First start - Check voltage

[sergio]

today I lit the amplifier and started verifying the first tensions. The problem is that I don't have a big difference between the various B+..points, etc.. I am checking to open circuit.

My supply board is 1k,22k,1k,2,2k

b+1 +475V
b+2 +471V
b+3 +465V
b+4 +456V reverb
b+5 +455V od
b+6 +454V clean

can someone give me explanations?

heaters voltage 6,83V
bias voltage -83,5V (without 27K resistor to ground)

Thanks Sergio

[skyboltone]

You don't have tubes plugged in yet. The dropping string needs a load in order to work. Nothing looks terribly amiss without tubes.

[sergio]

Ok , therefore , I must wiring all main board(clean,od, p.i.) and insert the tubes to check all voltages?

Thanks
Sergio

[Bob-I]

Ok , therefore , I must wiring all main board(clean,od, p.i.) and insert the tubes to check all voltages?

Thanks
Sergio

Everything seems in line so far. Take your time, make sure to get the bias resistor in place before inserting any power tubes.

Before putting tubes in, build a light bulb limiter. Wire a light bulb socket in SERIES with the AC line. The resistance of the bulb will help to limit current and drop voltages in case of an error in the wiring.

[Luthierwnc]

I second the bias voltage check. Complete the install on all the bias components and make sure it is in the correct range (and negative) for whatever tubes you are using. You can test this without having to put the tubes in. Usually I put component leads through the lugs or turrets and bend them for a little mechanical strength. On the bias resistor and a couple other areas, I usually leave the leads straight because you might have to make substitutions and it is easier to yank them out.

Your heater voltage is a little frisky too. Recheck that under load as well.

Cheers, Skip

[sergio]

I finished to wire bias circuit . The voltage go from -40.5 to -56.2
It's ok?

[skyboltone]

I finished to wire bias circuit . The voltage go from -40.5 to -56.2
It's ok?

Sergio, what size "tail" do you have from the bias pot to ground? Similarly what are you using between the bias tap and the diode? Are you using a bias tap (50-60 VAC) or taking your bias tap off the main winding. Which schematic are you using. You are certainly within range of the 6L6GC tubes but you may want to get down a little lower on the 25 watt plate disappation types like EL-34 and 6L6WGB/5881. If you've got a 27K in there try an 33K, or 39K. Alternately you could mildly increase the first resistor before the diode.

Come to think of it. Leave it alone for now. The transformer may burden a little when the tubes go in. This includes the bias circuit even though it doesn't get any load, it responds to the overall burden of the transformer.

Am I right here Bob and Skip? Am I thinkin' backwards?

http://members.shaw.ca/house-of-jim/Htm ... ables.html

[Bob-I]

I finished to wire bias circuit . The voltage go from -40.5 to -56.2
It's ok?

Should be fine. It may take some fine adjustment later but get it powered up and making sound first.

[sergio]

My schematic is #124, with 4x6l6

[Luthierwnc]

On the bias side, you just need to be sure it won't incinerate the tube. As long as it's close, you have plenty of time to fix it. I'd also like to see that filament supply come down under load. sh

[sergio]

HI , I have completed the wiring of the Phase-inverter and Power circuit , now I can insert the 4x6l6 with P.I tubes , power on ,and check the voltage?

Thanks for your support..
Sergio

[Bob-I]

HI , I have completed the wiring of the Phase-inverter and Power circuit , now I can insert the 4x6l6 with P.I tubes , power on ,and check the voltage?

Thanks for your support..
Sergio

I say yes, but make sure to use the light blub limiter I described above.

[sergio]

Ok , I power on my amp and this is the voltage on power tube anode: +458V

On P.I tube +302V and +313V.

Can be right?

Thanks

[heisthl]

Well within the ball park - the PI voltages vary depending on the tube used there. Use a "matched" long plate tube if possible and then use the trimmer (and your ears) to get the maximum second order harmonics (octave above) which in an ideal amp would be around a 3 to 6 volt difference.

[sergio]

Here my voltage:

V1 12AX7 SED CLEAN B+6= 317V

pin1=211V
pin3=1,57V
pin6=207V
pin8=1,64V


V2 12AX7 SED OD B+5= 323V

pin1= 208V
pin3= 1,71V
pin6= 212V
pin8= 1,63V

V4 12AT7 EH REVERB B+4= 327V
B+2= 262V (after 51K res)

pin1= 256V
pin3= 3,22V
pin6= 162V
pin8= 2,4V

V3 12AX7 SOVTEK Long Plate PI B+3= 453V

pin1= 307V
pin6= 314V


V5-6-7-8 6L6GC SED POWER B+1= 462V
B+2= 458V
pin3= 461V