50 yr Old 3 tube amplifier circuit?

[AnalogKid]

1970 and point-to-point - Zenith?

 

[audioguru]

My first color TV was a 1971 Philips designed and made in Canada. It had four pcbs. It used a "jungle" IC, a few other ICs, many transistors and a few high voltage vacuum tubes. I replaced it 26 years later in 1997 with a Sony that lasted only 8 or 9 years.

 

[Mikebits]

I have only made 1 tube amp project in my life. It was a single tube amp using the 12xxx family. I chose that one because it worked at 12vdc which I thought was cool. I can post a pic of it if anyone is interested. It actually worked

 

[audioguru]

I built a Heathkit stereo amplifier that had tubes in about 1961 or 1962. Its output tubes needed replacement every 3 months for its distortion to remain low. It heated my single room apartment. Then I built an Eico FM tuner kit then I built a stereo adapter for it when stereo was invented for FM. They also used tubes.

 

[AnalogKid]

Schenectady, NY, June 1, 1961, 12:01 a.m., WGFM.

 

[Nigel Goodwin]

I built a Heathkit stereo amplifier that had tubes in about 1961 or 1962. Its output tubes needed replacement every 3 months for its distortion to remain low.

There was something seriously wrong if you had to replace valves as often as that - well designed valve amplifiers went for years without needing replacements.

 

[audioguru]

They had a purple glow inside. Was the plate voltage too high to cause this?
Many rock groups replace their tubes (and maybe also their valves) for every show.

 

[Nigel Goodwin]

They had a purple glow inside. Was the plate voltage too high to cause this?

Something was obviously wrong, as they shouldn't glow purple

Seems a shame though, as Heathkit was usually really good stuff, and great kits to build.

Many rock groups replace their tubes (and maybe also their valves) for every show.

Not in my (considerable) experience, and particularly with the low quality of valves these days - you're as likely to fit ones worse than the existing ones, than better.

But for a band you certainly carry spare valves, as they can fail at any time - particularly the way they treat the gear.

 

[AnalogKid]

audioguru said:They had a purple glow inside. Was the plate voltage too high to cause this?

Something was obviously wrong.

Some *thing*?