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Old 8th June 2005, 11:47 PM   #1
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Question could 24A been power tube

I had some UY224 24A...... as the data sheet says. It could be use as amp tube. do anyone know how to design a pre-amp with it or even as a power tube. I had try to find but all of them were used in radio system. Thanks If any one could answer.
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Old 9th June 2005, 03:13 AM   #2
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It is the first AC-heat tetrode: two key innovations in one.

Tetrodes make awful amplifiers. Pentodes displaced tetrodes so fast it wasn't funny. (So-called Beam Tetrodes are pentodes. Details are different to avoid patent fights, but the electrons go through the same fields as a pentode.)

It is a small tetrode: no good for power. Maybe headphones.

It eats a lot of heater power for what it does. Heater-cathode insulation isn't that good.

It may be low distortion (if you stay out of the kinky-zone).

It does not seem to be at all rare: $5 many places.

It is a very pretty tube.

http://frank.pocnet.net/sheets/029/2/24A.pdf

Click the image to open in full size.

The grid bias could be a 1K8 cathode resistor. Output impedance would be the plate resistor, too high to run outside the box.

Looking at the plate-curves, another operating point could be: Plate supply 250V, grid voltage -3V (or 600 ohm cathode resistor), screen supply 90V, plate current 4mA, plate load resistor 22K. With cathode bypass, this gives gain around 25 and output impedance of 22K.

Screen grid voltage has to be stable: either a voltage-divider with several mA of current flowing, another winding on the power transformer, or regulated.

It should work as a triode (screen strapped to plate) but I can not find any data for this condition.
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Old 9th June 2005, 04:32 PM   #3
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yes it is easy to buy but not easy to find anyone use it?
looks realy nice one so I want to design an amp with it. maybe triode connect is a good idea but I have no idea to make sure the plate load plate votage Vg1 even the cath resist...... If i use it as tetrode it have some stability problems. so the pure tetrode was soon superseded.(from valve amplifiers p88) according to this book the 24A is not good in audio amp? how could i do with these tubes?
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Old 9th June 2005, 09:46 PM   #4
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> I have no idea to make sure the plate load plate votage Vg1 even the cath resist...... If i use it as tetrode it have some stability problems.

Nah. You just have to stay away from low plate voltages.

This should work as a line-amp:
Click the image to open in full size.

The dynamic loadline is about like this:
Click the image to open in full size.
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Old 9th June 2005, 10:18 PM   #5
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This should probably work as a "power amp", around 1 Watt with some damping:

Click the image to open in full size.

For Stereo: This needs a 2.5V 21 Amp heater supply, and about 50mA at 250V. And a dozen type '24 bottles, which isn't really a lot of cash (maybe $60-$75) compared to type '50, 2A3, and other old-reliables that have become fashionable.

In general: using "modern" triodes and pentodes, I could do what a '24 does but using 2/3rd the plate power and 1/4 the heater power. As a practical commercial matter: if this were 1928 all over again, I could make a good radio a lot cheaper with later tubes. However the world has turned topsy-turvy since 1928. We have reached the heights of high-efficiency 200-watt 8417 tube-amps, and have turned aside to low-efficiency pretty-bottle amps.
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Old 10th June 2005, 05:53 AM   #6
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Hmmmmm... I'm going to take a flying leap through a rolling grid-cap and guess that a triode-strapped '24 might be a lot like a '27 triode. It seems a '24 has a higher Mu than a '27, which makes some sense: the '24 is for large voltage gain into very high impedance, the -27 was used for modest voltage gain into moderate impedances.

If you have a heap of '24s looking for a good home, you may as well strap them into semi-'27s. Triode-strapping the pure-tetrode eliminates the wonky behavior at low plate voltages. And saves the awkwardness of a low-impedance lower-voltage screen supply.

This should cook over 1 Watt with excellent linearity. You could omit the 1.2K feedback resistor and be zero global feedback. OPT current is about 25mA. Going to a 10K load will reduce distortion and improve damping more than it hurts power.

Click the image to open in full size.

The first stage alone might be a good line-amp. Gain about 5 or 10, output impedance around 10K.

If you actually stick a dozen '24s on a box, I want a picture. In the light, and in the dark.
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Old 12th June 2005, 02:26 PM   #7
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thanks a lot I'll try as signal tube to drive 6528 or 6L6
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Old 6th April 2014, 06:30 PM   #8
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Default Resurrecting this old thread

I spotted this article on 6moons:
6moons audioreviews: JohnBlue Audio Art JB3 Sidebar I
it seems 24a is really good when using for preamp.
Incidentally I have a bunch of them...
Can everybody suggest other scheme?
Anyone tried the triode-strapped preamp described above (i.e. the first part of the last power amp scheme)?

Ciao
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Old 16th April 2014, 03:11 AM   #9
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I recently received about 40 of the 224 and 24 types as well and would love to hear of any practical uses for these as well.
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"A problem left to itself dries up or goes rotten. But fertilize a problem with a solution--you'll hatch out dozens." (N.F.Simpson)
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Old 20th May 2014, 06:15 AM   #10
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Quote:
Originally Posted by PRR View Post
Hmmmmm... I'm going to take a flying leap through a rolling grid-cap and guess that a triode-strapped '24 might be a lot like a '27 triode. It seems a '24 has a higher Mu than a '27, which makes some sense: the '24 is for large voltage gain into very high impedance, the -27 was used for modest voltage gain into moderate impedances.

If you have a heap of '24s looking for a good home, you may as well strap them into semi-'27s. Triode-strapping the pure-tetrode eliminates the wonky behavior at low plate voltages. And saves the awkwardness of a low-impedance lower-voltage screen supply.

This should cook over 1 Watt with excellent linearity. You could omit the 1.2K feedback resistor and be zero global feedback. OPT current is about 25mA. Going to a 10K load will reduce distortion and improve damping more than it hurts power.

Click the image to open in full size.

The first stage alone might be a good line-amp. Gain about 5 or 10, output impedance around 10K.

If you actually stick a dozen '24s on a box, I want a picture. In the light, and in the dark.
PRR,
pics are no longer visible!
Please, can you post them again as I'd like to build the preamp you suggested?

Thank you for your help!
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