Bauhaus Stereo by Braun

[tolivac]

Magnavox Concert Grand-still looking out my way-As I have stated before Higher end components are RARE this way-no Magnavox dealers in the Eastern NC area-closest at the time was Raleigh.And folks here just didn't buy them.Will have to look at Audio Classsics for the caps.Same with Antique electronic supply.would like to use the amps in my home theater system.3 of them perfect for L Front,Center,R Front-and the Mc 225 for the sorrounds.It needs caps as well.Replaced the voltage double supply in that amp with a full wave tubed rectifier-MUCH BETTER!!!Old SS voltage doublers are CRAP as far as quality is concerned-they are fine for TV sets or oscilloscopes-but for an amp they have too poor of voltage regulation for that application.Voltage doublers work OK for loads that draw a constant low current.At one time was able to get magnetic TT preamps from radio stations-my line of work.Commonly used instead of TT amps from the console maker-less expensive.And I could build it if required.Just need to find a Concert Grand for that experiment-have lots of surplus TT's from a radiostation.Techinics SP25.Common TT for radio stations.You won't find a TT's tape machines or cart machines at radio stations anymore.
for the classes of amplification-another consideration is the stages driving the output stage-esp cathodyne phase invertors-they cannot drive a class AB2 or B correctly-puts too much load on them.And deal with audio drivers in AM transmitter mod stages.Too many times run into transmitters they are distorted-the previous engineer didn't set the bias on the mod stage correctly.That will overload the driver-and bad mod stage tubes will do it.run into that problem at the site I work at now.Set the mod bias at the proper idle current-the Tx passes proof with no problem.And of course sounds better on air and can be modulated 100% without distortion.and thanks for the idea of the suppliers for the caps for the MC amps.If I can get them-no problem to install them.and oh yes-some movie theaters DID use MC amps for their speaker systems-BiAmp Altec "Voice of the Theater"Audio heaven!

 

[firedome]

The 225 is a nice amp, some think their best consumer tube stereo unit, I had several, 2 set on strapped mode, one for each channel...got rid of all of them even the MI-200, in favor of the Marantz and Sargent-Rayment stuff, finally dumped the M stuff too, at the crazy prices folks pay I was happy to sell it all off, the collecting days are over for me anyhow, don't need all the stuff, even gave the Altec Valencias to my son.
One common mod is to replace the selenium rectifiers with HEXFREDS, but a nice 5AR4 rectifier stage is far better. Long tailed pair works well as phase inverter. The common movie theater amp was WE, then Altec later, but I did get several Mc 75s out of a drive in once!

 

[tolivac]

RCA was another theater-cinema equipment supplier-even down to the Brenkart projectors-they had versions of these for TV broadcast use.I used to have a pair of 250W Altec Lansing amps that came from a DI theater that was demolished in the DC-virgina area.Had two 845's as the output stage,and 866 as rectifiers.
the unit I used with the MC 225 was an external unit that had a 5U4 tube.Worked great!Another person I knew that worked in a large drive in theater-had RCA equipment-he mentioned two amps-one in use-the other as backup.These used a pair of 4-1000 transmittting tubes in the output stage.That could mean up to 2,500W RMS!These tubes are used a lot in older AM broadcast transmitters-RF amps and modulators.Some RCA low band analog TV transmitters used them in low level RF stages.Some of our transmitters use them where I work-PP RF amp stage rated up to 6Kw.Those glass balloons are sure impressive when worked hard! plates glowing-HOT GLASS!Love the "firebottles!"Lots of those at this transmitter site.

 

[tolivac]

and--RCA even could supply the chairs for the cinema!screens and other equipment,too-next largest supplier to WE at one time.