5F2A First time builder Help Needed. Filaments and Low B+

[Bangy]

I have Completed my 5F2A build. The amp lights up with the following data.
I have Primary OT leads swapped from Dougs diagram which is color coded (I missed the color code and have cut the Red wire to the 6V6). I have red to the 6V6 and blue to the 5Y3. Q1-- Problem?

Line AC 120V, PT is the Mojo 759 reccomended by Doug.
B+ = 330V
Next Filter cap = 290V
Next FC = 240V

Question 2, I noticed the secondary high voltage of the power transformer is only 75mA @ 290V is this to account for modern wall voltage? I suppose it saves me from using my Brownbox which allows me to run a wall voltage of 110V. Yet even at 120 wall VAC I see only 330V B+.

Filament AC = 3.15V, Pilot light Lights up, 6V6 filament glow, 12AX7 if I wait long enough will warm to touch and I was able to get a very weak signal out of the amp. I am a novice, So I am a bit precise with my description (please bear with me). I grounded my Multi meter to the chassis, and read both lugs of the pilot light and saw the same 1/2 expected voltage AC.

My filament hook-up, Center TAp grounded to PT lug, both Filament wires twisted and soldered to both lugs of the Pilot light, then twisted 18Gauge solid core to the 6V6 Pins 2 and 7, then to 12ax7 pins 4/5 and 9.

So wondering if the OT being wired incorrectly can be affecting my B+, and what in the world did I do wrong in the filament circuit?

I did go through past posts as Im sure this has been answered before but I couldn't find anything just yet.

Bangy

Issue 1 low B+
Issue 2 Low filament voltage????

[shooter]

Issue 1 low B+
Issue 2 Low filament voltage????

pull the 6V6 and re-measure, you can check filaments also by putting the meter probes in the now empty 6V6 socket

[Bangy]

Pulled the 6V6 with the following results

Filaments up to 3.3V measured at both tubes and the Lamp.

Pre-Filter caps B+ 379, 359, 292
With a dif 6V6
323,292,255

Curious why the changewith tube pulled?

Thanks Shooter

[shooter]

Curious why the changewith tube pulled?

the 6V6 is basically the whole load for B+
I would expect maybe a 30volt drop with a 5Y3, 50 seems high.

your fil seems fine 3.15 to ground each side, should be 6.3 pin 2 to 7

OT being wired incorrectly can be affecting my B+,

I would re-wire correctly, but not because of B+, because the amp uses NFB and that "might" be a problem

put the 6V6 back in and monitor B+ for a couple minutes, is it dropping?  if so unplug.  do you have any sound? 

[Bangy]

Shooter--Thanks.  I figured one ting I was doing wrong.  When taking AC V readings off of the filaments wired as Dougs suggests, you must place your leads on each side of the circuit, not grounding one to the chassis, as the circuit is grounded to the center tap.

So now I have correct filament reading and always had correct filament voltage.

The output is almost nil and wickedly distorted. My tech has asked for the following voltages which I'll list if you have any ideas.

12ax7
1-Plate- 165
2-Grid 2 - 1.2
6 - Plate- 1 -156
7 - Grid 1 - 140

6V6
3 - 31
4 - 290
8 -14.6

So, Filaments are normal - B plus is close, but I have a snake in the grass somewhere. . .

Many thanks for the help Shooter. . . Bangy

[sluckey]

The output is almost nil and wickedly distorted. My tech has asked for the following voltages which I'll list if you have any ideas.

12ax7
1-Plate- 165
2-Grid 2 - 1.2   (should be zero)
6 - Plate- 1 -156
7 - Grid 1 - 140   (should be zero)
(need pin 3 and 8 also)

6V6
3 - 31   (should be about same as pin 4)
4 - 290
8 -14.6

Would you recheck all these voltages? Post again?

[Bangy]

BRB. Thanks Sluckey

[Bangy]

The output is almost nil and wickedly distorted. My tech has asked for the following voltages which I'll list if you have any ideas.

12ax7
1-Plate- 165
2-Grid 2 - 1.2   (should be zero)
6 - Plate- 1 -156
7 - Grid 1 - 140   (should be zero)
(need pin 3 and 8 also)

6V6
3 - 31   (should be about same as pin 4)
4 - 290
8 -14.6

Would you recheck all these voltages? Post again?

12AX7
1 -168
2 - 0
3 -1.2
6- - 158
7 - 0
8 - 1.2

6V6
3 - 315
4 - 292
5 - .018V
6 - 0
8 - 14.7

B+ 323, VAC 119

So Pilot error one more time with my Multi Meter. I have NOT changed the leads on OT primary to Blue to the 6V6 and red to the rectifier--

Thanks for the watchful eye Sluckey

Bangy

[sluckey]

I have NOT changed the leads on OT primary to Blue to the 6V6 and red to the rectifier--

Hold off for now. You may not need to swap them unless you get a loud howl or squeal from the amp once it starts working.

Click on the link in my signature line at the bottom of this message for a good method of verifying your wiring is correct.

