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Old 14th May 2014, 04:11 AM   #1
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Default First post from a tube noob: Found 9 tubes!

First the bad news - all used and will need to be tested (not sure where or how yet...)

4x of 7867 tubes
1x of OD 3
2x of 12AU7
2x of 5U4GB

I have almost no idea. I know that the 12AU7s are occasionally used in guitar amplifiers and I think that the 7867 are power amplification tubes. I am guessing that the OD 3 is a rectifier? 5U4GB - no clue. I'd appreciate information if anyone is willing.

Now - my story - I am 34 years old and I just started to play the electric guitar. I don't have an amp yet. I was looking at bedroom tube amps like Bugera V5, Epiphone Valve Jr. and whatnot and - through a reference to modding amps - I came across a few schematics that looked ridiculously simple. I thought to myself "why should I pay 200 dollars or more for something that I could solder together myself?".
That was before I found out that vacuum tubes aren't abundant cheap things that you can acquire for pennies.
Undaunted - I started to look through piles of old electronics at work. That's when I discovered a chassis with all of these tubes mounted. There's also 3 hefty-looking transformers of unknown origin that I haven't had a chance to remove yet.

I'm interested in building an amp for myself. I would like to keep the cost as close to "free" as possible but of course I would be happy to buy replacement tubes if need be, or a power transformer if the unknown transformers won't serve my needs. Is there a good way to identify the ratings of an unknown transformer?
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Old 14th May 2014, 04:22 AM   #2
AJT is offline AJT  Philippines
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7867 is a power tube... http://frank.pocnet.net/sheets/127/7/7867.pdf

keep looking around and you may find what you need....

meanwhile this thread is going to the Instrument section since you are building a guitar amp...
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Old 14th May 2014, 04:34 AM   #3
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Quote:
Originally Posted by AJT View Post
7867 is a power tube... http://frank.pocnet.net/sheets/127/7/7867.pdf

keep looking around and you may find what you need....

meanwhile this thread is going to the Instrument section since you are building a guitar amp...
I'm sorry for the mistake. Thanks for the drawing!

I did find 5u4 (gb?) listed as a full wave rectifier. I guess OD3 is actually a voltage regulator.
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Old 14th May 2014, 05:18 AM   #4
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That site is a great resource Frank's electron Tube Data sheets

A few more...
http://frank.pocnet.net/sheets/049/0/0D3.pdf
http://frank.pocnet.net/sheets/093/1/12AU7A.pdf
http://frank.pocnet.net/sheets/049/5/5U4GB.pdf
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Old 14th May 2014, 07:33 AM   #5
AllenB is offline AllenB  Australia
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Maybe building a stage around the 12AU7 would be a good place to start as it's a bit more flexible to set up. Later it can become the driver stage for something like the 7867, or part of a pre/effect.

If the transformer that came with these is still connected then you could trace the circuit. Resistors of a certain value are often used to bring the voltage down for each stage. If you use the transformer with less stages than it originally powered, or if you choose to use modern rectifiers (instead of the 5U4), these resistors may not be a large enough value. If you want to use the 5U4 and regulator it might be better to use them exactly as they were originally (once you clean it up).

You may want some capacitors that can handle the conditions, some don't age well and will want replacing.

Last edited by AllenB; 14th May 2014 at 07:37 AM.
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Old 14th May 2014, 01:32 PM   #6
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Quote:
Originally Posted by Illinest View Post
..........I would like to keep the cost as close to "free" as possible.......
Pls. note that cost saving is rarely achieved when building a tube amp, unless you've got all the expensive parts (tubes, transformers(!), speaker) already laying around. It will be rewarding and can be fun though!

OTOH: small tube amps (tops or combo's) can be found used for 100 EUR/150USD and can serve either as an amp, or as a modding-platform.
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Old 14th May 2014, 01:44 PM   #7
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Hi there!

I'm a long way off being even knowledgeable about toobz (I've only built a couple of em, and I was stronger on the building than the understanding), but it seems to me that you've most of the building blocks to make -something-.

I would imagine that with the chassis, transformers and tubes, you are indeed most of the way there - you just need to pick a circuit and wire her up! (insert safety comment here)

May I suggest you photograph whatever you have available (ie chassis, transformers, and toobz) and I'm sure a few folk can make suggestions as to what might be achievable.
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Old 14th May 2014, 04:11 PM   #8
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You have the tubes to make a 100-150 watt guitar amp head, with regulated voltage to the screens. Should be nice.
Daniel
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Old 14th May 2014, 05:50 PM   #9
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100 watts may be more than i can ever use. :-)

I was thinking something more modest like a fender champ. i like the features on the bugera v5 and the schematic isn't too bad either - so maybe a combination between that and the fender champ? I want it to sound like the champ but i'd love to be able to have more features like tone controls. Then add a reverb circuit and an attenuator of some sort. The bugera attenuator switch has been maligned by many for 'killing' the tone - so i'm guessing that whatever they did had to have been the "cheap way" -there's got to be a better way to reduce output. The bugera has ,1 watt, 1 watt and 5 watt settings. I think i'd be happy with that. I anticipate using the lowest settings more often than the highest settings, but i must admit that I wouldn't be opposed to a higher ceiling - maybe 15 to 20 watts or so...

But i am not really ready for that yet. I need to figure out what i've got to work with. A used bugera v5 might turn out to be cheaper in the end but I am interested in doing this for myself even if i end up having to purchase replacement tubes and iron and whatnot. I have one big advantage in that i'm working as an electrician in a very old foundry and there is discarded equipment on shelves all over the place. There is also a guy who works a lathe who can machine just about any piece i can think of and a pattern shop that has tons of scrap wood if i decide to use that. I think that photos of what i've collected so far is a good idea and i'll post some as soon as i can get a free moment. That might not occur for another 12 hours yet, but i'll get them eventually.
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Old 14th May 2014, 08:24 PM   #10
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Updated tube haul:

The first list was just the tip of the iceberg:

2x: 12ax7 (one new in box)
8x: 12au7 (in addition to the others)
Most of the rest of these are new in box:
3x: 3B28 (huge!)
2x: 6bg6
1x: 7867
1x: 5751
1x: oa4g
2x: 12bh7a
3x: 12sn7
3x: 12sl7
3x: 12h6
1x: 6av6
1x: 6x4
2x: 12sn7gta
1x: 6sn7gtb
4x: 115n045
3x: ob2
8x: 5u4gb
10x: od3
2x: 6cd6ga
2x: 6aq5a
1x: 6x5gt

The 12ax7 jumps out. I think i remember seeing 5u4gb as well but i'll have to check.

I think it's safe to say that i've got the tubes covered. I've also got more iron than you can shake a stick at and i've got rectifiers and diodes enough to build a bridge circuit if i'd like.

Maybe a dumb question but i need to ask: is there any reason why i couldn't wire any particular 480/120v transformer to transform 120 up to 480? I have never had any professional reason to do so but i can't think of any reason why you couldn't.
I've got many single tap coils (so far) in a range of kva values and at least one transformer from an old 8-track player that i know works and has 3 taps. 6, 12 and 20vac (with a 120 volt input)
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