D-lator router conversion?

[Luthierwnc]

I need to make a new Dumbleator and was considering a scrounged Cisco 2500 router as the platform. These are a single-rack height device and can be had on EBay for $10 plus shipping. They use 120 VAC input. The power supply puts out +5, +12 and -12 VDC. There is a little fan too.

I'm hoping to use the +12 VDC for the heater and pull 12 VAC off the transformer to run a 7v flatpak backwards for the high voltage taps. I can just gut it but there may be other options.

A related question is; does anyone know of a flatpak that has a 1:1 ratio? That would be about right for a voltage doubler taken off the inlet.

Has anyone messed with this one before? Thanks, Skip

[Structo]

Heck yeah, that should work.
If you happen to stumble upon a flatpack PT for it let me know where you found it.

Can you give me the dimensions of that box?
Is it 19" wide?

BTW, you can fill any of those holes with JB Weld epoxy.
It's made to patch metal.
But of course a new faceplate would work as well.
I had looked at a rack box like that one with the vents and all and they wanted $95 for it!
I don't think so....

[Luthierwnc]

Hi Tom,

I spent some time on the size too. In the computer biz they give you the size of the rack rather than the size of the component. This is from the Cisco site:

•Dimensions (height x width x depth): 1.75 x 17.5 x 10.6 in (4.44 x 44.45 x 28.62 cm)

Most of the surplus units have the Golden Gate Bridge emblem where the holes are in the front. This pic had both sides so I borrowed it from the seller. Try to find one with the rack ears still attached.

As far as the flat packs, Digikey has the Amveco brand. The one in my old unit is the 70030 which is a 120v to 7v encapsulated power trannie (see pic). It is 2" square by about 3/4" high and has two windings on each side.

Generally you would use a 12 VAC wall wart which gets back to my question of whether there is 12 VAC available inside the unit already. If I can poach a 12vac line after the step-down transformer in the power supply but before it is rectified, I can run it into what are supposed to be the secondaries of the flat pack. 120v divided by 7v is a ratio of 17.15 times a 12v supply gives me 206ish into a bridge rectifier for close to 300VDC on the plates. Use a 9 volt version on a doubler and you are a bit over 400 VDC. They are plenty stout for 1 preamp tube.

I'll get the router first since the useable AC (if there is any) is probably higher than 12v and I can do the calculations from there. With the choice of series or parallel connections on both sides of the winding, there are lots of voltage combinations in the product line.

I don't know what these things sold for new but I'll bet they weren't cheap. They are fully depreciated now -- perfect for obsolete electronic applications!

[Structo]

Hoffman has the Amveco transformer.
$22
It says 12vac gives you 240 out.

But, something about using a wall wart for the ac supply kind of bugs me.

[mlp-mx6]

Hoffman has the Amveco transformer.
$22
It says 12vac gives you 240 out.

But, something about using a wall wart for the ac supply kind of bugs me.

But Radio Shack sells a 12.6V transformer like the ones many use for a relay supply in an ODS. I have used the 12.6V ones bridge-rectified and regulated down to 12V. Seems this would be better than a wall wart, and you could build both xfmrs into the box.

[Luthierwnc]

It is a gamble -- which is why I'm getting the router first. Hoffman has a 9v transformer and the wall warts. His preamp power supply uses a FWBR for about 240 VDC. Into a doubler, 120/9*12 gets you around 400 VDC. The D-supply, as drawn, puts 135v into a doubler which should produce around 350 no-load VDC so the 9v version either comes in high or low.

I'm betting the 120v power supply comes in around 16 VAC after the transformer but before it is rectified into DC. 120/7*16 in a FWBR puts you at 375 -- pretty close. The flat pack I mentioned is 2 or 3 times the amperage as Hoffman's but still fits pretty nicely in the chassis and is a couple bucks less. I buy a lot of stuff from Doug and he has a very cool forum for more experimental builders (like me). Structo -- you are there, right? I'm hopefully finishing a 5879 hybrid from Geezer and Tubenit's designs.

