help with Dentron MT-3000A tuner

[gungatim]

Hope this is the right forum, but am having a really hard time understanding the watt meters on this thing.

I have been searching the net for quite some time and found a little info, but not enough to try and fix it.

my wattmeters don't appear to do anything. The buttons that are notorious for being sticky/falling out seem to have been clipped by a previous owner, and a single toggle switch installed next to them.

what I can't figure out is which switch is for what, what they are supposed to do, and which meter is for Tx and which is for Rx. the manual doesn't mention what they are for or how to use them.

Assuming I re-wire the original switches (one site mentioned they are SPDT), or replace with proper toggles, what am I supposed to use them for? are both supposed to be on or off?, is one scale 200 and the other 2000? if the buttons are off, is the meter off or just a different scale?

I am really confused. This is my first antenna tuner, and I can adjust it for my dipole wire antenna just fine on receive but can't seem to transmit anything on 40M...so I need the meters to work to see if I am getting power out of my rig or not (suspecting bad final tubes but not sure)

thanks for any help anyone can give with this vintage equipment...

 

[prcguy]

The original push button switches simply selected the 200w full scale or 2000w full scale readings. The top meter shows forward power and the bottom meter shows how much reflected power you have. There is no specific receive function on an antenna tuner like this.

The way I use this type of tuner is turn the two large matching knobs straight up then rotate the inductance switch until you get the most noise coming out of your receiver. Then peak the two large matching knobs for the maximum noise.

Then you can transmit a CW or AM/FM low power signal and adjust the two large matching knobs for the least amount of reflected power. Sometimes you have to go up or down one increment on the inductance to find the best match with various combinations of the two large matching knobs.

Once you tune a few bands you will get an idea of what inductor and matching positions you need for a specific frequency. If my memory is still good the A or B inductance are usually best for the 10m range and the highest letter positions will be best on 160m with the other bands falling in between somewhere.
prcguy

Hope this is the right forum, but am having a really hard time understanding the watt meters on this thing.

I have been searching the net for quite some time and found a little info, but not enough to try and fix it.

my wattmeters don't appear to do anything. The buttons that are notorious for being sticky/falling out seem to have been clipped by a previous owner, and a single toggle switch installed next to them.

what I can't figure out is which switch is for what, what they are supposed to do, and which meter is for Tx and which is for Rx. the manual doesn't mention what they are for or how to use them.

Assuming I re-wire the original switches (one site mentioned they are SPDT), or replace with proper toggles, what am I supposed to use them for? are both supposed to be on or off?, is one scale 200 and the other 2000? if the buttons are off, is the meter off or just a different scale?

I am really confused. This is my first antenna tuner, and I can adjust it for my dipole wire antenna just fine on receive but can't seem to transmit anything on 40M...so I need the meters to work to see if I am getting power out of my rig or not (suspecting bad final tubes but not sure)

thanks for any help anyone can give with this vintage equipment...

 

[gungatim]

thanks, I think I figured out how it is supposed to work, one button is 200/2000w for the Tx and the other is 20/200 for the reflected. wish the manual stated that but found wiring diagrams that indicate how they should work.

problem is, there are 4 wires from the circuit board, ground, clear, red, and black. the clear and ground go directly to the reflected meter and I get nothing.

then a jumper and ground goes to an add on switch that either connects the red or black to the transmit meter. again, I get nothing on that either.

apparently they wired the reflected direct to either 20 or 200 with no switch,

the clipped wires on the meters are green, yellow, and brown as well as clear and ground, which matches nothing....I think the board is fried...

 

[gungatim]

so after more digging and tracing the circuit board, I now realize my assumptions on how the buttons were supposed to work are incorrect, so posting this so there isn't bad info out there....

the schematic I found online shows a 100k pot on the 2nd switch. the factory documentation does not, which led to my confusion (in fact, the factory schematic shows only 1 switch, SW-1, the SW-4 switch does not exist, someone apparently made that wiring diagram up).

the bottom reflected meter is a 200watt scale all the time and not affected by the buttons.
the forward meter is switchable between 200 and 2000 watts, the 2 switches work together, not independently (which is a really stupid setup, no wonder they always broke).

so mine is actually wired correctly, they just don't show anything. I checked the meters with my digital meter and ran a little power through them and they move just fine, so the meters are not bad.

I loosened and moved the circuit board the meters run through and it looks like it was soldered by a toddler. several cold solder joints, one of the tuning resistors is loose and not connected, some broken ground connections, etc. also have the mismatched resisters everyone mentions, so I will be cutting this thing apart to get the board out and do some surgery...hopefully that gets my meters working!

but if not, I only paid $60 for it and it seems to work just fine, so I'm not out much...