Print Page - Ranger Grid drive problem

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

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

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.

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

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

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

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?]

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)

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.

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.

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

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)

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)

V4 grid to ground appears to be much higher now, for some reason (unless there was a typo before): currently -10.1 volts, previously -1.6 volts. I'm wondering what might be the reason for that change. I suspect it is because you don't have the drive control fully clockwise... as you did before... and, therefore, the voltage from cathode to ground is lower than it was before (even though you didn't measure it)... because the screen voltage on V4 is lower and, as a result, the cathode current of V4 is lower.

The V4 cathode to ground voltage of of 5.3 volts seems about right. This implies that V4 has an average (DC) cathode current of 5.3 volts / 470 ohms ~ 10 mA.

Since the DC voltage between the cathode and the grid of V4 is 5.3 volts - (-10.1 volts) = 16.4 volts... this implies that the rf signal driving the grid of V4 is now 16.4 volts in amplitude (32.8 volts peak-to-peak). This seems reasonable.

I agree that everything looks a lot better now. If your output on 40 meters is okay, then I think you should try a different 6CL6 for V4 (you don't need the multiplier tube V4 to act as a multiplier on 40 meters because the VFO is already putting out 7 MHz on 40 meters). At this time, the input rf signal on the grid of V4 seems high enough, and the output of V4 appears to be marginal.

The difference between 2 mA of 6146 drive current and the specified 2.5 mA of 6146 drive current corresponds to only a 25% increase in the r.f. output voltage of V4 at the frequency of operation.

Just to be sure that the problem isn't in the clamp tube (drawing grid current even though its grid voltage is -67.5 volts):

a. Disconnect the existing lead that is connected to the grid of the clamp tube (pin 7).
b. Insert a resistor between the disconnected lead and the grid of the clamp tube, having a value between 1000 ohms and 10,000 ohms (whatever you have on hand)

Turn the rig on in phone position, and measure the voltage across the resistor you inserted. The voltage should be zero, because there should be no current flowing into the grid of the clamp tube.

Stu

Also

Check to make sure that the 50 pF capacitor between the plate of V4 and the grid of the 6146 is ok. You can do this by tacking a capacitor across the existing 50 pF capacitor, having a value of between 100pF and .001 uF (or larger, if you don't have anything in that range). See if this has an affect on the obtainable grid current on 80 meters.

When you use the buffer control to peak up the grid current, do you get a sharp peak (indicating a high Q in the tank circuit at the output of V4). Check to see if there is more than one peak by rotating the buffer control through the complete 360 degrees.

sorry for the delay in getting back in.....

not paying to much attention to the grid drive ...
I can get about 40 watts out on 160,75,40 & 10
20,15 are pretty much dead ( grid & output)

grid is almost 3 on 160 , 2.5 on 75 and 2 on 40m
virtually 0 on 20 & 15
1-1.25 on 10

I left all the caps in except for the coupling between V4 & 6146, it didn't make any difference
I have it on the air presently on 160m --- they say it sounds good.

Thanks Stu and everyone else who helped ....
now to figure out the 20&15 ... buts it working again

I also changed out C52 to a .01 from a 500pf

Rich
n2ry

Hello Rich

I'm wondering why the screen voltage of V3 (314 v) is Higher than it's plate voltage (283 v) and also V4 has it screen voltage (289 v) is Higher than it's plate voltage(283v)?.

from the manual ,typical operating data and trouble shooting V3 has 310 v plate voltage and 95 v screen voltage
V4 has 310 v plate voltage and 185 v screen voltage.

since from your measurement the plate voltage is 222 v ,it means that the plate current is to high,and the screen current is to low,it can happen when the tuning is not right /out of tune,so it takes more current,automaticly when the plate current is high ,the screen current gets low and the screen voltage get higher (314V)since it was drop by R 8( V=I x R) from the B +(339 V) ,so maybe there' something wrong with the tuning circuit L5 and R 10,

Since the screen voltage is higher than it's plate voltage ,the tube don't work normally ,maybe it can damage the tube,

Regards

Gito.

Are you POSITIVE you are tuning this correctly? Not meaning your ability.. but that the knobs are aligned correctly? I used my ranger yesterday and was thinking about what your problem is. I could tune on each side of the caps and get different power outputs.

