 & 75 and have gotten good reports, but very little out on 40m and up.
where I really want to use it at.

So, any ideas. I was checking voltages, but none of teh docs I have have any voltage references.

Open to any suggestions,

thanks,

Rich
n2ry

[The Slab Bacon]

sounds like you got low grid drive everywhere. How does your buffer and driver current look?? My next step would be voltage and resistance checks of the buffer and driver tubes. Check to see if the plate and screen dropping resistors for the buffer and especially the driver havent gone high, or something else may be causing low voltage to those tubes.

                                                               the Slab Bacon

[WQ9E]

Rich,

How do your oscillator and buffer currents compare with the chart on P.21 of your manual?  Do you have a crystal you can try in place of the VFO?  These will help narrow down the section at fault.

If you have another 6146, give it a try.  In one of their notes for the Valiant, Johnson indicates inability to develop normal grid current may be due to previously overdriven final tubes.

Rodger WQ9E

[n2ry]

Thanks ... Will check those tonight
From a resistance measurement  standpoint - it's OK
to measure in circuit first (its should read much higher if out of tolerance ?)


Also approximately what should the plate and screen voltages be ?
I see the +300 volt line to the plate - so 270 - 300 is good ?
If I remember correctly, I was reading around 270 max off the Driver pot,
cranked all the way up.

I will double check tonight

Just saw the second post - I'll check the osc & buff currents in the manual tonight -
Yes - I do have a few 6146 spares ... I'll try that too


thanks,
Rich

[ke7trp]

Check the screen voltage and or swap the 6146 out.

Clark

[n2ry]

I swapped out the 6146, clamp tube and both 6cl6

I wrote all the voltages down and left the paper at home. But if memory is correct they all seemed a bit low

After the tube swaps,  grid readings appear about the same
20 & 15 are virtually none
160 is about 3
75 and up around 2ish still

I don't have a low voltage rectifier to swap

The buffer and osc readings are around 2 i think

Grid drive should always be around 2.5ma, on 160 I do have grid drive at 2.5, but still only manage out 25 -30 watts.

[ke7trp]

Check the resistance of the drive pot with a meter. They are known to short out.  I have had to replace that pot in every ranger and valiant I own.  Some have not had total dead spots.. but the overal resistance was off.

On my ranger I can run way past the 2.5MA figure with just a slight turn of the knob on any band.

Its also typical to find all the voltages high and not low.  The reason is that chart was made at 115 to 117volts on the wall plug. I bet you have 120 to 130 volts.  So maybe the LV rectifier is toast.

Also..I struggled with low power problem with a valiant and the guys here told me to check the screen volts. I did and found it was low at the 6146.  After I repaired the radio I had full power and the drive was right where it should be.. So make sure to check it..

Clark

[WB6NVH]

After you do all that, if the problem is still there, take a look at the mica coupling capacitor/s to the PA stage.  I had the same issue once but I no longer have the transmitter or the manual to recall what the exact story was.  I just recall a coupling capacitor being a fraction of the marked value, either because of failure or manufacturing error, and replacing it brought normal drive back.  Worth a look, anyway...

Geoff
WB6NVH

[n2ry]

heres what I've found voltage wise:

HV = 580vdc STDBY
        502vdc PHONE

LV = 354vdc STDBY
       314vdc Phone

Drive Pot measure around 20k and wiper goes from 0 to 339 vdc

V4 Multiplier

pin8,3 (screen)
STDBY = 340
PHONE = 289
TUNE =   302

pin 6 (plate)
STDBY = 339
PHONE = 283
TUNE = 300


V3 Buffer
pins8,3(screen)
STDBY = 339
PHONE = 314
TUNE = 320

Pin 6 (plate)
STDBY = 339
PHONE = 213
TUNE = 222

AC is 118.8

Does these voltages look low


           

[AB2EZ]

From your measurements, V4 is not functioning properly (symptom). I suspect that there is too little V4 screen current flowing when the rig is in the tune or phone position... and that is why V4's screen voltage is not being dropped below V4's plate voltage by the end-to-wiper resistance of the drive potentiometer R13. As a separate, but related problem/symptom: with the screen voltage of V4 having as high a value as the plate voltage of V4; and with the rf output signal from V4 being taken from only the plate (the V4 screen current does not flow through the V4 output tank circuit), many of the electrons flowing from the cathode will not "make it" to the plate of V4 and the associated V4 output tank circuit.  It appears that the input signal to the grid of V4 is essentially feeding through to the output of V4 without being amplified.

