[Amps] RF Power Labs V360 PA finals sub

[Will Matney]

Bruce,

I've never seen any stud mounted RF transistors with a high output rating, something like 50-60W at the most. The reason why is the heat dissapation of the substrate inside. The stud mount gives less cooling area. Anything over that were flange mounted and had a greater cooling surface. Motorola was the primary mfg. at one time for a huge number of private labeled RF transistors like the MRF series, which I wouldn't doubt that those are. That's who private labeled those for RF Parts.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 1/30/06 at 7:08 PM Bruce Brackin wrote:

>Has anyone ever run into one of these big old solid state 6M amps?   No 
>tubes but would qualify as boatanchor at well over 50 pounds.  A former 
>owner tried getting 1 kw out.  The amp is rated at 1 kw input so you can 
>guess what happened.  I'm in need of a set of final NPN transistors 
>(4).  The company is no more and the original finals were stamped with 
>their proprietary part number, so finding a cross reference hasn't 
>worked.  The owner/designer never gave out actual transistor specs, even 
>to employees.
>
>The V360 dates from the late 70's and has a big 24v internal supply.  It 
>runs two identical PA boards with two finals each so the 4 finals take 
>20w (max) coming from driver - split 4 ways - then back together with 
>stated 1Kw input for PEP or 750w for FM,RTTY,CW,FSK,AM and specs say 
>output of 500-600w PEP and 350-450w for FM,RTTY,CW,FSK,AM.  It 
>apparently took very little drive (<5w).  An email from a former 
>employee of RF Power Labs said 1-2w of drive would max most and blown 
>finals were a very common problem.
>
>The original finals are 0.5" stud mount (10-32 stud) and given amp 
>specs, it sounds like a 28v NPN rated at about 5w in and up to ~ 100w 
>out cw/fsk or 150w PEP rating at 50 MHz or about 12db gain figure for 
>each.  Most of the stud mounts I've found are only in the 30-50w range 
>and that may also explain some of the blown finals.  There may have been 
>a poor heat transfer problem right from the start due to the small sink 
>area.
>
>I've struck out so far.  If push comes to shove, there is the 
>possibility of some careful Demerel tool work and adapting to a flange 
>mount type.  It is otherwise a really well designed and laid out amp and 
>a shame so many sit with same problem.  The Philips BLW77 (SOT121B 
>flange) has been recommended by one person.  In addition the Advanced 
>Semiconductor HF220-28 or HF100-28 might work at 50 MHz.
>
>Open to suggestions and TNX in advance - Bruce, N5SIX
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