Feeler: EZ Tube Lunch Box

[ruffrecords]

Hi Ian,

I found a 4u sidecheek in the schroff pdf part number is 06108011. I just sent an email to schroff in the us to see if i can order from them directly...

Regards,

Pierre

I checked the Schroff UK web site for that part number but it is not recognised. Can you check it is the right one?

Cheers
Ian

Sorry Ian,
I don't know were that came from, the 295mm one is 34560-289.
It's on page 22 of the pdf catalogue i have.

Regards!

Pierre

Those 4U side panels are 8.14 GBP each. I had forgotten how the Schroff web site works. You can sign up for mySchroff which then allows you to get live on line quotes for individual parts,. You can add them to a basket and then send it off as a query. They respond with a quote including delivery IIRC.

If you send me the part numbers for the 1m front and rear rails I can get prices for those too.

Cheers

Ian

 

[ruffrecords]

I'm going to show my ignorance here - how does this compare to the Mixer project?  It this ultimately a way to simplify the build?

Excuse me.  :-[

Ian

The idea is to allow people easy access to the EZ Tube MIxer components without having to build a mixer and to standardise on a construction method. Since the PCBs are designed to plug into motherboard housed in a standard sub-rack, a lot of the mechanical issues are automatically sorted.

On the other hand, now that I have started work on the all in one PSU  board (HT, heaters and phantom power), there is no reason why you cannot build something based on the EZ Tube Mixer boards but in a standard 19 inch rack case.

Cheers

Ian

 

[anjing]

Ian, I just registered on the schroff website and made an inquiery we will see how it goes!
The 1m frontrails are 34560-101 and the backplane rails are 34560-401 .
Regrads,

Pierre

 

[ruffrecords]

I have nearly finished building the lunchbox PSU. Just the two regulators to fit and it will be ready for testing.

Cheers

Ian

 

[Holger]

Very nice, Ian. How many modules can be supplied?

 

[shabtek]

Superb Ian,

Our plates are nearly full.

I have spare 30837-405 schroff rails if someone is cobbleing together an enclosure

 

[anjing]

Yes Ian gives us more details! Looks very nice.

Pierre

 

[ruffrecords]

Very nice, Ian. How many modules can be supplied?

It is designed to supply up to 6 EZ Tube cards; that is up to 60mA HT and up to 2.7 amps at 12V for the heaters. The 48V phantom is rather over specified and the regulator and heatsink combination is capable of up to 100mA but I would suggest it would be sensible to limit this by transformer secondary specification.

Cheers

Ian

 

[mylesgm]

hi Ian, that PS looks great!  will it be possible to alter the heater voltage to 6.3, 12v or 24vdc and the HT to a range of volts? That would make it a very universal PS and one that I could see getting used for loads of projects.

 

[ruffrecords]

hi Ian, that PS looks great!  will it be possible to alter the heater voltage to 6.3, 12v or 24vdc and the HT to a range of volts? That would make it a very universal PS and one that I could see getting used for loads of projects.

The heater and 48V phantom power supplies are electrically identical - the PCB layout of each is identical. The only differences are that the 48V one is designed take a TL783 regulator and the 12V one  is designed for an LM338 and has space for a much bigger heatsink. This means the 48V can be tweaked to work from 24V to 240V if you wish just by changing component values and ratings. Current is limited to about 100mA by the size of the heatsink.

The 12V supply can similarly be altered from say 5V up to 24V. The only thing to watch with lower voltages is that the current output can be no more than the 12V value as it is once again limited by the size of the heatsink.

The HT supply is a simple CRCRCRC based on the design of my HT350 PCB so the only way to alter its output voltage is to change the transformer secondary voltage that drives it. The output current is limited by the current rating of the transformer secondary and how much ripple you can tolerate.

I'll post a schematic in the next few days.
Cheers

Ian

 

[mylesgm]

ah, that's great!  I've a bunch of valve modules that are -130v, 24vdc and will need 48v phantom too.  I need to look up current requirements but I'm hoping I can power 2-4 modules off of one ps.  Now to find a suitable power tx!

 

[ruffrecords]

I have set up a folder for lunchbox related stuff. At present it has a couple of pics of the power supply, a schematic and provisional BOM.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/lunchbox/

Cheers

Ian

 

[anjing]

hi Ian,

  Can't seem to find the 510AB heat sink, i think the part number is wrong, otherwise i prepared a mouser bom already....

