New Build

mat · Post by **mat** » Fri Jun 09, 2006 8:07 pm

Hello !

I just 'finished' my first D-build. It is from Normsters Bassman layout. It was a little tight build

I wonder how I'm going to fit the relays in there in future

I've measured every component and did wrote the values down for further need..

Anyways, I have few problems with it. First being loud static noise (sizzling) when switching the standby off. Secondly the reverb seems not to work. Also the minitoggles that I wired as on the layout, they seem to work upside down (no problem just have to resolder them).

I went trough the layout 3 times and the wires should (

) be ok as the tube sockets also.

I get sound (not very good) when plugging guitar in it, and the channelswitch, boost and bright switches works ok.

Here are the critical numbers, hope someone could direct me if there are wrong voltages in there. Some of them are quite out of those that Normster posted.

B+1 = 449
B+2 = 445
B+3 = 426
B+4 = 365
B+5 = 321

V1 - pin1 = 173, pin3 = 1.91, pin6 = 182, pin8 = 1.89
V2 - pin1 = 207, pin3 = 2.06, pin6 = 206, pin8 = 2.09
V4 (reverb) - pin1 = 427, pin3 = 14.4, pin6 = 89.2, pin8 = 3.39
V3 (PI) - pin1 = 280, pin2 = ____, pin3 = 67.2, pin6 = 290, pin8 = 67.2

V5/V6 - plate = 449/452, screen = 445/447, bias = -39mA

Here are some closeups of the build (be gentle

Here is how I made the ground connections:
[img

1200]http://www.pichotel.com/pic/16028B31e/39458.jpg[/img]

Any help appreciated, Thank You,

dogears · Post by **dogears** » Fri Jun 09, 2006 8:19 pm

The FET sim goes from B+5 to ground. Do it... It will help alot. (see note on voltages first)

The B+1 should only have 270k balance resistors...... The 100k is not needed.

Your V1 and V2 plate voltages are REALLY REALLY low relative to the B+ You have either bad tubes or the resistors are WAY out of spec or mislabeled.

What's up with the bias feed on the last output tube? Paralleled resistors??

Let me see what I else I can find.....

Normster · Post by **Normster** » Fri Jun 09, 2006 8:50 pm

I'll check my Bassman voltages when I get home, but your PI voltages look a little out of whack. Pins 2 & 7 should be in the 35V range and pins 3 & 8 should be around 55V if I recall correctly.

As for the 150k to ground, it may not be necessary since you are already drawing current from B+5 to the reverb tube. I think my V1 runs about 190/195V on the plates without the FET resistor.

Voltage is way too low on pin 6 of your reverb tube. (Should be closer to 200V) Since this is being fed by B+5 as well, there might well be some problem in this area.

jazzyjoepass · Post by **jazzyjoepass** » Fri Jun 09, 2006 11:58 pm

Dogears is right about the voltages - they are very critical to the tone.

Reduce the value of the dropping resistors to V1 and V2. I think you should target 200V on V1 and 220V on V2. I also suppose if your B+ voltages are not high, then there's no need for the 180k resistor to simulate the FET.

I suppose it could be the addition of the reverb tube that's loading the B+. Is that a 12AX7 or 12AT7? A 12AT7 draws more current and thus loads more on the B+

Also something I observed is that if voltages within a twin triode are hard to match closely, (eg. in your case between V1A/V1B and V3A/V3B), you'd might want to try GT Mullard reissues. I found them very consistent within both sections - that way you'd get good voltage balance between both sections of a twin triode.

My 2 cents.

Normster · Post by **Normster** » Sat Jun 10, 2006 12:42 am

I see one problem with your reverb wiring, the blue wire goes to pin one and the red goes to B+. If that doesn't bring it back to life, try swapping the reverb cables. Here are my voltage readings, not dead on but the amp does sound pretty good:

V1 - 1=202, 3=1.91, 6=211, 8=1.74
V2 - 1=207, 3=1.84, 6=208, 8=1.80
V3 - 1=426, 3=2.67, 6=207, 8=1.81
V4 - 1=293, 2=37.7, 3=57.2, 6=280, 7=37.0, 8=57.2
V5/V6 - 428 plate, 426 screen, -43 bias

B+1=432, B+2=430, B+3=417, B+4=334, B+5=332

Hope this helps. As dogears says, the voltages won't be exact, but you should be in the ballpark. Your reverb tube readings are definately out of range for pins 3 & 6.