[Bangy]

I have gone through the wiring a ton of times. Here is the the build. Is it safe to to say the power supply seems good?  I'll go through it again right now.

[sluckey]

Voltages look OK. Keep looking for a wiring error.

[Bangy]

Well, i found that I hadn't soldered the 500P cap on one end and no change on the 4 ohm output but the 8 ohm output is rocking.  Its still not so super powerful but neither is my vintage one.  Id like to try to give it more balls and volume.  Im wondering about that 15 watt single end OT classic tone makes.  Anybody have any experience with those in a 5F1a/5F2a?

Sluckey, i'll take a look at the RCA in the am, its bedtime now.

Thanks again for sticking with it.  In the end everything (sans maybe the RCA jack) was correct with a bunch of pilot error.  Jack Darr says to trouble shoot from the output backwards. . . I guess he has something. . .

[sluckey]

no change on the 4 ohm output but the 8 ohm output is rocking.

One of those speaker jacks is not wired properly.

Does your 8Ω jack have 3 solder terminals? Is there a jumper wire between 2 of the terminals? If so, cut/remove that jumper. Now try the 4Ω jack.

[shooter]

once you got the kinks out;

Its still not so super powerful but neither is my vintage one.

My 5F2 got plugged into a 4x12 stuffed with high-end jbls and all I could do was grin!  sounded like a 30watter!

[Bangy]

no change on the 4 ohm output but the 8 ohm output is rocking.

One of those speaker jacks is not wired properly.

Does your 8Ω jack have 3 solder terminals? Is there a jumper wire between 2 of the terminals? If so, cut/remove that jumper. Now try the 4Ω jack.

Yessir, I will remove that and report back.

Hey Shooter-- Did you do anything special on your 5f2a build? So through the 4x10's it sounded louder? Fuller Im sure. Id imagine the bass was tighter as well.  Was it closed back? I ask because I am building my own cabs for these.

  Its bizarre my real tweed champ kills my real tweed princeton as well.  Can the tone suck that much from a little amp? Or have I not found the snake in the grass in both my original and this build? They sound almost identical. Anywho my plan for these 5F2A's is 2 vox super low powered tens. They are 10 Watts 4 Ohms thus the need for the 8 ohm jack.  I will be building the cabinets Thursday and Friday. I have a few sheets left of 60 year old 3/4" pine, I'll use for the combo's. Great finish.

[shooter]

Did you do anything special on your 5f2a build

IIRC I only did minor TS tweaks, I'm not a player so, my Son n friends were playing through just a spare randall? 1X12.  They decided to take it to their friends guitar shop, asked which 4X cab was best in his store, he pointed to a marshall that had been re-speakered, they plugged in played, loud!, all the musicians started talking n the owner took the amp on trade for some serious guitar work my kid wanted done to his strat.  I got nothing as usual, except satisfaction

[Bangy]

Update:

Sluckey nailed it as I removed the the switch to gnd jumper on the 8ohm speaker jack and the 4ohm jack came to life in a big way.  I also went to humbuckers from p-90's which this circuit seems to prefer. The 4 ohm is actually a cleaner more polished output. The 8Ohm is a rawer quicker to distort output through a P10R vs the stock speaker in a 59 tweed champ.

Im tempted to try the NFB feed via the 8ohm Speaker replacing  the 4 ohm speaker load. I most likely will try that before I button this's one up and move on to chassiss number two. I also intend to use the blue sozo .022's in the second one leaving all else the same (i used the yellow Sozo's).  I have experience with the blue sozo's and prefer them to the yellows.  Not sure why I used the yellows.

But anyway, I want to thank all you guys who helped me make an amp for the first time.  Your generosity and insight was quite a comfort launching into a wickedly cool endeavor. Also Doug for being so patient with me when I wasn't smart enough to navigate through his VERY COMPREHENSIVE sight.

I will shoot you guys some pics when I finish my stereo rig of 5F2a's.

Peace ya'll

Bangy

[Bangy]

Did you do anything special on your 5f2a build

IIRC I only did minor TS tweaks

Sorry Shooter, I understand the acronyms????????

[Willabe]

IIRC = If I Recall Correctly

TS = Tone Stack.

[sluckey]

TS = Tone Stack.

That's correct in this instance. There are a lot of other instances where TS = Tough Shit.   

[shooter]

 

TS = Tough Shit

Im tempted to try the NFB feed via the 8ohm Speaker

put the NFB wire were the schematic shows, not which speaker you're using

[Willabe]

That's correct in this instance. There are a lot of other instances where TS = Tough Shit.   

          

[Bangy]

FYI

I tried them all today as a learning experience, using the 4 ohm, the 8 ohm and no NFB, and even with a impedance mismatch between output and speaker, the 4 ohm NFB hookup sounded best, hands down.

[shooter]

I tried them all today as a learning experience

you're exhibiting the 1st signs of builders addiction, admit it now!, then just enjoy it

[Bangy]

So true.  But at my level its a great brain workout which is a welcome change. . . .