Amplifier builds

[swamp_thing]

One of my pastimes is building and using tube electronics. Here are some pictures of a couple of tube stereo amplifiers I have built. They are built off designs by Matt at Cascade Amps. 

Both amps are about 5 watt ultra linear single ended. One is using 6L6 power output tubes and the other uses 6V6 power output tubes. They sound amazing.

[Dr.Hess]

That's cool.  I grew up learning tube theory and working on tube equipment.  Transistors were out of course, but the 1932 book I got at the library that I learned electronics from didn't have transistors in it.  I still have just about everything I need to make a 1.5KW output 100% duty cycle HF amp.  Plate transformer good for about 3.5KV at an amp, caps for that, 3CX1500B tube and a 4CX1500, if I want to go that route.  Tuning coil and capacitor.  Biggest thing I don't have (besides the chassis) is the socket for one of those tubes.

[swamp_thing]

I see there are sources for the sockets online with a wide range of prices. When it comes to the tubes, they are a bit pricy these days. 1150 dollars each would make a person think twice maybe. But then, like most everything, supply and demand has it's price. Even popular new old stock preamp and power tubes can get into the hundreds. I'll be sticking with new production tubes for my projects. My ears can't tell the difference.

[Horsefly]

Going to show my age. Stores like 7-11 and Whites Auto or Western Auto had tube testers where you take all your tubes in and plug each one into socket marked with tube number and needle would show good or bad. If bad there was a drawer underneath cabinet with new replacement tube. Amazes me you get sound and pictures out of tubes. I took Radio-TV class in high school 2 hrs. a day and it was just enough to confuse hell outta me. 1970 tubes were on their way out but vocation class was still teaching. Every hat I have is off to you for building from scratch. Amazing !

[FC]

How’d you learn to do this?
it’s tough to find someone who can work on old radios.

[swamp_thing]

Funny, I had one of those tube testers for a couple of years. The meter finally died and honestly they were not the greatest testers by any means. Still, they were much better than nothing.  I have learned a lot in the last 15 years about this hobby but will never have a complete grasp on how or why everything comes together. Thanks for the kind words Horsefly.

Dr Hess, you should put that hf amp together. Go for it.

[swamp_thing]

FC, when I was a kid some 55 years or so ago I was very interested in radio and such. Never did anything with it until about 15 years ago. Got started trying to repair a few tube radios with limited success by reading books my brother sent me and searching the web. Over time I built a few fender guitar amp clones, again using knowledge I gathered from internet sites. Then I spent a few years back repairing tube radios and finally have transitioned to hifi amps as well. It is addictive as there always seems to be that next project. As for repairng radios most all the repairmen are long ago out of business. Parts are hard to find or non existant and poeple don't want to spend what repairs would cost. It's more of a labor of love these days with a few die hards hanging on.

[Dr.Hess]

I think I have an old Fender guitar amp.  It was my father-in-law's.  Makes a bad hum when you try to power it up.  It's gotta be a small one, physical size is probably a foot tall.

Yeah, I need to do that amp one of these days.  Been hoarding the parts for it for over 40 years now.  I even have a pretty good sized squirrel cage fan to cool it.  Just the plate transformer today would be pretty expensive, I think.  It should do 4KV at an amp with capacitive input, weighs over a hundred lbs.  I might also have to run a 220 line to the "radio shack" for it.  Probably can drop it down from the AC unit in the attic.  "Just don't key up when the AC heat is on."  The tubes were "worked when pulled" stuff I came across.  I might even have something laying around for the heater element.

[swamp_thing]

3 hours ago, Dr.Hess said:

I think I have an old Fender guitar amp.  It was my father-in-law's.  Makes a bad hum when you try to power it up.

Sounds like the electrolytics in the power supply have given up the ghost. 

[Dr.Hess]

Yeah, that's what I figger.  However, I have zero interest in fixing it.  It technically "belongs" to my wife.  It will sit where it is forever, I suppose.  I'm pretty sure cheap Fender guitar amps are about worthless anyway.  Especially broken ones.

BTW, you can re-form the electrolytic caps if you have some kind of variable DC power supply.  We used to do it in TV Repair class in high school.  We had a whole lot of very old caps someone had donated.  You'd take one, put it on a variable PS, monitor the current, which had to be kept low, crank up the voltage slowly while keeping an eye on the current until you hit the operating voltage, and the "skin" in there would reform.

[FC]

My grandpa's Philco portable vacuum tube radio still works. It was supposedly one of the first portable radios. 

[AzRednek]

9 hours ago, FC said:

My grandpa's Philco portable vacuum tube radio still works. It was supposedly one of the first portable radios. 

My parents had a portable tube Philco AM radio. It used a large round dry cell battery. According to Mom they only used it a few times as the batteries were expensive and only good for a couple of hours. As a kid in the 50s I can recall bringing the radio into the foxhole we dug in the backyard to play Army. 

[Dr.Hess]

That battery was probably 3 batteries in one.  Plate, grid and filament heater.  That's why it would have been expensive.  Probably limited to only Philco radios, maybe only some of them and not generic.