Mine does 65 watts Carrier on 75 meters on the bird into a dummy. It cant really be loaded less then 50. I can run my Grid current way up if I wanted. In order to get it down to the 20 watts I needed to excite my transmitter, I had to roll the grid down so far the plate shot up and then as I lowered it down further the plate current finally went down.

Hope you figure it out!

Clark

Rich

Some of the caps that I asked you to tack across existing caps were okay to install for doing these tests, but they will cause problems on the higher frequency bands. The caps that you need to remove, if still present, are the caps I asked you to tack across the existing 50 pF inter-stage coupling capacitors. This would be particularly true for the inter-stage coupling capacitor between the output of V4 (the multiplier stage) and the input of the 6146.

I am still wondering why V4 doesn't seem to have the ability to produce its proper output. [Operating the rig with the "Buffer" control fully clockwise (or nearly so) for long periods of time is likely to damage V4... due to excessive screen current and excessive plate current. Therefore, it is still important to find out why the output of V4 is low for typical buffer control settings]

a. Make sure that the shield grid (pin 7) of V4 is grounded.
b. Tack a capacitor of value .005uF or larger from the screen grid (pins 6,3) of V4 to ground (across the existing .005uF screen bypass capacitor)

If the above has no effect, also try temporarily lifting the ground side of C85 (10 pF) to see if it is "leaky".

Stu

halo Rich

Looking at the schematic diagram,V3 is operated as an automatic bias,which G1 min bias is depended on the drive of the VFO or the excitation of the tube if used as an oscillator,without this drive there's no min bias, the screen voltage will soar up to the plate voltage and the plate current will be high.

looking at the screen voltage and plate voltage /plate current of V3,there's an indication there' a small/very small drive ,so the automatic min bias is to low. So V3 operate with high screen voltage(no/small screen current) and since it has no/little "min bias" the plate current is high(not caused by RF drive) and has a small/little RF output.

If you look at the schematic, the VFO output(6AU6) is coupled via C 22(300 pf) and in series with C 23 (22 pf) to G1 of V3 (if I'm not mistaken).

When V3 is operated as an oscillator C 23(22pf from G1 to kathoda of the tube,caused by SW2) working with C 24 (200 pf)in series with c 30 (0.005 by pas C ) as part of the exiting control of the tube (grid plate oscillator)

So may be C23 (22pf) is damaged or not soldered correctly,or SW 2 is damaged.
I believed that the trouble is in V3 .

V4 has a protective bias caused by R 12 (470 Ohm) ,when there's no/little drive it limits the plate current ( R12 x plate current makes the bias) .So even as the plate current is high,it's not because of the RF drive. But because the operating type of the tube.(class A amplifier),

With little drive of course there's a small RF output,and the screen voltage of V4 adjusted by R 13 has little effect on the RF output.

Regards

Gito.

Thanks for all the latest feedback ....
I know I still have issues, but I just wanted to put it on the air quickly and see how it went, now I know that I got a the thumbs up from 2 different stations, I'll continue the troubleshooting.

Again I really appreciate the assistance here, everyone here has taught me much over the last week.

And I will continue until its all correct.

I will continue on it tonight...

Also I need to stock up on some parts again too.

thanks again and I will check the recommendations that were mentioned

Rich

Hi

Sorry when I wrote my replies I looked at the old version Ranger schematic,that you used the key to make the cathoda of the oscillator and buffer on and of to ground.

After looking the new version of the ranger schematic ,it used min bias with 12AU7 as the min bias Keyer,so when it's in of position ,the min bias iis supplied to the grid of V1,V3 and V4 via R net work which is connected to pin 7 of 12 AU7 (control Grid),to minimize /cutoff the plate current of V3,and V4 and make V1 not operating.

When you keyed the transmitter the pin 7 of 12AU7 is grounded ,that makes the min bias of V1,V3 and V4 zero ,because R 43 connected to pin 7 is grounded.

So the min bias that is developed when You keyed the transmitter is a product of Rf drive and depended on the Rf voltage .Low min bias is because of low RF drive.also Low Rf output of the tube.

