Commercial AM/FM Broadcast Monitor
This was a Bogen TP-100 rack mount tuner. It's basically an analog AM/FM circuit, with a digital frequency counter for the display
readout. One of the audio magazines has rated this model as being in the top-ten for its FM performance, as measured in their lab, and
auditioned by their staff. Another professional reviewer rated it as number 4 on his all-time list of FM tuners.
I picked it up from an auction site for the cost of less-than a half tank of gasoline, found a schematic (hat tip to "The Manual Man" and
Carl, N1ORW), studied the circuit design, then proceeded to head for the shop and satisfy my incurable OCD addiction.
On the test bench, I was very impressed with the recovered audio on FM. No doubt, this thing is sensitive, clean of IM artifacts and
rendered some very nice broadband audio. But I am an incurable AM DXer ... another addiction that I enjoy. There is little doubt that the
Lear-Siegler engineers, at their Bogen division, put the same efforts into the AM section as they did with the FM. This thing is not a super
AM machine like some of the things I play with during my leisure listening hours, but it is simply a great, solid device. In AM mode it is very
hot in sensitivity. It has good filter bandwidth and passband shape. It has a quiet noise floor and respectable dynamic range. All-in-all, a
joy to use.
It is apparent that the lack of any serious internal radiation from digitally tuned circuits has its benefits. I could not hear any noise from the
digital frequency counter tuning display ... dead quiet.
Expanded shots of the left and right side of the unit. Forgive my very
The first draft of the new panel decal taped in place to mark out the control mounting holes.
The front panel machined and checked against the chassis for fit of components.
The high-resolution printing of the decal. This is prior to laminating. Note that it's done in two pieces to accommodate the 19" length of the
panel on a printer restricted to 11".
The machined panel, now painted and awaiting the application of the laminated decal. Micro-thin double sided tape is used for the
application...very tenacious and humidity proof.
Finished and playing. I do need to fabricate some new black plastic knobs for the three push buttons, but for now my OCD has been satisfied.
Here you can see the added LED indicators to show the center tuning, the RF Gain control, the Audio Level control, the Antenna Shunt switch and Power switch with
I'll snap some pics of the insides, in time.
Thanks for looking.
Note that I added an LED gauge to indicate the center tuning of the passband with a signal taken from the AGC circuit.
I also added an RF Gain control to avoid overload on my outdoor wire antennas.
Since this was a tuner, I added an 8-Watt power amp and a level control which the original did not have, but only supplied line-level audio signal.
I retained the line-level outputs in case I ever want to feed my SWL audio console.
I also added an Antenna Shunt switch and moved the Power switch and added a Power On indicator.