Ebs Valvedrive issue..

[SunofDoom]

Hello people!

I recently got an Ebs Valvedrive from a friend of mine who claimed that the volume of the pedal is pretty low..

I checked the power supply which is 12volt AC and it looked fine..Changed the two switches who seemed to act a bit strangely..but the volume is very low considering how loud it was..To get a decent volume like the clean signal you have to put the volume pot almost to maximum with the drive pot being over 12 o' clock..

There is a transformer inside the pedal that takes 12volt AC and converts it to 130V DC..If I recall correctly..

So what could be the problem there?Sould i measure the plate voltage to see if for some reason plate doesn't get 130volts? I haven't found any schematics till now..

What else could be the problem..??

[SunofDoom]

Is there anybody out there?

[duck_arse]

we're here, but we're waiting for a circuit or a tracing or some photos, or something to look at. is there any chance the volume pot or its wiring has become the problem?

[samhay]

There is some info at the other forum. Do you know how to safely work with high voltages?

Either way, I would try replacing the valve before doing anything else. Do you have a spare ECC83 / 12AX7?

[SunofDoom]

Ok here are some photos..hope it helps..

I'm not a master but i guess i can keep my fingers off anything i'm not sure..
Should i take some readings with my multimeter of the plate or somewhere else?

Do i have to disconnect the volume pot to see if it is the problem?(it seems to be working..)

http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/P_20140715_132916.jpg.html
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/P_20140715_132942.jpg.html
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/P_20140715_132951.jpg.html
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/P_20140717_123310.jpg.html
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/P_20140717_124220.jpg.html
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/P_20140717_124249.jpg.html
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/P_20140717_124303.jpg.html
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/P_20140717_124310.jpg.html

[SunofDoom]

Oh and as far as i know the tube was changed recently to see if that was the problem but it wasn't..

[SunofDoom]

any suggestions?

[SunofDoom]

Luckily i just found the schematic of the pedal..Hope it sheds some light..

http://www.aronnelson.com/gallery/main.php/v/diyuser/EBS+ValveDrive.png.html

[Fender3D]

R4 and R7 are too much small wattage resistors if 1/4W label is true...
Check plates voltage and swap those resistors with anything "fatter"

WATCH OUT THE HIGH VOLTAGE!!!

[PRR]

> too much small wattage resistors

It's only 160V supply, not 300+ like a "real" gitar amp.

R4 R7 are 100K in any Fender, and probably here also.

With 12AX7 100K 1.5K bias the plate sits at 70% of the supply. So about 112V, or 48V drop from 160V.

Power dissipation is 0.023W.

We should check worst-case: a shorted tube. Full 160V across 100K is 0.256W. Less if mystery-resistors R14 R15 R16 are considerable Ohms. If he's left a shorted tube in in for days, with 160V supply, yes a 1/4W part might be pretty toasted. OTOH he recalls 130V supply, which is also possible, and leads to far less than 1/4W in R4 R7.

At 320V (real amps) these powers would be 4X higher, so we *do* need full-Watt resistors in "real" amps.

> Sould i measure the plate voltage

You have our permission.

Remember DEADLY voltages.

C13 should show 150V-170V DC.

C16 should show about 95%-75% of that depending on R14 R15 R16 values.

Whatever you get at "Vc", the voltage at each plate should be 65%-75% of that. Or at least not half vc, or full Vc.

Voltage at cathodes should be around 0.72V. Not zero, not over a Volt.

I do not understand R2 R3. This is a Fender-inspired amplifier, and Fender would use 470K-1Meg at R3. This may be a mod to handle high-output basses and to mellow-out the sound.

The value shown for R9 is rediculously tiny. With that value, second stage clipping will get through tone-stack to output at very-very low level. I just saw R10 which, in "yellow" mode, makes level lower and screws-up first stage bias.

I would do any testing in the "red" footswitch position. The yellow position has a diode feedback clipper which was very nasty on some Ampegs, and IMHO could ruin an otherwise fine sound.

[SunofDoom]

Ok let's see

these are the readings of the tube

1:21.5
2:-0.34
3:0
4:11.99
5:0
6:27
7:-0.37
8:0.04
9:6.04

I guess this values are pretty low..Checked the transformer and he takes 6.3 and 6.5 AC(two seperate wires from the power supply?) and gives 13.5!? volts DC..(is something wrong with me maybe?)

C10:14.4v
C13:43.8v
c14:37.9v

Took measurements on both red and yellow function and had almost the same results..

Should i measure something else?Does this info help you find the problem?

Thanks for you time!

[chicago_mike]

R2 and R3 pad the signal down for active high out put basses.

I both owned and fixed a few of these at a shop I worked at. I have the service schematic on this as well as notes I believe. It helps to be at a shop that is certified to work on EBS. 

Plate Resistors are 240K 1/2 watt
R2 is 47K
R3 is 1Meg
Your B+ is actually supposed to be around 280 Not 110 or 170
Check voltages after the 4007's on both the plate and heater supplies

[chicago_mike]

Also check your 12 volt regulator

[PRR]

I wonder if that schematic is correct.

If so, then *both* C2 and C4 have shorted-out. Snip one lead of each cap, see if pins 8 and 3 come up nearer one Volt.

> B+ is actually supposed to be around 280 Not 110 or 170

That (incorrect??) plan shows two 130V AC windings parallel, which is 130V, times 1.414 is near 180V. Since there are two transformers in series (wall:12V and 12V:130V), and small iron sags, 150V-160V DC seems likely. If in fact the secondaries are series, with some reasonable drop in resistors we should have more like your figure.

> Check voltages after the 4007's on both the plate and heater supplies

Agree.

[Fender3D]

I wonder if that schematic is correct.
...
That (incorrect??) plan shows two 130V AC windings parallel,...

The first pic http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/P_20140715_132916.jpg.html shows the windings in series

[SunofDoom]

Hello,

readings from the 12volt regulator..Vout 11.8 volts and Vin 14.7 volts..


> Check voltages after the 4007's on both the plate and heater supplies

I am assuming that you don't mean the side connected to the transformer..

So heater voltage 14.7(which next goes to the regulator as i can understand and becomes 11.8?)

Trying to see whats going on..come back with numbers in a while..

Thanks for being so helpful!!

[chicago_mike]

How do I attach a pdf? I want to attach the schematic I have from ebs. 

[SunofDoom]

Hello!thanks for your time!

not sure if i can post links or passwords so here is the way..

http://www.diystompboxes.com/smfforum/index.php?topic=60421.0

[chicago_mike]

Sent you an email

[SunofDoom]

Thanks to chicago mike we've got the right ebs valvedrive schematic..

Is it ok to upload it in order to find a solution or is there any problem legal problem with that?