Regards,

Pierre

 

[ruffrecords]

hi Ian,

  Can't seem to find the 510AB heat sink, i think the part number is wrong, otherwise i prepared a mouser bom already....

Regards,

Pierre

It's this one:

http://uk.farnell.com/abl-heatsinks/510ab0500mb-to3/heat-sink-to-3-3-3c-w/dp/232660

Cheers

Ian

 

[ruffrecords]

I have completed some initial tests of the power supply. The 12V comes out a bit on the low side at 11.4 volts. Calculator indicates changing the 120R to 110R will raise it to 12.6 volts. With one amp load the heatsink gets slightly warn. I'll change the 120R to 110R and try it with a bigger load. Allowing for standard bridge rectifier voltage drops, a standard 15VAC secondary transformer will work well.

HT works as expected. The lower value heater elevation components act as a nice discharge path when the power is turned off. I have not tried the 48V yet but the PCB layout is identical to the 12V so there's no reason it should not work.

Cheers

Ian

 

[anjing]

Good news Ian!

 

[ruffrecords]

As reported in another thread, I have carried out some more tests of the supply at higher currents and the heatsink and the bridge rectifier both get rather hot. I plan to uprate both components and take the bridge rectifier off the PCB so it can be bolted straight to the metalwork. The next size up regulator heatsink will not fit on the PCB so it looks like a new PCB layout is needed.

Cheers

Ian

 

[ruffrecords]

I don't really want to do another PCB layout just to change the size of the heatsink. I had it mounted on the PCB in the hope the whole assembly could be mounted inside a sub rack but with the size of heatsing required this is not going to happen. So I have decided the PSU will definitely be external. The final decision cam after I modified the circuit to get closer to 12.6V output by changing the current the 12oR resistor to 110R and using a 15VAC secondary transformer. 15VAC is a very common value so there are lots of toroids you can buy for this. I needed the extra volts because the 110R raised the otuput to 12.2 volts (close enough) and increased the voltage across the regulator as well. The result was even greater dissipation in the heatsink such that with only a 2 ap load the temperature exceeded 80 degrees C - that's definitely too high.

With an external supply we can have as big a heatsink as we like and that should allow us to get 3 amps out of the 12V supply and power a full sub rack of six modules. Just need to find an enclosure big enough that everyone can get hold of. I tested the HT on four modules and the output voltage dropped to 340V so it will be good for six modules.

Just to whet your appetites, I recently took delivery of two new PCB designs,neither of which I have built or tested yet. One I call the 'Classic' has just two 6922 tubes arranged as mu followers and places for a couple of input transformers on a standard Eurocard with the EZ Tube Mixer 32 way connector for hooking it up. It is basically a pair of poor man's tube gain make up circuits plus input transformers on one PCB. The mu follower is the basic topology I use in my 'classic' mixer designs - hence the name. Using just one transformer you can make a mic pre with up to 80dB of gain with one of these boards. Or, if you fit two transformers you can make a pair of very simple mic pres with up to 50dB gain in a single 3U module - I call it the 'Economy'.  This means it should be possible to make a very simple low cost 10 into 2 all tube mixer in a standard 3U rack mounting sub-rack using a twin line amp for the mix bus and output amplifiers.

The other PCB is even simpler - basically a poor man's tube gain make up with an input transformer on one board with connections brought out to the EZ Tube Mixer 32 way connector. This was originally intended as a post fader gain make up and bus driver board for my more complex mixer designs. but pop a couple of these in a 2U rack box, add a couple of pots and a few toggle switches and some XLRs and you have a twin tube mic pre.

Cheers

ian

 

[rmaier]

My appetite is definitely "whet!" ;D

 

[ruffrecords]

A batch of the version 2 two module motherboards arrived the other day and are now on sale in the emporium.

Inspired by Holger's 2 module motherboard design for his 4 channel EZ Tube Mixer build, this new two module motherboard replaces the original 6 module motherboard. The XLR footprints and the simple pads for internal connections have all been replaced by rear mounted 3 and 2 way Molex KK connectors and there is space for a 6 way Molex connector to connect the mix buses together. Pads have been added to the HT and heater buses as test pads so you can check supply voltages..

The Molex connectors allow you to crimp audio cables to free connectors and plug then into the motherboard making for much simpler assembly, maintenance, trouble shooting, upgrading, tweaking etc. Suitable for use in the lunch box and a mixer of any size.

Cheers

ian