Schematic SVT-VRAP by Loud tech.

[charetteelectronics]

Hi all,
Looking for Schematic for the SVT-VRAP by Loud tech.
Many Thanks in Advance.
Charette

[bob p]

Since you're describing yours as a "VRAP" it sounds like you're reading the serial number for a USA built American vintage reissue.

Call Ampeg tech support and they'll help you. If you provide your exact serial number they'll be sure that you get the right schematic for your amp.

[MarkusBass]

Do you mean Ampeg VR? Like this one: Ampeg: Classic Series - SVT-VR ?

Mark

[Jazz P Bass]

http://music-electronics-forum.com/a...18-svt-vr_.pdf

[charetteelectronics]

Many Thanks for all the replies. The schematic I was looking for was the one posted by Jazz P Bass. It is the one with 3 adjustment leds and not the 5 led model. Minus 15 volt supply is low about -11.75. Adjustments work on output tubes but leds do not function properly. Replaced IC1 7812....shorted input to ground. Still -11.75 volts. R36 measures 100 ohm. Replaced D3 1N4744 and C12 470uf/35 volt. Replace IC 3 and 4 to no avail. What a pain in the ass. Test all resistors, diodes, and resistors in comparitor circuit and all good. Input to D3 is -17.5 volts. ARRRRRRRRRRRRRRRRRRRRRRR............

[Jazz P Bass]

If you have -17.5 Vdc going into R36 & -11.75 coming out, then either D3 (15 volt/ 1 watt zener diode) is bad or something downstream is pulling it down.
Do any of the IC's get hot?

[charetteelectronics]

Yep, Thanks for advice Jazz. Last thing in line is IC1 on preamp board. Really look forward to tearing that circuit board down also.

[g1]

You can't disconnect the power from the preamp board without removing it? Then you could see if the -15V supply comes up.

[hodgy]

Are the tubes good? What about the plate and grid resistors? You're not going to get the bias lights to work if you can't bias this thing.

[soundguruman]

Hi all,
Looking for Schematic for the SVT-VRAP by Loud tech.
Many Thanks in Advance.
Charette

I don't think they ever gave a complete schematic to this amp.

You call Loud Technology, you get and sign their "waver..."
and they give you what they have.

However, I would not depend on the schematic voltages being accurate.
so you might be pulling your hair out for nothing.

Production changes / revisions were made to the amps, and the documentation was not always updated.
That's typical for Crate. And this really is, a Crate amp.
Ampeg Logo on outside does not change Crate amp on the inside...

Usually, the failure to operate the bias lights correctly, is either bad tubes or blown screen grid resistors.
Let's ignore the difference between the schematic voltages and the actual voltages, for the moment.

A. carefully check that all the screen grid resistors are good. It is better to change all the screen grid resistors to 1 watt.

B. You will see that the output tubes are arranged in TWO triangles.
One triangle right side up, the other upside down.
There are 3 tubes on one side, three tubes on the other side.

C. Plug in 2 tubes per side. Now attempt to adjust the bias lights.
By process of elimination, this can help you find the bad tube(s).
When the bad tube is used, the amp will trip the protection...or fail to adjust entirely.

A bad tube may blow the 1/8 watt screen grid resistor, when you plug it in and operate. Keep an eye on that.

Eventually, by process of elimination, and trading tubes, you will find the bad tube(s).
The amp will operate with 2 tubes per side....or even 1 tube per side. If the tubes used are good.

BUT the bias lights will not function normally....until you are using 3 tubes per side, all 3 must be good tubes.
AND all of the screen grid resistors must be good.

This information will almost ALWAYS result in finding the problem, believe it or not.
AND the problem almost ALWAYS is, a bad tube or bad screen grid resistors.

Voltages on schematic?
Don't put a lot of faith in the schematic voltages. Ignore these while you do the tests, above.

ALSO: bad driver tubes.
Swap out the phase inverter/ driver tubes, that can cause a headache too.