So I messed up and bought an amp with stud mount transistors. Advice?

[Onelasttime]

So I bought this amp not knowing that some of them came with stud mount transistors. I had only seen flange mount versions of this amp.


I am not returning it because it works and the seller did nothing wrong. The mistake was mine and mine alone. It works but is kind of weak.


So I am not intersted in trying MRF453's and hoping it has better performance.


I am thinking about flipping the heat sink around drilling and taping for flange mount transistors. I would use a Dremel tool after tracing the pattern for flange mount transistors. I have no problem replacing the caps and resistors and retuning.


Thoughts.


It is an SCP 100T-BIL amp. The stock transistors are TRW PT9803 and have a date code of 1976 12th week or month. At 4 watts it gives 83 watts output. I want at least 100 watts minimum slightly more would be better.

I was planning to replace with transistors with MRF454, MTE317, NTE335, or HG2879's.


I have never actual worked on anything with stud mount and have never tried flipping a heat sink to replace a stud mount with a flange mount.

 

[nomadradio]

Biggest obstacle for me was always the need to gouge out the 'ears' on opposite sides of the round transistor hole. Gotta have access to the screw heads to bolt it down. Inserting it from below the pc board wouldn't work unless you bend all four leads upwards and reamed the round hole so they'll pass through from underneath. And then you still have to come up with a way to hold the transistors tightly against the heat-sink surface. A clamp of some sort? Not my kind of mechanical design challenge.

Kinda depends on how many foil traces get disrupted by gouging out the ear on each side of the round hole for screw-head access.

Never worked up the nerve to try it.

73

 

[Onelasttime]

I have not tried it before either. I am only 50 so by the time I got into CB and Amateur radio in the 1990's these where not a thing! LOL

I was planing on rebuilding this amp and sticking it in one of the small access panels in the wifes Toyota Hilander just in case! I figured I could stick it in some old tuberware and squirel it away just in case. Since it is not some gem I could stick it in there and forget about it!

I could drill it out for MRF453A's but those are not very powerful.

I have always liked tiny little 2 pill amp's. The heat sink area is very generious for it's power output. It is biased for SSB. Before I put it into long term storage though I was going to recap it, retune, fresh transistors etc....I was going to stuff a Realistic 465 in the little access area with it and 5 foot firestick.

With Russia launcing MRV's and IRBM's into Ukraine it can not hurt. Her vechile is AWD and larger than my 21 year old almost 22 year old Camry! LOL My 21 year old Camry though is manual transmission and almost as industructable as the HiLux Pickup's you see in the Middle East with M2 or Mini-Gun mounted in the bed! LOL

 

[Onelasttime]

P.S. Mechanicaly I am much more adept than electronicaly. I put a C4 ZR1 LT5 engine into a Toyota 4x4 HILUX Pickup truck making my own sand casting's for adapters and a custom accessory drive.

This was back around 1994 or 1995. In fact after that experince I put a 383 Chevy Small Block into my 4Runner and custom built a 700R4 to go into it with Double Transfer Cases. This was all done while I was in college in between quarters.

During this time I designed a custom set of heads for a guy using turbo charged automotive V6's in experimental aviation planes.

I am damn near crippled now. I need to reinvent myself.LOL

When it comes to electronics I have to look everything up, plan things out, ask questions, measure everything about 4 times and hope my hands hold out before they start trembling and shaking!

On top of chronic insomnia, diabete, and joint issues I am developing neurological issues with tremors, spasism and such! So I have a lot of irons in the fire trying to get ahead of my health issues!

 

[Shockwave]

Inserting it from below the pc board wouldn't work unless you bend all four leads upwards and reamed the round hole so they'll pass through from underneath.

73

That is the method I use to use, with a pair of low profile flathead screws to hold the transistors in place. Sometimes it required extra washers under the PC board mounting screws, in order to provide clearance under the board for the transistor mounting screws.

Just make sure the relays and everything else are in good working order because you probably will not get a second chance to bend those transistor leads, without replacing them in order to lift the board up again.

 

[Monk]

So I bought this amp not knowing that some of them came with stud mount transistors. I had only seen flange mount versions of this amp.


I am not returning it because it works and the seller did nothing wrong. The mistake was mine and mine alone. It works but is kind of weak.


So I am not intersted in trying MRF453's and hoping it has better performance.


I am thinking about flipping the heat sink around drilling and taping for flange mount transistors. I would use a Dremel tool after tracing the pattern for flange mount transistors. I have no problem replacing the caps and resistors and retuning.


Thoughts.


It is an SCP 100T-BIL amp. The stock transistors are TRW PT9803 and have a date code of 1976 12th week or month. At 4 watts it gives 83 watts output. I want at least 100 watts minimum slightly more would be better.

I was planning to replace with transistors with MRF454, MTE317, NTE335, or HG2879's.


I have never actual worked on anything with stud mount and have never tried flipping a heat sink to replace a stud mount with a flange mount.

Difference between 80 watts and 120 watts is nothing on the receive end. To raise the s-meter at the receiving end 1 S-unit takes 4 times the power out. So, 80 x 4 equals 320 watts. That is where you have to go to lift their S-meter by 1 unit. Same goes for 800 watts-3200 watts, 8000 watts-32000 watts. Aluminum is much cheaper than transistors or tubes.....