• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

25 watt output tube

I'd use a GU50, then it doesn't really matter how much power you want from it: it will be enough.

Sure. It is still alive even after short dissipation of 100+ watt. :)
Recently experimenting with monoblock with 4xGU-50 output I made a mistake in bias adjustment. However, it sounded very nice and very loud, but smelled like a burning paint, so I come closer to the amp to sniff what smells, I thought it was some resistor... But I found that anodes were red. :D
 
Are you actually going to build it? If you are only doing a design, you can use the 6CA7 (EL34) pentode in push pull for an easy 28 watts. The reason I suggest this one is that you will have no problem easily finding datasheets on-line for this popular tube as it is still widely manufactured. Other such options include the KT88 and 6550 pentode with even greater power. Single ended designs are simpler but 25 watts pushes way out on the envelope and I suspect you will struggle to find datasheets on these monsters.

If you are going to build it, then that's another matter.
 
Are you actually going to build it? If you are only doing a design, you can use the 6CA7 (EL34) pentode in push pull for an easy 28 watts. The reason I suggest this one is that you will have no problem easily finding datasheets on-line for this popular tube as it is still widely manufactured. Other such options include the KT88 and 6550 pentode with even greater power. Single ended designs are simpler but 25 watts pushes way out on the envelope and I suspect you will struggle to find datasheets on these monsters.

If you are going to build it, then that's another matter.


I will be building it as well yes.
 
I have the Radio Designer Handbook and Valve Amplifiers by Morgan Jone's. I'm just looking for a good output tube for a 25 watt amplifier.

Which tube is good depends on answers to questions folks asked you already. You forgot to define your targets, except power. Which power? Output power? Dissipation power? SE, or PP amp? And so on...
 

ChrisA

Member
2008-01-08 12:22 am
I have the Radio Designer Handbook and Valve Amplifiers by Morgan Jone's. I'm just looking for a good output tube for a 25 watt amplifier.


I think you have to learn how to write better more detailed specifications. For example. Should the amp sound good at 25W or just have 25W of power? Over what frequency range? Are we talking about stereo or mono and if stereo is this 25W per channel or two 12.5W channels. Is this for HiFi or a guitar amp or maybe for a PA system

OK if you want and easy answer and an amp that will be easy and low cost to build use a pair of 6L6 tubes in push pull. You can build the amp to accept an entire range of tube all of the same family. you amp might tale 6550, 6L6, 6V6, KT88 and so on, just make the bias adjustable.

What you will find is that the main componet of a tube amp is not the tube but the transformers. These can cost 5X the price of the tubes as one can find way-cheap tubes but not low priced transformers.
 
..But I found that anodes were red. :D

Same happened to me after a dry joint disconnected my (pentode mode) -20-25V (ish) bias that held them at 60mA on 430V. I discovered that because one of the tube's anode was orange with heat, a lovely even glow surrealistic in colour. The tube was undamaged and I'm listening to it now in fact!
 
Same happened to me after a dry joint disconnected my (pentode mode) -20-25V (ish) bias that held them at 60mA on 430V. I discovered that because one of the tube's anode was orange with heat, a lovely even glow surrealistic in colour. The tube was undamaged and I'm listening to it now in fact!


They were designed by Telefunken to survive being abused by army or government users so they won't complain (and you can imagine the way they were complaining there and then!). Anodes made from Nickel alloy.
 
Yes. 450V B+, 4K load, 620 Ohm cathode resistor shunted by capacitor. Needs about 100-120V of input swing. Input transformer may be used to drive by iPod or some other similar source. 100V to 16 Ohm speaker transformer may be good to drive it.

About 40W of idle dissipation, about 100 mA of idle current.
Many thanks; 450V- so the G2 rating is very conservative then-Good,that makes things much easier and I have a fair stash of them.I must say,they do look great and the triode connected curves that I have did look promising. A bit of a contrast to what I have just built-a power differential amplifier producing about 4 watts! Curiously, it is still enough to blow me out of the room!