Curtis-Mathes Stereo

[dalangdon]

I have a Motorola Hi-Fi console with tube amp, and had all of the tubes replaced last year, without any problems.

I know lots of guitar players insist on tube amps, even today.

 

[tolivac]

Car

WOW!!!-Gone full circle here-anyone of you remember those Vibrator tube car radios of the 50's?Used to have a small collection of them years and years ago.They got lost in a flood.They were very high quality once you got good tubes and a good vibrator in them.
Vintage tube Hi-Fi-stereo gear is now the rage with some folks-esp the Japanese-they love our vintage tube gear.Thats one of the reasons vin tage tube equipment is getting scarce and expensive-some of it is going to Japan.
Some recording studios have in the instrument stock for clients to use-Fender Stratocaster Guitars and Amps-(Vintage ones-not new ones)Hammond B3 Tonewheel organs and other similar things.They also try to buy up "Ampeg" guitar and instrument amps.
And they are restoring old tube mixer consoles and recorders.
New tube Hi-Fi stereos are availabe today-but the prices-better get a second mortgage on the house--they are getting more expensive than the house you put them in!!

 

[cadman]

Tubes, right up my alley! I don't know if I've shared this with you guys, but this is the amp I built for my system- It's a combination of two 100w power amp channels (EL34s), a 6 tube active equalizer (3-band), a grounded-grid preamp, and tube regulation all on one chassis. A microprocessor visible through round glass on the top orchestrates the chassis, including a thermal shutdown routine, a sleep timer, staged power-up and wireless remote. When you turn the amp on, the volume knob will rotate from zero to your last setting (if so desired) and the white glow under the knob turns red as volume increases. You just gotta see it : )

 

[cadman]

A closeup of the EQ section- full tube rectification and argon-filled gas tubes to regulate voltage

 

[cadman]

And the last shot of the underside. What you don't see here is the large toroid transformer for the power amp sections, that's hidden under the sheetmetal "case" on top where the microprocessor is also located. All finished off in Cadillac white-diamond paint!

Cory

 

[rickr]

Awesome Hi Tech tube amp!! It would be a treat for the ears to be able to listen to that! Turn it up,I might be able to hear it in Indiana,Iowa is only a couple of states away....
How long did it take to build? And did you design it yourself?

 

[tolivac]

Cadman--VERY NICE amp-Do you build those for others?The folks into tube gear would love that unit-a really nice intergrated amp.Like the idea of the VR regulated input and EQ stages.
your VR tubes remind me of the low level regulators in one of our transmitters in use right now-has the same reg tubes.they regulate the screen voltage for the low level audio in the transmitters modulator.Does the eye tube act as a level meter?or is it for use as a meter for setting output tube bias voltages?I also like the no circuit boards in the underside of your amp.Makes for easier repairs!!Maybe you can help me locate some capacitors for My McIntosh MC 60 and 75 amps. If I could fix them-will use them in my home theater instead of the recivers power amps-would then use the receiver as a preamp-processor and it would feed the "Mac" power amps.Got MANY tubes for my amps from radio stations "discarding" their unwanted tubes to me.and yes-many radio and TV transmitters STILL use tubes!!Like tube AM transmitters more so than SS transmitters.-and how many SS modules are going to last for 60,000 operating hours??A 50Kw tube transmitter I installed in a station in the wash DC area in 1985 is still operating on its original pair of final tubes!!The station may replace that transmitter with one that is digital (IBOC) compatible.That would mean a SS rig-BOO-Hiss!!The transmitters I am using now are all tube.

 

[drmitch]

Wow Cory thats something! I like to work on things but I cant imagine building one like that! Heres a 1972 Sears silvertone tube HI FI a friend gave me. It sounds as good or maby better than my Bose system. also have the original books and schematics for them.

 

[drmitch]

Heres the back, the amps a class a push pull type.

 

[drmitch]

Oh yeah, I thought you would like my desk phone although the trunk won`t hold as much as yours!

 

[cadman]

Thanks for the compliments guys- and way cool phone ; ) I can't take credit for the audio circuits, they are a newer design by a guy named Rozenblit, though the power amps originally called for Magnoval base russian tubes that were nothing but trouble, cracking and going to air. They were rated for 150w output PP. I modifed the ckts for 700v plate and 400 screen IIRC and used EL34s pushing them to their absolute limit. Everything that's computer controlled (including the 12 pages of code loaded into the microprocessor) are my handiwork, and throwing the active EQ into the mix worked out well. The eye tube is a 6AF6 and is a stereo version so you can monitor both channels at once, but it's more for grins than anything. A 12AX7 under the chassis behind that tube is the amp stage for it, and there's a gain control on the back. Etc. Etc. Talk about a long and time consuming project!! Never again ; )
Cory

 

[tolivac]

Cadman:Wow!! 700V for plates and 400 for the screens-Thats is pushing the EL34 to the limit. what sort of tube life do you get?The EL34-the workhorse of the Hi-Fi and audio amp industry.Those tubes also make good modulator drivers in AM transmitters as well.Gates,Sparta-Bauer,CCA come to mind of Tx builders that use EL34's as mod tube drivers.The EL34 can even pass video and MF RF-Sparta-Bauer transmitters used them in the low level RF stages.Looks like your Amp is a one of a Kind-you must be very proud of it.
Drmitch: Really nice Sears Silvertone Hi-Fi-didn't think Sears would want to sell anything of that caliber.I always thought of them for selling radios,tv, and small stereos.

