5f6a low power ( Resolved )

[makingnoise88]

I finished Hoffman 5f6a and it sounds good but is quite a bit quieter than I feel a 50 watt amp should be! My 12watt Princeton reverb reissue is deffenetly louder!
I've adding a picture of the build. I added a PPIMV even before I added it I tested it and I had this same problem.

[sluckey]

your voltage readings...

     http://el34world.com/charts/valve/ValveData.php?e=view&f=19878

[makingnoise88]

Stuckey, Thanks yes those are them.

[sluckey]

I assume you sorted out the MV?

[makingnoise88]

I actually pulled it out of the amp until I got it all sorted out.
I just had taken the picture before hand.
I assume I should keep it in the "Ground loop" that all the other pots are connected to but not ground the the right lug.

[sluckey]

According to your voltage chart, you're output tubes are idling at 11.2 watts each. Decrease your bias voltage to about -40 and recheck idle power.

[makingnoise88]

Sluckey,

This is where I get a little lost.
How are you getting 11.2 watts?
And what is the best way to check it?
haha I know I sound so dumb please forgive me I'm learning as I go!

[ac427v]

All the voltages are a little high...but the V3 cathodes (Phase Inverter) are 105 volts instead of 34. What does that mean?
--Craig

[sluckey]

This should answer every question you may have about biasing your amp.

http://www.duncanamps.com/technical/lvbias.html

[HotBluePlates]

All the voltages are a little high...but the V3 cathodes (Phase Inverter) are 105 volts instead of 34. What does that mean?

It could mean that R20 is a 4.7kΩ resistor instead of a 470Ω resistor.  Also possible is that R23 is a 100kΩ resistor instead of 10kΩ.  Maybe both.

I'm not sure I trust the 35.2v (?) measurement on V2 pin 2 (maybe it's 35.2 milli-volts).

[makingnoise88]

Just took that measurement again and it is 1.3mv
As far as r20 and r23 they look to be correc.
My concern is that the gray and brown look so close haha but I'm pretty sure it's right.

[PRR]

Is that a 100pFd cap from bottom of 10K to bottom of 1Meg?

Usually 0.1uFd (100,000pFd).

If 100 PEE Fd, the amp is push-pull above 1.6KHz but badly unbalanced below maybe 1KHz (all your meat and potatoes sound).

[sluckey]

Is that a 100pFd cap from bottom of 10K to bottom of 1Meg?

Good catch PRR.

[makingnoise88]

You guys are correct! I placed 100pfd in place of the .1 and the .1 in place of the 100pfd on the bright channel volume.
After addressing that i'm not sure I notice a huge difference.
So now i'm looking into the pots that I used ( Would this make a difference? ) the volume calls for a 1MA (1 Meg Audio Taper?)
I used a Alpha A1M pot. Is this correct?

[pompeiisneaks]

That's definitely the right pot. 

[pompeiisneaks]

Besides the volume pot wouldn't make a difference at max volume, all that means is that the resistor is passing next to nothing to ground, and the rest passes through untouched.  The idea of the volume pot is that you create a higher resistance path to the grid of the next stage and send most if not all of the signal to ground.  Therefore if the pot was 'too high' then it would work fine at max volume but attenuate the sound more quickly and you'd have no output at some odd point in the middle, and if it were too low you'd never get 0 volume.   It doesn't attenuate the signal completely or really at all if it's at max volume.

~Phil

[ac427v]

I usually start troubleshooting by looking at the voltage readings. They help focus attention on the part of the circuit that "needs improvement". Your voltages will be different after you fix the cap problem and re-bias per Sluckey. How do those readings look now?
--Craig

[makingnoise88]

Okay Got the amp Biased and the and the .1 and 100 caps straight now here are my updated Voltage readings.
My kids are asleep so I can't test the amp out now so I'll do that in the morning!

http://el34world.com/charts/valve/ValveData.php?e=view&f=19878

[frus]

Your power tube cathodes (pin 8) are at 41.3 VOLTS or 41.3 MILLIvolts?
Have you grounded them reliably?
If they are really 41 volts and the grids are at -40V, then they are deep in cutoff and it would be hard to get a peep out of them

[makingnoise88]

There are measures in MV

[sluckey]

FYI, switch your meter to "AC volts" when measuring pins 4 and 6 on the 5AR4.

Tubes are now idling at 19 watts. That's 100% of max plate dissipation. You may want to cool that down a bit. Most people are happy with running about 70%.

[makingnoise88]

So I should idle around 14watts?

[sluckey]

Some 6L6s like 6L6GC are rated for 30W max plate dissipation. For those 70% would be 21W. Which tubes do you have.

[makingnoise88]

I have the EH 6l6 the plate  dissipation is 30w according to the data sheet

[sluckey]

You're fine running them at 19W. Hopefully this fixes your 'low power' condition.

