tag board wiring

[Doc Stitches]

Will someone please tell me where the blue and yellow wires connect that run almost the entire length on top of tag board ?

I can not find this info on any schematics/layouts. This is a 1973 Super Reverb that I am changing to AB763. There is no sound coming from the speaker so I figure I have a wrong connection.

I will attempt to send a photo or two.

Thanks
Doc

[52 Bill]

If you are talking about the twisted ones that sit above the board, then the blue one is the output from the first preamp to the input of the power amp. The yellow ones are either the out of the second preamp to the power amp or a power supply line from the filter caps to the preamp stages.

It would take an hour to go over your photos and list all of the problems, but one thing that I noticed, is that the trem roach is in backwards. I also can't see where the cathodes of tube 3 (reverb driver) are wired to.

I'd start at the power supply and start checking everything from there forward. Is the rectifier tube socket carbonized?

[52 Bill]

Here are a few things that I noticed.

The output from preamp channel 2 is taken off the wrong side of the 0.022 cap. The 500 pf cap at the input to the reverb driver has been replaced with a 1 M resistor.

Tubes 1 and 2 pin 8 cathodes are not wired to the 820 ohm/25uF cap.

Output from tube 4 is taken from wrong side of 0.1 uF cap.

And the pin on the rectifier socket that I questioned was pin 2.

[Doc Stitches]

Thanks for the quick replies, Bill. I will get to it today and the rectifier socket is good.

Doc

[Doc Stitches]

update....Rectifier pin 2 has been carbonized......It looks like my schematics show I am wired the correct side to.022 cap of the preamp channel 2,....but I will follow your advice .

It also looks like the schematics show the output from tube 4 is taken from the correct side of 0.01uF cap. I will follow your advice.

Also...I have no voltage on pins 3 and 4 of the power tubes.

I am now hearing a very very low distorted guitar signal through the speaker.

Doc

[52 Bill]

...Rectifier pin 2 has been carbonized...

Then you should replace it, as it will get worse with time.

....It looks like my schematics show I am wired the correct side to.022 cap of the preamp channel 2,....but I will follow your advice .

It also looks like the schematics show the output from tube 4 is taken from the correct side of 0.01uF cap. I will follow your advice.

Don't just follow my advice, understand the concept. The capacitors that we are discussing are there to couple the signal from the tube's plate to the next stage. Part of the caps job is to block the dc voltage that is present at the plate from reaching the next stage of the amp. If the wire goes directly to the plate, the cap is out of the circuit and is not serving a function. When the wire is connected directly to the plate there will be around 160vdc being fed into the next stage.

Also...I have no voltage on pins 3 and 4 of the power tubes.

Pin 3 of the power tubes are the plates, they connect to the output transformer. The voltage that is supposed to be at the plate is supplied through the output transformer by way of the center tap on the primary winding. If there is no voltage at pin 3, there is either no voltage at the red center tap of the OT or the primary winding is open.

Pin 4 of the output tubes is the screen grid and is powered through the 470 ohm resistors that are connected on the sockets. The voltage should come from the second node of the power supply immediately after the filter choke. The photos don't show clearly how you have wired the choke and standby switch. I suspect that it needs to be rewired correctly.

If you search online for an original factory "Layout" drawing, you will find a pictorial view of how the chassis should be wired. This may help you to figure out your mistakes.

[greekie]

No reason to put big blobs of silicone on the filter capacitors. The "hood" of the "cage" should have a foam-lining that should do well enough to keep them from not bouncing around. If it is lacking, glue in a new one. It's waaaaay better than silicone in my oppinion, as the silicone can be conductive and give you all kinds of weird problems!

YM2C

Jake

[Prairie Dawg]

No reason to put big blobs of silicone on the filter capacitors. The "hood" of the "cage" should have a foam-lining that should do well enough to keep them from not bouncing around. If it is lacking, glue in a new one. It's waaaaay better than silicone in my oppinion, as the silicone can be conductive and give you all kinds of weird problems!

YM2C

Jake

Yes, I thought it looked like someone had had an untimed.........err.......excess of joy. If you've just got to shoot something out there, hot melt craft adhesive works fairly well.

[greekie]

Yes, I thought it looked like someone had had an untimed.........err.......excess of joy. If you've just got to shoot something out there, hot melt craft adhesive works fairly well.

I agree with you! I find that hot melt is better in many aspects - it's not conductive at the voltages we face in an amplifier, it's easy to apply, and most importantly; it's easy to remove as well! A quick shot with a cooling spray and it's removed easily with no extra tools!

Jake