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Cobra 450 XL four stage power selector replacement switch repair

S

snippits75

Sr. Member
Nov 11, 2019
510
778
103
Cobra Xl 450_board.jpg
Cobra Xl 450_face.jpg



Just bought a used Cobra 450 XL amp recently. The four stage power selector has a good bit of play between the power stages. The power selector has low, medium, high, and max. Pretty sure it won't be long before the selector switch develops dead spots.

I do have average soldering skills, so I want to do this repair myself. I need to know which rotary switch to buy, or how do I determine which switch will work? Greatly appreciate any help!

I snagged a couple pictures of the amp posted here on the forums, and will attach them here on this thread. Picture credits to CBRadiomagazine. My amp is just like the attached pictures.
 
Last edited:
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Great score on the amp!

Someone here will probably know exactly what you need. I tend to think a sp4t rotary switch, but its not terribly clear from the photo.
 
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snippits75 said:
View attachment 31998 View attachment 31999


Just bought a used Cobra 450 XL amp recently. The four stage power selector has a good bit of play between the power stages. The power selector has low, medium, high, and max. Pretty sure it won't be long before the selector switch develops dead spots.

I do have average soldering skills, so I want to do this repair myself. I need to know which rotary switch to buy, or how do I determine which switch will work? Greatly appreciate any help!

I snagged a couple pictures of the amp posted here on the forums, and will attach them here on this thread. Picture credits to CBRadiomagazine. My amp is just like the attached pictures.
Click to expand...



Just bought a used Cobra 450 XL amp recently. The four stage power selector has a good bit of play between the power stages. The power selector has low, medium, high, and max. Pretty sure it won't be long before the selector switch develops dead spots.

I do have average soldering skills, so I want to do this repair myself. I need to know which rotary switch to buy, or how do I determine which switch will work? Greatly appreciate any help!

I snagged a couple pictures of the amp posted here on the forums, and will attach them here on this thread. Picture credits to CBRadiomagazine. My amp is just like the attached pictures.[/QUOTE]


Nice amp I bought a NOS Magnum 6500R from palomar and it looks identical, I just keep the thing in max and regulate from the radio.
 
Last edited:
snippets75,
Not sure what this amp was built but the link below looks as though it might work as a replacement.

https://www.newark.com/nkk-switches/hs13z/switch-rotary-1pole-4-position/dp/09X9935?st=4 pole rotary switch

Important items to find a suitable replacement would be;
1. Number of poles of the switch (5 wires or leads attached would mean a 4 pole switch. 1 common input or output wire and 4 switched input or output wires)
2. Current rating of the switch. More is better if you have room physically.
3. Diameter and depth of switch.
4. Shaft size and length. This could be adjusted with a different knob if need be.

Good Luck
73
David
 
Dmans said:
5 wires or leads attached would mean a 4 pole switch. 1 common input or output wire and 4 switched input or output wires)
Click to expand...

Actually, that would be a single pole switch x 4 throw.

A four pole switch will control 4 separate circuits, and have a minimum (for a 4PST) of 8 terminals.
 
Wow, that linear has regulated bias and a 5 pole low pass filter on the output. Not bad for 11. About the only thing they missed was adding thermal tracking diodes into the bias and maybe a tuned input.
 
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This looks like the same amp inside except the fuse in the power line on the magnum 6500R.
20191123-140321.jpg


20191123-140344.jpg
 
Shockwave said:
Wow, that linear has regulated bias and a 5 pole low pass filter on the output. Not bad for 11. About the only thing they missed was adding thermal tracking diodes into the bias and maybe a tuned input.
Click to expand...

This is like the early Magnum Amps.
The Silver face ones had the filter, the regulators were heatsinked, jumpers that you could pull and stick your meter in line while adjusting bias, another jumper to select Lo or Hi drive and used 4x2879 Toshiba's in them.
The down side was I have seen more than a few with roasted transistors in them from people that don't know better adjusting the Bias vr's at random to get more power out of the Amp.
The " open the lid and turn everything to the far right " guys.
Charlie 3 used to sell these wholesale in case lots of 6 Amps to a case.
It was a very well built Amp.
They used a well thought out strip line design and the board itself floated in the slots in the heat sink allowing the amp to heat up and cool down without expansion/contraction stressing the tabs on the output transistors.
Wish someone would build them like this again.

73
Jeff
 
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"Charlie 3", you just dated yourself because I use to buy things from him too. Thanks for the additional info on the 2879 version. I noticed the "M" Motorola logo on the ones used here.
 
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