Possible causes:

1. There is a cold solder joint somewhere in the path from the wiper of the drive pot to the screen pin connections on the V4 tube socket, AND the point where you are measuring the screen voltage is on the wiper side of the path leading to that cold solder joint (i.e. you measure the voltage at point x, but there is no low resistance path for current to flow beyond point x to the actual screen pins of the tube. Possible, but not likely. More likely is one of the following:
2  The grid of V4 is being biased too far beyond cutoff because the V4 grid leak/biasing resistor, R11 is open or too high a value; or
3. The keyer circuit (V15) is not working properly... and the lower end (on the schematic) of R11 is being held at -56 volts (the bias rectifier voltage) or does not have a path to ground through the 47k ohm keying circuit resistor (R43). To check this, try grounding the lower end of R11 (the 100k ohm V4 grid leak/biasing resistor). If the problem with low 6146 grid current goes away, then you need to check the keyer to find out why it is not functioning properly. For example, the wire between the bottom of R11 and the keyer circuit could be open. Note: since the Ranger uses grid-block keying... grounding the lower end of R11 will result in the tube V4 being biased "on" when the "operate" switch is set to "standby". So... don't ground the lower end of R11 as a long term solution. Do this only to see if the problem is in the keyer circuitry.

Stu

[ke7trp]

Good post..


I wonder is this is the older ranger or the later one with the seperate board with the 6al5?  Can you take a picture of it?

Clark

[n2ry]

there is the seperate board with the 12au7/6al5,
its the small board over V3, elevated up by standoffs.

I found 2 100k resistors out of spec  (measured 115k instead of 100k)R11& R45

R41 is a 18k and it measures 32.25k, (dont have anything close at the moment)

When I measure the  junction of R45,R43,C89 I get: -43.05 - STDBY, -.7 - PHONE

When I ground the lower end of R11, nothing changes and I have continuity from R11 to R43
nothing changes .... grid drive is still low
160 is still about 3.+ and all the rest are still below 2

You only learn things when they don't work ....

Rich

[AB2EZ]

If the voltage at R43 is -0.7 volts when the operate switch is in the phone position, then it folows that the peak r.f. signal on the grid of V4 is only around 2 volts (or less). I.e. the DC voltage on the grid of V4 is around -2 volts (or less).

[What is the DC voltage on the grid of V4 when the operate switch is in phone position?]

This is too low to properly drive V4's grid.

You need a 2.5 mA x 27k ohms = 67.5 volts peak rf signal on the grid of the 6146; and V4 doesn't have enough gain to bring 2 volts of peak grid input signal up to 67.5 volts of plate output signal.

So...

Let's see if V3 is the problem.

Check to see of R7 and R45 are the correct values, and check the continuity between the grid of V3 to the bottom of R7... and from there through R45 and through R43 to pin 7 of the keyer tube V15.

[What is the dc voltage on the grid of V3 when the operate switch is in phone position?]

[n2ry]

V4 pin 9 (grid)   PHONE = -1.6
                      STANDBY = -35.6


V3 pin 9 (grid) PHONE = -.63
                    STANDBY = -44.4

R45 was replaced (original read 115k) its now a 100k

Check to see of R7 and R45 are the correct values, and check the continuity between the grid of V3 to the bottom of R7... and from there through R45 and through R43 to pin 7 of the keyer tube V15.

continuity shows about 207k V3 grid to pin7 V15

and thanks for help .....

[AB2EZ]

Temporarily run a jumper directly from the cathode of V3 to ground, and see if that helps.

Reason: V3 serves as either a crystal oscillator or a buffer amplifier for the VFO. In the crystal oscillator mode, the cathode of V3 is connected to ground through a combination of an rf choke and a 220 pF capacitor. In VFO mode, the 220 pF capacitor is bypassed to ground. The switching between these modes is performed by the crystal-vfo switch. If the 220pF capacitor is not bypassed to ground in VFO mode, then the gain of stage V3 will be significantly reduced.

When performing this test, back off the drive control (if grounding the cathode of V3 fixes the problem, you don't want to go from too little drive to too much drive)

[w3jn]

According to the manual, buffer and "OSC" current should be in the 15 and 23 range respectively.  ALso you don't have any voltage drop at the screen of V3 - should be 95, you have 300 ~.  You first need to get R41 right.  Then figure out why there's too little signal at V3 and onward.

Rodger asked above if you had a crystal to check out the osc.  The reason this is would be a good check is that it would rule out the VFO assembly and coupling cap from the VFO to V3 since V3 acts as the osc.   If you have a crystal, try it out.

My prime suspect here would be C22 - the coupling cap from the VFO to the grid of V3.   In any event, a scope wuold make short work of figuring out where you're losing the drive.

[n2ry]

Perhaps a Exorcism is in order here ....

I grounded the grid of V3 -- stilll no joy - grid drive was the same low value

I finally found a xtal, and still the  same grid drive value.

BUFF & OSC current both look to be in the range

I have to run to Rat Shack to get some resistors to make a close to 18k for R41

thanks again to everyone involved here ....
Happy Fathers Day to all ....

Rich
n2ry

[AB2EZ]

Rich

In your last post, I assume that you meant to say "I grounded the cathode of V3..."

