RE-Tube amp questions

Tubes are hot, transistors are co-o-o-ol >:-} ...Jim Thompson

The Magic eye tube was generaly used as a tuning indicator driven by the AGC (Automatic Volume Control)voltage and since you will neither have tuning nor AGC in you amp, a Magic Eye will not be of much use unless you drive it from the audio andjust let it wink 8-o away for Cool Looks.

That's the sort of thing that get audiphools aroused >:-} ...Jim Thompson

I used to have a Q meter that used a magic eye tube as a tuning indicator. The're kind of cool.

Cheers

Phil Hobbs

Yep. I played around with them when I was a kid.... used to be common-place tuning indicators on radios. ...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

You can buy fake tubes that have LEDs inside that look like filaments. Mount them on top of a nice Best Buy Panasonic receiver.

Sort of like this:

Yeah, yeah, yeah. Eric

I like new stuff and old stuff. I don't like fake stuff though. If I want the tube look then I'll use real tubes to do the job. I think that many things we use can be made esthetically pleasing, to me as well as others. When I make stuff for myself I make it to please myself. For example, when I make a special tool to use in my machine shop I will put on chamfers or radii or if made from steel I'll color the surface with a torch. Because it pleases me. I have several old motors that I use on shop made tools. I like the look of old motors and have found some pretty good looking motors for cheap at garage sales and the like. Eric

All my filaments glow blue too. ;)

Cheers

Phil Hobbs

No wonder they don't work. :)

Well, all I did was try saving a transformer by wiring all the filaments to 120V--parallel, right?

Cheers

Phil Hobbs

That's a fake thyratron. They cost more.

Some tubes wouldn't mind 120 VAC on the filaments. On the other hand, there were tubes with a pair of 1.5 VAC filaments at 1000A each. That would blow your fuses! :)

Damn, that's worse than a microprocessor.

What kind of tube needs over a thousand watt heater ? I mean, I can understand high power transmitting tubes but it really takes that much to cause thermionic emission ?

They must be wanting alot of emission.

A purist. Some of us understand where you are at. ("coming from")

Function counts, appearance only counts if it is functional.

Ditto the new/old dichotomy, if I'm building something that Tesla would, it is brass wood screws, oak cabinets, potting in beeswax, and a lot of time and effort at staying in context.

Programmable IC's get perfboard and plastic.

My childhood was all screwing tube sockets to wooden bases and point to point wiring. (and I miss it)

Copperclad is an art form.

stand high power transmitting tubes but it really takes that much to cause thermionic emission ?

The Harris BT18-L2 transmitter where I worked used 2 of these, one aural an d one visual. Note the filament power. Not quite what Michael mentioned but up there.

Did you ever post on AK ?

Anyway, the amp you referenced is not the amp I would build. There are alot of options. Another thing is that it needs 4 volts to hit maximum output. Dmanear have to run it off a headphone jack, and that is not always the hig hest of fidelity. It is usually better than what would go to the speakers b ecause it is unloaded, but most preamps do not put out that much, at least at low distortion. You would pretty much need a tube preamp and your choice s are vintage or expensive. Either that or build a custom booster.

There is a guy on AK right now with that problem but it is not a tube amp, it is a commercial amp designed to run off a mixing board. In that case, I could modify his amp to have higher gain. This would not reduce performance much because the open loop gain is probably high as hell. But not so in a tube amp. Upping the gain of those frequently runs you into problems pertai ning to harmonic distortion and even frequency response.

This was the power tetrode in a RCA TTU-25B. 3 KW of heater for visual, and 1.5 KW of heater for Aural. RCA designed the tubes for this transmitter. It was one of the first 'high power UHF transmitters' at 25 KW Visual output.