| Author |
Message |
    
Cm3885
Intermediate Member
Username: Cm3885
Post Number: 353
Registered: 12-2003
| | Posted on Sunday, April 18, 2004 - 9:35 pm: | 
|
What can be done to beef the supplier up inside the 2990? I had one once that i did some mods to the power supply and it worked out great but i forgot what parts need to be replaced and what parts to use to do the mod. Any help will be appreciated. |
Tech8541
Moderator
Username: Tech8541
Post Number: 171
Registered: 12-2003
| | Posted on Monday, April 19, 2004 - 10:04 am: |
|
replace the passive trans(the big silver ones on the back) with 2n3771's and add a fan. you can also add ballistors (resistors) to balance the output current from each transistor. these power supplies are the only ones i know that do not use this technique. |
Cm3885
Intermediate Member
Username: Cm3885
Post Number: 354
Registered: 12-2003
| | Posted on Monday, April 19, 2004 - 1:03 pm: |
|
Ill see about replacing the passive transistors(i replaced them on my old 2990 and it seemed to work pretty decent) and the radio already has a fan on the back..
TY for the help 8541!!! |
Cm3885
Intermediate Member
Username: Cm3885
Post Number: 355
Registered: 12-2003
| | Posted on Monday, April 19, 2004 - 1:34 pm: |
|
Another question i have doesnt regard the power supply but involves the replacement of Q51 2sb754 with a 2sb817 and replacing Q53 with a 2sa473 or equvalent. Is is mod recommended in the RCI 2950 chassis? |
Kc0gxz
Advanced Member
Username: Kc0gxz
Post Number: 756
Registered: 3-2003
| | Posted on Tuesday, April 20, 2004 - 12:03 am: |
|
Cm3885
Yes it is.
As a matter of fact, is was the 2950 and 2970 that this modification was originally intended for.
Usually, when anyone removes Q-32 (modulation limiter), it usually destroys audio quality on SSB. It also disables VR-12 (SSB ALC) and variable power for SSB. Also it makes the voltage regulators work harder especially on SSB. A good indication if this is a lot of bulb dimming on SSB.
To stabalize SSB regulation, it is recommended to replace Q-51 with a 2SB688 or a 2SB817. The original 2SB754 is a 60 watt 7 amp power regulator. The 2SB688 is a 80 watt 8 amp regulator and the 2SB817 is a 100 watt 12 amp
regulator. The 2SB688 is ok, but the 2SB817 is best.
Also, replace Q-50 with a 2sa1012. This will let the 2950 breath easier and will sound cleaner and run much cooler.
Jeff, kc0gxz. |
Cm3885
Intermediate Member
Username: Cm3885
Post Number: 356
Registered: 12-2003
| | Posted on Tuesday, April 20, 2004 - 1:06 pm: |
|
I know about replacing Q 51 and Q 53 but were is Q 50 located in realtion to the other two aforementioned???? |
Bullet
Intermediate Member
Username: Bullet
Post Number: 317
Registered: 7-2003
| | Posted on Tuesday, April 20, 2004 - 7:18 pm: |
|
Jeff good post.
its in front of the 2sb754. or right to the right of it if the radio's front is facing you. youll see it its real close. |
Kc0gxz
Advanced Member
Username: Kc0gxz
Post Number: 765
Registered: 3-2003
| | Posted on Tuesday, April 20, 2004 - 8:48 pm: |
|
Cm3885
I'm sorry. I meant to say Q-53 instead of Q-50. My mistake. But don't worry, I make them all the time and I'm pretty good at it.
Jeff, kc0gxz.
|
Cm3885
Intermediate Member
Username: Cm3885
Post Number: 358
Registered: 12-2003
| | Posted on Wednesday, April 21, 2004 - 1:05 am: |
|
LOL, OK Jeff ill overlook it this time! ;-) TY for the info guys.... I guess ive got some radio work to do this weekend. Ill post on hre how it went! |
