Noisy build, any suggestions?

[Structo]

What value do you have for the FET simulator resistor?
That would be the last resistor in your dropping string on the big cap board. Typically it is 150K to 220K.
I have mine at 150K.
That helps lower the V1 and V2 voltages.

Do you have both the PI plate resistors at 100K?
You may get better harmonics if they are 100K/110K.

I assume you have pins 3 & 8 jumpered on the PI? (can't see it in the photo) But it probably wouldn't even work if you didn't.

What grid and screen resistors do you have on the power tubes?

What is the switch between the bass pot and drive pot?

What is the extra switch back by the power and standby switches?

Something I found that helped my tone on my D'Lite 44 was to put a 100K resistor before the PI input cap (.02uf).
I can't tell if you have a resistor on your loop jack.

You seem to be missing a pot on the front panel.
Do you not have a presence control?
What is the 10K coming off of the PI tail?

The wire from the CL2 coupling cap should go to the OD relay, then from the relay to the Master Volume.
Yes if you can post some voltages I'm sure the experienced builders here can guide you to the sweet spots.

[wjdunham]

The early chassis did not have switches for the OD or PAB, just controllable through the footswitch. The switch between the Bass and Drive is the OD switch. The third toggle switch in the rear is the impedance selector, 4 or 8 Ohms. I put the master where the accent switch would have gone, I was going to put the presence pot on the back somewhere, but I don't have that implemented yet. The 10K resistor going nowhere is the GNFB resistor, which I haven't wired up yet. I got this chassis real cheap on Ebay, I wasn't intending to build an exact replica of an early model, just wanted an inexpensive ready made chassis.
I have the 150K FET simulator, and 470R/5.1K grid/screen resistors. PI plates are already 100/110K. I took a quick look at the voltages when I first fired it up, everything was in the range of 190-205, PI was 285 and 295, so things seem in order there. Time to start tweaking...

[butwhatif]

Something I have wondered about those heater balance pots is how much current is that pot handling?

W/ a 100 ohm pot

I=E/R = 6.3 / 100 = .063 = 63ma a/c

[Structo]

Something I have wondered about those heater balance pots is how much current is that pot handling?

W/ a 100 ohm pot

I=E/R = 6.3 / 100 = .063 = 63ma a/c

Oh, that was too obvious!
Isn't the pot more of a divider, so if it is exactly in the middle, wouldn't it be 50 ohms to ground?
So it would be 126ma? Which would be .793 watts.

I have seen some circuits that call for a 10KL hum balance pot as well.
But those also have a 15K tail to ground.

Also after some reading I see where it is usually a 5w wire wound linear pot that is used there because of the current.

Not being argumentative, just trying to understand it.

[butwhatif]

it is obvious. a pot is just a resistor, here 100 ohms across a 6.3v winding. the wiper is just a ground reference point across this winding, and there is virtually no current flow to ground because there is no circuit, the winding is floating. use any size pot u like, the physics is still physics. I=E/R

[wjdunham]

Now that I have the noise problems cleaned up and relays working, I'm on to tuning it. Mostly there, but I'm noticing that on this amp the tone stack seems to be eating a lot more of the signal than it should. I'm not getting anywhere near the drive I should on the OD channel, unless I hit the PAB. I have to keep the OD trim at 65K to get any reasonable overdrive with the PAB off. On the clean channel, there's a pretty good jump in volume when I engage the PAB. I think there's enough detail in the photo posted at the front of this thread to help spot any problems, if not I can snap another of just that section. Right now I have .05 mid cap, otherwise it's a skyliner EQ without any rock/jazz implemented. 250KB treble and mid pots, 500KA bass. I may have to pull those off and check them if noone can spot anything, but I'm pretty sure they are correct.

[talbany]

wjdunham

That's kind of a funky way to wire the PAB.. Kind of hard to see what you did on the other side of the relay...Also a point of suggestion here.. If you get the clean channel worked out and get some noise in the OD you should maybe run shielded wire from both drive and level control's coming from the 100k/150k...The little bit of shielded cable there does change the tone slightly as well...Just a suggestion ... Good Luck!!



Tony VVT

[wjdunham]

The PAB is a little non-traditional, I was attempting to save some wiring. I verified that then when the relay is off, the bass pot wiper and top side lug are shorted, and the connection between the treble pot and bass pot is made. When the relay is engaged, it opens up the bass middle and top connection, and disconnects from the treble pot. PAB mode sounds like it should, but I'm just not getting the proper gain out of the clean channel with PAB off. Voltages are pretty good, 185-195 on V1, 200 on V2. I don't have any extra 12AX7s to try different tubes, but I did swap around the three that I have in there (an EH, a Svetlana, and an old RCA). No noticeable difference. I'm going to check all the component values with a meter in the tone stack to make sure I don't have anything wrong or a bad component.

[Structo]

I notice with my amp that the boost on the clean channel is huge but not so big on the OD channel.

I suppose it depends where your OD level control is set vs the master volume.

Somebody mentioned to me at another forum that instead of lifting the tone stack by breaking the link between the bass and treble pots, that if you lift at the mid pot you can still keep your bass and treble tones but get a boost.

Is this like the Mega Boost we hear about sometimes?

This is what was suggested to me:

Instead of lifting the entire tone stack, try switching in a 33k-47k resistor with a .001-.005 cap in parallel off the midrange tab to ground. It boosts gain and volume without deactivating the tone controls.

I was going to try it next time I had my chassis out.