Rivera Bias trouble

[DrGonz78]

Sounds to me like it is possible that there is an intermittent open in one of the orange wires. From what I read you took the wires off the board and measured an open across the bias winding. Which that is the problem. However your statement that you now have bias supply voltage on the board must mean you reattached the wires to take that measurement. Makes me think that jostling around those wires could indicate that the intermittent open condition is not deep in the bias winding. I would disconnect the wires and measure across them while jostling the wires around to check if there is a weak point in the wiring. Then again it might not be a weak point in the wires themselves but at the connection point right at bias winding. Just as The Dude says. But as I recall you said the wires solder right to the board so there are no crimped on connections that attach to the board.

[Enzo]

An open winding when unloaded can still make readings on your AC volt meter.

[Valvehead]

Sounds to me like it is possible that there is an intermittent open in one of the orange wires. From what I read you took the wires off the board and measured an open across the bias winding. Which that is the problem. However your statement that you now have bias supply voltage on the board must mean you reattached the wires to take that measurement. Makes me think that jostling around those wires could indicate that the intermittent open condition is not deep in the bias winding. I would disconnect the wires and measure across them while jostling the wires around to check if there is a weak point in the wiring. Then again it might not be a weak point in the wires themselves but at the connection point right at bias winding. Just as The Dude says. But as I recall you said the wires solder right to the board so there are no crimped on connections that attach to the board.

no crimps----i also posted that when i go into Standby mode ( tubes in) , i get a very audible sizzle sound --directly from the PT . Ill do some more checking when i can .

[DrGonz78]

An open winding when unloaded can still make readings on your AC volt meter.

But he could confirm if connecting an ohms meter across the wires while wiggling them around and see if the open state changes at all. He measured voltage fine disconnected from the board but I think it was around 40v or something. It just seems strange that there was no voltage connected to the board and now there is voltage on the board.

[vintagekiki]

#29

If before and after R5 have 30VAC, and if D5 is correct and correctly polarized, before and after R6 (5.6k) there should be a negative voltage of the order -40VDC.
If there is no negative voltage check D5, C9 (100u), C10 (10u), R6 (5.6k).
If the components are OK, check the PCB lines between R5 (1k) and bias pot VR1 (10k) that there is no interruption somewhere or cold solder.

[g1]

#29

If before and after R5 have 30VAC, and if D5 is correct and correctly polarized, before and after R6 (5.6k) there should be a negative voltage of the order -40VDC.
If there is no negative voltage check D5, C9 (100u), C10 (10u), R6 (5.6k).

See post #1.

[vintagekiki]

#37

You don't follow the topic properly.

See post #29

[g1]

You don't follow the topic properly.

It will be of great benefit to all readers if you use proper quotes instead of post #'s.

[DrGonz78]

#29

If before and after R5 have 30VAC, and if D5 is correct and correctly polarized, before and after R6 (5.6k) there should be a negative voltage of the order -40VDC.
If there is no negative voltage check D5, C9 (100u), C10 (10u), R6 (5.6k).
If the components are OK, check the PCB lines between R5 (1k) and bias pot VR1 (10k) that there is no interruption somewhere or cold solder.

Yes this post here... We already have been there and done that. We are concerned that the bias taps on the PT read open circuit. In the initial post all those components were reported as changed.

[vintagekiki]

#40

post #36 is a comment post #29

1)

the initial post
0mv at either side of R5 and D5 . 0mv at tube sockets . The factory did not use the "Poly switch" you see right after the power trans it has a jumper there.

now i have 30VAC at TP42
and 30vac before and after R5

[DrGonz78]

But he could confirm if connecting an ohms meter across the wires while wiggling them around and see if the open state changes at all. He measured voltage fine disconnected from the board but I think it was around 40v or something. It just seems strange that there was no voltage connected to the board and now there is voltage on the board.

This too has been acknowledged here. That is why we are still wondering if the bias taps on the transformer might have some sort of intermittent open condition. We know bias taps removed from the board measured open, which is the focus of the current questioning. We know that even an open winding on the bias supply can measure voltage across it on the DMM when unloaded. When loaded to the circuit it was not reading any voltages. However, now it is reading voltages in circuit. So there has to be something intermittent going on with the bias winding directly on the PT. Hence why I mentioned jostling around the bias wire connections to check if that triggers any bad connections.

[The Dude]

It will be of great benefit to all readers if you use proper quotes instead of post #'s.

[Valvehead]

UPDATE-------

Finally got a new power trans from the fine folks at Rivera.

That was it........bad PT.

New one is in , bias is correct , everything is perfect , amp has been rockin for about an hour with zero issues !!!