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Valiant Restoration K3MSB




 
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Author Topic: Valiant Restoration K3MSB  (Read 8642 times)
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k3msb
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« Reply #100 on: February 21, 2018, 07:06:41 PM »

I removed my voltage dropping resistor from the solid state replacement for the 6BY5G.

This caused the reading at the downstream side of R50 to go from -225V to -240V.    If anyoneís interested, the current is 34 mA measured directly after the diodes.     Iím not sure where the -265V value on the manual schematics comes from; Iím running the radio at 115V, so maybe it was at a higher line voltage?

I am now able to adjust the modulator resting current to be within spec; 65 mA with the control at the extreme of one side.    This is still concerning, but at least itís in spec.

Drive on 80M is still 5.5 to 6 mA.    I tried another 5763 and got the same results.     I do not have the shunt resistor R56 marked as replaced as out of spec, but I will recheck that.

Someone asked about the LV.   I measured this at J8-4 with the transmitter tuned up on 75M AM

B+ OFF:        354V Key up,  314V Key Down
B+ ON:         345 Key up,    298V  Key Down.  

I will look at making the L6C coil next.
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73 Mark K3MSB
York, PA
k3msb
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« Reply #101 on: February 25, 2018, 08:30:59 PM »

I built and installed L6C as suggested by Clark.

The old and new grid drives are as follows:

Band   Old Grid(ma)   New Grid (ma)  Pwr Out  Drive control
160        8              8                     125           4
80        1.5-2          4                     150           9 (Saturated)
40         4              4                     160           9 (Saturated)
20        0.5-1          6                    160            9 (Saturated)
15         1              4.5                  140            9 (Saturated)
10         2              4                     150            9 (Saturated)

Ip was 400 ma for these tests.   Got dips on all bands.

I not quite sure what's up with 160M;  The aux control was at 10 and the Fine control at 5;  moving them around did very little.  This might be cockpit error on my part.

The manual says 8 mA drive on all bands;  is this really what's to be expected?   Perhaps an increase in L6C?   The drive being saturated isn't good.

The modification to remove the regulator current from the Ip Meter setting was already done to the radio.


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73 Mark K3MSB
York, PA
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« Reply #102 on: February 25, 2018, 09:57:14 PM »

You should be able to get 8mA of drive on all bands with the easiest being 160 and hardest being 10. If the drive stops increasing at some point then you might have a soft 5763 driver tube. I found that this tube needs to be in very good condition. Yeah, I know you tried another one...

The lower output on 160 might be due to the RF coupling/D.C. blocking cap in the plate circuit of the 6146s. Stock, thereís a single 500pF cap but itís become popular to double that up to 1000pF either by adding another in parallel or changing it out.


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KE5YTV
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« Reply #103 on: February 25, 2018, 10:07:51 PM »

I don't think a Valiant is ever fully repaired or restored. It just works a while between repairs. They are beautiful transmitters but I'll never have another. Life is too short.
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Mike
KE5YTV  Dallas, TX
"The longest trip begins with a stop at the ATM."
k3msb
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« Reply #104 on: February 26, 2018, 07:44:31 AM »

You should be able to get 8mA of drive on all bands with the easiest being 160 and hardest being 10. If the drive stops increasing at some point then you might have a soft 5763 driver tube. I found that this tube needs to be in very good condition. Yeah, I know you tried another one...

I don't have another in the tube pile, so I'll have to get some. 

Quote
The lower output on 160 might be due to the RF coupling/D.C. blocking cap in the plate circuit of the 6146s. Stock, thereís a single 500pF cap but itís become popular to double that up to 1000pF either by adding another in parallel or changing it out.

That blocking cap is 2000 pF 15 KV on mine.    I will do some more test on 160 tonight.   I can't see how L6C can make much of a difference on that band,  yet the Aux/Fine controls are set differently after installation.   10/1 (now) as opposed to 7/3 before.    We'll see.... 



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73 Mark K3MSB
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« Reply #105 on: February 26, 2018, 08:05:30 AM »

Itís possible that youíre finals are tuned to a harmonic of the 160M frequency. That band requires most if not all of the available loading capacitance and the AUX control should be on 4 or lower (a bit counterintuitive).

I use AUX 2 and FINE 8 for 1885.

Generally, itís best to start with these controls on the low side and bring them up to increase loading.
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k3msb
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« Reply #106 on: February 26, 2018, 09:49:11 AM »

In CW,  there's a huge difference in the coupling between 160 and 80,  yet not so much for AM.   I was using the CW settings as my testing is on CW ( I don't care to zorch a mod tranny if I don't have to......).

By the way,  what does "coupling" stand for (between the Aux and Fine settings on 160M CW ?   I can no find any references to it in the manual.    This might explain the big difference noted above?


