The counter is a Tenma 72-460 that a friend lent me.? I do not know it's specs,? Yes the 10V is adjusted properly.??

The HP 5385A is a nice counter. It is essentially an updated version of the 5305B and is just a bit more sensitive at 15mV RMS vs 20mV. I have been using a 5305B, which was made in the mid '70's, for at least 15 years and it's still going strong. If it ever dies, I will probably get a 5385A.

开云体育

In that case C1029 is your target. These radios are over 40 years old. If the crystal was on the edge of tolerance to start with it would not surprise me if it has aged out just enough to make adjustment challenging. It does not mean that anything is wrong, it's just old. I would expect that if you are getting stable and repeatable readings on your counter that means its sensitivity is adequate. Pad C1029 with a few pF and see where that gets you.

73,

-Jim
NU0C

On Wed, 20 Mar 2024 15:28:22 -0700
"Bill NZ0T" <nz0tham@...> wrote:

The counter is a Tenma 72-460 that a friend lent me.? I do not know it's specs,? Yes the 10V is adjusted properly.

I found an eBay photo that shows C1029 as a NP0 temperature coefficient. That's what you will want to use if possible for any added cap.

73

-Jim
NU0C

On Wed, 20 Mar 2024 22:04:18 -0500
"Jim Shorney via groups.io" <jimNU0C@...> wrote:

Pad C1029 with a few pF

Progress!? I went all the way back to the 10V setting which had moved to 9.1V for some reason - I can see why the 10 turn pots are a popular mod.? Got the oscillators? and VCXO within spec even the? 8.05 (just barely) without any cap padding.

So now I'm back to the transmitter alignment issues. I can get through the wattmeter null adjustment but the ALC adjustment is still wonky and, possibly because of that, the wattmeter is not working nor will it adjust. Will see what I can do tomorrow.

73, Bill NZ0T
?

Great! I've come to the point that 10-turn pots are a necessary upgrade. Those little trimpots can go off if you look at them wrong. They may have been primo parts in the day but time marches on.

Proper ALC depends on proper operation of the wattmeter circuit. Get the wattmeter working right. It's pretty much the same circuit as a W4. You can disconnect the FWD WM and REFL WM inputs from the ALC board if you want to isolate it, just watch your drive level.

73

-Jim
NU0C

On Mon, 25 Mar 2024 13:56:06 -0700
"Bill NZ0T" <nz0tham@...> wrote:

Progress!? I went all the way back to the 10V setting which had moved to 9.1V for some reason - I can see why the 10 turn pots are a popular mod.? Got the oscillators? and VCXO within spec even the? 8.05 (just barely) without any cap padding.

So now I'm back to the transmitter alignment issues. I can get through the wattmeter null adjustment but the ALC adjustment is still wonky and, possibly because of that, the wattmeter is not working nor will it adjust. Will see what I can do tomorrow.

73, Bill NZ0T

Thanks again Jim,

I wonder if one or both of the AA119 diodes are bad in the wattmeter circuit.? They test OK in circuit with a multimeter but maybe they go leaky with more voltage applied.? Won't be easy to replace tho.? And I doubt they are easy to find tho I think the 1N60 is pretty close.? They are germanium diodes.

I'll try checking voltages in the circuit in the morning.

73, Bill NZ0T

I don't think it really matters a whole lot. the TR7 wattmeter is not what I would call a precision instrument. Germanium was likely chosen for low forward voltage drop. A pair of decent Schottky diodes should work fine.

73

-Jim
NU0C

On Mon, 25 Mar 2024 17:28:39 -0700
"Bill NZ0T" <nz0tham@...> wrote:

Thanks again Jim,

I wonder if one or both of the AA119 diodes are bad in the wattmeter circuit.? They test OK in circuit with a multimeter but maybe they go leaky with more voltage applied.? Won't be easy to replace tho.? And I doubt they are easy to find tho I think the 1N60 is pretty close.? They are germanium diodes.

I'll try checking voltages in the circuit in the morning.

73, Bill NZ0T

Update:? All voltages on U1601 on the ALC board check out fine so I think the ALC board is fine.? Then I checked voltage on R2001 and R2002 on the low pass filter switch board which are the adjustments for forward and reflected wattmeter and ALC. Transmitting in CW I got voltage that varied with the carrier control on R2002 (reflected) but not any on R2001 (forward) which leads me to think that AA119 diode CR2001 is bad.? I hope my logic makes sense.

So looks like I need to replace CR2001 and CR2002 with working diodes.? Searching through my junk box I found two glass case diodes that unfortunately have no markings left.? I tested them with a 10K resistor and 13.8 volts and they showed 13.8V one way and .29 volts the other way which I'm pretty sure means they are germanium diodes.? So now I need to decide if I want to try those or order something that has a known value.? But I think (hope) I'm closing in on the ALC issue!

73, Bill NZ0T

It sounds like you are on the right track. AA119 diodes are available if you look around. Google and eBay turn up multiple hits but caveat emptor. Buy from reputable sellers and avoid anything from China. As I mentioned I think I would use Schottky signal diodes for replacement.



73

-Jim
NU0C

On Tue, 26 Mar 2024 09:20:30 -0700
"Bill NZ0T" <nz0tham@...> wrote:

Update:? All voltages on U1601 on the ALC board check out fine so I think the ALC board is fine.? Then I checked voltage on R2001 and R2002 on the low pass filter switch board which are the adjustments for forward and reflected wattmeter and ALC. Transmitting in CW I got voltage that varied with the carrier control on R2002 (reflected) but not any on R2001 (forward) which leads me to think that AA119 diode CR2001 is bad.? I hope my logic makes sense.

