Sidebar Sidebar
  • 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.

maco 750 tube amp

B

blaine

W9WDX Amateur Radio Club Member
Apr 22, 2009
169
3
28
57
I have a chance to pick up a maco 750 for $100.00 off of a local here,he tells me that when he keys up the fuse in the back blows,also tells me it has nine new 8950 tubes,I'm gonna get it, if nothing else to sell the tubes.But my question is, with only having $100.00 in it,would it be worth sending to someone and see if maybe it could be fixed?What is the most you guys would put into it?


Thanks
 

Pull the tubes out and then power it up and key it. If the fuse still blows you have a HV problem. Either with the supply itself or the transformer. Rebuilding the supply is not a major issue and probably should be done if it is the original one......but the transformer can be another issue. Finding one could be a problem and get expensive. You can just remove the plate caps from all the tubes and then see if it blows fuses. Be careful while doing this.........High Voltage in excess of 1000 volts DC is present in the amplifier.
 
If it had a fuse in it, more than likely it is diode bridge that is out. Probably just one section or leg of the bridge. Like I said "if" the fuse was in it the transformer was protected.
 
maco 750

Anybody known what the tune knob on the right hand side is for .I'll send a pic.
 

Attachments

  • 5I95Je5M83ne3G83Idc6496aaaadcf1af1475.jpg
    5I95Je5M83ne3G83Idc6496aaaadcf1af1475.jpg
    34.3 KB · Views: 89
  • Like
Reactions: 1 person
tune it to the max,

dip the load amd plat max the caps it pwr suply should be changed and the transformer can be rewound by maco...its magestic transformer in ky or tenn...one of the two dont rember...they only make high voltage transformers,it expensive but the tubes in it or very expensive,like one hunderred each,get them form sndtubes.com 73 de JW
 
The high voltage is on as soon as the amp is turned on. If any of the diodes/caps/HV transformer were bad, it wouldn't wait until you key the amp to blow the fuse. Same goes for the plate blocking caps. The 750 grounds the cathodes to key the amplifier. It almost has to be a plate to grid short in one of the tubes.

beachboy: That is the plate tune for the 2 drivers in the second driver stage.
 
  • Like
Reactions: 1 person
DoctorAudio said:
The high voltage is on as soon as the amp is turned on. If any of the diodes/caps/HV transformer were bad, it wouldn't wait until you key the amp to blow the fuse. Same goes for the plate blocking caps. The 750 grounds the cathodes to key the amplifier. It almost has to be a plate to grid short in one of the tubes.

beachboy: That is the plate tune for the 2 drivers in the second driver stage.
Click to expand...

Doc your right your one of the good old guys,I didn't known there were any of you fellow still around.(May the force be with you and yours)
 
  • Like
Reactions: 1 person

dxChat
Help Users
  • No one is chatting at the moment.
  • @ Wildcat27:
    Hello I have a old school 2950 receives great on all modes and transmits great on AM but no transmit on SSB. Does anyone have any idea?
  • @ BJ radionut:
  • @ ButtFuzz:
    Good evening from Sunny Salem! What’s shaking?
  • dxBot:
    63Sprint has left the room.
  • dxBot:
    kennyjames 0151 has left the room.


      Top Bottom
      Back