Author Topic: 5F6-a Bassman not working.. (Read 42519 times)

plexi50 · « **Reply #150 on:** October 30, 2015, 07:09:08 pm »

Ok no problem. Throw a 56k in there. You will wind up with 48.9 --50 volts. I want to hear this amp working tonight!

plexi50 · « **Reply #151 on:** October 30, 2015, 07:11:02 pm »

What is the bias resistors value in the amp now??

silat · « **Reply #152 on:** October 30, 2015, 07:43:08 pm »

Quote from: plexi50 on October 30, 2015, 05:57:45 pm

STOP!!!!! The 15K across the (2) bias capacitors stays. Change the bias resistor that is connected from the 15K side going to the positive capacitor leads. That's the bias resistor/ What is that resistors value?

Pay no attention to the yellow wire on my bias system. I am not using a diode. You are.

It is 56k...

plexi50 · « **Reply #153 on:** October 30, 2015, 07:43:56 pm »

And you have -38 ? Are you using a Digital Multi Meter or Analog Meter?

silat · « **Reply #154 on:** October 30, 2015, 08:04:11 pm »

I am using digital.

plexi50 · « **Reply #155 on:** October 30, 2015, 08:28:04 pm »

What resistor values do you have on hand? Try a 33K. Or take a 33k and 10K in series and you will have 43K.

silat · « **Reply #156 on:** October 30, 2015, 08:29:15 pm »

I did it took down to -32

plexi50 · « **Reply #157 on:** October 30, 2015, 08:33:09 pm »

Quote from: silat on October 30, 2015, 08:29:15 pm

I did it took down to -32

You did what to take it down to -32 volts?

silat · « **Reply #158 on:** October 30, 2015, 08:37:49 pm »

The 33 K resistor took it down to 32 I can take a picture if you like?

plexi50 · « **Reply #159 on:** October 30, 2015, 08:42:19 pm »

What is the voltage on the Red & Blue trace bias lead in A/C volts going to the silicon diodes anode? Where the silver band on the diode is.

Should be 45 volts a/c

silat · « **Reply #160 on:** October 30, 2015, 08:44:18 pm »

Quote from: plexi50 on October 30, 2015, 08:42:19 pm

What is the voltage on the Reb&Blue trace bias lead in A/C volts going to the silicon diode?

+46 AC

plexi50 · « **Reply #161 on:** October 30, 2015, 08:46:41 pm »

Ok you say you have a 33k bia r in there now. Check the plate voltage again on the power tubes and tell me if the voltage went up or down.

silat · « **Reply #162 on:** October 30, 2015, 09:01:16 pm »

Like I said I put in the 33K and just now checked and it is at -32 it has not moved. It was - 38 with the 56K

Willabe · « **Reply #163 on:** October 30, 2015, 09:03:51 pm »

Quote from: plexi50 on October 30, 2015, 08:46:41 pm

Check the plate voltage again on the power tubes and tell me if the voltage went up or down.

No, the PLATE dcv on the power tubes.

plexi50 · « **Reply #164 on:** October 30, 2015, 09:05:13 pm »

Voltage on Pin 3 of the power tubes again?

silat · « **Reply #165 on:** October 30, 2015, 09:09:12 pm »

473,474

plexi50 · « **Reply #166 on:** October 30, 2015, 09:19:33 pm »

Something is very wrong here. Tack a 82k or 100K in the bias resistor spot. Turn on the power but leave the standby off. Do not power the amp full on. What is the pin 5 voltage reading?

Willabe · « **Reply #167 on:** October 30, 2015, 09:28:37 pm »

He changed the -bias but the plate voltage only changed ~1dcv.

Think maybe the power tube K's aren't hooked up to ground?

plexi50 · « **Reply #168 on:** October 30, 2015, 09:30:59 pm »

Quote from: Willabe on October 30, 2015, 09:28:37 pm

He changed the -bias but the plate voltage only changed ~1dcv.

Think maybe the power tube K's aren't hooked up to ground?

I know. This is weird. My next question is are the positive leads of the bias caps going to ground side.

Think maybe the power tube K's aren't hooked up to ground?

I guess were going to find out.

silat · « **Reply #169 on:** October 30, 2015, 09:32:02 pm »

-44 with 100k in the bias and standby off.

plexi50 · « **Reply #170 on:** October 30, 2015, 09:34:51 pm »

Ok -44 is going in the direction we want. We want -48. Are your bias capacitors positive leads going to ground?

silat · « **Reply #171 on:** October 30, 2015, 09:36:17 pm »

Quote from: plexi50 on October 30, 2015, 09:30:59 pm

Quote from: Willabe on October 30, 2015, 09:28:37 pm
He changed the -bias but the plate voltage only changed ~1dcv.

