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832 / GU32 tube push-pull amplifier project
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Author:  Gio [ 20 Dec 2009, 11:05 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Nice Ben. Glad to hear that it is an improvement over the first one. You could also try a 5751 instead of the 12AX7. The 5751 should provide enough gain for you portable player and I like the sound much more than the 12AX7.
Cheers

Author:  CrazzyAbtTubes [ 21 Dec 2009, 13:06 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

That is one compact amplifier! :P Looks really nice, but how is the frequency response with those mighty small transformers?

Author:  Bennybuis [ 23 Dec 2009, 19:21 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Hallo everybody, about the frequency response I don't know. The amp sounds really nice and the output transformers were the stock transformers from the K16LS kit from S5. I really don't know the specs, but they just might have found their place in this amp. If it works it must be right. Well I am gonna scope the whole thing shortly and post the results. I am quiet pleased with the outcome, still don't really like my wiring, but then it's my first try and to me it is a total success. It is standing on my desk, the place where I spend most the time in my house and running day and night. I am using the K272preamp kit to drive the amp. this combination works good, too. Will build me a real pre amp soon, though.

I am still waiting on output transformers from Edcor I ordered and payed for long ago. I am very careful with Edcor now, I really feel lied to. It is x-mas and I cannot finish any of my projects because I do not have any output transformers. Just ordered a couple of hammonds, I can get those within a few days out of Germany. Won't get them this week either because of x-mas, but I will next week. I wonder how I will like them.

Author:  Bennybuis [ 23 Dec 2009, 19:31 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Hallo everybody,

I still got 4 of those GU32 laying around and Bruce from OddWatt came up with that schematic for a two tube per channel version pp connecting the tubes internally parallel.
Attachment:
GU32 WhatWatt pp parallel.jpg

This is gonna be my next project, it is not tested, so if you wanna join me, your own risk. Well I had that thing in a little bit different version running on a bread board, but now way for me to test UL since I do not have any trannys with 40% tap, but I am sure it'll work. I got all the holes in the enclosure, pics are coming tomorrow. It'll be a lot bigger than my first amp, more space to maybe do a nicer job wiring this time. After that I got 6 GU50 laying around and really no schematic for it. I will just build Gio.\,s kit like the GU50 were KT88 and drop the grid 2 voltage via resistor to 250 volts and hope for the best. But that is a bit of topic, sorry, I will start another one in time.

Author:  Soundbrigade [ 24 Dec 2009, 03:46 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Talking of which, I found a schematic for a 6R3S-amp using a single tube (+ a 6N8S) per channel. :D
Will do some testing later.

Author:  rparsh [ 24 Dec 2009, 20:48 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Three weeks ago I ordered one power trans and two OPTs from Edcor and they told me on the phone that they won`t ship any thing until the end of January 2010. Everyone must wait..............Thanks, rparsh

Author:  Bennybuis [ 02 Jan 2010, 12:09 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Hallo everybody,

my output transformers are here, almost. I wasn't home, so they are in the post office until Monday morning. No big deal. I have to pay almost 50 dollars fine, because Edcor didn't put enough postage on it, but I payed Edcor round 40 dollars postage, so they damn sure charged me. Well ,I will except the package, of course I do, waiting on it sooooo long, but I am a bit disappointed. Well I ordered another pair, because they are good, but I will get a couple of hammonds, too. I don't like to be that depended on anybody.

Anyway, I got all the parts now for the 4 tube version of the amplifier, with UL trannys on Monday. Bruce from OddWatt has that very same thing up and running, so it's working, if anybody wants to try. I love the sound of the GU32, not a bad sounding tube at all. :D My new hammond enclosure will get here Tuesday, I suppose. I have to somehow bite the holes in there without screwing it up, too badly. Dremel and a 2 mm drill and lots of patience is my way of doing that. A jig saw with a metal blade would be a good thing, too, I suppose. How do you guys do that?

Author:  Gio [ 02 Jan 2010, 18:39 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Hi Ben,

For drilling aluminum I use a stepped drill bit like is shown on the left of this photo.

viewtopic.php?p=8037#p8037

Cheers

Author:  Loren [ 02 Jan 2010, 22:54 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

Bennybuis wrote:
My new hammond enclosure will get here Tuesday, I suppose. I have to somehow bite the holes in there without screwing it up, too badly. Dremel and a 2 mm drill and lots of patience is my way of doing that. A jig saw with a metal blade would be a good thing, too, I suppose. How do you guys do that?

I cheated! I have a Bridgeport milling machine. However, here are my suggestions (for those that don't)...

1. Use hole punches for tube sockets. You can try an electrical outlet wholesale supply store. Punches are not cheap, so you might get lucky and find someone that can loan them to you.

2. A hand nibbler tool is a good tool for cutting rectangles. This is an example of one such tool: http://www.mytoolstore.com/klein/76011b.html

3. A hand reamer is a good way to make round holes larger.
Image

4. Small hand files and masking tape.

5. A center punch. The automatic spring loaded ones are the best.

6. A centering drill. These are short and very stiff type of drill that are designed to cut into metal without walking all around.

The aluminum chassis from Hammond are very thin sheet metal and flex and bend easily (ask me how I know). You need to work slowly and carefully. I would clamp a piece of wood on one or even both sides when drilling through. Masking tape is a good way to protect the surface and you can mark and draw right onto the tape.

If you have a CAD program you can print the pattern on paper and then glue the paper right to the chassis before cutting holes. Use a spray adhesive and double check the dimensions of the printout. Sometimes printers do not print to scale. I usually add a rectangle of known dimensions on the page and measure that rectangle in height and width to verify it printed correctly.

Take your time and have fun!!!

Author:  Soundbrigade [ 03 Jan 2010, 04:08 ]
Post subject:  Re: 832 / GU32 tube push-pull amplifier project

I am using these drills that I have a set of:
http://www.vt4c.com/shop/program/main.p ... group_id=8

Image

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