Boomer? 100?

[Cable Guy]

I can't make out the name but I think it's a boomer. The pills aren't really documented either, can't find anything about them. It works, just curious about it. Pills show Msrf 2512g. I haven't been able to Google things right lately as I believe they are deleting the internet, or search engines are pushing more ads and junk than what they have been. In the early 2000s I could find ANYTHING on Yahoo or Google. Anywho, have y'all seen this before? Does about 125 pep per my eval.

 

[BC Coyote]

I had that exact amp for years and years ! It finally died when I accidentally put 100 watts into the wrong end of it. Oops.
It was a great amp when it worked though I only got about 95 watts max from mine. Also be aware that it is biased class C so it will sound awful if you use it on sideband. I also recall I had to make some kind of modification to the preamp in order for it to work properly; not sure what it was it was long ago.......

 

[BC Coyote]

Forgot to mention.... It is a Boomer for sure, though the exact same circuit was also used in other amps of the period too.

 

[AudioShockwav]

SRF part numbers are select/ premium Motorola transistors relabeled for RF Parts from years ago.
Likely high gain MRF 454 transistors much like the SRF 3795


73
Jeff

 

[BC Coyote]

Yes I just looked at mine and it has 2 MRF-454A in it.
Also noticed that while mine is nearly identical to the picture above, it also has a variable pre-amp level control on the right side of the panel. Maybe it's just not visible in the pic.

 

[Cable Guy]

Hi. This box does not have the variable pre-amp but the pre-amp seems to attenuate the Rx somewhat and is in need of repair. I don't use the pre-amps anyways. That's interesting about the premium Motorola transistors and why I can't find much info on this particular.

 

[AudioShockwav]

why I can't find much info on this particular.

They changed weekly while avoiding the FCC.
Different names different locations different parts.
Most had very little paperwork, very few had schematics untill someone sat down to hand draw them.
Transistors were used as they were bought, this month it was more 454's, next month 3795's then 1446's, what ever the builder could get a deal on for that run.
Small changes made that were never documented, even worse for tube amps built back in the 70's.
Seems they would change things on each build run.

73
Jeff

 

[Cable Guy]

Fascinating insight into manufacturing processes and times. These appear to be stud mount pills, not flange, so upgrading will be limited using this enclosure. Thanks Audioshockwav and BC Coyote.

 

[AudioShockwav]

Any 455,454 ect with the a suffix is stud mount, rare as hens teeth now.

73
Jeff

 

[lonestarbandit]

Here's a variable about same age, though strangely it appears to be labeled rec?

 

[BC Coyote]

Rec stands for "Receive" the control only adjusts the level of amplification of the receive pre-amp. Transmit output power is not adjustable.

 

[Cable Guy]

What numbers should I be seeing out of this amp with a 3 watt dk and 18 pep? I know it should be driven from about 1 watt dk but the radio I'm testing with isn't variable and I don't want to pop the hood on it. I'm currently seeing 40-110 dk from low to high but only ~300 pep on high. Friend said it was about 450 watts before but he could've been overdriving it, entertaining a reading from a happy meter, or both. I want it to be right before I give it back to him and not pop the $200 investment in this old box.

 

[BC Coyote]

If you're seeing more than 100 watts something is either seriously wrong with the amp and it is spewing harmonics, or your meter needs to be tossed in the garbage and replaced.....

 

[Cable Guy]

My numbers were a recollection, I may hook it back up and verify.

 

[Cable Guy]

I reinstalled it for more accurate numbers (as accurate as the meter(mfj-870))
Dk 3 watts is low 30, med 65, hi 100.
Peak 18 watts is low 130, med 260, hi 325.
Into dummy load.