New build startup issues

[Bob-I]

V1- 6.4V
V1+V2- 6.3V
V1-3- 6.19V
V1-4- 5.745V
V1-5- 5.568V This seems low to me- is it???

That looked OK enough to me to attempt some B+.... Threw the standby- no major glow on the limiter.... So I measured B+:

B+1- 262.4
B+2- 257.9
B+3- 215.8
B+4- 205.6
B+5- 196.7

Obviously this not right....but the bias was at max negative.

So I checked the bias V-it's range was only -18 to -26

So something is really not right here at all...

Any further ideas???

Ron

With or without the lightbulb limiter?

With the limiter you're about right, without you're getting too much voltage drop. The light bulb limits and drops some voltage.

As for the heater wiring. Some folks think that reversing the phase of the heaters between tube is quieter, some think they should stay in phase. I'm sure that's not a problem.

[Ron Worley]

All the values and results I've stated is with the limiter.. dumb fuk here..... I don't know if what I'm seeing makes sense...

[Firestorm]

The light bulb thingy just protects you from the consequences of an accidental short. You powered it up; the light bulb was bright as the caps charged and then dimmed. So everything looks peachy keen. Time to get the limiter out of there. Bring it up in Standby mode. Check to make sure you've got -33 to -35 bias volts and go for it. You can't really measure voltages with the limiter in the circuit.

[Ron Worley]

OK, I'll give it a spin w/o the limiter.... hell, I got nothing to loose at this point..lol

It will be to funny if it was just the limiter throwing me off... but that's a high quality problem to have... so long as the guts have not been fried....

[skyboltone]

Ron:
I'm talking about the spike protection diodes between the power tube plates and ground. I can't see real well what you've got there but rip those out for now.

Next, simply disconnect the high voltage AC leads from Power Transformer to the rectifier diodes.

Now we'll just deal with the filaments. We don't want ever to put high voltage on the plates of cold tubes.

Dan

[skyboltone]

The light bulb thingy just protects you from the consequences of an accidental short. You powered it up; the light bulb was bright as the caps charged and then dimmed. So everything looks peachy keen. Time to get the limiter out of there. Bring it up in Standby mode. Check to make sure you've got -33 to -35 bias volts and go for it. You can't really measure voltages with the limiter in the circuit.

Wait a minute. Did I misread? I though he gots no glow. No filament heat, That don't sound peachy to me.

[Ron Worley]

Dan-

I have filament heat- it's just low voltage as I add tubes- see the previous post where I show the heater voltage values as I added tubes. I start off at 6.4V and it drops to about 5.5 with all tubes installed. It's all just plain weird. Every voltage level is low- but some have said that the limiter I'm using could be the culprit.... I will fire it up tonight or tomorrow without it to see what voltages I really have...

I do like the idea of isolating the heater circuit though, to see if that part of the tranny is good. Is it possible for a problem in the power / signal side of things to pull down the heater voltage??

[skyboltone]

---------<multiple> Dan

[skyboltone]

-------- <multiple>Dan

[skyboltone]

Dan-I have filament heat- Is it possible for a problem in the power / signal side of things to pull down the heater voltage??

Yes. Hang in there, you'll find it. Be sure to lift the Heater Winding Center Tap OR the 100 ohm artificial center taps.

Dan

[Ron Worley]

Dan- I have the heater center tap grounded.... what do you mean specifically by "lift" the tap?? Just want to be clear....

I think you mean to lift the heater circuit by grounding the center tap......

Ron

[gearhead]

I'm pretty sure Ron doesn't have an artificial center tap.

Before you remove the limiter, for completeness, I'd measure the incoming voltage VAC (measured at the switch).

[Ron Worley]

GH-

That makes good sense.... even with the limiter, the voltages should be line level I would think... the limiter should only affect current, right???

I know V=IR... but I don't know if R changes with the light bulb when it is lit or not... if that makes any sense....

Yup, no artifical tap- just the TS supplied center tap....

[Moose]

Finally got to where I could DL those pics...

Where have we left off?

Did you pull the flyback diodes from the power tubes to see if that helped?

Also, have you installed JUST the power tubes and done a B+ check? I'd be interested to know if you're getting ~390V there without the preamp tubes in.

Looking at the heater voltage, it seems to be acting like normal voltage sag -- like there's SOME resistive element, or some great current draw, in the system.

Since this is a very stiff supply, I'd expect only a few volts sag at the plates.

One other thing to check -- when you put in the power tubes, check voltage before the rectifier diodes and, I know it's silly, check the wall voltage coming off of the fuse. Since you're there, you might as well see exactly where the voltage drop is happening.

[skyboltone]

Dan- I have the heater center tap grounded.... what do you mean specifically by "lift" the tap?? Just want to be clear....

I think you mean to lift the heater circuit by grounding the center tap......

Ron

I meant to disconnect the center tap of the heater circuit from ground. But if you don't have a 100 ohm resistor between each leg of the 6.3VAC winding then you don't have an artificial center tap. I thought you did. KF did in Francisca. Leave the heater CT conneced.

https://tubeamparchive.com/viewtopic.php?t=5047
In the whole gut shot you have what appears to be a diode from pin 1/8 (grounded) to pin 3. The blue/brown connected to pin 3 are the OT primaries. Is that what I see? I'm just suggesting that for now, take that diode out of there. It is not essential and besides KF used three 4007s in series and ran them to chassis. Also, asked before, are the grid stoppers pointing straight up with leads from the board attached at pin 5? That would be fine except I don't much care for grid leads resting in direct contact with a wirewound screen resistor, this can lead to direct feedback and nasty current drawdown. Anyway, said screen resistor is between pin 4 and pin 6 correct? That's OK and then the red/yellow from the PS board connects to pin 6.
Now, move over to the power supply board. As a temporary measure, disconnect the yellow PT primary wires from your high voltage diode strings. We do want to rig it so that the bias supply remains connected. You can accomplish all of this buy disconnecting the cathode leads from the first diode in each high voltage string. OK? Now you've got bias, and you've got filament voltage. Also, while we're at it, on the main board, for now, on the 4th turret at the top to the pot, you have a yellow wire. Pull that away from everything so that it really is in free air. You'll tune the amp with this wire once we get it going. Report back

Dan