Try placing a wire from the left side (on the schematic) of R12 to ground. Also verify that the resistance from the cathode of V4 to ground (after you put this wire in place) is 473 ohms (approximately +/- 10%)

Reason: The cathode of V4 is connected to a 3 ohm resistor (shunt 2: for measuring the cathode current of V4), and then to a 470 ohm resistor, and from there to the operate switch. In phone position, the left side of this 470 ohm resistor should be switched to ground. If the left side (on the schematic) of the 470 ohm resistor is not being grounded by the operate switch, then V4 will not function properly. Since the cathode of V4 is also connected to a .005uF capacitor that goes to ground, the grid of V4 will have a negative voltage on it (because the gird-to-cathode diode of V4 will still conduct)... but V4 will not be able to draw normal screen and plate current on the positive peaks of the signal on the V4 grid.

[n2ry]

Yes - my bad -- I did mean cathode ...

Resistance is 493.2 with the left side of R12 grounded.
Its the same without the ground wire and rotating thru Phone & Tune

[AB2EZ]

Let's check the screen current on V4 in "phone" position, as follows:

1. With the Ranger off, rotate the drive pot so that the resistance between the "300 volt" (hot) side of the pot and the wiper is around 10k ohms. The exact value doesn't matter, just make a note of what it is.

2. Turn on the Ranger, and put it into "phone" position (don't rotate the drive pot)

3. Measure the voltage on the screen of V4 (should be the same as the voltage on the wiper of the drive pot), and measure the voltage on the plate of V4 (should be the same as the voltage on the hot side of the pot)

The screen current is the difference of these two voltages / the resistance of the pot

[AB2EZ]

Also

I'm wondering if there is a problem with the 50pf coupling capacitor between the plate of V3 and the grid of V4.

[The voltage you measured on the grid of V4 (-1.6 volts) is too small for V4 to act as a multiplier. This voltage needs to be around -8 volts DC to bias V4 off... so that the V4 plate current will contain harmonics of sufficient amplitude. On 160 meters and on 40 meters, V4 doesn't have to act as a multiplier, because on those two bands the VFO output is already at the right frequency. On those bands, the grid bias voltage you measured on V4 is probably sufficient to allow V4 to put out enough rf voltage to properly drive the 6146. On 75 meters and 20 meters, V4 must act as a doubler, and it must be biased with something closer to -8 volts on the grid (corresponding to an 8 volt peak rf signal driving the grid of V4)].

Try tacking a separate ceramic capacitor across the existing 50pf capacitor. The value is not critical for operation on the lower frequency bands (160, 80, 40)... so you can use anything between 50 pF and .001 uF (1000 pF)

[n2ry]

I tacked a .00047 across C29
The gird meter on 80m came up I think just a little bit more, I can now adj about 30-35 watts on 80m
But the over all grid drive is still low.

What I did find was this:
R37 reads 36.11K need to replace this one
R41 reads32k still need to replace this one.

[AB2EZ]

Ok

The negative grid bias on the 6146 is the product of the grid current and the value of R37. Since R37 has an actual value of 36k ohms (instead of its nominal value of 27k ohms), in order to get 2.5 mA of grid current you would need to apply an r.f. signal to the grid of the 6146 whose amplitude is slightly over 36,000 ohms x 0.0025 amps = 90 volts (180 volts peak-to-peak).

The multiplier (V4) may not be able to deliver that much voltage on the bands where it acts as a doubler (20 meters) or a tripler (15 meters) or a quadrupler (10 meters).

More important, the target grid bias for the Ranger's 6146 is -67.5 volts (27,000 ohms x 0.0025 amps)... and setting the bias to -90 volts will lower the output power (because the tube will be conducting for a smaller fraction of the r.f. cycle)

Replacing R37 with a new 27k ohm resistor will fix the above problem... but I doubt if that is the entire problem.

Returning to V4:

Plan A: Tack a capacitor (.01 uF or larger) from the cathode of V4 to ground (in parallel with the existing cathode bypass capacitor C34). See if that makes a difference.

Plan B: The multiplier tube (V4) is cathode biased because of the presence of R12 (470 ohms) in the path from cathode to ground. You previously verified that the resistance of R12 is correct. Measure the DC voltage from the cathode V4 to ground when the transmitter is in the "phone" position... and measure (again) the voltage from the grid of V4 grid to ground.  Knowing what those two DC voltages are will provide an estimate of the peak r.f. voltage on the grid of V4. Knowing the voltage between the cathode of V4 and ground will also provide an independent measure of V4's cathode current (cathode current = cathode-to-ground voltage / 470 ohms) 

[n2ry]

I replaced both R41 and R37
I tacked the cap to the grid to grd - not much of a change

I can seem to get more plate current than before.
grid current on 75 and 20 have gone up to around 2ma now.

Output seems to be around 30-35 now.

V4 cathode to ground is 5.30 volts
V4 grid to ground is - 10.1 volts

[ke7trp]

It would seem to me that its time to swap tubes around.  Your are close.. Within 10 watts now..  Mine will load to 60 watts but it is solid stated and has a real hot amperex final tube.

Clark