Adding Aux Input to Motorola HiFi Console 6k22b

[Obcradio]

I have a 1957/58 Motorola mono HiFi console, I believe it is model 6KT22 (has the 15” Jensen, and 3 5.25” speakers, turntable and the optional AM/FM tuner). I paid $5 for it at a garage sale 15 years ago and it has been great. The thing is all original, very low hour system. Recently I’ve recapped the whole thing, and replaced a couple of tubes. I’d like to add an AUX line level input. The way it is currently setup, RCA jack goes from turntable into an RCA input on the tuner. Tuner has a selector switch for Am/Fm/Phono (power is switched on the turntable). Then an RCA cable goes from the tuner to the phono input on the Amp.

The amp is the HS619 chassis, from 10 of 1957. Some models came with a Tape input on the back of the chassis, but mine does not have that. Would I be able to add that line input? If I try to plug in a line input to the RCA phono input, it works and sounds great but I barely can crank the volume since it’s a phono stage input that feeds right into the 6AU6.

Any input would be appreciated. This is an absolutely superb sounding amp, but I want to do more than vinyl, and the turntable on this thing isn’t really something I want to play my albums on. I know my way around a soldering iron, how to read a schematic/check values with a meter and replace components when necessary, but I’m a little fuzzy on circuit design and theory.

Thanks Guys!

 

[century tek]

Welcome!

The tuner power should not be operated solely by the turntable switch. There has to be another on/off switch somewhere.

Does it have FM multiplex?

The phono stage is not a magnetic cartridge phono stage but rather for a ceramic cartridge. It may be a little hotter than most but it is essentially a line level input.

The amps inputs are line level so if you plug anything into them, you will need some sort of volume control as the amp itself is full on.

Do you have any pics?

 

[RWood]

I’ve worked on some of these amps-they have the largest output transformers I have ever seen on a 6V6 amp. They do sound nice.

I’ve also had a Moto console with add-on tuner and yes, the power on sequence was unruly, difficult to explain to the wife and did involve the turntable needing to be On when running the tuner. It almost drove me crazy and I removed the tuner. Still have the console.

Your amp has the three lightup dials for Vol Bass and Treble right? And the input to the amp is line level as Century Tek said. I think you are going to need a switch to select either Tuner or you new Aux, something to pad the signal down (does your source have a volume control on it?) and then finally a way to wye a stereo signal into mono.

For starters I’d like to see how Motorola did it on the models that had Aux In. Do you have a chassis number for that one?

 

[Dswankey]

You might find this extensive thread useful if you care to learn more about Motorola consoles

https://www.audiokarma.org/forums/i...otorola-consoles.251084/page-28#post-13236176

 

[Obcradio]

I’ve worked on some of these amps-they have the largest output transformers I have ever seen on a 6V6 amp. They do sound nice.

I’ve also had a Moto console with add-on tuner and yes, the power on sequence was unruly, difficult to explain to the wife and did involve the turntable needing to be On when running the tuner. It almost drove me crazy and I removed the tuner. Still have the console.

Your amp has the three lightup dials for Vol Bass and Treble right? And the input to the amp is line level as Century Tek said. I think you are going to need a switch to select either Tuner or you new Aux, something to pad the signal down (does your source have a volume control on it?) and then finally a way to wye a stereo signal into mono.

For starters I’d like to see how Motorola did it on the models that had Aux In. Do you have a chassis number for that one?

Chassis number is HS619. Yes it has the three light up dials for volume, bass and treble. The add on tuner sits on the other side of cabinet in what would’ve been a record storage bin. I’ve got it currently ripped apart, so I’ll post some pictures below.

I’ve got a couple setups for the input. Feeding into a stereo to mono RCA plug. One is a Bluetooth base station, so I can control volume. Other was a CD player.

according to schematics I’ve found, the tape input would’ve been on the rear of the amp chassis near the external speaker plug. As you can see in the pictures, I have everything ripped apart.

 

[century tek]

That's a mono integrated amplifier. I was thinking it was one of the Motorola stereo consoles with the separate amps.

This is a common mono integrated amp I see around here quite often. I actually have the Sam's PhotoFact of this model. The amp itself is line level on the input and since it has the volume and tone controls, you should be able to use it just like any other mono integrated amplifier. The phono input is hotter because it is going through the 6AU6 before the first 12AU7 tube. If you know how, you can eliminate the 6AU6 tube altogether.


EDIT: That tuner is the same one that's in my Motorola stereo console. My turntable is stereo with the 3 channel stereo push pull 6AQ5 power amplifier but the tuner is mono only. If its connected correctly like mine, when the tuner is in the phono position, the switch on the turntable should turn on the amp only. If the turntable switch is off, the tuner should turn on along with the amp when you select from phono to either AM or FM. This is how mine works factory stock.

 

[Obcradio]

That's a mono integrated amplifier. I was thinking it was one of the Motorola stereo consoles with the separate amps.

This is a common mono integrated amp I see around here quite often. I actually have the Sam's PhotoFact of this model. The amp itself is line level on the input and since it has the volume and tone controls, you should be able to use it just like any other mono integrated amplifier. The phono input is hotter because it is going through the 6AU6 on the tuner before going to the amp.
View attachment 1835933

It does have a separate amplifier and tuner. It’s hard to tell becuase I have the unit disassembled, but the the pictures I took show both the amp and the separate tuner chassis. The unit I have, came optionally with an AM/FM tuner, it is not integrated with the amplifier.

The AMP only has 1 phono input. The seperate tuner, also has a phono input. When you have the optional tuner, you plug the phonograph into the tuner, and then plug the tuner into the phono input on the AMP. The tuner chassis acts as switch, switching between phono, AM and FM. It then outputs, via rca cable, to the amplifier plugging into the phono input.

if the phono input on the amp is indeed line level, then I can just plug into that and be done with it? I just don’t want to overload or damage anything because I’m plugging in an audio source into the phono stage of the AMP. That’s why I was wondering if I’d have to basically create my own “Tape” input on the chassis (my unit did not have the option) that bypasses any phono stage on the amp (if it has that).

 

[century tek]

Any amplifier with built in volume and tone controls is called an integrated amplifier. That's what you have with that 6V6 amplifier. The phono input on the amp is a line level input and you won't damage a thing. Like I said, If it's too hot at the amp input, you could remove the 6AU6 tube and go straight into the first 12AU7 tube.

My tuner is the same as yours with the same connections. The only difference is that yours has the mono turntable and mine has the stereo turntable. My preamp controls have a mono/stereo switch for when I want to listen to the radio through both left & right channels. It is a stereo phonograph console with a mono AM & FM tuner. No FM stereo in this model.

 

[century tek]

if the phono input on the amp is indeed line level, then I can just plug into that and be done with it? I just don’t want to overload or damage anything because I’m plugging in an audio source into the phono stage of the AMP.

As mentioned earlier, this is not a phono stage for magnetic cartridge turntables but rather for ceramic cartridges such as the one you have there and is basically line level.

Yes, you can go directly into the input jack on the amp and be done with it!

EDIT: Looking at the schematic, it looks like you need to leave the 6AU6 tube in the amp as it is associated with the treble control and circuit.