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A Receive Pre-Amp you can build!
- Thread starter Dmans
- Start date
IMHO the RF gain knob has to be one of the most underrated functions on a radio, learning how the RF gain, squelch and volume work when all set to work together can do wonders for your receive.
Dmans , we all have our opinion , but it some cases it's a button you just have to push ! Like the time brother told me on his new Camaro SS " Don't push that button " ( I was driving ) My response was , Why ? " It's the traction control you won't be able to hold on to this car , He said . Guess what I did ..... !
I believe Workman makes that or is selling it. A month or so ago I was placing an order with the wholesaler I deal with and saw these things. So I figured they might have a use and maybe I could make a buck off them. So I ordered a few and they came in, tossed them in the corner and hadn’t thought more about it.
Came across this thread and tried one out in a Galaxy. I can’t get it to work. The directions say to remove C43 and install the wires in the vacant holes. No matter which way I swap the wires, I lose all receive. I cut the heat shrink off and it’s exactly what’s pictured in this thread.
My wholesaler is reputable and they’re new pieces. While my sanity is questionable, I’m pretty sure I haven’t goofed up connecting it. So what gives that it won’t work?
Came across this thread and tried one out in a Galaxy. I can’t get it to work. The directions say to remove C43 and install the wires in the vacant holes. No matter which way I swap the wires, I lose all receive. I cut the heat shrink off and it’s exactly what’s pictured in this thread.
My wholesaler is reputable and they’re new pieces. While my sanity is questionable, I’m pretty sure I haven’t goofed up connecting it. So what gives that it won’t work?
It is, on my service monitor it receives fine down to about -120. It’s a 77 I’m fooling with but there’s a bunch more in the shop I could try it in. All of them listed for a Galaxy day the same capacitor, so idk.
Ok, is there a silkscreen?
If you read the posts I made earlier in this thread - they may have inadvertently reversed the transistor pinout - the silkscreen may be in reverse to the part...and you may have "blown" the transistor if it was installed backwards.
Else it may be too strong in power signal being applied it swamps out L6 "quadrature" pre-selector coil.
IF a receive mod has already been done to the radio - this insert may not work...
If you read the posts I made earlier in this thread - they may have inadvertently reversed the transistor pinout - the silkscreen may be in reverse to the part...and you may have "blown" the transistor if it was installed backwards.
Else it may be too strong in power signal being applied it swamps out L6 "quadrature" pre-selector coil.
IF a receive mod has already been done to the radio - this insert may not work...
Then Houston, we have a problem...
Well, my guess is the pinout is way different - I thought these things were supposed to be standardized - this latest PDF shows different...
So, locate the junction of your input cap, the one that takes up from the board...D1 (Diode's Banded side) and the 6.8K resistor - where the three parts have leads that meet up , merge - heads off to Q1 - it should be the base lead of that transistor...
Note the leg it goes to - with the part mounted and numbered face of Q1 facing you - Is it on the Left - Right or Center leg?
Because as shown in another graphic of the same part from a NEC - the Part is ECB - but in the photo PDF above is EBC with BASE in the middle...
So there's our quandary...
Well, my guess is the pinout is way different - I thought these things were supposed to be standardized - this latest PDF shows different...
So, locate the junction of your input cap, the one that takes up from the board...D1 (Diode's Banded side) and the 6.8K resistor - where the three parts have leads that meet up , merge - heads off to Q1 - it should be the base lead of that transistor...
Note the leg it goes to - with the part mounted and numbered face of Q1 facing you - Is it on the Left - Right or Center leg?
Because as shown in another graphic of the same part from a NEC - the Part is ECB - but in the photo PDF above is EBC with BASE in the middle...
So there's our quandary...
No receive mod done to the radio. I guess I could remove the 1675 and check it with the peak atlas and see if it’s blown and/or its pinout.
It would be a shame to see all those RF amp mods "kits" - all "Dead" due to pinout problems on the part that makes them go...
WOW...
WOW...
I’ll post pics of mine later, pull the transistor out and check it with the Atlas and post my findings. I was only trying it out just to see if it was worth a dang.
I think I’ll try it in another radio too. On this one, there’s that “super ears” mod where you add a 1.5k resistor to D7. I tried that before on another 77 just for fun and it actually did make the receive louder, don’t know about actually pulling in weak signals. However, on this one, it actually killed down the receive. Just thought of that, I’ll try another radio after I test that lil’preamp.
I think I’ll try it in another radio too. On this one, there’s that “super ears” mod where you add a 1.5k resistor to D7. I tried that before on another 77 just for fun and it actually did make the receive louder, don’t know about actually pulling in weak signals. However, on this one, it actually killed down the receive. Just thought of that, I’ll try another radio after I test that lil’preamp.
Well that’s what I did. I set the service monitor up and at -120 without the preamp installed you could hear the tone fine.
Removed C43 and installed the preamp. You couldn’t hear the tone. I can’t recall if I increased the signal or not, a lot going on right now and my memory is cloudy.
Reversed the wires, just to make sure, no tone.
Removed the preamp and put C43 back in place and there’s the tone again. The radio receives fine, so it’s not the radio. The instructions list a green and orange wire which is actually a green and yellow wire. I’m sure Andy is in to something about the reversed leads/pinout of the transistor. I haven’t had time today to get in the shop and test the part yet.
Removed C43 and installed the preamp. You couldn’t hear the tone. I can’t recall if I increased the signal or not, a lot going on right now and my memory is cloudy.
Reversed the wires, just to make sure, no tone.
Removed the preamp and put C43 back in place and there’s the tone again. The radio receives fine, so it’s not the radio. The instructions list a green and orange wire which is actually a green and yellow wire. I’m sure Andy is in to something about the reversed leads/pinout of the transistor. I haven’t had time today to get in the shop and test the part yet.
- No one is chatting at the moment.
