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Mrt4d
New member
Username: Mrt4d
Post Number: 4
Registered: 8-2005
| | Posted on Wednesday, September 26, 2007 - 2:00 pm: | 
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President dwight d 858 chip, I want to add variable power! |
Penrider
Intermediate Member
Username: Penrider
Post Number: 215
Registered: 1-2007
| | Posted on Tuesday, October 02, 2007 - 6:29 pm: |
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The dwight d is an am only radio, but otherwise identical to the 858 washington. I just Un-Installed variable power from one. Ensure you have done a full alignment of the tx power chain first, Very Important!, then Substitute a variable ohm pot in place of the AM power adjustment. The Main output power adjustment is L15. A combination of L15, L12, L11 is required for a full alignment. Make sure you Use L15 for your variable power location. Also, make sure you use an Identically valued VR pot to subsitute or your tuning will go crazy. That was why I had to Un-install it from the radio I just bought.
Sean
CEF867
Two tin cans and a string, it's still a contact...BTW, I need my can back when we're done!
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Road_warrior134
Intermediate Member
Username: Road_warrior134
Post Number: 139
Registered: 12-2006
| | Posted on Wednesday, October 03, 2007 - 6:30 pm: |
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DO NOT remove L15 as this is a vital part to the output impedance of the radio instead find the VR(Variable Resistor) possibly marked AM POWER , as I do not have a schematic for that radio I cannot tell you the VR number but someone out there might know it , these VR's are usually 50k so replacing the VR with a front mounted pot of the same value would give you variable power on the front of the radio , is there any specific reason WHY you want variable power on the Dwight D ???
JIM
Road Warrior134
CEF#858
HAM#230
CVC#116
Wavin' a hand at ya' fae Scotland 
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Penrider
Intermediate Member
Username: Penrider
Post Number: 216
Registered: 1-2007
| | Posted on Friday, October 05, 2007 - 12:29 pm: |
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In the last three Dwights I've worked on the AM Power adjustment has been L15 in conjunction with L12 and L11. I've never even seen one that had a separate vr for am power. If there is, it's not marked on the board, the schematic, nor any of the mod lists. I don't just start turning pots to see what they do. So if someone knows of it for sure please let me know. Yes, The L-series are Vital to the radio, which is why I said to use an Identical Value Replacement. Basically just moving it from the board to the radio face. The typical power output vr is the proper/preferred way, but since I don't know what or where it is I suggested an alternate method.
I'm not sure either why someone would want var. power on a low-power am only radio.
Sean
CEF867
Two tin cans and a string, it's still a contact...BTW, I need my can back when we're done!
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Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2618
Registered: 9-2004
| | Posted on Sunday, October 07, 2007 - 1:20 am: |
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penrider,
L15, while it does affect the output power; is not an AM power control.
it is an inductor, and has a certain spot where it resonates best.
thats why this adjustment is "peaked" instead of turned up to max.
it is not possible to move this part up to the face of the radio, as it adds all kinds of stray inductance.
also, when this part is tuned to anywhere but the sweet spot, the impedance of the radio is off.
sorry Mrt4D,
you cant add variable power to an AM radio in this way.
there may be a way, but it will involve a swing kit like is used on the 25/29 series cobra radios.
ive never heard of someone adding a kit to an old AM only 858 chassis, but thats not to say its not possible.
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
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Penrider
Intermediate Member
Username: Penrider
Post Number: 217
Registered: 1-2007
| | Posted on Monday, October 08, 2007 - 12:00 am: |
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KV and Jim, you have me there. I wasn't Positive about L15 being possible. But, since like you stated, it requires a "swing kit" to achieve var. power normally I thought that L15 may do it. The swing kit is what I had to remove from My washington and from the dwight d. I recently repaired. The washington has of course an AM Power adjustment. I've honestly never been able to find it on the dwight d. or PC-33 which are very similar.
Sean
CEF867
Two tin cans and a string, it's still a contact...BTW, I need my can back when we're done!
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Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2621
Registered: 9-2004
| | Posted on Monday, October 08, 2007 - 12:28 am: |
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you wont find an AM power control in any AM only radio.
SSB TX circuits are very different beasts.
later,
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
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Ccwaters
New member
Username: Ccwaters
Post Number: 1
Registered: 10-2008
| | Posted on Friday, October 10, 2008 - 5:56 am: |
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Vicious is correct there is no AM power control in most of the AM only radios, that includes the Dwight D. There is an old Mod called Super-talk which consists of a few simple to obtain parts which works quite well to add an effective variable power set up. If you Google "Tip 120 super talk" you'll come up with simple instructions for putting one together and installing it. |
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