 

[kenmore1978]

Tube site

Anybody see this site yet?

http://https//vacuumtubes.net/

 

[kenmore1978]

vibrators

Most of the power sections of car radios that used vibrators are being converted to Solid State since th vibrators are realy getting hard to find, and aparently they don't age well, so even ones still new in the box apparently fail fairly quickly.

 

[tolivac]

Vibrators

I used to have and work on those vibrator radios over 30 years ago.Then vibrators were still available and still would work.Nowadays-they would be no longer made and those still around the rubber supports and other parts for the vibrator reed would be stiff and rotted out.That sure would kill the operation of the vibrator.At that time I was experimenting with solid state circuits to replace the vibrator.Found some cicuit designs that did work.the vibrator is essentually an electro-mechanical mutivibrator oscillator circuit.It could be duplicated(in the circuit I was using)a multivibrator cicuit using power transistors.Unfortunately that data got lost with those radios in the Rapid City S.Dak flood of 1972.I would have to imagine today someone must make a solid state plug in "vibrator" today?Haven't worked on radios like those since then.also remember those "0Z4" rectifier tubes used in those radios?Didn't have a filament-was a cold cathode device-and VERY reliable.also seen 6X5-12X5 tubes used as well.

 

[kenmore1978]

solid state

Well, that knowledge has been duplicated, so vibrators can be eliminated. Also, the latest in the old car hobby is solid state ignitions and voltage regulators that are totally hidden in the original distributors and regulator boxes so everything looks tatally original yet has the advantage of modern car technology. And also there's the "quartzing" of car clocks that make them much more reliable and accurate.

 

[kenwashesmonday]

Vibrators, Solid State Ignition, and Clocks

New solid state vibrators are currently available. They plug in the same way so the radio is not butchered. Don't forget to also change the buffer capacitor.
Often, a new-old-stock vibrator can be made to work by carefully cleaning the oxidation from the points with bond paper, then once you get it to start, let it run a while and the points will clean themselves.

I don't understand why so many people in the old car hobby convert to electronic ignition. Why make the car more complicated and difficult to diognose? I drive my '65 Rambler daily and it's no big deal to change the points and set the dwell once a year.

Car clocks, well, I guess I really wouldn't fault someone for converting to quartz, but they don't make the same sounds and the second hand movement is different. These little things are part of the "trip" of riding in a classic car. The original clocks will usually run pretty well with little effort. The clock in my '60 runs well after a simple cleaning, I unplug it when the car sits for weeks.

Conversion is NOT restoration!

Ken D.

 

[kenmore1978]

conversions

"I don't understand why so many people in the old car hobby convert to electronic ignition. Why make the car more complicated and difficult to diognose? I drive my '65 Rambler daily and it's no big deal to change the points and set the dwell once a year. "

I've changed many a set of points in my time and truthfully, it's a PITA unless it's a GM V8 distributor with the little window in the cap

As for car clock conversions, I've often wondered why they don't use the same type of mechanism a household quartz clock uses where the second hand "steps". Instead, the car quartz second hand goes around like an AC powered household clock (which you may have noticed, are virtually impossible to find new nowadays). Some old car owners are lucky in that not al car clocks HAD second hands so "quartzing" doesn't take away from the authenticity.

And let's face it, solid state voltage regulaters keep much better tabs on the voltage than the old mechanical units. I've had to replace more than one wiring harness that burned up because the cutout relay in the regulator went bad and allowed the battery to try and turn the generator into a motor.

 

[tolivac]

I like the idea of the newer solid-state vibrators-and no mods to the radio-thats better yet-you don't destroy the collector value of it and much less work.At the time I was experimenting with vibrators-My conversion had to be wired into the radio.It was too large for a "plug in" the early power transistors and capacitors-and the heat sink-made it too big to fit in the vibrator area.Used the radios case as a heat sink.
I don't think I would want to put a modern Quartz clock in an older car either.Drather have the "charm" of the old one.
I can go along with the reulators. The relay soleniod types can't keep up and can fail if the contacts stick and cause damage to other equipment.But a solid state one shorting isn't pleasent either.