I'll study your pics and see if anything stands out. I can't tell for sure, but it doesn't look like a 150k resistor feeding pin 6 on your reverb tube. Hard to tell, but it almost looks like a 15 Ohm. (brown/green/black?)

mat · Post by **mat** » Sat Jun 10, 2006 2:38 am

dogears wrote:The FET sim goes from B+5 to ground. Do it... It will help alot. (see note on voltages first)

The B+1 should only have 270k balance resistors...... The 100k is not needed.

Your V1 and V2 plate voltages are REALLY REALLY low relative to the B+ You have either bad tubes or the resistors are WAY out of spec or mislabeled.

What's up with the bias feed on the last output tube? Paralleled resistors??

Let me see what I else I can find.....

Hello,

Its 5:32am here. Could not sleep thinking of the amp all the time. I look like this -

The B+ has 325K resistors in it. The bleeder is just for the safe, I'll take it of.

I have 10K + 2K2 in series just before B+5, I'll take the 2K2 out.

Both bias feeds have 180k + 20k in series (did not have 200k 1W) - the bias adjustment is working nicely (two pots trough the backpanel).

I'll try to sleep for a while and get back after few hours.

Thanks for answering,

Bob-I · Post by **Bob-I** » Sat Jun 10, 2006 3:38 am

Looks pretty good. A tad cluttered by the output tubes but otherwise very nice.

mat · Post by **mat** » Sat Jun 10, 2006 12:00 pm

Hello,

Some further info:

PT is Trafomic TV7 230V//345-0-345V 0,210A/6,3V 8A / 55V 0.02A

OT is New Sensor Corp. (fender replace) NSC 018343 50w (2,4 and 8ohm) primary 4000 ohm

RT is NSC-022921 989 0525

Choke is NSC125C1 A 989 0430

Power tubes are Svetlana 6L6GC

Preamp tubes are JJ ECC83 (12ax7) for V1, V2 and PI. JJ ECC 81 (12at7) for reverb - all tubes are brand new.

Here are the new numbers:

2k2 taken away before B+5 , reverb B+ resistor 149k4 checked (purple-green-black-orange..), reverbtube changed from 12au7 to 12at7

V1 - 1=181, 3=2, 6=191, 8=1.98
V2 - 1=211, 3=2.1, 6=209, 8=2.11
V3 - 1=437, 3=5.79, 6=161, 8=2.46
V4 - 1=281, 2=23, 3=67, 6=290, 7=24, 8=67
V5/V6 - 450/449 plate, 446/447 screen (pin4), -39.9 bias

B+1=449, B+2=447, B+3=428, B+4=369, B+5=336 B+6=335

I got the reverb working by changing the pan cables another way around. Did this earlier but did not fix it. Now the reverb works OK! The wiring is as on the layout.

The tone is getting better. The switches seems to work all ok. The buzz is horrible. It gets very loud when turmimg the master or drivepot (in OD ch) or presence up. I could make a sound sample if I just know where to put it.
The boost 'on' sounds pretty good but boost 'of' the mid and bass pots seems to do anything and the sound is very 'thin'.

Yes Bob-I its guite ugly on the powertube area

Big Thanks to all,

Normster · Post by **Normster** » Sat Jun 10, 2006 12:58 pm

Mat, try moving your preamp ground to the other side of the rail. In your pics it looks like it's too close to the power supply. Most Dumble pics I've seen show the ground connection at the input side.

