DIY Audio Projects Forum

DIY 50EH5 / 25EH5 Tube Amplifier
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Author:  Gio [ 09 Feb 2009, 20:19 ]
Post subject:  Re: DIY 50EH5 / 25EH5 Tube Amplifier

Hi Alan,

I updated the Single-Ended (SE) 50EH5 Tube Amplifier page over the weekend. You may have to "refresh / reload" the page to see the changes. I also added a link at the bottom of the project page to this forum thread which contains the info for your project.

Those new Rikens are pretty pricey and hard to justify for a little amp project like this.

Your audio output transformers are quite a bit larger than mine so it is not really suitable for headphones. Mine is limited to driving ~60-80Hz and up.

Author:  CrazzyAbtTubes [ 10 Feb 2009, 16:35 ]
Post subject:  Re: DIY 50EH5 / 25EH5 Tube Amplifier

Well I suppose you could upgrade the iron to edcor's, it would be an improvement from the outputs you have now. I'm not sure what the frequency response of my amp is but it sounds like it will do down 20hz, I should take some scope measurements some day, if I can figure out how to use the one I have, it is really old but it seems to work.

I payed $5.40 for the two 62 ohm Rikens from Parts Connection, I don't know if that is a standard value but it seemed worth the extra gold. In the end I spent about 50 bucks for the entire project, which is a good price for the performance I get from such a simple amp. :P

I wonder if the 6AQ5 could be used as well, I will check the pin outs but I doubt they will be the same, and the tube probably runs at a different bias as well.

I shall check the updates now... :geek:

Author:  CrazzyAbtTubes [ 24 Nov 2009, 21:52 ]
Post subject:  Re: DIY 50EH5 / 25EH5 Tube Amplifier

It has been nearly a year since I had this project pugged in and running, and over the last couple of monthes I have been reconstructing the amplifier and have after finally making a suitible 24V regulated power supply I hooked the amp up for a test run on my big JBL's, for the first time ever!!! :)

At first I didn't think it would have near enough power to drive them, but it did just fine, although lacking a bit in the low frequencies but even so it sounded amazingly good, actually better than when I first built it, and runs amazingly quiet! Quieter than my Mini preamp!! :o

If I threw a sub along side the amplifier it would probably sound as if I had a 50 watt system at hand because the amplifier seems to have alot of kick for only 1.4 watts per channel.

I have yet to take some pictures of the amplifier, as it looks much more complete than it did before. I painted the transformer, sanded scuffs and sharp edges around wholes on the chassis and added some basic lables with a sharpie marker, just in case the amplifier is not simple enough to understand as is. ;)

There are a few added features too, the 24V filament supply is seperate from the amplifier and has its own mains switch and power cord, so there is a 24V relay inside the amplifier that controls the mains power to the amplifier, meaning that the 24V supply has to be running to pre heat the 25EH5 filaments in order to turn the amplifier on. I also added a 315mA 250V fuse to one side of the HV secondary AC, and a really neat feature with the power supply setup that Gio created is that there is no on/off pop when the high voltage is turned on. Other than the changes said above, the power supply is the only section that I rewired to solve some noise problems and grounding problems.

I hope this to be encouraging news to Gio and good listening to all. :headphones:

Author:  Gio [ 24 Nov 2009, 22:57 ]
Post subject:  Re: DIY 50EH5 / 25EH5 Tube Amplifier

Hey Alan, great to hear you are still enjoying this little amp. My output iron is even smaller than yours so I get even less low end. Single-ended can sound pretty nice.

Author:  CrazzyAbtTubes [ 26 Nov 2009, 19:13 ]
Post subject:  Re: DIY 50EH5 / 25EH5 Tube Amplifier

Like I said, using a sub that problem could be solved, or even just making a bi-amp set up, have a nice SS amp driving the low end and the tube SE amp for the mid and high end. :)

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