New 5F1 done... Issue...

[SleepLess]

Hi there!
This one is for me. Damn, I'm cursed with 5F1s, I never seem to get them right upon first lit up... So here's the gist of it:
- The amp works and I can play but:
- It sounds very distorted, loss of volume.
- It hums badly even on 3, doesn't hum on 5/6, hums as loud as hell on 11.

Here's what I've done so far:
- Pulled V1 out to see if the hum would stop and it didn't.
- Pulled the 6V6 out and the hum did stop but I guess that's normal. Tried another 6V6 and it also hums.
- Tried another 5Y3GT and it also hums...
- Checked continuity for all the underboard jumpers and it's all there.
- Checked wiring and it seems it's all good.

I have the two 100 ohms resistors soldered to V2 pins 7/8 and 2/8.
Dang, here are some pics. I hope it's not one or both the two yellow Astrons that are bad but that's what I'm leaning toward so I'd like a confirmation before I take one of those guys out, I'd rather not harm them with trial and error tests...





Here's a voltage chart with the amp ON and all tubes in:
   
               V1                        V2                       V3
1            214                        29                        0
2              0                       3.31AC                  333
3            1.7                        314                       0
4            3.33AC                   334                     311AC
5            3.33AC                   14                        0
6            217                         0                       311AC
7             0                         3.27                      0
8            1.7                        29                       333
9            3.26AC

I suspect pins 1/8 (linked) and 5 of V2 to be wrong... They should read 0 shouldn't they? What can I check?
Thanks a lot guys!

[tubeswell]

- It hums badly even on 3, doesn't hum on 5/6, hums as loud as hell on 11.

Check that your input jack tip switches are making proper contact when there is no plug inserted.

[SleepLess]

- It hums badly even on 3, doesn't hum on 5/6, hums as loud as hell on 11.

Check that your input jack tip switches are making proper contact when there is no plug inserted.

They do, I have just checked... Brand new from Doug's store here...

[sluckey]

I suspect pins 1/8 (linked) and 5 of V2 to be wrong... They should read 0 shouldn't they? What can I check?

Good suspicion!

Pins 1/8 are OK but pin 5 should be zero. Lift one end of the .02 coupling cap. If pin 5 now reads 0v, replace the cap.

EDIT... BTW, that 6V6 is cooking, but that should be fixed when you get pin 5 to zero volts.

[SleepLess]

I suspect pins 1/8 (linked) and 5 of V2 to be wrong... They should read 0 shouldn't they? What can I check?

Good suspicion!

Pins 1/8 are OK but pin 5 should be zero. Lift one end of the .02 coupling cap. If pin 5 now reads 0v, replace the cap.

EDIT... BTW, that 6V6 is cooking, but that should be fixed when you get pin 5 to zero volts.

Crap, lifted one leg of the coupling cap is now at 0.11V... That Astron is dead...  I still read 19V on pins 1/8. Gonna change that cap!

[sluckey]

I still read 19V on pins 1/8. Gonna change that cap!

19v on pin 1/8 is perfectly normal. Nothing wrong there. The 6V6 is no longer cooking.

Why are you using those old caps in a brand new build? I'd want some new shiny ones.

[SleepLess]

I still read 19V on pins 1/8. Gonna change that cap!

19v on pin 1/8 is perfectly normal. Nothing wrong there. The 6V6 is no longer cooking.

Why are you using those old caps in a brand new build? I'd want some new shiny ones.

Cuz I'm a fool who got stung by the vintage Astron Tone myth (I wouldn't have done it in a bigger build though, $55 for them both was completely stupid, I shall do it no more, promise!)... Anyway, replaced that cap with a new Jupiter Yellow cap and I now have 0V on pin 5 of V2, but the hum problem remains exactly the same...  

Do you think I should replace the other cap and see?

[sluckey]

Disconnect the NFB from the speaker jack (may be easier to lift the bottom leg of the 22K on the board). This 'may' fix the hum, but in any case, leave it disconnected until the hum is gone.

[SleepLess]

Disconnect the NFB from the speaker jack (may be easier to lift the bottom leg of the 22K on the board). This 'may' fix the hum, but in any case, leave it disconnected until the hum is gone.

Oh I also tried and reversed the OT wires going to V2 în 3 and the board, it diodn't change a thing. The OT is correctly wired... Will do what you say sluckey, thanks!