Think maybe the power tube K's aren't hooked up to ground?

I know. This is weird. My next question is are the positive leads of the bias caps going to ground side.

Think maybe the power tube K's aren't hooked up to ground?

No they are going the right way with the ground pointed toward the diode and the 15Kr like it shows on the layout.

I guess were going to find out.

plexi50 · « **Reply #172 on:** October 30, 2015, 09:38:50 pm »

No the question is are your bias capacitors positive leads going straight to ground.

Additionally are your power tube pins #8 grounded to the chassis?

silat · « **Reply #173 on:** October 30, 2015, 09:42:01 pm »

No Number 8 pins they are also tied in to number 1 on the power tubes are not grounded to chassis. I have no idea what you are talking about with the ground on the bias caps the 2 -8 UF caps if that is what you are talking about?

Willabe · « **Reply #174 on:** October 30, 2015, 09:45:26 pm »

Quote from: silat on October 30, 2015, 09:42:01 pm

No Number 8 pins they are also tied in to number 1 on the power tubes are not grounded to chassis.

Aha!

plexi50 · « **Reply #175 on:** October 30, 2015, 09:46:24 pm »

Major revelation!!!!!!!!!

You must run a wire from pins #1 & #8 straight to the chassis. They must be grounded. This is the cathode of the power tubes and what turns the power tubes ON. That why we don't have a bias of -48 volt give or take. Put the 56k bias resistor back in place and turn the amp on after you have grounded pin 1 & 8 of each power tube

silat · « **Reply #176 on:** October 30, 2015, 09:48:35 pm »

Quote from: Willabe on October 30, 2015, 09:45:26 pm

Quote from: silat on October 30, 2015, 09:42:01 pm
No Number 8 pins they are also tied in to number 1 on the power tubes are not grounded to chassis.

Aha!

Well it is nice you are having an aha moment but you will have to help me? I did have them(The 6l6's) grounded to chassis but they red plated my power tubes. I never thought anymore about it....

Willabe · « **Reply #177 on:** October 30, 2015, 09:49:56 pm »

He probably doesn't have a big enough iron to solder that steel chassis, he needs to us a solder lug that get's bolted to the chassis with 1 of the power tube socket bolts.

Willabe · « **Reply #178 on:** October 30, 2015, 09:51:13 pm »

Quote from: silat on October 30, 2015, 09:48:35 pm

I did have them(The 6l6's) grounded to chassis but they red plated my power tubes. I never thought anymore about it....

What do you mean exactly?

We are trying to help you, nobodies making fun of you.

plexi50 · « **Reply #179 on:** October 30, 2015, 09:53:52 pm »

The power tubes red plated at that time because the bias resistor value had to be wrong. And you also at that time had the PT wired using the 720 Volts CT leads.
Turn your volume down Silat cause you about to hear a loud amp. Check the bias first and look for -48.9 --50 volts using a 56K bias resistor.

Willabe · « **Reply #180 on:** October 30, 2015, 09:59:37 pm »

If you disconnected the power tubes cathodes (K's) from ground to get the power tubes to stop red plating that will do it. But then they will not be able to draw any current.

Like Plexi just said they were red plating because the -bias was wrong.

More -dcv = less current.

plexi50 · « **Reply #181 on:** October 30, 2015, 10:02:23 pm »

Quote from: Willabe on October 30, 2015, 09:59:37 pm

If you disconnected the power tubes cathodes (K's) from ground to get the power tubes to stop red plating that will do it. But then they will not be able to draw any current.

Like Plexi just said they were red plating because the -bias was wrong.

More -dcv = less current.

I want to hear this working tonight. OR HEAR THAT I HEAR IT IS WORKING WITH THE RIGHT VOLTAGES TONIGHT.

Willabe · « **Reply #182 on:** October 30, 2015, 10:04:31 pm »

He might have killed the PI tube, he had 500+dcv on it early on.

silat · « **Reply #183 on:** October 30, 2015, 10:07:58 pm »

Eureka! I have sound and it is good and loud but my bias voltage is still at -38...

plexi50 · « **Reply #184 on:** October 30, 2015, 10:08:25 pm »

Quote from: Willabe on October 30, 2015, 10:04:31 pm

He might have killed the PI tube, he had 500+dcv on it early on.

Maybe. I think 380 is insane for a 12ax7. Ive seen that on more than one occasion.

plexi50 · « **Reply #185 on:** October 30, 2015, 10:09:52 pm »

Quote from: silat on October 30, 2015, 10:07:58 pm

Eureka! I have sound and it is good and loud but my bias voltage is still at -38...

