183 build questions

[professormudd]

I believe that I have completed the assembly of this amplifier, though I have not yet powered it on.

I'm going to go over the layout and schematic again to check and make sure every connection is accounted for.

I am also still waiting for my tubes to arrive, so there's no urge to rush. I've ordered a matched quad of Electro-Harmonix EL34, 2 gain matched Mullard reissue CV4004 12AX7, and a JAN 12AX7WA.

I also went ahead and put the knobs on it and mounted it in it's enclosure (a Carol-Ann head cabinet) because I really wanted to see how it looks.

[xtian]

Lookin' SWEET!

[ijedouglas]

Congrats!

[Abe5150]

Wow Looks great!

[professormudd]

Welp, hit a snag already....

I still do not have tubes, but I wanted to go ahead and power it on to check what I could. B+ from the rectifier is 465 +/- so I believe that is good.

I noticed my power LED was not lighting up. I checked the secondaries coming off of the relay transformer and they are only reading at 1.7VAC and I am only getting a few mV DC out to the footswitch jack. I did verify that there is 120VAC coming into the transformer at the primaries.

I wonder if this transformer is bunk. Any ideas?

[sluckey]

Did you connect the center tap of that 12VAC transformer to ground? If so, disconnect it. You'll likely need to replace two of the rectifier diodes too. Hopefully the transformer is still alive.

If you did not connect the CT to ground, then disconnect both of the secondary wires from the board and check for 12VAC across the two wires.

[Abe5150]

Your secondaries have an output of 3.6 so a 1.8 reading would be correct because each secondary wire caries 1.8 for a total of 3.6. What relays are you using? And did you wire the relay transformer rectifier as just a plain rectifier or rectifier and voltage doubler?

[sluckey]

Your secondaries have an output of 3.6 so a 1.8 reading would be correct because each secondary wire caries 1.8 for a total of 3.6.

No, he's using this 12VAC CT transformer...

https://www.hammfg.com/files/parts/pdf/166F12B.pdf

[Abe5150]

Your secondaries have an output of 3.6 so a 1.8 reading would be correct because each secondary wire caries 1.8 for a total of 3.6.

No, he's using this 12VAC CT transformer...

https://www.hammfg.com/files/parts/pdf/166F12B.pdf

Yup disregard what I said Sluckey is right.

[professormudd]

Did you connect the center tap of that 12VAC transformer to ground? If so, disconnect it. You'll likely need to replace two of the rectifier diodes too. Hopefully the transformer is still alive.

If you did not connect the CT to ground, then disconnect both of the secondary wires from the board and check for 12VAC across the two wires.

I did not ground it. I capped it off with heat-shrink and tucked it away.

I removed the secondaries from the relay board and measured 14VAC across the secondaries.

[pompeiisneaks]

Did you connect the center tap of that 12VAC transformer to ground? If so, disconnect it. You'll likely need to replace two of the rectifier diodes too. Hopefully the transformer is still alive.

If you did not connect the CT to ground, then disconnect both of the secondary wires from the board and check for 12VAC across the two wires.

I did not ground it. I capped it off with heat-shrink and tucked it away.

I removed the secondaries from the relay board and measured 14VAC across the secondaries.

Then this means either there's a short on the relay board, or your secondary is shorted somewhere and loading it makes it go bad, I'd guess the first is more likely. Remember relays and their power supplies should be left floating, not connected to chassis... you might have done something to the relay power supply components by grounding it as Sluckey mentioned.

~Phil

[professormudd]

Did you connect the center tap of that 12VAC transformer to ground? If so, disconnect it. You'll likely need to replace two of the rectifier diodes too. Hopefully the transformer is still alive.

If you did not connect the CT to ground, then disconnect both of the secondary wires from the board and check for 12VAC across the two wires.

I did not ground it. I capped it off with heat-shrink and tucked it away.

I removed the secondaries from the relay board and measured 14VAC across the secondaries.

Then this means either there's a short on the relay board, or your secondary is shorted somewhere and loading it makes it go bad, I'd guess the first is more likely. Remember relays and their power supplies should be left floating, not connected to chassis... you might have done something to the relay power supply components by grounding it as Sluckey mentioned.

~Phil

The layout for 183 shows a ground from the relay board to GND 5, as well as from the footswitch jack to GND 5. I used the same grounding scheme.

I am going to spend some time nosing around on the relay board.

[professormudd]

Crap. Mis-oriented the diodes.

[pompeiisneaks]

OH sorry I was thinking about a different relay setup that's used by hoffmans boards, not the ones for dumbles... must not have had enough coffee yet

Glad you found the diodes backwards.

~Phil

[sluckey]

Quick and easy find. But don't feel special. You're not the first to do that!

Better check all four of those diodes or just replace them all. I bet there are some dead ones now.

It's perfectly OK to ground the relay supply to chassis since you are using a dedicated PT. "Floating" the relay supply only becomes important if you are stealing 6.3VAC from the filament string. Even then, it's not necessary in all cases. But if you don't know those cases it's just best to float rather than sink.