no cathode voltage on 2/3 preamp stages

[g1]

Have you tried replacing the plate resistor?

[Tom Phillips]

Have you tried replacing the plate resistor?

Good point.
1) Does the plate resistor measure ~100k Ohms?
2) If so. Is the measurement still ~100k from the top of the tube socket to the B+ supply side of the resistor. (Power off & caps drained of course)
3) Can you see both heaters glowing inside the tube?

[cooldude666]

Sorry! I feel like a heel. Ya'll were trying to help and I just ditched. I moved so this project fell by the wayside for a minute. I'm finally back on it and this is really killing me. To answer your question Tom.
1. Yes
2. Yes
3. Yes both heaters are glowing, and I measure 6vac between pins 4/5 and 9.

I changed the plate resistor, no change. Could it possibly be the socket?

[Tom Phillips]

...I changed the plate resistor, no change. Could it possibly be the socket?

It could be the socket but that's not usually high on the suspect list. Physical inspection of the socket is always a good idea.

In post #14 you reported measuring "820 ohms from top of socket to ground." What ground point is that? Was your probe just on the other side of the resistor or was it at the ground point of the power supply or at the ground of a cathode resistor on one of the tube stages that is working correctly? I'm just trying to determine that "ground" is really the amp's circuit ground. Not investigating ground loops and such.

[cooldude666]

the other end of my probe is usually connected to chassis or the ground side of the power supply caps.

[g1]

Was just wondering what the grid is connected to. What model amp is this and can you post schematic?

[cooldude666]

Grid is connected via resistive divider to the previous gain stage and reverb recovery stage comes in here. Amp is home brewed, I dont have a real schematic right now. I should, i know but when i get that hot iron in my hand i just cant stop.

[g1]

It is possible there is a cracked pin in the socket, sometimes they crack but measure ok for resistance due to pressure of the meter probe.

[tubeswell]

No tube current in that triode means either the heaters, cathode or plate aren't connected (or the bias is so high that the tube is in cut-off (unlikely))

Seeing as how the heaters are okay, have you checked that you've got the plate resistor (Rp) and cathode resistor and bypass cap (Rk/Ck) connected to the correct socket pins (and not the other way around)? (Remember Plates are Pins 1 and 6, and Cathodes are Pins 3 and 8 in a noval dual triode)

[cooldude666]

I'm going to replace my sockets. Something is goofy with one of the pins of my power tube too. When I power it on it's dead until I poke it with a probe, then it comes to life. I've replaced the resistor, and resoldered the joint a few times and no change. I wish it were something as dumb as I hooked up the pins wrong, but I don't think so. Here's a shot of the guts. We're talking about V2A here. V3 is reverb send which isn't wired up, and V2B is the return, also not hooked up.You can see that pin 1 is hooked up to B+ (after Rp) and pin 3 is to ground (after Rk).

[Tom Phillips]

...Here's a shot of the guts...

The link doesn't seem to be working. Please edit post #25 and try replacing the photo.

[Enzo]

Please do with power off, but I suspect your voltage readings were taken at socket pins. So install a tube, but pull it slightly out so you can get a probe tip on the pins under the tube. Now do you still get 820 ohms to ground from the actual tube pin, not the socket pin? And is there continuity from the p[late pin on the tubes all the way to the plate resistor. That is the only way I know to test the actual socket to pin connection.