Newly Built 5F2a, Low and Bad Sound...

[PFCnR]

Hello Folks,

I have just finished my first built amp 2 days ago and it was meant to be Fender 5F2a clone ( used Weber layout ). For the first time i ran the amp there was no noise but hum and buzzy sound. Then i realized i have some mistakes about wiring (although i was too careful) after i fixed the wrong wiring i got the sound but its all bad and low ( people told me that 5w way too loud for apartment use ). I have made some changes on the diagram like some switches (NFB and Stand-By). By the way when i turn on Stand-by it even gives more buzz from speaker tone pot affects the sound in a bad way. I have artificial CT on power tube's legs between 7-8, 8-2 (1w 100k each)

Here is the layout:
https://taweber.powweb.com/store/5f2a_layout.jpg

And the grounding like this:

HV CT goes to nearest ground point which is next to PT.
First Block is:First three filter caps get together and they also go to same point.
Second Block is: Everything between the last 8uf and 0.022uf gets together and go to the same point as above.
Speaker Jack also goes to same point.

Tone,Volume, Input Jacks and Preamp Tube's third leg goes to different grounding point. (But they all get together at the same grounding point).

Funny Experiment when i plug my guitar in and get away from the amp, it gets even nastier. Hum,buzz,hiss you name it.

Here some values from the amp:

B+ was 17,5v without any tubes installed but i get 0v now i do not know why? Which one is good?

B+ is 478v with only 5Y3

B+ is 395v with 5Y3+ 6v6

B+ is 395 with all tubes installed.

And how can i learn the tubes pins voltages? so i can put them here to inform you all.

What to do? any idea?

Thanks.

[electrochronic]

If your using a Weber PT , use the 600Vac B+ secondary tap, not the 660Vac one. There is no benefit in having a B+ too high. That goes for Heaters too.

Despite other opinions, B+ at 470-480 is too high. to adjust B+ to lower value you must use a trasnformer that has lower B+ , but not lower current.

[PFCnR]

If your using a Weber PT , use the 600Vac secondary tap, not the 660Vac one.

Nope i am using mojo PT i bought that from tubedepot.com

Are the values really high?

[electrochronic]

Take your DMM and measure each leg of your 5y3 pin 4 and 6 - DO NOT MEASURE THEM WITH TEST LEADS ACROSS BOTH , YOU WILL KILL YOUR METER. BLACK LEAD GROUNDED TO CHASSIS AND RED LEAD TO EACH PIN
ONE AT A TIME. SET METER TO AC VOLTS. each leg should give you between 300 to 350 or more. Then multiply that by 2 ( example 350 vac x2 ~700vac B+ unrectifed). This will tell you if your transformer is putting out too much B+, when comparing to your transformer specs. If its it higher than your trasnformer spec then your rectified voltage will usually be elevated past what I consider normal.
take measurements in a loaded circuit for accuracy.

Keep in mind , that if everyone gets the same voltage with the same transformer , it does'nt mean its normal. Try to hit your target voltages.The target voltages are on the schematic. If you can't hit your target voltages from the schematic then your PT B+ is putting out too high. This is common issue. Higher voltages on tubes are not good for tube life especially if you plan to use NOS tubes. This is why it is important to hit your target voltages from the schematic.I would not trust any other explanation for higher B+ and rectified DC across the power supply and tubes.

Read thru my post here in same forum , I 'm going thru and extensive bench testing build on a very simple amp with initially very high B+ and DC voltages. Russian 5Y3 tubes will raise your DC about 20v over a NOS tube. The effect is it raises voltages throughout the circuit needlessly and at the cost of tube life. Higher
voltages do not give better sound there is a threshhold.

Hum and buzz are grounding and layout issues that take experimentation to get right. Use of Center taps for heaters - highly recommended. As well as placement of the OT to proximity of your PT. The OT needs to be kept at a opposing right angle and min distance to keep 60hz hum very low. buzzing is most often from heaters and heater wire routing. Paired Heater wires must be twisted tightly before their solder points. maybe you already know this , not sure.

[PFCnR]

HV rating of the PT is 700v in total, by the way B+ is 478 if i only install 5Y3 tube rectifier (it is NOS) when i install all tubes the B+ is 395v. Even 395v high for B+?

My tubes are:
5Y3 GE NOS
6v6GT Tung-Sol
5751 Philips Jan

I will check values of the tubes' legs and will post it here soon

[MWJB]

395vdc B+ is fine, not a problem in the slightest. 478vdc with just the rectifier fitted is to be expected as there is no current load on the PT to pull the voltage down to normal operating spec.

Have 2 ground points, one at a PT bolt, the other at the input jack ground.

PT centre taps, main filter cap, screen filter cap can go here. Run separate wires from each component.

Preamp cathodes & preamp filter cap get grouinded to the input jack, again use separate wires from each ground point, don't daisy chain along the circuit board.

Speaker jack is grounded throught its connection to the chassis, no ground wire to any other point is required.

12AX7 tube voltages - read the plate voltages (dc, black probe to ground) by touching red probe the lower leg of each of the 100K plate resistors feeding pins 1 & 6, read cathode voltages at the lower leg of the 1.5K resistors connected to pins 3 & 8 of the 12AX7.