One other thing, I just noticed that you have a B+6. The wiring on your board (from the Bassman layout) uses B+5 for V1 and V3. You can do one or the other, but not both. If you have a seperate cap feeding the reverb, disconnect the wire between V1 & V3.

mat · Post by **mat** » Sat Jun 10, 2006 2:39 pm

Normster wrote:Mat, try moving your preamp ground to the other side of the rail. In your pics it looks like it's too close to the power supply. Most Dumble pics I've seen show the ground connection at the input side.

One other thing, I just noticed that you have a B+6. The wiring on your board (from the Bassman layout) uses B+5 for V1 and V3. You can do one or the other, but not both. If you have a seperate cap feeding the reverb, disconnect the wire between V1 & V3.

Hi Normster,

I'll do a new grounding point immediatly at the input side and connect it from there, thanks for the tip

The PS board is also Your design. There is the B+6 but I don't use it. I just thought I might need it someday. Did I understood right that I shouldn't use the B+5 for both V1 & V3 ? Could I wire the B+6 to the reverb and disconnect the wire between V1 & V3 ?

Here is what I did today and what I got for result:

10.6.

V1 plate resistors 150k,220k to 125k3, 178k3
V2 plate resistors 149k5,178k5 to 125k4,147k8

V1 - 1=197, 3=2.15, 6=204, 8=2.08
V2 - 1=226, 3=2.23, 6=224, 8=2.24
V3 - 1=440, 3=6, 6=158, 8=2.47
V4 - 1=281, 2=24 (loud pop), 3=68, 6=290, 7=24 (speaker thump!), 8=68
V5/V6 - 450/451 plate, 447/448(pin4) screen, 39.9 - bias

B+1=451, B+2=449, B+3=428, B+4=370, B+5=334, B+6=333

The boost switch makes bigger boost in volume now and the bright switch is rather innoticeable now ?

There is slight reduce of buzz when turning the mid pot to zero. Bass pot does nothing.

OD channel is very buzzy and when letting the cord ring, it will break ocassionally.

The sound is so much better with humbuckers than sc's.

I will go thru the layout again and after that I'm going to put the tolex on the box..

thanks,

Normster · Post by **Normster** » Sat Jun 10, 2006 3:16 pm

If you're not using B+6, you can just leave things as they are. My Bassman uses a 2k2, 22k, 1k dropping string for the power supply. On the PS board that I posted, I broke the 22k into 12k/10k to send a bit more voltage to the reverb tube (B+4) and still provide the correct voltage to V1 & V2. If you're not using B+6, you can either change the dropping string or just move the wires over one terminal. Since your voltages are pretty close, you could also just leave things where they are.

I would recheck the resistors in your PI circuit. On all of my amps, (Bassman, Dumble, and Trainwreck) the long-tail pair seems to give a 20 volt difference between pins 2/7 and 3/8. You have a 40 volt difference which seems high. It could also be a grounding/resistor problem at your presence control so maybe give that another look. (Shorted cap on the presence pot?)

Although your reverb is working, it still seems odd that your pin 6 voltage is so much lower than the plate voltage on V1 since they both use the same B+. Could be a bad tube so maybe try swapping in a different tube.

Lastly, never work on your amp after sniffing Tolex glue!

mat · Post by **mat** » Mon Jun 12, 2006 6:06 pm

Normster wrote:If you're not using B+6, you can just leave things as they are. My Bassman uses a 2k2, 22k, 1k dropping string for the power supply. On the PS board that I posted, I broke the 22k into 12k/10k to send a bit more voltage to the reverb tube (B+4) and still provide the correct voltage to V1 & V2. If you're not using B+6, you can either change the dropping string or just move the wires over one terminal. Since your voltages are pretty close, you could also just leave things where they are.

I would recheck the resistors in your PI circuit. On all of my amps, (Bassman, Dumble, and Trainwreck) the long-tail pair seems to give a 20 volt difference between pins 2/7 and 3/8. You have a 40 volt difference which seems high. It could also be a grounding/resistor problem at your presence control so maybe give that another look. (Shorted cap on the presence pot?)

Although your reverb is working, it still seems odd that your pin 6 voltage is so much lower than the plate voltage on V1 since they both use the same B+. Could be a bad tube so maybe try swapping in a different tube.