So looks like I need to replace CR2001 and CR2002 with working diodes.? Searching through my junk box I found two glass case diodes that unfortunately have no markings left.? I tested them with a 10K resistor and 13.8 volts and they showed 13.8V one way and .29 volts the other way which I'm pretty sure means they are germanium diodes.? So now I need to decide if I want to try those or order something that has a known value.? But I think (hope) I'm closing in on the ALC issue!

73, Bill NZ0T

I scored some new Semtech 1N60P Schottky diodes from the USA on Ebay.? Should be here by next week.

Should work. I was looking to restock my 1N5711s and found a 250pc spool for 25 bucks. I have a lifetime supply now.

73

-Jim
NU0C

On Wed, 27 Mar 2024 12:05:19 -0700
"Bill NZ0T" <nz0tham@...> wrote:

I scored some new Semtech 1N60P Schottky diodes from the USA on Ebay.? Should be here by next week.

I've been busy with yard projects and a new deck railing but got back to the TR7 today.? I replaced the AA119 diodes CR2001 and CR2002 with new 1N60P which made no difference.? The? meter still deflects below zero and the two adjustments make no difference. The old diodes tested OK in circuit but it seemed worth a try.? So I guess I'll turn my attention back to the ALC board now.

73, Bill NZ0T

I don't think your problem is with the ALC board. You need to find out where the voltage that is causing the meter to deflect downward is coming from. The meter is driven by the wattmeter sensor in transmit and the ACG system of the 2nd IF/Audio board on RX. There is something crossed up on the 2nd IF/Audio board or the associated wiring.

73

-Jim
NU0C

On Tue, 16 Apr 2024 12:48:29 -0700
"Bill NZ0T via groups.io" <nz0tham@...> wrote:

I've been busy with yard projects and a new deck railing but got back to the TR7 today.? I replaced the AA119 diodes CR2001 and CR2002 with new 1N60P which made no difference.? The? meter still deflects below zero and the two adjustments make no difference. The old diodes tested OK in circuit but it seemed worth a try.? So I guess I'll turn my attention back to the ALC board now.

73, Bill NZ0T

The meter works fine on RX and the S- meter adjustment worked perfectly. The problem is in TX where the meter reflects down below zero. In the circuit description in the SM on page 1-2 that there is a variable attenuator consisting of a PIN diode that is controlled by the ALC circuitry. ?The outputs of the forward and reflected wattmeter and the carrier control are summed to create a controlling signal for the attenuator. ?Is the PIN diode and attenuator located on the 2nd IF/audio board? ?I’m too tired to be looking at schematics tonight lol. ?I’ll look in the morning. ?I do think if I can get the ALC working properly the rig should be OK.

The PIN attenuator has no connection to the meter circuit. The forward wattmeter voltage is also fed to a Norton op-amp on the ALC board though diode CR1602 in parallel with a .01 capacitor. This is where the summing happens. There are no negative voltages there. Yes, the PIN attenuator is on the 2nd IF/Audio board but it is in the IF signal path.

Attached is a simplified meter circuit diagram. The meter is connected to the wattmeter sensor and an AGC buffer and referenced to ground via the Meter Zero pot. This is why the +10V adjustment and S-Meter/ACG alignment is done before the wattmeter calibration.

Also worth noting is that there were some production changes done to very early IF/Audio boards. See:



In particular check that your IF/Audio board has the R1112 and R1127 mods if it looks like a very early board. Later boards have these corrections in the board layout. I don't know if this could cause your problem. I have only seen one board that did not have these mods and it was years ago.

As I think I already mentioned at some point, you can entirely eliminate the ALC board from the equation if you disconnect the FWD ALC feed from the wattmeter sensor.

73

-Jim
NU0C

On Tue, 16 Apr 2024 19:26:12 -0700
"Bill NZ0T via groups.io" <nz0tham@...> wrote:

The meter works fine on RX and the S- meter adjustment worked perfectly. The problem is in TX where the meter reflects down below zero. In the circuit description in the SM on page 1-2 that there is a variable attenuator consisting of a PIN diode that is controlled by the ALC circuitry. ?The outputs of the forward and reflected wattmeter and the carrier control are summed to create a controlling signal for the attenuator. ?Is the PIN diode and attenuator located on the 2nd IF/audio board? ?I’m too tired to be looking at schematics tonight lol. ?I’ll look in the morning. ?I do think if I can get the ALC working properly the rig should be OK.

--

73

-Jim
NU0C

Thanks!? This is very helpful!!? Really appreciate your patience with me and my poor technical skills.

73, Bill NZ0T

I just ordered 10 turn pots for the power supply board from Mouser.? Seems that if I just look at the damn things they change so a bit over $35 shipped will be well worth it IMO.

73, Bill NZ0T

You will not regret it. When I do it I measure the existing pots so I can ballpark the new ones before I do the alignment. Makes it a bit easier.

On Fri, 19 Apr 2024 08:55:26 -0700
"Bill NZ0T via groups.io" <nz0tham@...> wrote:

I just ordered 10 turn pots for the power supply board from Mouser.? Seems that if I just look at the damn things they change so a bit over $35 shipped will be well worth it IMO.

73, Bill NZ0T

--

73

-Jim
NU0C