Back to Back PT orientation

[Ripthorn]

Is there any kind a rule regarding the orientation of back to back power transformers? I ask because mine will be in close proximity and I don't know if any hum can or will be induced if I just stick them on there. Thanks.

[M Fowler]

I have seen them so close its rediculous but they had no problems, take HAD for instance look at some pictures of Dumbles.

But there is a test for everything electrical.

Mark

[paulster]

Look up the 'headphone trick'. You can very easily hear for yourself whether there will be any induced noise before you drill the mounting holes.

[Phil_S]

Here's my 'wreck variant. It works just fine. Hard to see in the picture, but they are less than 1/4" apart.

[M Fowler]

Yeah but Phil yours are plates are turned 180 degrees to avoid problems.

Some builders have them side by side with the plates running parallel to each other like HAD did.

Mark

[Structo]

Don't you have to use a flux capacitor in between when the space is small?

[Zippy]

Here's my 'wreck variant. It works just fine. Hard to see in the picture, but they are less than 1/4" apart.

Hey, Phil. You're gonna have to 'xplain those test points, extra jack, switch, and knob. Please???

Adjustable fixed bias or master volume?

[Phil_S]

Hey, Phil. You're gonna have to 'xplain those test points, extra jack, switch, and knob. Please???
Adjustable fixed bias or master volume?

The two tall tubes are 6AQ5's instead of a pair of 6V6's. The two red test points furthest to the rear, furthest from the transformers are for the plates of the 6AQ5's. Stick your meter probes in there set for Amps if you like and bias by the shunt method. Personally, that gives me the willies, so I measure voltage and use the R of the OT to compute the mA draw of the power tubes.

The next red test point, between the 6AQ5 and the knob on the deck is the power tube grids.

The fourth red test point, in the middle of the deck, near the transformers is to check B+ at the first node.

The metal thing, curled up, between the knob and the B+ TP is the ground. It is just a lug and goes to the same bolt that is the amplifier circuit ground. I couldn't work in a test point there, so you just clamp your meter onto it.

The knob on the deck is the bias pot.

In the back, the two jacks on one side of the switch are 4 ohm and 8 ohm outputs. The jack on the other side of the switch is technically speaking a 12 ohm output, but meant to use as if it is 16 ohms. The switch needs to be pointed at the output jack you are using.

The output transformer is from www.musicalpowersupplies.com. It is 6600 ohm primary and there are two separately wound secondaries, 4 and 8. The switch reconfigures them in series, lifts one ground, etc, to make the 12 ohm tap. More trouble than it's worth to make that.

That's it.