Rivera Bias trouble

[Valvehead]

Ive got a Rivera Jake 50w here. No bias voltage. Checking with no tubes in it . Ive checked everything in the bias circuit . I also replaced C204 , c205 , c9 , c10 . Swapped out D5 with 2 different diodes even though it tests good in circuit . Replaced the bias adjust pot .

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. This amp has 1 owner and never been opened.

So........its got to be the power trans ???? If i put tubes in it they red plate within 10 seconds and the bias skyrockets up !!

Heres a scem of the 100w version .

[TomCarlos]

How do the orange wires connect to the circuit? Are they soldered into a pc board? Molex connector? Maybe you tried this but if you disconnected the orange wires from the circuit, do you see any ac voltage?

[Valvehead]

yes 41vac , on the orange wires un-hooked , 1 goes to ground . soldered to pcb , ground verified

same result with power tubes in , but if i connect the cab , i get a loud hum , the bias skyrockets and i get red plating . Also--when i go back to standby mode , i hear a loud Sizzle sound coming from the power trans for about 1 second !!

[Jon Snell]

What have you got on point A?
Zero means either the diode is short circuit or one of the feed resistors has failed or maybe C9 has a short.

[Valvehead]

see post 1

[TomCarlos]

And you are sure you have the diode and caps (C9, C10) connected properly?

If you shut off the power, remove the orange lead going to the 1K ...

What is the resistance across the 1K? (Verify to make sure it is ok).

What is the resistance of the Diode? Measure in both directions.

What is the resistance from one end of R6 to the outside edge of R7 (so you are measuring R6, VR1, and R7 and lift one end of the caps)?

[Jazz P Bass]

Well this makes absolutely no sense.
If the Org wires read 41 VAC unconnected, what do they read when everything else is hooked up?

[vintagekiki]

How much is the bias voltage (TP41) without power tubes (V6 -V9)?

[Valvehead]

Well this makes absolutely no sense.
If the Org wires read 41 VAC unconnected, what do they read when everything else is hooked up?

0.1 vac and around 370mvDc

[Valvehead]

How much is the bias voltage (TP41) without power tubes (V6 -V9)?

it starts at 30mvdc and creeps down to 0mv over about 20 seconds

the new bias pot has no affect

[Valvehead]

And you are sure you have the diode and caps (C9, C10) connected properly? Yes

If you shut off the power, remove the orange lead going to the 1K ...

What is the resistance across the 1K? (Verify to make sure it is ok). it tests 1k

What is the resistance of the Diode? Measure in both directions. i ve tried 2 different New diodes there , original measures Open and 7 Meg..tests ok in diode mode

What is the resistance from one end of R6 to the outside edge of R7 (so you are measuring R6, VR1, and R7 and lift one end of the caps)? 34K

[The Dude]

yes 41vac , on the orange wires un-hooked , 1 goes to ground . soldered to pcb , ground verified

same result with power tubes in , but if i connect the cab , i get a loud hum , the bias skyrockets and i get red plating . Also--when i go back to standby mode , i hear a loud Sizzle sound coming from the power trans for about 1 second !!

You should not be installing power tubes with no bias voltage!

[The Dude]

Disconnect the orange transformer wires and measure the resistance between the two points where the wires plug into the circuit board.

[Jazz P Bass]

For sure there is something loading it down.
My bet is a cooked capacitor.

[Valvehead]

For sure there is something loading it down.
My bet is a cooked capacitor.

c9 / c10 / c204 / c205 all new. maybe C7 ???