[sluckey]

Try another known good 6V6 now that pin 5 is correct.

[SleepLess]

Try another known good 6V6 now that pin 5 is correct.

Done... Tried three other new tubes. Same hum. It sounds like an aircraft flying... 

[sluckey]

I'd try a gator clip jumper wire on the filter cap grounds next. Connect one end of the clip lead to chassis. Connect the other end to each filter cap NEGATIVE lead, one at a time.

If that doesn't give any relief, I'd try bridging a filter cap across each of the three filter caps, one at a time. Get a spare cap, something between 10 and 40µF, value is not critical. connect the negative lead to your gator clip lead that's still connected to chassis. This next part will take some nerve, so if you're jumpy, better to use another gator test lead. Hold the test cap in your hand. DON"T TOUCH THE POSITIVE LEAD! Now use the cap as a test probe. The positive lead will be your probe tip. Touch the end of your 'probe' tip to the eyelet that the right 10µF filter cap positive lead is connected to. Hold it there. (There will be a spark and an un-nerving pop when you touch it.) If the hum is still there, move to the next cap and repeat. And finally repeat for the 16µF.

If bridging any of those caps eliminated or greatly reduced the hum, replace the cap. Oh, and don't just put that test cap back in your parts bin. DISCHARGE IT! Or get someone else to retrieve it for you the next time you need it.

If this hum is not associated with the filter caps, you need to go over your wiring again. Does the amp make any guitar sounds?

[SleepLess]

Does the amp make any guitar sounds?

Absolutely, I can definitely play, although it sounds crappy...

Will try what you say!
Thanks sluckey!

Edit: OK, done your test with a 16uF 475V cap... Amp still hums... 

[SleepLess]

If this hum is not associated with the filter caps, you need to go over your wiring again. Does the amp make any guitar sounds?

Sluckey isn't there something else that is strange in my voltage chart? In my previous 5F1 build I had 443VDC on pins 2 and 8 of V3 (I have 333V on this one) and I had 440V on pins 3 and 4 of V2, I have 314V now... I have more than 100V missing on those pins compared to my last build... 

[Willabe]

Same PT?

And what is the PT you are using? What are the specs for it?


          Brad    

[SleepLess]

Same PT?


          Brad    

No, there were Classictones in the previous build and are Mercuries in this one. But more than 100V, that's huge...? That's more than -25%...!
Both schematics state the same 330V HV on the PT data sheet...

[sluckey]

What AC voltage do you actually measure on pin 4 and 6 of the 5Y3. (Black lead on ground)

What is the PT supposed to put out on the HT winding?

The low voltage 'could' be related to your hum if something is dragging the B+ down or you have a faulty rectifier tube. But probably not. Give us the answers to the above two questions.

[SleepLess]

Forget what I said about the 100V missing on this build. I looked up my previous build voltage chart and the 440V I had was because the data were taken with V2 pulled out... I have pulled out V2 on this build and I have 440V as well...

So all voltages are good, but it hums and doesn't sound like it should....  

[SleepLess]

What AC voltage do you actually measure on pin 4 and 6 of the 5Y3. (Black lead on ground)

What is the PT supposed to put out on the HT winding?

The low voltage 'could' be related to your hum if something is dragging the B+ down or you have a faulty rectifier tube. But probably not. Give us the answers to the above two questions.

With all tubes in I have 318VAC on pins 4 and 6 of the 5Y3, with V2 pulled out I have 328VAC.

The PT is supposed to have a 330V B+ and 6.3V@4A for the filament, 5V@2A for the rectifier.

I also tried another 5Y3 and I have the same hum...

[punkykatt]

Double check the two 100 ohm resistors on the 6V6GT socket with you ohm meter.

[tubeswell]

What AC voltage do you actually measure on pin 4 and 6 of the 5Y3. (Black lead on ground)

What is the PT supposed to put out on the HT winding?

The low voltage 'could' be related to your hum if something is dragging the B+ down or you have a faulty rectifier tube. But probably not. Give us the answers to the above two questions.

With all tubes in I have 318VAC on pins 4 and 6 of the 5Y3, with V2 pulled out I have 328VAC.

So do you have more-or-less 159VAC loaded on each side of the HT winding? Or are the voltages on each side of the winding different?

[HotBluePlates]

- It hums badly even on 3, doesn't hum on 5/6, hums as loud as hell on 11.