Looking at the screen voltage of V3 ,thats high (310v) that means the Rf drive is to small since if only 1 ma flows in R6 (68K)caused by the Rf drive. the screen voltage will drop by 68 v =240 v.
You can used the screen voltage of V3 as an indicator ,when the Rf drive is high the screen current is higher ,so the screen voltage is lower.

It can also caused by an weak tube (V3).
So I still believed the trouble is around V3 and its wiring.

Regards G

Gito

Hi Rich

After reading again your treatment of your transmitter ,I overlooked that You wrote That R41 has changed it"s value to 32K ,ohm and you changed it back to 18 K,after looking the schematic diagram again R41 has a role to set the protecting min bias of V1 (VFO) via the half part of V13(12 AU7) which make V1 not running/off when the KEY is off ,When the KEY is On the Grid min bias of V1 is supposed to be of/zero volt .But because R41 has changed it's value,maybe there still a min bias on V1,and changed the operation of V1.
So after you changed R41 ,the VFO gets higher output,drive V3 and gets more RF output that makes the grid V4 - 10V , higher than before.(-!,1V)
In the old version Viking Ranger Schematic, the end of R1(100k) that's connected to the plate/pin1 of 12AU7/V13(in the new version viking ranger) is directly connected to ground.(old version)
Try to jumper this End of R1 to ground on phone operation.
Maybe the power output i of the transmitter increased.

Regards

Gito

PS sorry for my English

OK - sorry for the delay .... since I've been away for a few days, I decided to start anew here.

I've taken voltage measurements on V3 and V4 in 80m & 40m, in STANDBY and PHONE mode.

I can get about 40 watts out , plate current just under 150ma.

PIN V3 40m V4
--------------------------------------------------------
STND PHONE STND PHONE

1 (cathode) 0 .06 .19 8
2,9 (grid) -29.9 -2.12 -39 -.69
3,8 (screen) 335 103 243 190.6
6 (plate) 339 230. 340 303.5
7 (suppres) 0 0 0 0

----------------------------------------------------------

PIN V3 80m V4
--------------------------------------------------------
STND PHONE STND PHONE

1 (cathode) 0 0 -0.5 8
2,9 (grid) -30 -15.6 -30 -5.3
3,8 (screen) 336 125.1 336 92
6 (plate) 339 303.6 339 223.3
7 (suppres) 0 0 0 0

----------------------------------------------------------

Rich
n2ry

Rich.

Looking at the data/speck you gave for 80 meter band , it seem that your transmitter is okay, why don't you try to turn the wiper of R13 (25k variable potentiometer) to boost the screen voltage of V4,with a higher screen voltage you get more RF output from V4.

Have you changed R 37 to its original value /27k ,because it has an influence to the clamp tube,which also control the screen voltage of 6146 , with enough drive and a higher screen voltage ,the transmitter will get a higher power out put.
check also R15 is it still 30K ,
have you peak the grid current of V4 by tuning L3,and tuning C7 to peak the 6146 grid current ?

Regards

Gito.

Rich
Gito

Hi! I will try to make further suggestions that complement those of Gito... and I will let Gito take the lead in providing advice.

Two comments

1. I am concerned that your voltage measurements are not "accurate" because the meter you are using: a) disturbs the circuit when r.f. is present (due to the capacitance of the meter to ground) and b) is, itself, disturbed by the presence of high levels of r.f. at its input.

Note, for example, that the input capacitance (grid-to-cathode+screen) of a 6CL6 is about 11pF, and the capacitance added by the meter and its leads may be much larger than that.

This may lead to errors in your table of measurements that are making it harder to diagnose the problem

Suggestion: make up a probe that looks like the attachment to use in conjunction with your meter.

2. Why is the amplitude of the r.f. input voltage to V3 (as determined from the negative DC voltage between the grid and the cathode of V3) so much smaller on 40 meters than on 80 meters?