I used a Hoffman (ElectroHarmonix) wart for the last one and it worked great. 120 VAC in on a fairly long cord and 12 VAC out on a smaller cord with a unique bladed tip so you can't accidently plug it into a DC device. Both cords are molded into the box so you don't have to sweat it coming apart. 1-amp IIRC so plenty of power for this application. The Dumbleator was in a rack with a TC G# so I needed a 120v source anyway. I wouldn't have any qualms about getting another but if I already get one built-in (with a quality on-off switch and cooling fan), why not use it?

As to the Radio Shack trannie, the power supply already gives me 12v DC to run the heaters. It's the HV that I have to monkey with and the RS transformers I use for the relay supply usually come in around 14-15 VAC so I can't run it inside-out and get the voltage multiplier. That trannie probably isn't built for audio applications. If it has the same care and design standards as their other products, there may be some hum to get rid of. That could be a part of why the relay grounding system is so rigorous. Before D, I used to just use a stereo jack and chassis ground for relays. Never had a problem. Those toroidal trannies are quiet as the grave.

I've got a bid in on the router. When I crack it open, I'll post a gut shot and tell you what I find, sh

[Mill Creek Audio]

Or you could try one of these for the whole power supply...

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... K:MEWNX:IT

Cheap and great!

[Luthierwnc]

A few years ago I posted this thread on making a Dumbleator out of a Cisco 2500 series router chassis. It is a full-length, single rack space and they are available on Ebay for less than the cost of shipping. The top and bottom are almost identical. They fit together so perfectly there is only one screw to secure the pair.

The problem is that you can't work on the front and back controls because each piece of the shell has a face. I got around that on this build by making a PCB for the control panel and floating it at the right height with a couple blobs of silicone. Once the pots and switches are bolted in, it is really solid.

I used the existing power supply for the 12vdc heater and added a toroidal trannie for the HV. It is a basic Mouser 120/120 in 120/120 wired parallel/series. 365VDC at the second node.

It is probably more extra work than I saved in just getting a BUD box but I do this for fun. The switch on the far right is a 3P2T mini that controls the bypass and lights one of the LEDs when active.

Good luck with your projects, Skip

PS If you are tempted to try this yourself, get a chassis that already has the rack ears. They aren't any more expensive but the rack ears alone are almost as much as the chassis. sh

[ElectronAvalanche]

Hi skip,

https://tubeamparchive.com/viewtopic.ph ... ht=#175901

I did this many moons ago. Started out as a router. I used back-to-back flatpack transformers (230V - 9V - 9V-230V). Heater voltage was derived from the 9V secondaries of the first transformer into 7806 regulator (filtered etc.). 6V DC on the heaters. Works nicely.

You will not get the 370Vs on the B+, but lower voltages are ok as long as the CF does not clip with high signals (adjust resistors on CF to avoid clipping).

I am currently putting the innards into a "nice" 19" chassis. See thread linked above for details.

Cheers and good luck with your build!

Electron

[Luthierwnc]

I've replaced the transformer in the router D'lator with a larger toroidal. This one is from Antek for $25 and shipping. They have a wind made mostly for preamps that has 0-260/280 on the HV and two 6.3v secondaries. You can just shoehorn it into a 1U rack. I actually had to grind down the bolt and use a furniture capture nut so it would clear the top. This is the one I used:

https://www.antekinc.com/details.php?p=639

It is wired with a FWBR with the 280 volt tap. I've got a 47u cap at the B+, a 4k7 first dropping resistor with a 33u cap takes 359VDC to the return plate resistor and an 82k second dropping resistor and another 33u cap puts 255VCD on the send plate.

Sounds great, quiet and stays cool. If you've been looking for a power supply that you can cram in the chassis, take a look. Skip