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73 Mark K3MSB
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« Reply #107 on: February 26, 2018, 10:15:10 AM »

"Coupling" and "Loading" both refer to the setting of power transfer to the antenna. For example, minimum amounts would produce a very steep dip in plate current at resonance and low output. Increasing coupling or loading increases the transfer of power to the antenna and the amount of power drawn by the finals. In this transmitter, this is done by reducing the capacitance in the output of the tuning circuit.

The most number of capacitors, greatest capacitance, lowest coupling occur at "0". Lower frequencies require more of this condition than higher frequencies.

"Loading" is referred to in various ways, which can be confusing, which is why the Valiant probably uses "Coupling". There are also historic reasons...

Since CW requires greater power transfer, the settings are higher than they are for AM. The 160/80M CW/AM difference is likely due to the greater amount of capacitance needed for a given change in coupling at lower frequencies.

A frequency counter may show that your 125 Watts is on an 80 meter frequency.
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k3msb
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« Reply #108 on: February 26, 2018, 10:30:09 AM »

I guess I wasn't clear what I was asking;   Table 4 says "Coupling 1" for 160M,  so it's trying to tell me something.  None of the other bands / mode combinations have this notation.    There's no extra controls around anywhere,  so how do I effect "Coupling 1" on 160M without using the AUX and Fine settings?  I assume they put that notation there for a reason.  Maybe that answer is buried in the manual,  but I haven't found it yet.
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73 Mark K3MSB
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« Reply #109 on: February 26, 2018, 11:03:34 AM »

Ah gotcha.

It might have been a typo. After typing that whole manual by hand (1957) the person might have said "fooey", or whatever obscenity was in vogue at the time, and left it.
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k3msb
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« Reply #110 on: February 26, 2018, 08:31:07 PM »

>>I use AUX 2 and FINE 8 for 1885.

I assume that's for AM and not CW?    I'm getting 150W out @450 mA Ip and 8 mA Ig on 1880 CW,  and the inline counter shows 1881.

Tonight I moved the Valiant off the bench and over to the operating position.   I want to use it on the air for a while before deciding what to do next, if anything.

Clark, thanks for all you help!   Stay tuned......

 
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73 Mark K3MSB
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« Reply #111 on: March 15, 2018, 07:05:19 PM »

Well I've had fun playing with the Valiant on  15, 40 and 80 CW.   

I'm noticing a drift on CW;  not a chirp.   I've done the "Johnson VFO chirp frequency jump" mods as per W8JI.

What I'm hearing is that the TX frequency will change between 70 and 110 Hz over about 2 minutes on CW,  with most of the change occurring closer to the start of a CW transmission.

I'm measuring this with my in-line frequency counter.

I've checked for ground issues etc.   Also, I'm not sure if this is "typical" of a Valiant on CW.

Comments appreciated.
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73 Mark K3MSB
York, PA
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« Reply #112 on: March 15, 2018, 09:17:49 PM »

Most likely caused by a rise in temperature within the xmtr due to the average plate currents in the tubes.  Does this drift also occur on AM?
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« Reply #113 on: March 15, 2018, 11:56:32 PM »

Drift is normal as component temperature stabilizes during the first 30 minutes. Do you get additional drift after this period?  Try setting the Oscillator switch to Zero to see if it drifts with just the low level stages energized.
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k3msb
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« Reply #114 on: March 17, 2018, 02:42:42 PM »

The drift occurs on AM.   I just tried it on 7290 into a dummy load;  the frequency increased as I keyed the mic (no audio) and stabilized at +100 Hz after 120 seconds.   The Valiant was on for 2.5 hours before this test.

For the CW tests I was in the Novice Rig Roundup as I figured that would be a good place to try CW on a number of bands in a short amount of time,   and the radio was on for hours before I'd start making contacts over several days.
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73 Mark K3MSB
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« Reply #115 on: March 17, 2018, 02:48:34 PM »

Does the drift occur when the Oscillator switch it turned to "Zero"? This turns on all the low level stages. You might need to put a frequency counter pickup near the driver tank coil.
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« Reply #116 on: March 17, 2018, 11:35:23 PM »

A number of things can cause that drift.  When you key up you add load to the AC line.  This will cause a slight drop in filament voltage.  This will cause a drift.  The added heat from plate currents will cause a drift.

When those transmitters were made nobody had fancy freq counters to see a 100Hz drift.

In my HB xmtr the VFO is on all the time.  The VFO filaments are run from a separate regulated 6.2VDC supply.

Fred
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k3msb
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« Reply #117 on: March 18, 2018, 06:04:30 PM »

I ended up putting a multi-loop pickup coil on top of the 5763.

Started out at 7291.34 and ended up at 7291.31/0 after 120 seconds.

Fred, yes I know we didn't have frequency counters back then, but the drift is noticeable on CW.  My 5100B drifts a bit on CW as well but nothing like this, which is why I was curious if this was just what a Valiant did.
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73 Mark K3MSB
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« Reply #118 on: March 24, 2018, 10:07:25 AM »

Iím still concerned about the modulator resting current.   With R61 at one extreme I can adjust the current to be about 70 volts.    The last time I was on the air I checked and it was more like 75 mA.     

