A decent tube amp? "Worldwide 300B Builders"

[blueroomelectronics]

Creatron Inc now sells vacuum tubes and the owner Lawrence carries was looking for a good tube amp / preamp to make into kit form. Tubes are NOT my forte but I was Googling and came across this site. Some really nice looking project photos.
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[audioguru]

I made a Heathkit tube amp in about 1961. It sounded good when new then got bad.
I took it to a Macintosh Amplifier Clinic and they showed 12% distortion at only half its rated power. I replaced its output TOOBS and had it retested and it was powerful with low distortion. The distortion retuned in a few months.
TOOBS WEAR OUT!

My tube amplifier was Hi-Fi. It didn;t have the high second harmonic distortion of guitar amps.

You can buy very expensive amps with glowing tubes on top. The tubes are for show and are not part of the amp's circuit.

 

[Mikebits]

Yeah it seems as though tubes have been revived as Rock guitarist seem to prefer the sound of a good tube amp. I saw a site where the PA tubes sold for like $300. per amp in a pushpull configuration.

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[Speakerguy]

Don't they still use tubes for radio transmitters?

 

[Mikebits]

Don't they still use tubes for radio transmitters?

Prey tell, why would they? Semiconductors can produce mucho power these days, without the high fail rates of tube devices.

I suppose some old Ham types might just build one to be nostalgic.

 

[audioguru]

There are some huge vacuum tubes made for radio transmitters. Semiconductors can't stand 100kW and more with thousands of volts with hundreds of amps at RF.

 

[3v0]

Back in the late 80's I heard talk about an amp that HP engineers had developed for their personal use. The plans were passed from division to division. It was said to to better then anything you could buy but I do not have a clue where to go to find them.

 

[Mikebits]

Well I must confess I was thinking 1KW type transmitters. I really never thought about larger ones. Back in my Navy days, we had a 40KW magnetron that was water cooled. Quite a large setup.

 

[Mikebits]

200 KW solid state.
https://www.electro-tech-online.com/custompdfs/2008/07/dx200.pdf

 

[Nigel Goodwin]

I agree with the rest, I come from the valve/tube days, and it makes me laugh what people will pay for high distortion, high noise, and poor bandwidth these days

Where valvew amps are usful is guitar amps, because many guitarists are looking for that specific highly distorted sound - but far more actually use transistor amps, and even the valve amp fans often use transistor amps in the recording studio.

What you must NEVER do is run a transistor amp into clipping, as they sound really horrible.

 

[Speakerguy]

They also fall over themselves to get Allen Bradley carbon comp resistors. The one thing I don't want is something that a) dries out and b) has "voltage coefficients of [insert anything]".

 

[CynicalMan]

What you must NEVER do is run a transistor amp into clipping, as they sound really horrible.

There are some decent solid state amps that can distort just fine.

Clipping opamps sound like crap.

 

[crutschow]

They also fall over themselves to get Allen Bradley carbon comp resistors. The one thing I don't want is something that a) dries out and b) has "voltage coefficients of [insert anything]".

Plus excess noise from any dc current (unlike pure metal resistors which only have thermal noise).

 

[Nigel Goodwin]

There are some decent solid state amps that can distort just fine.

They would have to be specifically designed to clip, more an overdrive circuit than clipping the amplifier - it's usually done with clipping diodes in the preamp, and not by driving the output stage past the power rails!

 

[Centretek]

Valve amps are inherently better sounding because they don't generate odd harmonics like semiconductor devices because of the difference in inter-electrode capacitance.
As a youngster we made guitar amps with 120W RMS outputs from 6DQ6 s in push-pull.
These tubes were used in BW TV sets for the horizontal outputs.

If your valve amp kept degrading tubes then their heaters were being run to hot. Some valves had the cathode material coated onto the heater wires and it got depleted by excessive heat. The heater voltage should be 6.3V AC and NEVER higher than 7 Volts.
The anode plates of an audio valve should NEVER glow.

 

[audioguru]

I recall seeing the gas inside the output tubes of my amplifier glowing purple.

Harmonics are distortion. Solid state amps have extremely low distortion, much less than tube amps. The tubes and the output transformer were non-linear. The output transformer provides poor damping of the resonances of speakers. Solid state amps provide excellent damping.

 

[Nigel Goodwin]

Valve amps are inherently better sounding because they don't generate odd harmonics like semiconductor devices because of the difference in inter-electrode capacitance.

So 0.001% odd harmonic distortion from a transistor amp sounds worse than 10% even harmonic distortion from a valve amp? - I don't think so!

 

[audioguru]

A single-ended tubes or transistors amp produces even harmonics distortion. When they are operated push-pull then the even harmonics cancel and the result is a form of compression of the higher currents which results in odd harmonics distortion.

The phase-shift in the output transformer of a tubes amp limits the amount of negative feedback that is used so the distortion is much higher than a transistors amp.

 

[petrv]

Hi, (sorry to revive an old thread but I think it is better than starting a new one).

I have also noticed this renewed interest in tube/valve technology and it certainly brings nostalgia - I used to play with it long time ago but the question is why ? Some companies selling tube amp kits have fantastic claims about the performance of their amps - for example:

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Hard to believe but anyway I like retro technologies sometimes - just to play with it and remember those old days - I am not going to replace my amp. with tubes in the same way as I remember those days of 8-bit computers like C-64, ZX-Spectrum and Atari-800 but I am not going to use them instead of my PC

So it would be interesting to hear your opinion about the reasons for the renewed interest in tubes/valves.

Petr

 

[audioguru]

The 30W per channel (pretty low power) tube amp has its distortion rated at only 1W. Its distortion at full output is probably horrible.
Its damping factor is not mentioned probably because it is very low and it allows speakers to resonate.
There is no guarantee on how long the tubes will last or how soon the distortion will be much worse.