Lastly, never work on your amp after sniffing Tolex glue!

Hi Normster,

Here are my latest voltages:

V1 - 1=192, 3=2.12, 6=199, 8=2.05
V2 - 1=224, 3=2.21, 6=222, 8=2.23
V3 - 1=443, 3=6.01, 6=155, 8=2.41
V4 - 1=282, 2=24 (loud pop), 3=68, 6=290, 7=24 (speaker thump!), 8=68
V5/V6 - 450/451 plate, 447/448(pin4) screen, 39.9 - bias

B+1=454, B+2=452, B+3=430, B+4=366, B+5=327, B+6=326

I found bad ground connection on B+5 grounding point. I fixed it and hoped for the noise to go away... Did not happend.

I soldered 4 shielded cables (grounded on the pots) to same place that are in Your build - no help.

After that I made the preamp ground next to input jack + put the PS board grounds on one point - no help.

I swapped additional tubes on different places - no help, so I suppose its not the tubes.

Then I pulled out V1 tube - same noise.

V2 - same noise.

V3 (reverb) - same noise.

V4 (PI) silence !

The problem is possibly on the PI area. Any idea what to look after in there ?

The tolex glueing was actually very relaxing

-after many hours of trying to find where the poroblem of the noise lays.

I will check the resistors around PI.. I think I will also buy some more 3w resistors and try to put in the 2k2 22k and 1k on the PS string.

Thank You,

mat · Post by **mat** » Mon Jun 12, 2006 6:56 pm

(Shorted cap on the presence pot?)

Normster BIG thanks to You !! I _was_ connecting the ground wire of the presence pot on the wrong side of the cap !!! Now it is dead silent (exept the guitar sound

)

I will measure the voltages again tomorrow and try to reach the 200V on V1. Btw. is it just safe to change the plate resistors until I will get desired result (200V) on V1 ? Also is it ok to lower the V3 reverb plate1 resistor to get closer to 200V in there ?

Again BIG BIG thanks !!

One happy dude

dogears · Post by **dogears** » Mon Jun 12, 2006 7:11 pm

Hi Mat,

I would change your string a touch..... Raise the B+4 resistor to like 18k and lower the B+5 resistor to around 3.3k Or some similar combination. Basic idea is to lower V2 voltage by 10v or so and raise the V1 back to where it is now. 210v is ok btw..... 200v is not an absolute, just a suggested ballpark. I actually have something similar to Hybrid A in my amp. 22k and 2.2k I believe. You could try that.

Do not touch the plate resistors! Only change the dropping string resistors.

mat wrote:
(Shorted cap on the presence pot?)
Normster BIG thanks to You !! I _was_ connecting the ground wire of the presence pot on the wrong side of the cap !!! Now it is dead silent (exept the guitar sound )

I will measure the voltages again tomorrow and try to reach the 200V on V1. Btw. is it just safe to change the plate resistors until I will get desired result (200V) on V1 ? Also is it ok to lower the V3 reverb plate1 resistor to get closer to 200V in there ?

Again BIG BIG thanks !!

One happy dude

mat · Post by **mat** » Mon Jun 12, 2006 9:04 pm

I would change your string a touch..... Raise the B+4 resistor to like 18k and lower the B+5 resistor to around 3.3k Or some similar combination. Basic idea is to lower V2 voltage by 10v or so and raise the V1 back to where it is now. 210v is ok btw..... 200v is not an absolute, just a suggested ballpark. I actually have something similar to Hybrid A in my amp. 22k and 2.2k I believe. You could try that.

Do not touch the plate resistors! Only change the dropping string resistors.

Oops I have already lowered the plate resistors

(have some wild series combos of carbon film/carbon composites in there

) I'll get some 3w dropping resistors for the PS and put the 1w resistor values (metal film) back that are in Normsters layout (V1=150k/220k , V2=150k/180k).

I'll follow Your suggestions and report back.... but tomorrow I just _have_ to play for a while first

without that nasty sizzling

Thank You dogears,

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