AMP182BA tuning pots

[dougp59]

Hi all.

My '58 Fantasia has the AMP182BA amplifier and the 54-03 series tuner (-10 variant).

Whilst trying to trace down and fix a weak horn volume on Ch 2, I came to discover the workings of the three metal pots on top of the AMP182BA.
They are marked:
Ch.2 Bass
Ch. 1 Treble
Ch. 2 Treble

I have looked for documentation on the AMP other than the schematics (which I have), and found none so far.

Turning all three pots hard left turns off the bass on BOTH bass speakers down to negligible and turns off both horns to negligible.
In fiddling with them (driving somewhat blindly), I turned the Ch. 2 knob to about halfway. I turned the other two to the right of center, and I settled on a setting that seems balanced and performing quite well; in fact, the best this unit has sounded in a very long time.

Has anyone else worked with these and can provide additional information?

[TC Chris]

I'm not familiar with your amp, but I wonder if those pots have got gunky from nonuse. Maybe try rotation back'n'forth repeatedly, and maybe some DeOxit or similar miracle goo.

Chris Campbell

[electra225]

Those pots control the relative output of both sets of amplifiers. Your stereo has one of the (in)famous Magnavox bi-amp amplifier chassis. It has separate amplifiers for treble and bass. The tone control is a Rube Goldberg mix of caps and resistors and nobody can tell you exactly how it works. Those two pots, in conjunction with the three tone controls are alleged to control the tone and output of the amplifiers. They have treble, bass and timbre controls. There is a setup you need to do to balance both amplifiers to each other and to left and right channels. On my Concert Grand amps and on the amp in my Imperial, there are no bass control pots at all. Careful adjustment of controls in conjunction with matched audio tubes are essential to get maximum performance.

I just looked up this instrument in the 1958 Magnavox catalog. I wasn't familiar with it. Apparently, it was directly under the Concert Grand in the model lineup. Where the Imperial was in 1959. Sounds like the electronics are basically what was found in the Imperial later. I'm glad we got to see this one....

What version of the Collaro changer was used in this?

[TC Chris]

By the way, bi-amping is a big thing in ultra-high-end audio circles these days. Magnavox was ahead of the game in that regard. I was always puzzled about why they never offered magnetic cartridges for extended high-frequency response. It would not have cost much and would have added some cred to their higher-end models.

Chris Campbell

[dougp59]

When you say what version of Collaro, there are no identifying tags or marks on its underside.

On the top right corner is a round Magnavox badge. Other Collaro’s from adjacent years have a sort of triangular logo.