Do tubes do anything well in circuits?

[SIY]

Do you think the amp in my previous post would be distinguishable in a double blind test vs a D'Agostino Progression M550?

Depends on the output impedance.

 

[Doodski]

The tube amps that powered Woodstock had pretty respectable performance!

View attachment 165727View attachment 165728

Wowow. 350w/ch is good tube power. Can you say what amplifier that is?

 

[Murray A]

Wowow. 350w/ch is good tube power. Can you say what amplifier that is?

Mac MI-350 aka MC-3500. The visible onset of clipping is 470 watts.

 

[escksu]

Wowow. 350w/ch is good tube power. Can you say what amplifier that is?

350W froma tube amp............that is unheard of.....wow...

 

[Doodski]

Mac MI-350 aka MC-3500. The visible onset of clipping is 470 watts.

Very nice. It looks like 350w/ch/470w too.

 

[mhardy6647]

350W froma tube amp............that is unheard of.....wow...

Horizontal output ("sweep") tubes push-pull parallel.

 

[Doodski]

Horizontal output ("sweep") tubes push-pull parallel.

Here is a service manual if you want to see the circuitry topography. I know next to nothing about tube circuitry so it's all eye candy to me.

 

[Murray A]

Here's the patent for the MC-3500. The best descripton of circuit operation I've seen.

 

[mhardy6647]

The Mac was actually a pretty good amplifier. The trick of using horizontal output tubes for... things besides TV sets originated, AFAIK, with a cheap way to make linear amplifiers for HF ham (and ahem CB) radio. Mac's just reintroduced a vacuum tube "monoblock" amp that is apparently their modern reboot of the MI-350.

"Sideshow Bob" Carver (of Flame Phase Linear fame, and others over the years) has been known to get pretty generous with output tubes on occasion.
Note that, unlike the suspiciously similar looking Atma-Sphere OTL amplifiers (which use scads of output tubes to get reasonable output impedance without an OPT), these Carver monstrosities are "just" massively PPP, transformer-coupled amplifiers. Frightfully inelegant, to my way of thinking.

I dunno -- at my house, we like the KISS approach.
3.5 watts (ish) via a single 2A3 DHT per channel.

015b by Mark Hardy, on Flickr

 

[Doodski]

How often should the bias calibration be done on a amp like this? The service manual does not mention this.

 

[Murray A]

How often should the bias calibration be done on a amp like this? The service manual does not mention this.
View attachment 165762

The amp has a handy bias meter and switching to measure the individual output tubes. The amp is very stable and rarely requires adjusment. Unlike most power amplifiers of the period, these amps could and were run at full rated output continuously in industrial applications.

 

[Doodski]

@Murray A the power switch gives off a, "I mean business" kind of appearance. I had issues with power switches on big amps. It can be a pain in the butt finding a suitable package for the mounting configuration. So I appreciate a robust power switch. What is a industrial application for a amp like this?

 

[DonH56]

350 W? Phhhuiii...

750 W:

Reference 750 SEL Mono Amplifier – Audio Research

audioresearch.com

500W -- OTL!!! http://atma-sphere.com/en/ma-3.html

 

[Doodski]

500W -- OTL!!! http://atma-sphere.com/en/ma-3.html

Cool.
"The MA-3's power supply has a built-in AC line processor that regulates the line voltage coming into the amp! As a result, line voltage has no effect on the MA-3; it will make full power even if the AC line level has dropped to only 100 Volts."

 

[Rottmannash]

This is only true for tubes driving low impedance - i.o.w. output stages of power amps. Tubes in preamps and lots of other applications do not require transformers at the output.




Yes, the buffer stage (typically a cathode follower) is very transparent and doesn't have a "tube sound" (contrary to what most say about tubes)

Like the one in my Freya+?

 

[Rottmannash]

Off topic, but when the US got their hands on a MIG-25 in the mid-70's, they were amazed to find that most of the avionics was miniature valves - which they then realised was actually an advantage because of the resistance to an EM pulse.

Miniature valves? How small can a tube be made?

 

[MakeMineVinyl]

Miniature valves? How small can a tube be made?

This small.

 

[Rottmannash]

This small.

Wow-tiny.

 

[Murray A]

@Murray A the power switch gives off a, "I mean business" kind of appearance. I had issues with power switches on big amps. It can be a pain in the butt finding a suitable package for the mounting configuration. So I appreciate a robust power switch. What is a industrial application for a amp like this?

The double circuit breaker incorporates two coils for sensing current in the output tube screen and cathode circuits. Will quickly shut down the amplifier if an output tube fails.

Industrial apps: vibration exciters, variable ac source to drive syncro/gyro devices for aircraft/missle guidance systems, shake table drivers (kodak), ac source for instrument calibration, submarine pingers, record cutter head amp, guitar amp etc.

 

[Doodski]

The double circuit breaker incorporates two coils for sensing current in the output tube screen and cathode circuits to quickly shut down the amplifier if an output tube fails

View attachment 165768

That's pretty nice. It appears you have done some MODs to the amp like capacitor upgrades?. I love that General Radio variac with the meters.
What is this thing?