Volting a Cobra 148 GTL final?

[Handy Andy]

Oh I can give you a L-o-o-ng story over the issue of Stainless ...

Happened at an earlier job not too long ago, before - and because - it was how I got the last job I had to give up for Mom to take care of family issues.

Yeah, Stainless being high in Carbon, Nickel and other trace materials - and it's sheer brittleness in some "mixes" the (in)ability to machine and condition it - not everyone like the results nor would they...LOL!

There was a discussion or two about the LAMINATE cores and the different alloy mixes used to make some transformers more efficient at permeability without too much "memory" or latency effects back in the CB Tricks days...

 

[1iwilly]

Dark Star if you change your mind and not doing the mod if you want to sell the transformer i'll buy off you ??

Well I picked one of these up from fleabay just in case I feel motivated to do this mod down the road....maybe with a Mosfet final to handle the extra.

 

[kc8mob]

This fella talking about coupling the audio AC signal to the 12vdc feeding the final is absolutely correct.

The cap mentioned blocks DC voltage from the output stage (pin) from the audio amplifier IC and the low value filter choke presents a higher impedance to the audio signal then the final output transistor, thus the audio sinewave (signal) imparts its effects on the final and modulates it just like the driver stages. The choke also keeps the 12v power rail from eating the AC audio signal due to its impedance or equivalent load it would present.

Why the hell this never occurred to me I dunno but by reading the old Motorola engineers comments I realized right away this same principle applies to export style rigs with shorting bars in the back.

I'm an original 2950/2970 hound. Had them in high school and you the deal.

Anyhow I always run my 2312 finals in either model off of 12vdc thinking I'm doing the 2sb817 AM regulator (Stock is 2sb754) a big favor!

Well Damnit. They need Audio signal applied or "modulated" to the 12vdc supplying them too.

I would add that the final bias in a 148 is set under no signal ssb operation and in ssb mode the 148 applies 12vdc to the final. Granted the duty cycle is clearly different but people should run additional and properly mounted heatsink surface area to the back of a 148 if you're going to smack it in the ass and call it names.

I love my Philippines 148gtl. My 11 year old uses it to work me mobile. I'm going to make these changes to it and see what the differences are by recording my current improper NPC mod and then this more complicated and seemingly correct way on my other HF setup.

Glad I came across this

 

[kc8mob]

Going to a stud mount final is also and interesting idea. There was a MRF450a as well as MRF455a

I even have both. The 450a has allot of gain if I remember correctly.

There will be pictures added to this soonish