Vox - V491 Valve Effects Loop Buffer

moltenmetalburn · Post by **moltenmetalburn** » 14 Jan 2009, 19:43

how would i check these voltages?

how would i test the switches?

lolbou · Post by **lolbou** » 14 Jan 2009, 20:58

To check the voltages: a multimeter in VAC position (approx. 350V), one lead to the red wire, one to the green.

Maybe you could also check the B+ with the same multimeter in VCC position (approx. 300V). The red lead at the positive lead of the 20uF, and the black lead to the negative end of the same capacitor (mind your hands!!)

And with the black lead at the same place, you could point the red one to A1 on the tube socket PCB, just to see what's the HT after the 100K resistor.

To check the switches, use:

- an ohmeter : R is 0 when the lugs are connected

- a voltmeter in VCC -> marks 0 if the lugs are connected

This can be and should be done with the unit unplugged from the mains, while avoiding touching the big caps ends unless they are discharged...

That's it...

moltenmetalburn · Post by **moltenmetalburn** » 15 Jan 2009, 18:15

To check the voltages: a multimeter in VAC position (approx. 350V), one lead to the red wire, one to the green.

which green wire? red wire/ red lead green earth wire/ black lead read 120VAC.

Maybe you could also check the B+ with the same multimeter in VCC position (approx. 300V). The red lead at the positive lead of the 20uF, and the black lead to the negative end of the same capacitor (mind your hands!!)

I have AVC and DCV on my multimeter. not VCC. cant reach the 20 uf when mounted in chassis and not gonna power up out of chassis. anywhere else to read this?

And with the black lead at the same place, you could point the red one to A1 on the tube socket PCB, just to see what's the HT after the 100K resistor.

anywhere else to connect black lead? HT?

diodes are 4004 not 4001 as previously stated by me.

crimped end of silver cap is lead closest to tube socket.

lolbou · Post by **lolbou** » 15 Jan 2009, 18:36

DCV is VCC (french way volts courant continu, sorry about me being lost in translation)...

For the capacitor, can't you even reach it from under the pcb? or you can get b+ from the A1 lug on the tube socket pcb...

You can connect the black wire to any ground point on the pcb or jacks...

You have black wires coming from the mains on one side of the transformer. On the other side, there's a pair of yellow wires which should measure 6.3VAC for heaters, and two other ones being red and green measuring an AC High Voltage (on the pcb there are between the fuse and the diode).

Just check between them...

Great effort anyway, thank you so much...

ps: can you remove the fuse to read the something like F1.5A or so?

edit: and any info about the pot values (with an ohmmeter on the two external lugs with the wiper in the middle position?)

moltenmetalburn · Post by **moltenmetalburn** » 15 Jan 2009, 19:13

I used the ground trace from the jacks pcb that goes to the transformer chassis ground.

on ACV setting:

both yellow wires measure 3.2

red wire measures 118.5

green wire measures .1

on DCV setting:

both sides of 20uf cap measures 253

20 uf cap neg. to tube A1 measures 168

ALL markings on fuse already listed above.

with pots in approximate center position, black lead outer lug, red lead center lug, meter set to 1M Ohms:

send measures .129

return measures .100

[smilie=wine.gif]

moltenmetalburn · Post by **moltenmetalburn** » 15 Jan 2009, 19:20

So does anyone want to get a schematic together at this point, id say with a schematic a PCB layout cant be far behind and we can move this one to the ready to build section!

lolbou · Post by **lolbou** » 15 Jan 2009, 19:30

Well, if it can be done, a complete schematic would be great... But the rack-size PCB might be hard to fit in a 1590BB

I guess the 3.2V times 2 are the 6.3VAC...

