The Amp Garage

Our administrator, pompeiisneaks, built that Dual 50 several years ago. Give him a shout. He can give you the good and bad on that project. I think he has a build thread on TAG or maybe Hoffman's forum. Try searching on those forums. Sadly, I had to give up the woodworking due to COPD. Using a prope...

Be careful with that scope. If you connect a probe to the primary of the OT you may end up with a dead scope.

If it’s one end and center - then it’s the same either way, correct? And if that’s the case - there’s truly no best practice for which end is “in” and which is “out” then? Correct on both questions. And since you are using DPST switches if the bat is not oriented correctly for your faceplate you wi...

dezmoduo wrote: ↑Sun Oct 11, 2026 5:28 pm AA864 does look like it. Great and Thank you. I have more than my share of bassman variants. I'll pursue a simple Princeton.
I'll put a label on the board for when I don't recall in 3 years.

In case you ever decide to build an AA864, change one resistor.

But I think they orient the “on” position of the bat differently, don’t they? No. You would need to move the wires on the bottom lugs to the top lugs to change bat orientation. Or, physically rotate the body of the switch 180°. I always thought that switches like this are either open or closed - bu...

Raoul Duke wrote: ↑Sat Oct 10, 2026 7:11 pm Second drawing, right?

Both drawings do the same thing.

My cheap variac is terrible and looking to get a U.S. made one. Is the Weschler one any good. I think I can get a refurbished one for not crazy money. That's a good brand. I have a 10 amp Superior Powerstat 3PN116C Autotransformer made in USA. Very good quality. Plenty available on eBay. Expect to ...

Don't forget, when you start to reconnect everything, stretch that white wire and connect it to one of the center lugs of the standby switch.

Put the tremolo tube on a separate power supply node. Connect a 1K to the screen node and then a 40µF cap from the 1K to ground. Use this new node to supply the tremolo circuit. Does that help the thumping?

Turn the amp on and measure the B+ at the rectifier positive terminal. If OK, then you really don't have to replace anything.

That NE2 bulb test won't work on a single winding device such as a choke. Just use your ohm meter. Resistance for that choke should be about 100Ω.

Does this 10Hz waveform show up on any of the B+ filter caps?

So using the drawing as reference, I get forward voltage with the common lead on DC+, red lead on either AC with OL if I put red on DC+ and common to the ACs. That's good. However, I get no forward voltage on anything else/any combination. This leads me to believe that I only have one side working ...

I think that’s every combination. I’m a little confused… I bet you are! Rather than trying to measure everything all at once, break it down. There are four diodes in that block. Measure one diode to get a front to back ratio. Then move to another diode and repeat. Do this for all four diodes. The a...

Long story short: both negative to AC read OL and both AC to positive read 1.1. Nothing wrong with those readings. But the test is only half completed. Now you need to swap the meter leads and repeat the same test. The readings should all flip. IOW, a previous reading of "OL" will now read "1.1" an...