5F6-a Bassman not working..

[Stevewdewitt]

I have myself done some silly things in the past. And looking back you wont forget them once found. I used to expect the Fn worst. But 9 times out of 10 it usually turns out to be something so simple that it makes you feel dumb.

Keep going. No rest for the weary.

I just want tosay ditto. I just finished my 5f6a build and made a super simple mistake and replaced nearly every component and it turned out to be the simplest thing. You will get it.

[silat]

I still have not found the problem.... I spent some time on it. I reheated up some suspect looking  joints but have nothing... I moved my cap-board on the outside of the of the chassis instead of the inside so I could see better. I am at a loss....

[silat]

I think I may replace the tube sockets and see if that may do it.

[plexi50]

Silat i really believe that you have it wired wrong under the board at the 10K - 8uf filter cap junction that is feeding V2 which is also why V1 plate voltages are way higher than they should be. I wage a virtual 12AX7 tube on it.

[silat]

Ok I will look again. I have looked several times, but that does not mean I did not miss it somehow. Thanks for all your help.

[Willabe]

I am going to start tracing soon.(Using Doug's little handy dandy method)

Did you do this?

[silat]

Silat i really believe that you have it wired wrong under the board at the 10K - 8uf filter cap junction that is feeding V2 which is also why V1 plate voltages are way higher than they should be. I wage a virtual 12AX7 tube on it.

I took it off and it is not wired wrong. I looked it over really close. I took a yellow marker to my layout and put my fingers on the component as I was tracing it. I have no sound at all but maybe some white noise now.

[Willabe]

I took a yellow marker to my layout and put my fingers on the component as I was tracing it.

Not just the components, wires too. 1 at a time.

[silat]

I took a yellow marker to my layout and put my fingers on the component as I was tracing it.

Not just the components, wires too. 1 at a time.

When I say components I  mean wires also.

[plexi50]

Do you have the input jacks wired correctly?

Plug instrument cable  into hi input and clip your DVM leads to the tip and sleeve of the cable.

You should read 1Meg just + or -. Then plug into the low input. You should read roughly 134K.

What are your readings. We must know to help rule out other issues.

[silat]

Do you have the input jacks wired correctly?

Plug instrument cable  into hi input and clip your DVM leads to the tip and sleeve of the cable.

You should read 1Meg just + or -. Then plug into the low input. You should read roughly 134K.

What are your readings. We must know to help rule out other issues.

7.17,  7.56

[plexi50]

Your inputs are wired wrong. Have a pic of them?

[silat]

I really do not think so but at this point I will try anything.

[Willabe]

If the red circle on the jack is the sleeve ground lug and that wire is going to 1 of the 68K grid stopper R's than it's wired wrong.

[Willabe]

Drawing from Doug's Tube Amp Library of information, link for it can always be found at the bottom of any page on the forum.

They should be wired like this, G=ground, S=switch contact, T= jack tip/hot input.

[silat]

That got me some sound! Although very faint and very distorted where I am putting a speaker up to my ear to hear it.

[Willabe]

Do you have the input jacks wired correctly?

Plug instrument cable  into hi input and clip your DVM leads to the tip and sleeve of the cable.

You should read 1Meg just + or -. Then plug into the low input. You should read roughly 134K.

What are your readings. We must know to help rule out other issues.

Now try this test from Plexi50 again to confirm it. 

[silat]

Do you have the input jacks wired correctly?

Plug instrument cable  into hi input and clip your DVM leads to the tip and sleeve of the cable.

You should read 1Meg just + or -. Then plug into the low input. You should read roughly 134K.

What are your readings. We must know to help rule out other issues.

Now try this test from Plexi50 again to confirm it. 

1078, 1076

[Willabe]

That's still wrong. It's either wired wrong or your meters lying or messed up or it's not set right?

Sometimes guys get false readings if the meters batteries are low. Try a new set of batteries and then check some spare R's you have laying around and see if it's reading correctly.

If good then try the input jacks again. 

(I just measured 1 of my amps that has Fender type hi/low input's and it read just like Plexi said.)   

[Willabe]

Plexi right that it's the input jack wiring as you can see. Get that fixed and you may have a working amp.     

It's very good that you did hear a little sound through the speaker. That may be because the rest of the amps working.

[plexi50]

Get your jacks lined up and it will make more sense. Solder the (2) center tab terminals together (upper jack & lower jack) and then add the 68k wires to each one as shown.

[silat]

Plexi, I am sorry but I m not understanding what you are saying here? Could you be a little more specific?

[plexi50]

Read again. Look at pic.

[silat]

Read again. Look at pic.

Sorry, you had a different  picture of the tube sockets and it was confusing...

[plexi50]

YEAH I PICKED THE WRONG PIC FOLDER FOR A SECOND.

[Willabe]

Get your jacks lined up and it will make more sense. Solder the (2) center tab terminals together (upper jack & lower jack) and then add the 68k wires to each one as shown.

The 2 center tabs/solder lugs?

Here this might be better to see, it's rotated like it should be in the amp.

