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832 / GU32 tube push-pull amplifier project
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Author:  Bennybuis [ 14 Dec 2009, 06:20 ]
Post subject:  832 / GU32 tube push-pull amplifier project

Hallo everybody,
I am Ben from Holland and I decided, after some thoughts with Bruce from OddWatt and Gio, to post a very simple project for the beginner. I have been playing around with those GU32 dual tetrodes, because I think they are so beautiful.
Attachment:
GU32 illuminated.jpg

Now I have several schematics involving this tube, I tried them all with about similar result. The one provided from WhattWatt and improved from Bruce from OddWatt sounds the best, but also implies the most parts. I came across a very simple schematic and after altering it a bit, like adding a bit of NFB (negative feed back) and I changed the values of some resistors, left the choke away, simply, because I don't have such a thing and wound up with a very simple, good sounding amplifier. My primary goal is to make it so easy that everybody dares to do that and will still end up with a good sounding tube amp. And that project gives you lots of space for improvement. If anybody is interested in building that with me, I can hook you up with some GU32 and sockets for little money. Well the next pictures show the raw enclosures I used. They are simply made of wood and painted with some fancy stone effect paint. Looks good enough to me. I used AC heating, just to keep it as simple as possible. Check out the photos. If you use AC for the filaments, you should twist the wires as much as possible to avoid hum. You see the power supply on the left with filter cap and the green and yellow wires are for the filament.
Attachment:
IMAGE_423.jpg

The second schematic has the feedback drawn in from Bruce from OddWatt, but it still contains the choke. I will hand draw the final schematic and upload it today.
Attachment:
832PP schematic ver2.JPG

Next step, I will start wiring the whole thing. I will post pictures as I progress. If anybody is interested in joining me and my little project, please drop me a private message, I can hook you up with GU32. Good listening and Thanks to Gerd Reinhoiefer for providing the original schematic and special thanks to Bruce Heran from OddWatt. He is supporting me and that little project with his knowledge, patience and he also supplied the auri caps, very nice sounding coupling caps. Very special thanks to Gio, he has been just as supportive to me, answering patiently all my stupid questions. Without those both I would have not gotten that far that fast.

Greetings from Holland.

I will remove the filter cap again or solder a 100k resistor temporary across it, cause it charges with 270 volts and I got shocked a couple of times. BE CAREFUL

Author:  Soundbrigade [ 14 Dec 2009, 06:38 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

You DID mount blue LEDs under the tubes? :P

Author:  Bennybuis [ 14 Dec 2009, 07:01 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Here are a couple of pics from the top of the amp. Cute little thing.
Attachment:
IMAGE_427.jpg

Now I will wire that thing and post pictures asap. I really hope I can get someone excited to try this simple good sounding amplifier, it's almost to easy not to try. Greetings from Holland.

Author:  Bennybuis [ 14 Dec 2009, 10:08 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Hallo everybody, here is the schematic just like I will build it, without the choke and with a bit lower values on the grid resistors. That one is tested and works good that way.
Attachment:
Simple amp GU32.jpg

Author:  Geek [ 14 Dec 2009, 17:08 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Looking good so far :D

I always shudder when I see LTP's misused like that. Check your AC balance across the LTP anodes and you'll see why most designers use 82K/100K on the anode instead of 100K/100K ;)

Cheers!

Author:  Bennybuis [ 15 Dec 2009, 10:10 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Hallo everybody, here comes the final schematic with the NFB drawn in.
Attachment:
832 simple schematic final.jpg

I build that exactly like that and it does work alright. It has a warm sweet sound, not bad at all. This is definitely a nice little projhect for the beginner. I will play with it as is a couple of tdays and than change things around again. I want dc heating and I want a phase splitter with more gain, but that is a different story.
Attachment:
IMAGE_444.jpg
I am not really happy about my wiring either. Well it is my first real project and every beginning is tough. Nonetheless it works good no hum everything worked right away, so my wiring cannot be that bad, but really eye candy it's not, I am a little bit disappointed. But on the other hand, when I think about my first home mad4e PC boards, they looked terrible as well. It is my practice project and I have a lot of fun with it. Next time I will try to make it look better.

If anybody is interested in this project I can hook you up with tubes. Just drop me a message.

Did you know, real amps glow in the dark.
Attachment:
IMAGE_428.jpg

Author:  Gio [ 15 Dec 2009, 13:12 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Nice work Ben. What tubes are you using for the driver stage?
Geek wrote:
Check your AC balance across the LTP anodes and you'll see why most designers use 82K/100K on the anode instead of 100K/100K

Hi Gregg, what does LTP stand for? Also, what throws off the balance?
Cheers

Author:  Geek [ 16 Dec 2009, 07:58 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Hi Gio,

LTP = Long Tailed Pair.

Balances are thrown off in the tube driven by the signal will always be slightly stronger than the tube coupled via the cathode.

This is compensated by the smaller resistor on the driven tube with the larger one on the slave tube.

At near full drive, I've measured as much as 5VAC difference between the anodes with a tube that has perfectly matched sections.

Cheers!

Author:  Bennybuis [ 17 Dec 2009, 23:21 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Hallo everybody, my telephone and with it my only digital camera died, so I cannot take and post pictures right now. Sorry.

Author:  Bennybuis [ 20 Dec 2009, 09:43 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Hallo everybody, I can take pictures again. A few days after I started this topic, I changed just about everything inside my amp around again. Now I have almost to the dot the WhatWatt amp, only that mine is still AC heated. No hum, though. Why did I do that? Well, the very simple design does work, not bad either, but the WhatWatt amp works a lot better, since it is much more taken care of blocking all ends to keep that thing from receiving the local am radio station. I had much more noise with the simple amp than I do now. The schematic as provided from Bruce works great, but doesn't give me the amount of gain I need to directly drive it with my mp3 player. Rolling the pre tubes against ECC83 fixed that entirely, now I got enough gain and a very good sounding amplifier. If you look at the picture, you see the power supply build in the left corner and kept away from the signal path at all times. It still looks messy, mostly because of the tight space,l but it works great. I am happy and ready to build something new. :)
Attachment:
Buizenversterker side.jpg
Attachment:
GU32 What Watt PS 23NOV09.jpg
Attachment:
GU32 WhatWatt.jpg
Attachment:
under the hood.jpg

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