Opamp frequency mixer

This would be the genuine Soviet method:

But why heptodes? Here they show one with just ordinary transistors so it could also be done with triodes:

They have also been built with ordinary triodes and pentodes:

If it absolutely has to be semiconductors I'd use the MC1496.

--
Regards, Joerg 

http://www.analogconsultants.com/

I'd go with the MC1494... if you can get it. It has the level shifting built-in... quite adequate for audio, and immensely eases the pain of doing your own level-shifting. ...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Nice! Thank you!

Ah yes, I'd forgotten about that one.

Looks like a nice chip, but if this exercise turns out well I might make a PCB and do a small quantity run...and yeah, oooof. Mostly non-stocked here, and while there seem to be some available new from China, they're really expensive! :-(

I second the thought of using a MC1496 or MC1494 if you're going to use semiconductors. The NE612 may also suit, but you'd need level shifting.

But you don't do tube projects unless you're planning on using an excess of parts. See if you can find a pre-1964 ARRL Handbook and look through it for mixers, or do a search on "tube mixer circuits" -- there's a lot more ways to do it than with heptodes, that's for sure.

You could make a 180 degree shifter and summer by making an appropriate transformer (probably at least mildly resonant at good toob impedances) from signal A, with the secondary center-tapped and fed with signal B. Feed a pair of triodes with the transformer outputs, and poof! you have a single balanced mixer.

Or, you could use one miniature heptode.

--
www.wescottdesign.com

The LM13700 can be used as a four-quadrant multiplier...it has a unity gain bandwidth of 2MHz and a slew rate of 50 V/uS...seems like it should be fast enough to use at low RF?

With tubes it doesn't have to end up in excess, except for power consumption, of course. When I was a kid I built a receiver that could demodulate AM as well as SSB. It contained only two tube stages and very few other parts.

For 180 degree shifting all you need is one triode as a follower. Make the anode resistor the same as the cathode resistor. Then the anode carries the 180 degree signal.

I only know the combination ones as available (for a lot of money):

The DK96 is probably completely unobtanium by now:

--
Regards, Joerg 

http://www.analogconsultants.com/

Also, I have about a hundred LM13700s I picked up dirt cheap in the DIP package somewhere around here in a box ;)

Anything the MC1496 can do, the AD633 can do more painlessly. The AD834 and AD835 can do it a lot faster.

--
Bill Sloman, Sydney

Any tube will mix: diode, triode, pentode, CRT, PMT. Armstrong didn't need any fancy-pants megagrid tubes when he invented the superhet:

A PMT would make an optical superhet. LO one of the dynodes.

That's always the best solution ;-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Armstrong was an amazing guy--he invented the oscillator!

Also the superhet, the superregen, FM radio, and many other things.

One of my technical heroes.

Chees

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

I'm just finishing this one

which is pretty cool. It's amazing what a jerk DeForest was, and how crazy Tesla was. And how many great inventors died poor.

Hans invented the 555 chip, which makes the few glaring errors in this book all the more strange.

I've read about the story of Armstrong and it's very sad. I often found myself wondering why, at some point, someone didn't urge him to cut his losses, come to some kind of settlement with Sarnoff and RCA, and then just walk away.

It would have been far better for his health in the long run. What good is pride if the end result is a 12 story swan dive off a hotel balcony?

Only problem then is that the two outputs have wildly differing output impedances, which could be a problem...

I'm not a big fan of pride in general, but it's easy to get fixated on your own rights.

Cheers

Phil Hobbs

Yeah, I could see that. For my part, sometimes knowing when to fold 'em has kept me fairly sane these past 30 something years.

You and me both, brother.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Forget tubes or opamps. The semiconductor solution is called a Gilbert cell (Google for it). With unsorted transistors from the same batch, you will get a far better mixer than with tubes. Do not forget the low-pass filter after mixing.

In the Theremin case, you do not even need fight with the dynamic range in the same way as radio receiver designers do.

You should eject the idea of using tubes at all. A couple of FETs will get a far better thing. If you need the dull glow of heaters and associated show, use one or some tubes with only heaters.

--

-TV