If not the filter caps, then...

A.C. wires to Volume knob power switch too close to the signal wires on the volume knob?

[DummyLoad]

i thought you're supposed to ground one side of the filament string on the champ? do you have 2 x 100R virtual center tap? this is SE, so there's no hum cancel in output stage. use a test lead and ground one of the green wires of the PT.

do you have a ground wire run to the input jacks? you should not. if you do, then you just created a ground loop since the jack body is grounded to the chassis.

--pete

EDIT: forgot: switch the neutral, not the hot lead. keeps 120V AC away from signal.

[ac427v]

Hi Sleepless,
Can you share more about your layout? If you followed the original fender layout diagram and attached one of the PT green heater leads to ground and attached pin 9 of the 12AX7 and pins 1 and 2 of the 6V6 to ground you can't use the 100 ohm artificial ground for the heaters.
Craig

[SleepLess]

Hi Sleepless,
Can you share more about your layout? If you followed the original fender layout diagram and attached one of the PT green heater leads to ground and attached pin 9 of the 12AX7 and pins 1 and 2 of the 6V6 to ground you can't use the 100 ohm artificial ground for the heaters.
Craig

It's not the stock Fender layout. The heaters are wired the "usual" way with two wires going to pins 7 and 2 of the 6V6 and then to pins 4/5 and pin 9 of V1.
The 100Ω resistors thing on the 6V6 socket was advised my sluckey himself in my previous build in order to keep the noise/hum even further down. It did the trick.

Double check the two 100 ohm resistors on the 6V6GT socket with you ohm meter.

Done. I have 51.4Ω between pins 8 and 2 and 51.5Ω between pins 7 and 8.

So do you have more-or-less 159VAC loaded on each side of the HT winding? Or are the voltages on each side of the winding different?

I don't understand your question, sorry. I posted all my voltages above.

[SleepLess]

If not the filter caps, then...

A.C. wires to Volume knob power switch too close to the signal wires on the volume knob?

Nope, have moved them around and nothing changes...

[sluckey]

I'd like to see some tube pin to ground resistance checks. Turn the amp off and drain the filter caps. Make all these resistance checks with one meter lead connected to chassis and the other lead directly on the tube socket pin. Also turn the volume control max CCW (off). For V1, measure resistance for pins 2, 3, 7, and 8. For V2, measure resistance for pins 5 and 8. Report all 6 readings.

Where is the HT centertap (red/yellow) connected? It appears that it is connected directly to the negative lead of the 16µF cap on the board. If so, do you also have a wire connecting that eyelet directly to chassis?

I see a ground connection on the right end of the chassis near the input jacks. Are those wires soldered securely?

[SleepLess]

I'd like to see some tube pin to ground resistance checks. Turn the amp off and drain the filter caps. Make all these resistance checks with one meter lead connected to chassis and the other lead directly on the tube socket pin. Also turn the volume control max CCW (off). For V1, measure resistance for pins 2, 3, 7, and 8. For V2, measure resistance for pins 5 and 8. Report all 6 readings.

V1:
2   35.7KΩ       3   1.45KΩ       7  1.8Ω        8  1.5KΩ

V2:
5  235KΩ      8  470Ω

Where is the HT centertap (red/yellow) connected? It appears that it is connected directly to the negative lead of the 16µF cap on the board. If so, do you also have a wire connecting that eyelet directly to chassis?

I see a ground connection on the right end of the chassis near the input jacks. Are those wires soldered securely?

Yes and yes for those two points. The HT CT is going to the negative lug of the 16uF cap and a ground wire goes from there to the upper right PT bolt. I also tried to solder the HT CT to the ground cord ground wire lug and the hum doesn't cease either...

[sluckey]

Resistance readings look good. Here's another quick test. Connect one end of your gator clip test lead to chassis. Now I want you to connect the other end of that clip lead directly to the grids of each tube. BE CAREFUL! Ground V1-2, then V1-7, and finally V2-5. Does the hum go away with any of those grids grounded?

[SleepLess]

Resistance readings look good. Here's another quick test. Connect one end of your gator clip test lead to chassis. Now I want you to connect the other end of that clip lead directly to the grids of each tube. BE CAREFUL! Ground V1-2, then V1-7, and finally V2-5. Does the hum go away with any of those grids grounded?

I'm still alive... 

