Contex 500 Tube Amp

[Shadetree Mechanic]

Hey guys,
I just bought a Context 500 for use on 11 meters in my new little shack. Does anyone have a manual for this or know where I can get one? I am looking for information on the tuning procedure for setting the drive and the load etc. I assume it would be the same as any other amp? It has five 6LQ6 tubes and appears to be recapped. I don't have it in my hands yet, just trying to learn all I can about it. There is surprisingly little information about it when Googled. Any and all comments welcome.

This is not the actual unit, just a picture I found of one.

 

[Shadetree Mechanic]

Just got the amp and took the cover off. Looks fairly clean and looks like it is all there.



Looks like the big caps have been replaced at some point.

 

[Shadetree Mechanic]

Can anyone tell me what the indicator light on the front is? Some kind of overload indicator? Just trying to get this thing going. Any help is appreciated, Thanks.

 

[nomadradio]

It is wired to the tubes' heater supply. Should be a 6.3-Volt pilot lamp like a #47 or #755.

73

 

[dozerman]

i had the little green 2 tube contex a long time ago. i had the manual with it. best i remember, it tunes to peak and thats it. the light in the front is a tuning indicator. the brighter it gets, the better tune it has. atleast thats how my context was. it think mine had jg6's in it.

 

[nomadradio]

The tuning lights were kinda cool. If you didn't have a meter in line you could still peak the thing.

This one is wired to pin 5 of the nearest tube socket. Heater on this tube is at pins 4 and 5.

73

 

[jessejamesdallas]

AM only? no SSB delay...so sad.

 

[nomadradio]

Doesn't have any fixed grid-bias voltage on the tubes. The tubes will tend to draw excess current with a low drive carrier level, or on sideband where there is no carrier.

The carrier from the radio serves to set the tubes' operating current. With zero bias, they will cherry up and smoke something.

The SSB switch on a lot of older sweep-tube amplifiers is a borderline fraud to begin with. Could easily be labeled "Suicide Selector".

73

 

[Shadetree Mechanic]

It is wired to the tubes' heater supply. Should be a 6.3-Volt pilot lamp like a #47 or #755.

73

I will double check what bulb is in it, I plan on pulling the cover back off so I can study it some more. So this light should be lit the whole time the unit is powered up? Sorry for the Noob Questions, Thanks!

 

[Shadetree Mechanic]

i had the little green 2 tube contex a long time ago. i had the manual with it. best i remember, it tunes to peak and thats it. the light in the front is a tuning indicator. the brighter it gets, the better tune it has. atleast thats how my context was. it think mine had jg6's in it.

I think I saw one of those on eBay too. That would be a neat little amp to have.

 

[Shadetree Mechanic]

The tuning lights were kinda cool. If you didn't have a meter in line you could still peak the thing.

This one is wired to pin 5 of the nearest tube socket. Heater on this tube is at pins 4 and 5.

73

The heater on the 6LQ6 is pins 4 and 5. Taking notes. I learned transistors In tec school but they didn't teach us tubes. I will have to find out what the plate and the grid are all about. Thanks.

 

[dozerman]

I think I saw one of those on eBay too. That would be a neat little amp to have.

it was. a splatter box for sure. no fan so after a while of ratchet jawing, you could fry eggs on the cover. wish i still had that thing

 

[Shadetree Mechanic]

AM only? no SSB delay...so sad.

I plan to run this on my AM rig (Sonar 2340) and it would be nice to have an SSB mode for when I get an SSB radio. Gives me an excuse to buy another amp. LOL

 

[dozerman]

The heater on the 6LQ6 is pins 4 and 5. Taking notes. I learned transistors In tec school but they didn't teach us tubes. I will have to find out what the plate and the grid are all about. Thanks.

yeah thats what im doing too. i follow these tube amp posts closely. all the tube techs around my neck are gone or going, save one in memphis. i pester a few of the techs on here with questions.

 

[Shadetree Mechanic]

Doesn't have any fixed grid-bias voltage on the tubes. The tubes will tend to draw excess current with a low drive carrier level, or on sideband where there is no carrier.

The carrier from the radio serves to set the tubes' operating current. With zero bias, they will cherry up and smoke something.

The SSB switch on a lot of older sweep-tube amplifiers is a borderline fraud to begin with. Could easily be labeled "Suicide Selector".

73

That's interesting to know that the bias is set with the carrier level. I plan on running this with a Sonar 2340 that has a 1.5w dead key swinging to 18w. Should I turn the dead key up a little so I don't kill the tubes?