I bought this 1963 console stereo for quite cheap. It had a layout drawing on the back containing a couple recognizable tubes, 12AX7A, a pair of 12AT7's and bunch of stubby 7-pin tubes that I didn't recognize and I presume they are used for the tuner section -- and I know nothing (and care very little) about radio.
Before I bought it, I turned it on and it worked fine, sounded like a typical console; boomy/muffled with open back speakers, etc. but it worked. It struck me odd that the output section wasn't listed on the diagram, only the tuner/pre-amp. When I got it home I discovered why; it had a 4 output transistor quasi-comp amplifier. Ha ha. what a disappointment. I'd never heard of a hybrid unit like this.
Any ideas what I can do with it? I'm not much interested in the tuner section. I could not find a schematic, but it should be simple enough to trace out. Maybe I'll just re-use the nifty copper [looking] chassis for a tube amp. It's in nice shape.
Here's the diagram on the back of the console. Mostly tuner by the looks of it. But I suppose it's got a usable tube preamp section. All the switching and phono input is handled in the tube section. The amplifier section has a separate sub-chassis and strictly for output amplification. It's pretty much useless/valueless to me.
..Todd
Before I bought it, I turned it on and it worked fine, sounded like a typical console; boomy/muffled with open back speakers, etc. but it worked. It struck me odd that the output section wasn't listed on the diagram, only the tuner/pre-amp. When I got it home I discovered why; it had a 4 output transistor quasi-comp amplifier. Ha ha. what a disappointment. I'd never heard of a hybrid unit like this.
Any ideas what I can do with it? I'm not much interested in the tuner section. I could not find a schematic, but it should be simple enough to trace out. Maybe I'll just re-use the nifty copper [looking] chassis for a tube amp. It's in nice shape.
Here's the diagram on the back of the console. Mostly tuner by the looks of it. But I suppose it's got a usable tube preamp section. All the switching and phono input is handled in the tube section. The amplifier section has a separate sub-chassis and strictly for output amplification. It's pretty much useless/valueless to me.
..Todd
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I got one of those sitting in my warehouse somewhere. I found it at the trash dump, and I think I may take it back there some day. It has a really big power transformer that should be good for something.
I saw a few hybrid consoles in the 60's. I think it had to do with "beating the cost curve". Manufacturers are always under price pressure from the big retailers. Every new model is cheaper than the last model that had similar features. Where is the biggest cost savings realized? In the output stages (pesky transformers). It is convenient that the retail chain stores is where you see this stuff first. Sears (Silvertone), Montgomery Wards (Airline) and others were the first hybrid consoles that I saw. I may have seen a Magnavox too.
The germanium transistors of the day were capable of opreating at the frequencies used in radios. There are plenty of old portable radios with an FM band and tons of CB walkie talkies to prove this. In the early 60's a transistor cost as much as a tube.
Again, the cost curve. The vibrator and power transformer needed to generate 300 volts for the tubes were big, heavy, and expensive. Space charge tubes were developed that would work with only 12 volts on the plate. These were not capable of supporting the current needed for output stage duty so a big fat germanium power transistor handled the output chores. Silicon came later.
Yeah, I think you're right, George. They couldn't wait to switch to transistors for the amp section, just to get rid of the output transformers. Back then, transistors were the cool new high-tech approach. And most importantly it was much cheaper/easier to manufacture and resulted in a smaller lighter product.
This console was built by CGE (Canadian General Electric). Nicely built.
Is anything salvageable here? (Besides the three 12v tubes tubes and chassis?) are any of those 6 volt tubes useful for amp/pre-amp purpose, or are they just used for RF?
..Todd
This console was built by CGE (Canadian General Electric). Nicely built.
Is anything salvageable here? (Besides the three 12v tubes tubes and chassis?) are any of those 6 volt tubes useful for amp/pre-amp purpose, or are they just used for RF?
..Todd
Some of the tubes that we use all the time in audio amps were designed for RF use, like the 12AT7. The 6AQ8 is similar. The 6AU6 makes a good low level amp or driver. I have tried them in the red board, they work. There is quit a bit of variability and some can be microphonic. The 6BE6 was designed as an RF mixer. It has been suggested that it works excellent in triode mode but I haven't tried it. The 6BA6 is designed to be non linear on purpose. It generates a lot of distortion when used for audio especially on strong signals. It should be OK in LTP since much of the distortion should cancel.
Hey thanks George. You're a goldmine of insight and experience. (But you already know that).
The 6BA6 might be fun to play with in a guitar pre-amp, depending on what the distortion sounds like.
..Todd
The 6BA6 is to the 6AU6 like the 6SK7 is to the 6SJ7. Both are remote cotoff versions of their respective sharp cutoff tubes (and plug in compatible). The very early Fender Champs used a 6SJ7 pentode input stage. I got some cool sounds by replacing the 6SJ7 with a 6SK7 and using a fuzz box made with germanium transistors. With proper adjustment of the volume controls on the guitar and amp, you could change the tone from almost clean to rude and nasty just by how you played the guitar.
I used a gain pedal for such a purpose, and 2 opto pairs (actually, 2 photo resistors and one 6.3V bulb) in the amp: one to increase input to the tube, another to decrease output from it. As the result, objective power variations were much less than subjective audible loudness variations.
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