Possible reasons:

a) The voltage reading is wrong, for the reasons stated above (possible, but not my first choice)

b) There is an amplified 40 meter r.f. signal (from the transmitter output itself) being coupled into the the grid of V3 when you make the measurement (possibly being picked up by the leads of the meter). The reason this effect would be much bigger on 40 meters than on 80 meters is because the signal at the output to the VFO on 80 meters is at half the frequency of the rf output of the transmitter (160 meters). On 80 meters, V4 acts as a doubler. On 40 meters, the output of the VFO is at the same frequency as the output of the transmitter. Therefore, if you couple some of the output of the transmitter into the grid of V3 when you make the measurement, the effect will be much smaller on 80 meters.

Suggestion: use the circuit shown in the attachment for making the measurements. This will significantly reduce the r.f. that is coupled into the grid by the leads of the meter.

hi
Stu and Rich.

It's true what Stu wrote that RF voltage disturbs the voltage reading of the transmitter,it just cross my mind.
I used to measured RF voltage of transmitters that used fixed bias with RFC that is connected to the grid of the tube with a resistance in parallel with the min bias,with is bypassed for RF, before drive and after it's drived .calculating /measuring the voltage ,so we can know the grid current(Rx I).

looking at the schematic that used no RFC in the grid circuit ,it.s true what Stu wrote. We can't directly measured it,We must used an RF probe,like Stu wrote.or change the 100 k resistor with a RFC.

Yes,it's wrong to measured the voltage of control grid of V3 and V4 directly ,but actually we can "measured" it by looking at the Meter that shows milliampere of the kathoda 1 and Kathoda 2,if the RF drive is relative the same at all bands .the kathoda meter must show a relatve same current.
We can also see the grid current of the 6146.If the RF drive is relative the same,we must get a relative same grid current at all band.

we can also measured the Screen grid of V3,V4 and 6146(with a high impedance volt meter) directly since its was decoupled for RF with C to ground.
With higher RF drive to the tube ,the screen current is high ,so the screen voltage must be lower than the screen voltage with lower drive ( lower screen current) because the screen voltage (300 v-(R x I screen).

Maybe V1 the VFO is at fault ,since the 80 meter band used a different LC circuit than the 40 meter band.Maybe SW 1 is at fault.

Stu can we used an external Rf generator and inject it to C 22 (coupling C to grid 1)and temporary disconnect the conection to R6 and L2 and pulled V1 out.SW 2 is set to VFO,just to prove if V3,V4 and 6146) works well.
and SW3 is set to the RF band we inject.

Regards

Gito.

Ps sorry for my English

Gito

Your English is a lot better than the English of some of the US-born students I know. Anyway, I can't speak any other language... so I won't complain.

Yes, as JN has pointed out, this would be a lot easier if we had it in a shop with test equipment like a scope and an external rf source.

Rich has one or more crystals... and by running the rig using a crystal he can compare the behavior of the rig v. using the VFO. I have to look back at the thread, but I know he tried this at least once, and didn't see any difference... but maybe he can try it again with a 40m crystal.

The grid inputs of V3, V4, and the 6146 make nice r.f. peak detectors [(cathode voltage to ground) - (grid voltage to ground) = peak r.f. input signal], provided the peak rf input signal is larger than the DC cathode voltage-to-ground.

Rich could also turn his DC voltmeter into an r.f. peak detector by using the circuit in the attachment.

Stu

This is an interesting puzzle.

[As an aside, in standby, the grid voltage on V4 is probably -39 volts on 80 meters... just as it is on 40 meters. From the schematic, in standby, the grid voltage on V3 should be approximately 0.75 x the grid voltage on V4... and that was what Rich measured on 40 meters. This is probably just an error made in filling out the table or making the measurement]

In standby, the screen voltage on V4 will be determined by the setting of the drive potentiometer. From the table, Rich must have had the drive potentiometer fully clockwise when he made the measurements on 80 meters, and about 70% of fully clockwise when he made the measurement on 40 meters.

It is clear... even considering the effect of making the grid and plate voltage measurements, in the phone position, with a DC voltmeter (unless one fabricates some kind of an r.f.-blocking probe)... that V3 just isn't putting out anywhere near enough r.f. voltage in the phone position.