This morning I hauled (ugh) the Valiant back to the bench.

R61 measures 4.9K.    To get 70 mA of resting current, itís adjusted so that the CT to ground reading is maximum.    With all wires connected to R61 thatís about 4.1K.

I disconnected R15 from R61 and the wire from R61 to T4 CT.

R15 is 15K.   

I measure 522 ohms from the disconnected wire to V17-5 and 467 ohms to V16-5 which goes through T4.

R46 is 101 ohms and R47 is 102 ohms Ė both OK.

R50 is 960 ohms, which is OK.

Iím not sure what could be the problem as the resistance measurement look fine.  Iím really considering adding a 1K resistor between the R61 CT and T4 CT  (Clark is cringing at that statementÖ.).

Not the optimal solution, but the radio is playing pretty well now......
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73 Mark K3MSB
York, PA
k3msb
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« Reply #119 on: March 24, 2018, 08:51:30 PM »

Well adding in the 1K did nothing.  In fact, adding in any additional resistance didn't do much.   Probably because the current flow through there is so small.

The manual says I should have -46V on pin 5 of the modulator tubes.    I have -49.7 to yield 70 mA modulator resting current.   If I change R61 to get -46V the modulator resting current is 200 mA !

So, maybe change the 15K resistor to a smaller value to put more drop across the pot?   

Leave well enough alone?   The 70 mA is in range... at the top end.....
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73 Mark K3MSB
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« Reply #120 on: March 25, 2018, 10:10:32 AM »

So there are two issues here: frequency drift and mod bias

Frequency drift: "Started out at 7291.34 and ended up at 7291.31/0 after 120 seconds."  That's with the Oscillator switch turned to "Zero" and the transmitter *not* keyed, right? This is important to confirm.

Mod Bias:  R15?  That's the screen dropping resistor for the RF finals. Did you mean R63? Yes, it should be 15K. Forget the -46 Volts in the manual. The grid current is everything. Check to make sure you have at least -265 Volts at the bias supply (- lead of C93A). I had bad filter caps in a Valiant and that caused low bias voltage.

If all that looks good, gasp, then you could try adding a resistor between R63 and R61 to increase the bias setting range of R61.
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k3msb
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« Reply #121 on: March 25, 2018, 03:40:17 PM »

Frequency drift: "Started out at 7291.34 and ended up at 7291.31/0 after 120 seconds."  That's with the Oscillator switch turned to "Zero" and the transmitter *not* keyed, right? This is important to confirm.

Yes.

Mod Bias:  R15?  That's the screen dropping resistor for the RF finals. Did you mean R63?

Yes.

Yes, it should be 15K. Forget the -46 Volts in the manual. The grid current is everything. Check to make sure you have at least -265 Volts at the bias supply (- lead of C93A). I had bad filter caps in a Valiant and that caused low bias voltage.

If all that looks good, gasp, then you could try adding a resistor between R63 and R61 to increase the bias setting range of R61.

A while back, to address this issue, I removed the voltage dropping resistor from the solid state replacement for the 6BY5G.

This caused the voltage at the - lead of C93A to go from -225V to -240V.    Perhaps decreasing R50 to bring it up to -265V?  I don't see any other way to do that.    The other way would be to leave R50 as is and add a resistor between R63 and R61.



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73 Mark K3MSB
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« Reply #122 on: March 25, 2018, 04:31:16 PM »

R50 should be left at 1k since thatís part of the ďPiĒ filter. Either something is loading down the supply or one of the filter caps isnít right. Is R23 9k? You could also try disconnecting R63 to see if full bias gets you between 50 and 70mA.

I would have also suggested that the shunt wire R59 might be out of spec but the voltage youíre getting from the bias supply is very low, particularly considering todayís high line voltage and the solid state rectifiers.

The next drift test is to compare the bands. 160/80 use a different circuit than 40/20. The two parameters are drift in Hz and % difference between bands.
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k3msb
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« Reply #123 on: March 25, 2018, 07:16:06 PM »

R23 is 9K and all electrolytics are new.

I should have mentioned that I'm running the Valiant at 115V off of a Variac.
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73 Mark K3MSB
York, PA
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« Reply #124 on: March 26, 2018, 12:25:18 AM »

R23 is 9K and all electrolytics are new.

I should have mentioned that I'm running the Valiant at 115V off of a Variac.


That's ok but I would measure the filament voltage at the 6146 and adjust the variac for 6.3vac regardless of the variac output voltage. Doing this will help get the rectified voltages closer to where they should be.
In my experience....the fil voltages are always low when the line is 115vac.
There is always some loss in the line cord and the wiring in the transmitter.
You probably have already checked the line voltage but again....I would set the 6.3vac fil voltage with the variac.
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