'61 Ampeg R12-R Hum

[g1]

Where does the red/yellow wire connected to the cap can ground go? It may be the pt center tap.

[ca7922303]

Where does the red/yellow wire connected to the cap can ground go? It may be the pt center tap.

Red/yellow wire goes to PT.

[ca7922303]

Where does the red/yellow wire connected to the cap can ground go? It may be the pt center tap.

If red/yellow wire is pt center tap to can cap ground, any other possibilities to reduce hum? Thanks

[g1]

It looks like that is a 4 section cap can. Measure AC volts from each of the 4 lugs to ground.

[The Dude]

I see the CT wire going to the can cap lug, but it's hard to tell from the picture, so I'll add. Make sure the can cap ground lugs are well soldered to the chassis. They can crack loose. The lugs will often look well soldered, but if you grab the can and give it a wiggle, you can see lugs moving and cracked solder joints.

[ca7922303]

It looks like that is a 4 section cap can. Measure AC volts from each of the 4 lugs to ground.

Can(1.3/1.1/1.4/0.8) final reading on each lug.. can seems to be tight when trying to wiggle

[ca7922303]

Can(1.3/1.1/1.4/0.8) final reading on each lug.. can seems to be tight when trying to wiggle

Do these readings look correct?

[g1]

Yes those are good readings for AC ripple on the caps. Does not seem that your hum is related to the cap can.

[ca7922303]

Yes those are good readings for AC ripple on the caps. Does not seem that your hum is related to the cap can.

SHould I start testing all the caps?

[ca7922303]

SHould I start testing all the caps?

Or try to trace down the hum with oscope?

[g1]

Ground pin1 of the PI tube (V4), see if that kills the hum.

[ca7922303]

Ground pin1 of the PI tube (V4), see if that kills the hum.

5Y3 pin 1 to ground does not kill the hum.

[Enzo]

5Y3 is the rectifier tube. g1 asked about pin 1 of the phase inverter tube, which is V4.

[ca7922303]

5Y3 is the rectifier tube. g1 asked about pin 1 of the phase inverter tube, which is V4.

Sorry about that. Yes V4 pin 1 to ground does kill hum.

[The Dude]

........... and you are lucky that pin 1 of the 5Y3 is an unused pin or that they didn't use the pin as a jumper connection.

You asked in another thread how someone could get killed? This is one example of how- grounding pins of a rectifier tube.