Possibilities:
a. The r.f. plate load on V3 is too low. The plate load on V3 is different on 80 meters than on 40 meters. On 80 meters there is an extra 4.7k ohm resistor in series with the the plate load inductor. This 4.7k ohm resistor is shorted out by the band switch on bands above 80 meters. [The label on my copy of the schematic is blurred... but I think it is labeled R9].
I am wondering if there is something wrong with the inductor L5 or the 33k resistor R10. For example, could the actual value of R10 be much lower than 33k? Could there be some other low resistance or some capacitance bypassing L5 and thus making its impedance much lower?

A suggestion... take a good look at L5. Make sure that there is nothing shorting out any of the turns of L5. Disconnect one end of R10, and make sure its resistance is reasonably close to 33 kohms (+/- 20%)

Stu

V3 is driving the input capacitance of V4 plus whatever stray capacitance is associated with the wiring etc.

If one assumes this is a total of 15 pF, then the impedance across the output of V3 associated with the input of V4 is

on 75 (3.885 MHz) meters: 2731 ohms
on 40 meters (7.290 MHz): 1455 ohms

Now, in order to keep the total load impedance across the output of L5 high enough to produce the required output voltage from V3, Johnson used L5 (in series with 4.7k ohm resistor R9 on 160, 80, and 40 meters*) to add some inductive reactance in parallel with the input capacitance of V4.

If the inductance of L5 is way off (v. Johnson's design intent), i.e. too small an inductance, then the total output load impedance on V3 will be too low, and its r.f. output voltage wll be too low.

So...

L5 is shown as an adjustable inductor. Try adjusting the tuning slug to see if if has too little inductance (the tuning slug may be too far out).

Stu

*Note: Correction to my earlier post: looking at the band switch more closely, it does not remove the 4.7k ohm resistor that is in series with L5 (i.e. it does not short it out) on 40 meters. It removes it on 20 meters and above. Therefore the 4.7k ohm resistor is in series with L5 on 160 meters, 80 meters and 40 meters.

Hi

After reading again the first Question from Rich,I again overlooked one thing,Rich wrote that 160 m has 3.5 ma grid Current(6146) 75 m has more than 2 ma, 40 m-1.5 ma,20 m-1-1.5 ma,10 m-2 ma,
When Rich swap tubes (V3 and V4) - 160m has 3 ma,75 ma ,20 m --are virtually none.

So after swapping tubes Rich had less Grid current,that means one or both tubes is weak.
Try to used new tubes.

Looking at the operating data in the manual it Needs only 2.5 ma grid current(6146).
looking at the first Rich data --160 m has 3.5 ma grid current ,it's more than enough,
So at the first Setting (tubes has not been swap) V3 (oscillator/buffer) is good enough,
I supposed that V4 is weak,if you changed it with anew tube ,I bet the grid current is higher.
I"m sure that one ,or both tubes are weak ,seeing the difference of the grid currents after swapping.

It' good to replaced all the resistors to it's original value.
And I'm curios ,like Stu wrote that L 5 is a adjustable inductor,first try to peak the Grid Current (6146)by adjusting L 5 ,especially on the higher frequencys( 20 m -15 m band),and after that re tuned C7 (V4) looking at the highest grid Current(6146)(step by step) ,don't stick to Dial setting manual,it can vary with actual setting,just tune and try to get the highest Grid current, later if the grid current is to high you can lower it to 2,5 ma , by reducing the Screen voltage of V3 by R13 ,variable pot.
Output tuning .it's a pi network that used C 9 as a loading cap,and C8 as the resonance /dipping Cap.again don't stick to the manual,Because it depends on the load,the SWR and also the tube conditions (good ,weak, bad ),

C 9 is the loading Cap, by opening and closing it you can vary the loading of the tube. So by opening (less Cap) or Closing (more cap) and than dipping the plate current of 6146 by opening (more cap) and closing it(less cap) of C8) till you get the plate current you want(at resonance,at the plate current dip),you get the power output you want. Usually less' cap (C9) gives a higher ,power output .
,High plate current (6146) did not automatically produce high power output, if it is not properly resonated ,we got high plate current and less power output.(out of tune)
So don't stick to the manual dial setting.

Regards

Gito

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THE AM BULLETIN BOARD => Technical Forum => Topic started by: n2ry on June 17, 2009, 10:32:25 PM