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Old 23rd Oct 2010, 7:39 am   #1
6AL5W-Martin
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Default Building a tube Ghetto Blaster

hello friends,
after a very long time of planing I have started to build a homebrew tube Radio in "ghetto blaster desgin".

My idea was, to have this very special case design.

The plan...

AM/FM stereo superhet with IF 455kHz AM and IF 10,7mc FM, including tube stereo decoder and "3D Sound".

3D sound, some old german radios use this, is simply to insert additional 2 speakers in the right and left side of the case,
the sound power amp use 3 transformers, one SE for left, one SE for right, and a center PP for front, all this with only 2 power tubes.
I will do it with 6AQ5 = EL90.

The special problem to build a ghetto blaster design is the very small space inside, the project will not go without exactly mechanical plan and design.

The Deepness of the case cannot be large, a question of design.
So I made the construction :

<--> 500mm
height: 200mm
deep: only 125mm ( 1" = 25.4mm)

The "buttons" have to look like cassette player buttons of a ghetto blaster..
The tuning scale, I decidet to make a hallicrafters design to it.
The magical eye tube, small and nice, EAM86
Upside a cover, containig the ferrite antenna, cooling, pots.
2 telescope antennas.
wood case for good tube sound. Black glossy painting.
aluminium parts for small weight.
a lot of fun and a lot of time !

Now, start
When I`m finished, I will give exactly plan of construction for a easy rebuild.

greetings
Martin
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Old 23rd Oct 2010, 7:51 am   #2
raditechman
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Default Re: building a tube ghetto blaster

Look forward to seeing some photos when it is finished. Hope you have got room for batteries, assuming it is portable.

John
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Old 23rd Oct 2010, 8:38 am   #3
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Default Re: building a tube ghetto blaster

Yes, if it's as loud as it looks you may need big batteries!
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Old 23rd Oct 2010, 9:55 am   #4
6AL5W-Martin
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Default Re: building a tube ghetto blaster

I think that will not be possible,
this radio will blow out 6 to 8 Watt, what means, with battery tubes it`s not possible.
a 6AQ5 will eat roundabout 10Watt Anode + 3A heating, there are 2 ...

Maybe I use a seperate Bag with 12V7Ah and a low cost transverter.
The radio self, 230v~

greetings
Martin
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Old 23rd Oct 2010, 10:05 am   #5
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Default Re: building a tube ghetto blaster

I used to do that, build the box first and then try to fit it all in. Always ended up with a very cramped bit at the end.
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Old 23rd Oct 2010, 12:55 pm   #6
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Default Re: building a tube ghetto blaster

In my younger days, when working for a well known hi-fi manufacturer, that was always how it was done. Marketing said 'This is the size/shape/colour/facilities we want' and the Designers had to get it all in.
It wasn't always an unqualified success
Alan
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Old 23rd Oct 2010, 5:26 pm   #7
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Default Re: building a tube ghetto blaster

The case looks a really strong job, but a bit risky to build this first. I would start with a large chassis then work from the centre outwards,get the design working ,then trim the chassis to minimum requirements. A bit tedious I know but it could save a lot of frustration.
Good luck anyway. Mike
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Old 23rd Oct 2010, 7:31 pm   #8
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Default Re: building a tube ghetto blaster



Wouldn't it be easier to start from one end- then you would only need to trim off one bit
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Old 23rd Oct 2010, 7:50 pm   #9
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Default Re: building a tube ghetto blaster

You could always use something like an ELL80 (?) to get the valve count down. I'm not sure but think there is a triode/twin pentode valve, maybe an ECLL80? too.
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Old 23rd Oct 2010, 9:25 pm   #10
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Default Re: building a tube ghetto blaster

Quote:
Originally Posted by Boom View Post
I'm not sure but think there is a triode/twin pentode valve, maybe an ECLL80? too.
It was an ECLL800 with, I think, a common cathode for all three sections.



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Old 23rd Oct 2010, 10:14 pm   #11
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Default Re: building a tube ghetto blaster

If it has a common cathode, you wont be able to use the triode section as a phase splitter, assuming of course you wanted push pull output stages.
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Old 23rd Oct 2010, 11:47 pm   #12
AlanBeckett
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Default Re: building a tube ghetto blaster

The rsdiomuseum doesn't agree - see
http://www.radiomuseum.org/tubes/tube_ecll800.html
However, it does depend on your definition of phase splitter.
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Old 24th Oct 2010, 12:55 am   #13
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Default Re: building a tube ghetto blaster

Clever! Presumably the triode only manages unity gain. It must have a low gm, ra or both.
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Old 24th Oct 2010, 7:39 am   #14
6AL5W-Martin
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Default Re: building a tube ghetto blaster

hello Friends,

ELL80 and ECLL800 are tubes with a short life time, also they are rare and very expensive.
So i decidet to 6AQ5 (7pin), a low cost tube with enough output.
EL95 (=a half ELL80) is better, only 0,2a filament, but it requires 10k A-A

greetings
Martin
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Old 24th Oct 2010, 9:04 am   #15
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Default Re: building a tube ghetto blaster

I stand corrected!

Ingenious
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Old 24th Oct 2010, 12:23 pm   #16
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Default Re: building a tube ghetto blaster

Can't wait to see the finished system...

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Old 24th Oct 2010, 4:42 pm   #17
6AL5W-Martin
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Default Re: building a tube ghetto blaster

one of the tricks to keep space is, to put the filters in downside of the chassis,
they must not have case, only a little aluminium separation plate. Some filter coils can be wired on amidon toroids (not all).
The (hot..) audio stage will be flown upsid, behind the scaling.
I have planed in Corel, but its a fight for every space

But the switching area will look , like most tube radios, not so perfect, short wires and a lot of coils there

greetings
Martin

Last edited by 6AL5W-Martin; 24th Oct 2010 at 4:50 pm.
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Old 25th Oct 2010, 9:04 am   #18
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Default Re: building a tube ghetto blaster

Sorry Chris, starting from one end and trimming off the other would not work, perhaps I should explain. I place all the major components on a large sheet of aluminium and when I am happy with the layout I cut all the holes for the valve sockets transformers ect. This is far easier to do anyway on a flat sheet than on a folded up box. I then trim and fold the sides to form the chassis, both operations being done with a Warco bending jig. Admittedly this method does produce a small amount of waste but not as much as finding you have to start from scratch as you find you cannot fit everything in.
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Old 27th Oct 2010, 6:44 am   #19
6AL5W-Martin
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Default Re: building a tube ghetto blaster

Continue

The "buttons" have to look like cassette player buttons of a ghetto blaster.. ... done.
next step comming soon: Dial.

greetings
Martin
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Old 27th Oct 2010, 7:46 am   #20
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Default Re: building a tube ghetto blaster

Add a spot for an iPod dock or at the very least an iPod/mp3 input. Looks great.
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