• You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
  • Notice: You may not use this site to facilitate the unauthorized selling of copyrighted material including, but not limited to, in the public dxForums, dxGallery, dxChat and private messsages. If you get caught doing this, you will be permanently banned with no second chances. A notice will be placed on the site of why you were banned and any information collected by this site about you will be made known to the copyright holder.

28 volts pills

Alexis Mercado

Well-Known Member
May 17, 2016
232
133
53
46
Hi. I am looking for 28 volts pills. What number should they be ? I am planing to replace my 4 pills 2SC2879 for ones rated at 28 volts. Any suggestions ?
 

Shockwave

Sr. Member
Sep 19, 2009
3,778
3,269
273
Use it in a semi- truck
If you are going to apply 28 volts, without increasing the impedance in the output section, you are going to blow those transistors up, long before it makes the output it did when it was stock. The output impedance should be double what it is on 12 volts, to make the same output on 28 volts. Forcing the output into an impedance that is half of what it should be, will exceed current and dissipation ratings, very quickly!
 

Alexis Mercado

Well-Known Member
May 17, 2016
232
133
53
46
If you are going to apply 28 volts, without increasing the impedance in the output section, you are going to blow those transistors up, long before it makes the output it did when it was stock. The output impedance should be double what it is on 12 volts, to make the same output on 28 volts. Forcing the output into an impedance that is half of what it should be, will exceed current and dissipation ratings, very quickly!
I’ll take the amp to an amplifier builder. He will do some changes to accomplish what you are telling me.
 
  • Like
Reactions: Shockwave

Shockwave

Sr. Member
Sep 19, 2009
3,778
3,269
273
Double? or times four? Thought a square law was at work here.

73
If we just consider input power for simplicity, it only takes half the current, at double the voltage, to produce the same power. Half of the current, means that the output load impedance, is now....

Well, as I think about this more, for current to drop in half with a doubling of voltage, impedance must go up by 4 times. You are correct Nomad. Thanks for pointing this out.
 
Last edited:

9C1Driver

Sr. Member
Aug 13, 2008
3,635
1,545
173
I’ll take the amp to an amplifier builder. He will do some changes to accomplish what you are telling me.
That's probably a good idea. They will probably tell you what your wanting to have done is a bad idea. A 4 pill amplifier with 2879 finals will work just fine in a semi truck run off the trucks 13.8-14.6 volts.
 
  • Like
Reactions: Alexis Mercado

Naysayer

Member
Mar 6, 2020
12
10
13
New York
The OP's plan did not sound impossible. Zetagi makes a line of MRF422 amps with no unusual looking OP Transformers. Raising the impedance of the OP Transformer requires altering the turns and perhaps the cores as well.
Problems would be worse below 40 meters.

What about the Input Transformer?
 
Last edited:
  • Like
Reactions: Alexis Mercado

SuperLid

Member
Feb 6, 2020
23
11
13
NY/NJ
The OP's plan did not sound impossible. Zetagi makes a line of MRF422 amps with no unusual looking OP Transformers. Raising the impedance of the OP Transformer requires altering the turns and perhaps the cores as well.
Problems would be worse below 40 meters.

What about the Input Transformer?
I have not had the amp I was speaking of, on the air in quite a few years. I just acquired a pile of power supplies, that I need to build up to run this amp. Unfortunately, I used rivets to close the cabinet. I was planning to drill them out anyway. When I do, I can take a photo of the modules with both 2879 and MRF422, as I have a similar 8x2879 amp that was gutted as a parts donor for a 8x MRF422.
 
  • Like
Reactions: Alexis Mercado

dxChat
Help Users
  • No one is chatting at the moment.