Fender DRRI test bias points mod problem

[jerryd]

Hi all, I'm new to the forum and hoping someone can help with a Fender Deluxe Reverb reissue I am having. I purchased some bias test point jacks to add to the DRRI for quick biasing without having to remove the tubes. Basically there are 3 test points(1 is black and 2 are red). The wiring has the black test point connected to ground. Each of the red test points is connected to the black test point with a 1 ohm resistor. Then, as per the instructions, pin 8 of one the 6V6's goes to one red test point and the other 6V6 pin 8 goes to the second red test point.

It said in the instructions prior to installing to remove the wire at each of the 6V6's pin 8 that were connected to ground. The only wires that were connected to the pin 8 of each of the 6V6's was going to the main board so I disconnected them there. The problem is now I just get a loud hum. Anyone know what is going on here?

[funkmeblue]

everything seems right, where did you ground the black jack?

[M Fowler]

Here is an example for test bias points.

[funkmeblue]

he must of lifted ground to something else

[M Fowler]

Yup I think so too.

We need pictures of the wire connections you removed.

[funkmeblue]

I have a '66 deluxe and there is no wire going from pin 8 to the board

[CapnCrunch]

The OP has a Re-Issue Deluxe Reverb so the circuit is likely slightly different. Here is a link to the service manual which includes schematic and layout for the re-issue DR.

http://www.ampwares.com/schematics/65_D ... erb_RI.pdf

[funkmeblue]

ya, I looked at that, confusing, He's probally got it figured out by now

[Structo]

Mark I'm curious about the ground point on that layout.
Why is it over by the filter board?
Seems as if you would want it directly below the test points?

[M Fowler]

Tom yes I grounded mine by the test point.

Mark

[leadfootdriver]

How do you take the plate voltage reading? Are you lifting 1 power tube high enough to got your test lead on the plate pin?

[Structo]

When reading high B+ voltages inside a live amp, it is best to clip your test lead onto the point you want to measure before energizing the amp.

Don't try to probe around a congested area, if you slip it can be catastrophic to you or the amp.

I in fact did this about a week ago.
I wanted to measure my screen voltage and plate voltage on a 6L6.

I slipped and shorted the plate to the heater.
Luckily all it damaged was the 100R heater resistors.

So to be safe, clip your lead on to the amp, then turn on the amp and take your reading.
Then turn off the amp, discharge it and take the clip off.

Safety first, right?

[leadfootdriver]

Right on! I have a bunch of test wires with gator clips that I can use.

[IMG:360:203]http://i258.photobucket.com/albums/hh26 ... 58_std.jpg[/img]

Safety first!

[rogb]

How do you take the plate voltage reading? Are you lifting 1 power tube high enough to got your test lead on the plate pin?

I think you need to be measuring (using the hand in back pocket method) from inside the chassis on the solder tag of the tube socket?

Am I right in saying what you are suggesting is to lift a powered-up tube from its socket far enough to get a probe on a pin?

If I have got this wrong, I apologise but not if it saves you and your amp

[Structo]

Oh, yeah you don't want to do that.

You measure from the inside of the chassis where all the components are.

When measuring DC (which is most of the circuit) clip the black negative lead of your meter to a good chassis ground.
That may be a ground point or just a bare metal part of the chassis.

You leave that there then probe with the red probe.

Try to measure on the board if possible to avoid close quarters on the tube sockets.

So for example, to measure V1 plate (on a 12ax7), look where pin 1 on the socket has a wire from it to the board.
Usually this will go to a plate load resistor.
Measure where this wire goes to this resistor and that is plate voltage for V1a.

We all started some place and had to learn how to do this.

BUT, please be careful and only probe with one hand.
Stick the other hand in your pocket.

This is to avoid getting a shock across your body and your heart.