Heaters ain’t heating!

[sclinchy]

I just replaced and rewired a couple of the preamp tube sockets on my Hoffman Princeton Reverb, and I’m not getting correct voltages on my heaters. With no tubes installed, I get 6.7 VAC on the lamp and both of the power tubes. On the preamp tubes I get a little over 2 VAC.  I’ve checked continuity on the heater wires, and that looks good. I checked, and I’m getting continuity from the pin 4&5 pair to the chassis. Is that normal?


Any ideas would be greatly appreciated.


Thanks!

[AlNewman]

Why did you replace the sockets?
Where are your points of measurement?
Can you share a schematic and photos of the amp?

[sclinchy]

Thanks. I required most of the amp, because I’d done a pretty sloppy job of it the first time, although it worked. When I went to plug tubes back in, I had apparently managed to slop some solder into the sockets. Replaced those two sockets, and here I am.


Layout attached.

[mresistor]

It's best to insert a tube into the socket ( I use old dead ones ) when you are soldering on socket pins, so the solder doesn't wick down into the socket and make it diffucult of impossible to insert a tube.

[sclinchy]

Good idea, thanks.

[AlNewman]

Depending on how your amp is wired, it makes a difference whether you're measuring to chassis or the opposing pin in your heater circuit.

[sclinchy]

Opposing pin, except of course when I measured continuity to chassis. Should have been clearer.

[AlNewman]

I don't know what resistors you're using to float your heater circuit, but you shouldn't have continuity to chassis, unless you have a chassis return.  With 100/100R resistors, you should read minimum 50 ohms at any point in your heater circuit to chassis with no tubes.

[Willabe]

I don't know what resistors you're using to float your heater circuit, but you shouldn't have continuity to chassis, unless you have a chassis return.  With 100/100R resistors, you should read minimum 50 ohms at any point in your heater circuit to chassis with no tubes.

He's not measuring resistance. He has the meter set for continuity.

If the ground reference is a CT or a faux CT with resistors, with the meter set for continuity it will show continuity to the chassis. Because the heater wind is connected to the chassis.
   
Set your meter for resistance.

With tubes out, start to measure the heaters across the wind legs, start with the power tubes, pins 2/7, then with the small tubes, 4/5 - 9, keep going until you find where you don't have 6.3acv.

[AlNewman]

If the ground reference is a CT or a faux CT with resistors, with the meter set for continuity it will show continuity to the chassis. Because the heater wind is connected to the chassis.

My bad...  if the heater winding has a center tap which is connected to chassis, then yes, I agree.

[sclinchy]

I’m seeing the reduced voltage begin at V4, which is the first of the preamp tubes after the power tubes, and continue for all of the preamp tubes. The power tubes read correctly.

[Willabe]

I’m seeing the reduced voltage begin at V4, which is the first of the preamp tubes after the power tubes, and continue for all of the preamp tubes. The power tubes read correctly.

And that's with ALL the tubes out?

And how are the heaters referenced to ground, heater wind CT or a pair of resistors for a faux ground?
 

[sclinchy]

Yes, all tubes out. I believe it’s CT. AA1164.

[Willabe]

I’m seeing the reduced voltage begin at V4, which is the first of the preamp tubes after the power tubes, and continue for all of the preamp tubes. The power tubes read correctly.

Ok, so somethings wrong starting at V4, figure out what it is. Cold solder joint, wire just barly shorting out, broken wire inside it's insulation.

Chances are if you get the right acv at V4, then the rest will be right too.

[acheld]

Photos of your build would be helpful.   Include all wiring that involves your heaters.

[sclinchy]

Willabe was correct!  Resoldered all the heater connections and everything is working great.


Thanks to all who contributed.