But the other AC voltages are weird to me somehow...

moltenmetalburn · Post by **moltenmetalburn** » 15 Jan 2009, 21:19

maybe

1590C 4.70"L x 3.70"W x 2.22"D

1790NS 5 5/8"L x 4 5/8"W x 1 9/16"D

theehman · Post by **theehman** » 16 Jan 2009, 17:45

Here's the actual schematic to help you out. See? I'm not such a bad person.

theehman · Post by **theehman** » 16 Jan 2009, 17:48

Forgot to mention. I was going to build a couple of these for me and a friend using the EH tube pedal chassis and the tube pedal power transformers. Bought all the parts, just haven't found time to do it yet. Thought I might even have room in the chassis for a pedal power supply ala the VHT Valvulator.

lolbou · Post by **lolbou** » 16 Jan 2009, 17:56

theehman wrote:Here's the actual schematic to help you out. See? I'm not such a bad person.

Sure you are, since you've once forwarded me some nice piece of information about the Deluxe EM (remember those alignment stuff?)... Still trying to fix it by the way...

But you're late in posting, aren't you ?

Where do you get the parts you specify in your post (chassis and transformer)?

theehman · Post by **theehman** » 16 Jan 2009, 18:07

lolbou wrote: But you're late in posting, aren't you ?

I don't spend a lot of time here. I usually just pop in for a few minutes, see what's new, then move on.

lolbou wrote: Where do you get the parts you specify in your post (chassis and transformer)?

I bought them directly from New Sensor a while back. Unfortunately they don't offer them any more.

You need to get that DEM up and running! I just found a circuit board for one in my garage. Know where I can get a chassis?

chicago_mike · Post by **chicago_mike** » 16 Jan 2009, 18:25

Go to hoffmanamps.com for tranny and chassis for tube pedals.

lolbou · Post by **lolbou** » 16 Jan 2009, 19:02

theehman wrote:
I don't spend a lot of time here. I usually just pop in for a few minutes, see what's new, then move on.

Was saying this thinking af my whole night dreaming (almost nightmaring) of components values and so on... Man, I'n not good at tracing...

theehman wrote:You need to get that DEM up and running! I just found a circuit board for one in my garage. Know where I can get a chassis?

Yes I will make it!! (at least I hope so

)... Sorry but I think I will keep the housing (which is quite worn by the way), except if I'm brave enough to design a smaller PCB to have it rehoused in a smaller enclosure...

Damn, I do have a lot of project in my mind, but can't reaaly seem to get them finished easily!!

noelgrassy · Post by **noelgrassy** » 17 Jan 2009, 17:28

Bernardduur wrote:I have something sililar in my Dumble amp called a Dumbleator and man, that really makes a difference. I never put anything in the loop just turn it on and even out the volumes (Dulbleator also has a double bright switch for both the volume pots) and it really adds something to the signal!

Wow! Can you post some pics in another thread? Here's one an associate built.

lolbou · Post by **lolbou** » 17 Jan 2009, 17:48

noelgrassy wrote:Wow! Can you post some pics in another thread? Here's one an associate built.

Nice!

Have you been manufacturing this on your own? If so do you have a different schematic and/or parts list?

moltenmetalburn · Post by **moltenmetalburn** » 17 Jan 2009, 22:25

THAT IS SO FUCKING BEAUTIFUL!

noelgrassy · Post by **noelgrassy** » 18 Jan 2009, 04:52

loubou, As I said, it's a Dlator built by an associate. Below are schemas and a layout pic. These have been gleaned from actual Dumble circuits. The most expensive part is the damn rack mount box.

lolbou · Post by **lolbou** » 18 Jan 2009, 10:43

noelgrassy wrote:loubou, As I said, it's a Dlator built by an associate. Below are schemas and a layout pic. These have been gleaned from actual Dumble circuits. The most expensive part is the damn rack mount box.

Sorry about the name of the unit, I missed the pictures' names... What about the transformer? And the choke? Which one is used, and where do you get them?

Thanks!

It's a really nice build, does your associate use jack cable (purple) for his assembly, or is it a custom cable that can be found somewhere?

moltenmetalburn · Post by **moltenmetalburn** » 18 Jan 2009, 15:41

That purple cable looks like shielded cable to me.

Vox - V491 Valve Effects Loop Buffer [schematic]