Ok check the plate voltage now and tell us what it is. Don't leave the amp on for long becasue we still need to get the bias set right.

Your power tubes will red plate again until you get the right bias resistor in there and obtain -48 + volts

plexi50 · « **Reply #186 on:** October 30, 2015, 10:29:53 pm »

Quote from: silat on October 30, 2015, 09:42:01 pm

No Number 8 pins they are also tied in to number 1 on the power tubes are not grounded to chassis. I have no idea what you are talking about with the ground on the bias caps the 2 -8 UF caps if that is what you are talking about?

Are the positive leads of each bias cap going to the chassis ground? The positive leads. Not the negative leads

silat · « **Reply #187 on:** October 30, 2015, 10:32:06 pm »

Quote from: plexi50 on October 30, 2015, 10:09:52 pm

Quote from: silat on October 30, 2015, 10:07:58 pm
Eureka! I have sound and it is good and loud but my bias voltage is still at -38...

Ok check the plate voltage now and tell us what it is. Don't leave the amp on for long becasue we still need to get the bias set right.

Your power tubes will red plate again until you get the right bias resistor in there and obtain -48 + volts

plate voltage is still 438 on both pins 3 on the 6l6's

Willabe · « **Reply #188 on:** October 30, 2015, 10:33:05 pm »

Quote from: silat on October 30, 2015, 10:32:06 pm

plate voltage is still 438 on both pins 3 on the 6l6's

That's much better.

plexi50 · « **Reply #189 on:** October 30, 2015, 10:34:21 pm »

438VDC is excellent and will be 425VDC or less after the bias is perfect @ -48 volts. Please re-read and answer the bias capacitors question.

silat · « **Reply #190 on:** October 30, 2015, 10:39:26 pm »

yes it is.

plexi50 · « **Reply #191 on:** October 30, 2015, 10:40:14 pm »

OK YOU HAVE THE 56K BIAS R IN THERE NOW CORRECT? PUT IN 33k AND THE BIAS SHOULD BE JUST OVER -52 VOLTS.

And plate voltage on power tubes should drop to under 420VDC. Confirm this. If not do tell.

silat · « **Reply #192 on:** October 30, 2015, 10:42:44 pm »

Quote from: plexi50 on October 30, 2015, 10:34:21 pm

438VDC is excellent and will be 425VDC or less after the bias is perfect @ -48 volts. Please re-read and answer the bias capacitors question.

I do not understand you are going to have to draw picture because I thought but I do not. Sorry plexi50 and Thanks to you and Willabe for sticking with me on this and helping me even in my ignorance but I have learned but have a long way to go.

silat · « **Reply #193 on:** October 30, 2015, 10:45:08 pm »

Quote from: silat on October 30, 2015, 10:42:44 pm

Quote from: plexi50 on October 30, 2015, 10:34:21 pm
438VDC is excellent and will be 425VDC or less after the bias is perfect @ -48 volts. Please re-read and answer the bias capacitors question.

I do not understand you are going to have to draw picture because I thought but I do not. Sorry plexi50 and Thanks to you and Willabe for sticking with me on this and helping me even in my ignorance but I have learned but have a long way to go.

I did put the 56K back in the bias.

Willabe · « **Reply #194 on:** October 30, 2015, 10:45:14 pm »

Plexi did it.

plexi50 · « **Reply #195 on:** October 30, 2015, 10:45:59 pm »

Bias cap positions.

plexi50 · « **Reply #196 on:** October 30, 2015, 10:46:46 pm »

Quote from: Willabe on October 30, 2015, 10:45:14 pm

Plexi did it.

Willabe did it!

silat · « **Reply #197 on:** October 30, 2015, 10:50:01 pm »

yeah that is just how mine are and I was for sure that was what were talking about on the bias caps but somehow miscommunicated.

uki · « **Reply #198 on:** October 30, 2015, 10:51:45 pm »

So is it working !?!?

plexi50 · « **Reply #199 on:** October 30, 2015, 10:54:54 pm »

Quote from: silat on October 30, 2015, 10:50:01 pm

yeah that is just how mine are and I was for sure that was what were talking about on the bias caps but somehow miscommunicated.

NOTE: Do not think you are finished yet and start playing the amp until we get the bias right. Otherwise your power tubes will red plate again and possibly destroy them. I'm glad you have it working. Now i am going to take a beer bath. Too late for that now. Not recommended.

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Author Topic: 5F6-a Bassman not working.. (Read 42519 times)