New Build - Express

[ToneMerc]

Pull the bulb limiter and and install tubes V1-V3 only. Then check heater voltage at V1.

[Picker]

Here's a pic of the wires coming from the PT. The two brown wires are going to my heaters on V5

[IMG:799:531]http://i54.photobucket.com/albums/g94/r ... C_0888.jpg[/img]

[Picker]

As suggested, I pull the limiter and installed the Preamp tubes. Now I get

6.4 volts at the heaters on V1

Also, I switched the DMM to VDC and at the bottom of the diode stack I got 412 volts dc. (I think. I was running up and down stairs and didn't write it down.)

[amplifiednation]

Those should be correct as long as they weren't wired incorrectly at the factory. I'm sure that's a long shot.

Follow ToneMerc's lead, he knows his stuff. Try with the tubes

[ToneMerc]

As suggested, I pull the limiter and installed the Preamp tubes. Now I get

6.4 volts at the heaters on V1

Also, I switched the DMM to VDC and at the bottom of the diode stack I got 412 volts dc. (I think. I was running up and down stairs and didn't write it down.)

ok, that's better thats where it should be. With only V1-V3 installed, take the amp out of standby.

At V1-V3, check voltages on pins 1, 3,6& 8 and record them. They will change slightly when all tubes are installed though.

At V4 & V5, with the bias pot fully CW(or whatever direction is most negative), check voltage on pin 5

[T Wilcox]

Hey glad to see your getting good heater voltage now.
Sorry to give suggestions then disappear, was at work and things got busy all the sudden.
Anyways only thing I see in pics that is different than mine so far is I do not see 1k5 2watt tied to pins5 on both output tubes where your yellow and blue wires land, but it could be my eyes or the fact that I am working off the ceriatone layout?

Todd

[Picker]

Valve___Pin1_____Pin3_____ Pin6_____ Pin8
-----------------------------------------
V1_____ 198.9_____ 2_____175.1_____1.6
v2_____ 254 ______2.8 ___ n/a______n/a
V3_____ 205_____ 36_____217______ 36

V4 409
V5 405

Max negative bias still shows as -29

[ToneMerc]

Valve___Pin1_____Pin3_____ Pin6_____ Pin8
-----------------------------------------
V1_____ 198.9_____ 2_____175.1_____1.6
v2_____ 254 ______2.8 ___ n/a______n/a
V3_____ 205_____ 36_____217______ 36

V4 409
V5 405

Max negative bias still shows as -29

Install V4 & V5, set bias and check all voltages again.

[Picker]

Okay, but how should I be setting the Bias? Doesn't the -29 indicat that I am to low to be able to bias it properly?

[T Wilcox]

Hey Picker
Just to confirm that I am blind, do you have the 1k5's installed at R18 & 19 , pin 5 of each output tube?

Todd

[Picker]

Yes, the two resistors are there. If you go back to page four of this you can see them without the wires attached. The top-down more recent view makes them hard to see.

[Picker]

I just replaced the ground wires on V4 and V5 with resistors, removed the pin 1 - pin 8 jumper, and am not going to try and go bias. Also, instead of the old Sylvania EL34s that I was using I am switching to a newer pair of GT tubes. I'm not sure what shape the Sylvanias are in (particularly after red plating one of them so I thought the GT tubes would provide more consistent results.

[T Wilcox]

Ok sorry just could not see them in the last pic, I will go back and reread through the whole thread before posting again.
I am looking at the voltage chart BTW and the listed max bias is -28 so -29 is in range but not ideal.
Carry on

Todd

[Picker]

Arrgh.. Now I'm doing something wrong with biasing.

1. Unsoldered the Pin 1-Pin 8 Jumper
2. Pin 1 goes to ground still
3. Soldered 1 ohm 2w resistor between Pin 8 and ground.
4. Used DMM - black probe to chassis and red probe to the resistor (between resistor and ground) set to 200m VDC

I get 0.00 reading



What did I miss?

[T Wilcox]

OK I havent read through whole thread yet but, why did you remove jumper from pin 1- 8. heres link to pic of working amp with 1 ohm res in place.
Jumper from pin 1 - 8 remains then instead of a jumper to ground it should be a 1ohm from either pin 1 or 8 ( doesnt matter electrically ) to ground.

http://www.ceriatone.com/images/complet ... on/b5B.jpg

Its early still so hopefully Tonemerc will jump in but this is just my observation.

Todd