Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: pullshocks on June 10, 2018, 04:36:07 pm

Title: PT and OT are both lay down style. Will this be OK, or...
Post by: pullshocks on June 10, 2018, 04:36:07 pm

I want to do a build  with transformers I have on hand.  Both PT and OT are lay down style.  The PT has metal caps on both ends.  The OT has a metal cap on top only.
From what I've read transformer orientation and placement can cause noise problems.  And that the way to prevent it is to have the transformers oriented at 90 degrees to eachother.  But I'm not clear whether it is the planes of the laminations, or the axis of the coils that need to be 90 degrees.


If it is the axis of the coils that needs to be at90 degree orientation,  that is possible with 2 lay down transformers.


If it is the planes of the laminations, then it seems like I need to

make some brackets for the OT to flip it 90 degrees, and add some kind of cap over the other end.

Thanks in advance for your assistance.

Title: Re: PT and OT are both lay down style. Will this be OK, or...
Post by: shooter on June 10, 2018, 05:02:21 pm

Quote

https://en.wikipedia.org/wiki/Lenz%27s_law

here's a start if you're really interested  :icon_biggrin:

also keep in mind you have a 3D box, taking the trannies off the "same plane" helps

Title: Re: PT and OT are both lay down style. Will this be OK, or...
Post by: labb on June 10, 2018, 05:55:52 pm

Give the headphone trick a try:

 This is the best way to find the quietest place to put a reverb, output, driver, or any other signal transformer to get the least hum. CAUTION: THIS INVOLVES WORKING ON THE AMP WITH WALL VOLTAGE PRESENT. WALL VOLTAGE CAN BE FATAL.First set up the power transformer. If it's not installed yet, all the better, but if it is, this will still help. If the PT is not installed, wire up the primaries to a power cord, but do not wire up any secondaries-- tape the ends of the secondaries. If the PT is installed, fine, just make sure there is no circuit on any of the secondary leads (pull all tubes, and disconnect leads and tape them as necessary).
Now set up the signal transformer (output, reverb, whatever). Hook one set of OT secondaries (your choice, but I usually go from ground to the highest impedance tap, don't worry about impedance matching here!) to a set of headphones. Tape the primary leads.
Put the headphones on, plug in the power cord, and start moving the signal transformer around. Try it all over the chassis, and also rotate it. While you might expect the least hum with the transformers as far from each other as possible and at right angles (and that may be the case for you), it might come at an odd angle and/or position. Sometimes the least hum occurs when the transformers are side by side. When you find the quietest spot, use a permanent marker to mark where the mounting holes should be.

Title: Re: PT and OT are both lay down style. Will this be OK, or...
Post by: MFowler on June 11, 2018, 11:10:24 pm

Place the OT and PT on opposite ends of your chassis and problem is solved.