Fender Deluxe Reverb speaker jack question.

[Stratz]

Hi all, I'm just starting a Mojo Deluxe Reverb kit build and after wiring only the black and green wires from the OT both the Speaker and EXT speaker jacks test as grounded. No matter which point of either jack I test they all read that the entire speaker jack assembly is going to ground. I plugged in a 1/4" jack just for the hell of it and they still read 100% grounded no matter where I put my test probe.

The red, brown and blue wires are not hooked up yet.

Is this normal?????

The primary winding's read about 25 ohms offset (~70 ohms brown/95 ohms red to blue) and the speaker side reads .004 ohms.
Thanks.

[Stratz]

Update. I just unsoldered the transformer leads from the jacks (I left the jumpers for the parallel connection in place) and I'm still getting the same test results.
Is this normal??
Thanks.

[pdf64]

The OT secondary winding is a fairly short length of fairly thick wire, so a low resistance reading is to be expected.
I think that the DR OT is simple, non-interleaved, which may tend to increase the resistance discrepancy between the primary coil start to CT, and CT to coil end; the wire length of the latter is greater.

[Stratz]

I'm beginning to think that I may have read the diagram wrong.
Heres a pic of the layout and of my work. It was much neater before I pulled it apart and re-soldered it. Did I hook the jumper up backwards?

Thanks.

[pdf64]

I think that's correct; the idea is to short across the socket when nothing is plugged into the main speaker jack.

[Tom Phillips]

Hi all, I'm just starting a Mojo Deluxe Reverb kit build and after wiring only the black and green wires from the OT both the Speaker and EXT speaker jacks test as grounded. No matter which point of either jack I test they all read that the entire speaker jack assembly is going to ground. I plugged in a 1/4" jack just for the hell of it and they still read 100% grounded no matter where I put my test probe. The red, brown and blue wires are not hooked up yet. Is this normal?...

Update. I just unsoldered the transformer leads from the jacks (I left the jumpers for the parallel connection in place) and I'm still getting the same test results.
Is this normal?...

Both jacks are physically fastened to the chassis so the plug shaft contact of the both jacks are always grounded.
There is a wire installed between the switching lug and the ground lug of the speaker jack so that grounds the tip contact of the speaker jack.
There is a wire attached between the tip contact of the speaker jack and the tip contact of the external speaker jack so that grounds the tip of the external speaker jack.
Therefore, everything is grounded and that is normal.

When you insert a plug into the speaker jack (and if that plug is not shorted or attached to a speaker) then you should read an open circuit between the tip contacts and the chassis if the output transformer secondary is not connected. If the OT secondary is connected then you will still read a very low resistance between the tip contacts and ground. Inexpensive meters will often read that very small resistance as a short.

If the tip contacts are still shorted to ground with the output transformer secondary disconnected and an open plug inserted into the speaker jack then something is incorrectly wired, damaged or otherwise shorted. Perhaps the end of the wire shown in the attached marked up photo.

[Stratz]

Thanks guys. It's 100% proper.
Tom, the wiring mess there was only because I had originally dressed everything perfectly and later had to remove all but the jumpers to rule out the OT.
It's all fixed now and nice and neat again.

I have a new issue now. The power transformer that came in the Mojo Deluxe Reverb kit doesn't have the center tap which is required per the schematic. Any suggestions?

Plus it looks like it's going to have a bit over 500VDC
The filter caps are only 475 V and the amp will be running 6V6's
The transformer is Mojo part #761

Thanks very much.
Rob.

[Mick Bailey]

That drawing shows red/yellow as the 0v centre tap.

[Stratz]

That drawing shows red/yellow as the 0v centre tap.

Sorry Mick, I should have been more specific. I need 2 center taps. The one in the drawing shows the CT for the high voltage winding.
I also need a CT for the 6v heaters which is for all 9 valves so I'm not exactly sure what to do at this point.

[Dave H]

I also need a CT for the 6v heaters which is for all 9 valves so I'm not exactly sure what to do at this point.

You could use the usual 2 x 100R artificial centre tap.

[pdf64]

You could use the usual 2 x 100R artificial centre tap.

eg see PT TR1 http://bmamps.com/Schematics/fender/...c568_schem.pdf

[Stratz]

Thanks very much guys, the artificial CT is done.
Much appreciated.
Rob.

[Tom Phillips]

Did Mojo supply instructions with their kit? Any words of explanation from them concerning differences between their kit and the original amp design?

[Stratz]

Did Mojo supply instructions with their kit? Any words of explanation from them concerning differences between their kit and the original amp design?

A few drawings and schematics. One layout is pretty good size but I still need to reference other drawings, schematics etc that I found on line. There are no "step by step" assembly instructions if that's what you're asking.

Luckily for me I have a '68 Bandmaster Reverb which I pulled the chassis out of sitting only a few feet away so I have a very good reference at hand. Some component values are different on the BMR but the layout is the same as the Deluxe Reverb.