[plexi50]

Get your jacks lined up and it will make more sense. Solder the (2) center tab terminals together (upper jack & lower jack) and then add the 68k wires to each one as shown.

The 2 center tabs/solder lugs?

Here this might be better to see, it's rotated like it should be in the amp.

Yeah i messed up saying to solder the (2) center tab lugs. But as i have it anyway as the jacks are positioned.

[Willabe]

But as i have it anyway as the jacks are positioned.

Yep.   

Your the guy who sniffed out the input jacks. 

[plexi50]

His input grids have been shunted to ground all along. But theres another issue with 350+vdc on V2 8 that bothers me.
 

[Willabe]

His input grids have been shunted to ground all along.

I think your right.

But theres another issue with 350+vdc on V2 8 that bothers me.

Agree, I think Sluckey brought that up too?

[plexi50]

His input grids have been shunted to ground all along.

I think your right.

But theres another issue with 350+vdc on V2 8 that bothers me.

Agree, I think Sluckey brought that up too?

Yes Steve did. Think about this: If the 10K & 8uf filter cap were wired correctly and the B+ was passing through that 10k on to pin #6 then there is no way there could be 350+ on V2 pin #8 or V1 @ 190+

But i am assuming he is using a 325-0-325 PT

[Willabe]

I'm looking at the schemo and I agree with you. 

I know you have built this amp and know it well.   

[plexi50]

Silat: Following V2 pin #8 wire to the board,slope resistor,treble peak cap & 100k resistor.

Is the 100k from that junction across and through that resistor to the other side of the 100k lead grounded?

[silat]

Silat: Following V2 pin #8 wire to the board,slope resistor,treble peak cap & 100k resistor.

Is the 100k from that junction across and through that resistor to the other side of the 100k lead grounded?

Yes the 100K is grounded.

[Willabe]

I myself have somewhat of a hard time wiring up 2X hi/low input jacks.

I need to have a very clear drawing in front of me to get it right. (Switches are also another thing that can be difficult for me.)

It's been said MANY times before here and else where, 'divide and conquer'. 

So......

Get the input jacks wired up correctly 1st. No input, no output. You can confirm (and need to) that their their wired up correctly by testing them with your meter as Plexi posted.

THEN if the amp still isn't working, go to the V2 dcv problem.       

[silat]

I think I might have found the problem as to why my voltages were so high  on V2. My Power transformer (W022798 INT) shows 720 V Center tapped  that is what I had. I switched to the red and white  wire and that gave me 330-0-330 or 660v it brought my V2 down to  Pin8 161, pin 7 156, pin6 356. Still the sound is very faint and distorted.

[plexi50]

First answer the question about your input jacks. What do they read  on the high and low jack inputs.
We need to know if you have fixed them before going onto any other issue.

[plexi50]

Yes you need to use the two red/white trace wires to the rectifier socket pin 4&6
That is why i asked you to pull the rectifier tube earlier in this thread and give us the voltages of each lead to the rectifier socket

Every step of the elimination process and questions asked have to be answered or we can only guess. Guessing can get you killed with high voltages like this. We want to hear success as bad as you do.

[silat]

First answer the question about your input jacks. What do they read  on the high and low jack inputs.
We need to know if you have fixed them before going onto any other issue.

When I measure a  1 meg resistor I get 1014 But I get 538 and 131 on my input jcks but I wired them just like the drawing showed that you all gave. Unless my meter is messed up. It must be right.

[plexi50]

This is what you have to have for input jack readings + or minus a little.
Low input top pic/
High input bottom pic/

If not they are not wired right. Again please be more specific. Is the 131K (not ohms) reading your low impedance jack? That would be fine.

[silat]

1069, 141  I have no other way to set from that. That is what I have and the only reading I can get from my meter.

[plexi50]

Ok that's beautiful and all good. That is on each channels inputs (both high and lo jacks)?

What is your B+ plate voltage measurement on pin#3 of each power tube.

I am assuming you are using 6L6GC tubes

[silat]

Ok that's beautiful and all good. That is on each channels inputs (both high and lo jacks)?

What is your B+ plate voltage measurement on pin#3 of each power tube.

I am assuming you are using 6L6GC tubes

475, 476, yes I am using 6L6's

[plexi50]

Ok the plate voltage on each tube is even. But you may still have a problem. What is you bias grid voltage on pin #5 of each power tube?

[silat]

Ok the plate voltage on each tube is even. But you may still have a problem. What is you bias grid voltage on pin #5 of each power tube?

It did not move it stayed at -38

[plexi50]

Ok what is your bias resistor value in the amp now?

[silat]

Ok what is your bias resistor value in the amp now?

 15k

[plexi50]

Change that resistor to 56K. MINE WAS ACTUALLY CHANGED TO 47k SO YOU MAY HAVE TO DO THE SAME . WE NEED TO SEE -48 VOLTS ON PIN #5. YOUR PLATE VOLTAGE WILL COME WAY DOWN AS WELL WHERE IT SHOULD BE. 475 IS TO HIGH. My typing sucks/

[plexi50]

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.

[silat]

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.

I figured that out... No worry's I stopped to eat a bite. I do not have any 47K's to try though.