V1-2 and V1-7 grounded and that didn't change anything. However, grounding v2-5 GREATLY reduced the hum and I have no more varying hum as I turn up the volume. It hums (still too much than normal I think) but it's not unbearable like it used to.

[SleepLess]

What can I do now? 
Thanks!

[sluckey]

We've tried most of the logical checks. Time to reexamine the build closely. Look at all the components to verify correct values (measure resistors if in doubt). I've compared your board to the layout and I don't see any problems with component values. I did notice an added cathode cap that's not on the original, but that won't cause your hum problem.

Check the front panel wiring and the tube socket wiring. Verify that wires go where they should and that solder joints are good. Use an ohm meter if you can't actually see where the wires go. Examine all your grounds and verify that there is a good connection at every one.

Check the 100Ω resistors on the 6V6 socket. Be absolutely sure that one connects between pins 2 and 8 and the other connects between pins 7 and 8. Verify that the dc voltage between pin 2/7 and ground is the same as the dc voltage between pin 8 and ground.

This is such a simple amp that the problem has to be simple too, even though we haven't discovered it yet. I think that a good visual exam backed up with ohm meter should reveal the problem. You may need to lift the board to find the problem. Is this a semi-flexible fiber board? If so, is there a backer board under it?

[tubeswell]

Forgive me if I missed seeing this in all the above posting, but have you swapped in a substitute pre-amp tube yet?

[SleepLess]

We've tried most of the logical checks. Time to reexamine the build closely. Look at all the components to verify correct values (measure resistors if in doubt). I've compared your board to the layout and I don't see any problems with component values. I did notice an added cathode cap that's not on the original, but that won't cause your hum problem.

Check the front panel wiring and the tube socket wiring. Verify that wires go where they should and that solder joints are good. Use an ohm meter if you can't actually see where the wires go. Examine all your grounds and verify that there is a good connection at every one.

Check the 100Ω resistors on the 6V6 socket. Be absolutely sure that one connects between pins 2 and 8 and the other connects between pins 7 and 8. Verify that the dc voltage between pin 2/7 and ground is the same as the dc voltage between pin 8 and ground.

This is such a simple amp that the problem has to be simple too, even though we haven't discovered it yet. I think that a good visual exam backed up with ohm meter should reveal the problem. You may need to lift the board to find the problem. Is this a semi-flexible fiber board? If so, is there a backer board under it?

OK, will check all these things. There is a backer board yes.

Forgive me if I missed seeing this in all the above posting, but have you swapped in a substitute pre-amp tube yet?

I have yes. And I have also pulled V1 out and the hum is still there. Looks like the problem is not in the preamp section... I said earlier on that grounding pin 5 of V2 with an Alligator clip greatly reduced hum and got rid of the "varying" hum as I turn up the volume pot, what does it mean?

Thanks guys!

[rzenc]

Are you able to tell if it's 60Hz or 120Hz?

On the pics you posted I see heater wires close to B+...maybe too close? Have tried to move wires?

Also, unsolder all OT primary leads. Isolate exposed wiring.
Connect headphone to speaker out. Power the amp and listen. If PT is inducing HUM on OT you will be able to tell. Then you will need to move OT to another spot.
Be very careful while performing.It's basically the headphone trick to determine best OT location. Remember to be very careful!

[HotBluePlates]

If PT is inducing HUM on OT you will be able to tell.

I don't think that's it, just because grounding the grid of the 6V6 stops the hum. That seems to indicate the hum is before the output tube (and OT), but after the preamp tube (because removing it doesn't stop hum).

Have you tried tacking in filter caps as Sluckey suggested?

Prime candidate right now is the 2nd 10uF cap (the one after the 22kΩ resistor). Since the hum is between the preamp tube and the grid of the output tube, the only things left are the 2nd filter cap, the 22kΩ resistor, the plate load resistor, the coupling cap and the 220kΩ resistor.

Is the 22kΩ really 22kΩ? Does that 2nd filter cap have a good ground (close to the rest of the preamp grounds)? Can you tack in a filter cap across that 2nd 10uF? Verify the 220k is really 220k and is well-grounded (100k looks right in the pictures).

