Hot Rod deville Bias??

[nosaj]

I have a Hot Rod Deville That is redplating . The mV reading is 262 at the bias test point is this even possible?

Rotating the bias pot will move that value up and down but nowhere under 200 mV..
Suggestions?

thanks
nosaj

[The Dude]

What is your bias voltage? What is voltage at the output tube grid pins?

Edit: I'd pull the output tubes while checking to prevent damage.

[Chuck H]

Yep. Pull the power tubes for diagnosis.

The usual suspects? Bad pot, tubes, Ecaps, coupling caps.

[Jon Snell]

I would suspect C26, 27 & C37 firstly.
Remove the output valves and test for -54v across C38, then -50 or soon pin 5 of the 6L6s.
If those voltages are correct, fit new balanced 6L6s.

[nosaj]

Here's what i got no tubes installed.
plate 509
screen 507
control grid -24.69

voltage across c38 -25

Sorry for delay this notification stuff cat wait to get fixed.
nosaj

[nosaj]

Heres what else i got cp15-cp17 57.8 Vac
cr10 shows .097 Vdc
CR15 one side -35.75 other side 3.5Vdc

So based on these I presume is either a bad solder joint or a bad cap I really should remember to check them before i solder them in.. So another fun job of removing the pcb.
nosaj

[Jon Snell]

Read the service manual diagrammes and cross reference the voltages. Bear in mind, the voltages are just a ball park number.
The Cathode voltage on CR15, (CR10 side), is meaningless as it is swamped with chopped AC from the capacitor and CR10. It is a voltage doubler circuit.

[nosaj]

cr15 anode side is -35.75 so that means c37 is not pumping enough enough electrons for voltage doubling?
nosaj

[Helmholtz]

Is there a reason for not posting the complete schematic?

[TomCarlos]

I am following along on this thread. Here is the schematic: hotrod_deville_schematic.pdf

[nosaj]

cr15 anode side is -35.75 so that means c37 is not pumping enough enough electrons for voltage doubling?
nosaj

Does anyone concur or am I barking up the wrong tree?
nosaj

[g1]

Does anyone concur

Yes, try replacing C37.

[Helmholtz]

Does anyone concur or am I barking up the wrong tree?
nosaj

"Pumping" doesn't make sense to me here.
Check C37 and C43 for capacitance and leakage resistance.

[Chuck H]

"Pumping" doesn't make sense to me here.
Check C37 and C43 for capacitance and leakage resistance.

???
As in C37 isn't holding and releasing charge as it should (pumping?). I had no trouble with the adjectives. C37 isn't performing. (<period) That said, I always appreciate corrected terminologies so I might not be misunderstood by the engineers and techs here. So, thanks. But go easy please..

[g1]

I believe voltage doublers are often referred to as an example of 'charge pump' type circuits.