[makingnoise88]

I got to sit down with the amp for a while today, I'm still convinced that it's quieter than it should be. Up against my ac30 it's a good bit quieter! It's pretty low until 3/4 of the way up and wide open it sounds good but not at loud still as I feel it should.
What are some other areas to look at when thinking about not putting out enough volume?

[pompeiisneaks]

The AC30 is LOUD a lot louder than equivalent 30W amps, believe me, I have an AC30 and a Fender Blues Deluxe that's also two 5881's that should be about 40 watts as well and it sounds about half the volume honestly. 

[ac427v]

You have fixed two things but still not loud---we want loud! I'm still stuck on the idea that it is related to the PI circuit because of the 102 volt reading on pins 3 and 8. I have similar readings on my blackface ab763 when using a 12AT7. Any chance of the wrong or "tests good but..." tube in V3? Or can there still be some effect from the removed PPI Master Volume experiment? It sounds so close to being righteous.
--Craig

[sluckey]

wide open it sounds good but not at loud still as I feel it should

Wide open should hurt your ears unless you're in a basketball gym or outdoors.

Could be many different things. You've already discovered one error on the board. Look for others. Since V3 pins 3,8 have such a high voltage, turn the amp off and measure resistance between pin 3,8 and chassis. What have you? Should be about 14.5K.

Also, in the last pic you posted there is a 27K resistor with a green wire connected to one end and a white wire connected to the other end. Does that white wire connect to the presence pot? And what is the value of your presence pot?

[makingnoise88]

Sluckey,
With the amp completely off?
Common to ground and lead to v3 3&8 nothing when the amps off.
As far as the white it does go to the first lug of my presence knob. Whit has doesn't seem to really do much if anything. And the green wire is connected to the output jack.
The presence knob is a 5KL.

[sluckey]

With the amp completely off?
Common to ground and lead to v3 3&8 nothing when the amps off.

***NEVER CHECK RESISTANCE WITH POWER ON!***
You did switch your meter to read ohms, right?

There is a 470Ω resistor, a 10K resistor, and the 5K presence pot all in series between V3-3,8 and chassis. That adds up to 15,470Ω. Any of those three components could be bad or you have a bad connection somewhere in that chain. Should take about a minute to figure it out.

[makingnoise88]

Sluckey,
I was on the DC Setting.
I'm getting 037! So I see the 470 ohm resister but I'm a little confused on where and how it's connected to a 10k resister and then on the the presence pot.
With more resistance than should be there, that means one of the components is larger than it should be?

[sluckey]

I was on the DC Setting.
I'm getting 037!

You measure resistance with the meter set to ohms. I have no idea what 037 means. That could be 37 miles per hour. Need the unit of measure also.

Use this pic to trace the circuit from the tube socket all the way to chassis ground. Follow the yellow highlighted path.

[makingnoise88]

Yup I guess that would help! Haha
I had the meter set to 2000k ohms
It reads 037 at v3 pin 3&8 at the 470ohm and 10k resister. At the top of the 10k where it ties into the 27k it switches to 027 and reads 027 even on the pot for the presence

[HotBluePlates]

It reads 037 at v3 pin 3&8 at the 470ohm and 10k resister. At the top of the 10k where it ties into the 27k it switches to 027 and reads 027 even on the pot for the presence.

You measure resistance with the meter set to ohms. I have no idea what 037 means. That could be 37 miles per hour. Need the unit of measure also.

"037" what?  Ohms? Kilo-ohms? Megaohms? "37 feet"?

You need to include units of measure with every measurement; make sure you follow how your meter indicates these (which may be a number and a range setting).

[makingnoise88]

Yup I guess that would help! Haha
I had the meter set to 2000k ohms
It reads 037 at v3 pin 3&8 at the 470ohm and 10k resister. At the top of the 10k where it ties into the 27k it switches to 027 and reads 027 even on the pot for the presence

Hotblueplate ☝🏻️

[sluckey]

Take a picture of your meter showing that 037. I want to be able to see every little thing that's lit up in the display window.

[HotBluePlates]

 

Sorry, I give up.

[sluckey]

Forget the pic. I've got it figured out.

The readings you have are 37KΩ and 27KΩ. This means the 5K presence pot is either bad or one leg is not connected to chassis as it should be. The 27K reading is through the 27K feedback resistor and OT secondary winding.

A simple test to prove this... Connect one end of a gator clip test lead to chassis and the other end to the white wire on the pot. Turn the amp on. It should be very loud. The fix is to ensure that one leg of the pot is connected to the ground buss (or chassis). If that's not it, replace the pot.

[makingnoise88]

OMG! SLUCKEY YOU ARE LEGEND!
That was it! I completely missed grounding the lug!
I feel so dumb haha ok well I will never make that mistake again!
Thank you so so much!