[Platefire]

What about those wires you have running underneath the board. They might be in close in contact with something that's causing the noise. Might try moving them around to see if it makes a difference. Plate

[SleepLess]

Hi there.
I have eventually managed to isolate the source of hum. It is located on the output jack. I used an old style RCA jack and moving the OT wires stops the hum. I suspect that the grounding provided by this jack is inefficient. I'm gonna try and replace it with a more usual output jack but I don't really get why I would get hum with this...
Will let you know but in the meantime if you see or have a hunch... Here's one pic of the jack:



So sluckey, here's your measures:
100Ω resistors read 51.5Ω each, but I suppose that it's normal.
DC voltage on pins 2, 7 and 8 of V2 to ground is 20.5V.

I have changed the output jack for a switchcraft and the amp still hums... I'm now leaning more toward either a bad OT or a bad speaker... But I don't have any 4Ω speaker around. I have an 8Ω speaker though, I think I can use it just as a test as long as I don't play the amp. I'll try that tomorrow, it's almost midnight here.

If you have any tips, don't refrain from shooting!
Thanks!

[sluckey]

I don't suspect the OT or the speaker.

[jeff]

What about adding an extra filter cap/250ohm resistor before the first filter cap trick?

[HotBluePlates]

100Ω resistors read 51.5Ω each, but I suppose that it's normal.

Yes. Why? Cause the resistors are joined at one end (which you have connected to the 6V6 cathode), and the other ends are conencted to either end of the heater winding. That winding is a coil of fat wire, with a very low resistance. That's the same as those ends being connected together.

So when you measure the resistance of either 100Ω resistor, you're measuring them both in parallel.

[SleepLess]

Have you tried tacking in filter caps as Sluckey suggested?

Hi. Yes I have for all three of them...

[SleepLess]

Guys I found it and you won't believe it... I was hitting the amp everywhere with a chopstick and got a lot of pops around the 10uF cap on the right. I hit real hard, moved the + leg and the hum stopped... The amp now works. I don't really get it... Maybe a wire underneath the board was/is not enjoying getting squeezed between the boards... I played with it for an hour and it works...
Thanks!

[sluckey]

I was hitting the amp everywhere with a chopstick and got a lot of pops around the 10uF cap on the right. I hit real hard, moved the + leg and the hum stopped... The amp now works.

Is moving the + leg the only thing You've done?

I would also reflow the solder joint on that eyelet.

[HotBluePlates]

Guys I found it and you won't believe it... I was hitting the amp everywhere with a chopstick and got a lot of pops around the 10uF cap on the right. I hit real hard, moved the + leg and the hum stopped... The amp now works. I don't really get it... Maybe a wire underneath the board was/is not enjoying getting squeezed between the boards... I played with it for an hour and it works...

I wonder if the leg is damaged running into the body of the cap. But definitely reflow the joint as Sluckey recommended.

[SleepLess]

I was hitting the amp everywhere with a chopstick and got a lot of pops around the 10uF cap on the right. I hit real hard, moved the + leg and the hum stopped... The amp now works.

Is moving the + leg the only thing You've done?

I would also reflow the solder joint on that eyelet.

I will reflow it yeah... It is the only thing I did, hitting around the leg onto the fiberboard and then moving the leg...
Jeez, 6 hours of head scratching for this ridiculous thing... 
Thanks!

[sluckey]

Glad you got it without having to pull the board. Most problems seem to be simple after you fix them.    But simple problems can have a way of hiding right in front of us.

Touch the end of your 'probe' tip to the eyelet that the right 10µF filter cap positive lead is connected to.

I'm surprised this test did not reveal the problem. Did you perhaps touch the cap positive lead rather than the eyelet?

[SleepLess]

Glad you got it without having to pull the board. Most problems seem to be simple after you fix them.    But simple problems can have a way of hiding right in front of us.

Touch the end of your 'probe' tip to the eyelet that the right 10µF filter cap positive lead is connected to.

I'm surprised this test did not reveal the problem. Did you perhaps touch the cap positive lead rather than the eyelet?

No no, I did touch the eyelet... Strange indeed...

[DummyLoad]

Did you perhaps touch the cap positive lead rather than the eyelet?

that's what I do simply b/c usually it's safer. the further from HV my fingers are, the better...

 

good to read you got it sorted out.   

[SleepLess]

good to read you got it sorted out.   

It's not 100% perfect. Played it with a strat and it was okay but with my SG I got some frying I don't like. I need to put my nose in it again... Damn, 5 hours to fully build it from 0 and will be 10 hours to debug...