Actual pictures of your build would be most useful, if your amp is really correct as per the layout you posted, then it works fine & you don't have any problems! :-)

[electrochronic]

after the circuit is loaded down and everything drops in range then , no worries.

what does your schematic tell you as far as what your voltages should be ? Keep it in this range
and all is good.

[PFCnR]

PT centre taps, main filter cap, screen filter cap can go here. Run separate wires from each component.

Preamp cathodes & preamp filter cap get grounded to the input jack, again use separate wires from each ground point, don't daisy chain along the circuit board.

Speaker jack is grounded through its connection to the chassis, no ground wire to any other point is required.

What do you mean by screen filter cap? or should i say which one is the screen filter cap?

I will take some pictures for you soon and will read the values right away.

And yeah it should have worked perfectly if i done everything according to the circuit I checked it hundred times maybe but i guess i am missing something.

[MWJB]

Screen filter cap is the filter cap (8uf) that sits between the 10K & 22K resistors in the power supply, a wire from here feeds pin 4 of the 6V6, which is its "screen grid", hence the reference.

[PFCnR]

395vdc B+ is fine, not a problem in the slightest. 478vdc with just the rectifier fitted is to be expected as there is no current load on the PT to pull the voltage down to normal operating spec.

Have 2 ground points, one at a PT bolt, the other at the input jack ground.

PT centre taps, main filter cap, screen filter cap can go here. Run separate wires from each component.

Preamp cathodes & preamp filter cap get grouinded to the input jack, again use separate wires from each ground point, don't daisy chain along the circuit board.

Speaker jack is grounded throught its connection to the chassis, no ground wire to any other point is required.

12AX7 tube voltages - read the plate voltages (dc, black probe to ground) by touching red probe the lower leg of each of the 100K plate resistors feeding pins 1 & 6, read cathode voltages at the lower leg of the 1.5K resistors connected to pins 3 & 8 of the 12AX7.

Actual pictures of your build would be most useful, if your amp is really correct as per the layout you posted, then it works fine & you don't have any problems! :-)

I have done grounding like you said, each component has its own wire now (as you mentioned)

For my Preamp Tube Values:
Pin 1 = 162v
Pin 3 = 1.7v
Pin 6 = 164v
Pin 8 = 1.7v

Are they normal? if so what can i do more?

I will take the pictures when my sister gets home with her digital camera.
Is there any special place to see exactly? I can take lots of pictures

[MWJB]

Hmmm, I'd like to know the voltage at the juction of the 10K & 22K resistors in the power supply please. Based on the current draw through you preamp tube, this should be around 50v & 240v, so in the region of 290v, which seems like a big drop accross the 10K (100v/10mA)...I'd expect more like 60-70v drop across the 10K (6-7mA).

[PFCnR]

Hmmm, I'd like to know the voltage at the juction of the 10K & 22K resistors in the power supply please. Based on the current draw through you preamp tube, this should be around 50v & 240v, so in the region of 290v, which seems like a big drop accross the 10K (100v/10mA)...I'd expect more like 60-70v drop across the 10K (6-7mA).

Here the values that you asked from me:

First Cap : 390v
Second Cap : 390v
Third Cap : 331v
Fourth Cap : 280v

10k resistor is 2W
22k resistor i am not sure but it might be 1w smaller than the other

and there is one more thing i think the other resistors are 1/4w they look really small though. I bought them from a local shop and told the guy they should be 1/2w. For them being 1/4w would affect the sound?

[MWJB]

Ok, that's about right, voltage drop from B+ to screens is 60v @ 6mA.

Drop from screens to preamp is 50vdc @ 2.27mA, sounds about right.

Voltage drop accross 100K plate resistors is 120v/1.2mA per triode, which confirms the curent draw through the 22K. So far so good...

The 5751 you have in V1 just threw my expectations a little, as this draws more current than a 12AX7.

22K in the power supply can be 1/2W (bigger is better/more reliable).

1/4W might be fine for plate resistors pins (1 & 6 12AX7) as long as you use a 12AX7/5751 only BUT the rule of thumb is to use a resistor at least twice the Wattage that is dissipated accross the resistor, e.g. 100K plates drop 120v accross them, square this then divide by resistor value in ohms..

(120*120)/100000= 0.14W...if you stick a 12AY/12AU/12AT in there then dissipation will go up.

But the 1500ohm cathode resistors (pins 3 & 8 of 12AX7) are already dissipating 0.2W...it's a bit borderline.

I probably wouldn't set out to use 1/4W resistors in a build, but in your 5F1 I doubt that they are the cause of your issues.

[PFCnR]

I probably wouldn't set out to use 1/4W resistors in a build, but in your 5F1 I doubt that they are the cause of your issues.

It is 5F2a not 5F1 So what can be the problem(s) here? When volume and tone control at zero i got the sound from my speaker like buzzing of PT. When i turn on volume i get hum and hiss. If i off the stand-by switch gives me a creepy buzz sound. And my amp is not even loud at the full volume all bad sound...

Is there any specific place for me to take a picture?

Thanks a lot for taking your time looking over my problem.

[MWJB]

"Is there any specific place for me to take a picture?"

The wiring of the power transformer, shwing how all leads are terminated.

The wiring of the tube sockets from above.

The wiring of the tone & vol pots & input jacks.

And a shot of the circuit board.

In the mean time, pull out the preamp tube, power up, how does this affect hum. If you still have hum with the power tube only installed, power down, pull it out and see what noise you get with just a rectifier.