New Build

[dogears]

You can use 1W dropping resistors. 2W if you want on the B+3 3W is not needed.

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,

[mat]

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.

Hello dogears,

I changed the string as You suggested (2k2,17k5,3k3) and did put the right values oj the plates again. Here is what I got:

V1 plates 178V,188V
V2 plates 194V,194V
V3 (reverb) pin1=447V, pin3=6, pin6=156
V4 pin1=284, pin2=24, pin3=69, pin6=288, pin7=24, pin8=69

B1=457
B2=456
B3=436
B4=341
B5=331

Bias 39.9

Actually the amp sound better than before the changes ?!? But obviously I have again too low voltage on the plates.

[dogears]

Hi Mat,

I don't understand how you have 178v-188v on the V1 plates with 331v on the B+5. Seems like something is wrong..... What tubes?? Did you measure exactly the resistors for plates and cathodes? Maybe bad tubes?? I believe you should get at least 200-210v with 330v on the B+ If the sound is not quite right, I would figure out why the voltage abnormality....

Maybe you should take the Reverb voltage from the screen supply with a dropping resistor and dedicated reverb cap.... Something is worng here.... Pulling the reverb from the V1 and V2, if that is what is happening, must be bad in my completely non technical opinion......

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.

Hello dogears,

I changed the string as You suggested (2k2,17k5,3k3) and did put the right values oj the plates again. Here is what I got:

V1 plates 178V,188V
V2 plates 194V,194V
V3 (reverb) pin1=447V, pin3=6, pin6=156
V4 pin1=284, pin2=24, pin3=69, pin6=288, pin7=24, pin8=69

B1=457
B2=456
B3=436
B4=341
B5=331

Bias 39.9

Actually the amp sound better than before the changes ?!? But obviously I have again too low voltage on the plates.

[mat]

Hi Mat,

I don't understand how you have 178v-188v on the V1 plates with 331v on the B+5. Seems like something is wrong..... What tubes??

JJ ecc83 and JJecc81 on reverb

Did you measure exactly the resistors for plates and cathodes?

I have measured every resistor before soldering. I'll lift the cathode resistor from ground and measure them again.

Maybe bad tubes?? I believe you should get at least 200-210v with 330v on the B+

I've swapped different tubes in with same results on V1 and 2.

If the sound is not quite right, I would figure out why the voltage abnormality....

Can I just lift the B+5 from the reverb tube and see what happends on V1 and V2 ?

Maybe you should take the Reverb voltage from the screen supply with a dropping resistor and dedicated reverb cap.... Something is worng here.... Pulling the reverb from the V1 and V2, if that is what is happening, must be bad in my completely non technical opinion......

Normster had it working + some others too if I remember right. I have no idea how to take the voltage from screen supply. Do You mean pin4 of the first driver ? And go from there to the point where B+5 (for the reverb tube) went ?

Thanks,

[dogears]

I'll see if Glasman can chime in.........

You can measure the cathode resistors to ground in circuit.

Also, the JJ ECC83S is not a true 12AX7 They are always low on voltage abd the current draw is odd.... Try diff tubes maybe?

You can disconnect the reverb and try it btw...

[mat]

I'll see if Glasman can chime in.........

You can measure the cathode resistors to ground in circuit.

Also, the JJ ECC83S is not a true 12AX7 They are always low on voltage abd the current draw is odd.... Try diff tubes maybe?

You can disconnect the reverb and try it btw...

I measured the cathode resistors and they were ok. I have two 12ax7's. I'll put them on V1 and V2 at first thing in the morning and report what happends.

[Bob-I]

Mat,

I'd find out where the voltage is being dropped. Measure the voltage drop across the power supply resistors and see if perhaps you have a bad cap or something else dropping voltage.

For example you're seeing 331 at B+5 and 178 at B+4. That means that the resistor between the 2 must be dropping 153V. That's not likely so you need to determine what's dropping that voltage.

Disconnect everything from the power supply and you should see the same voltage at every node. No current, no voltage drop. Then add things back in one at a time and observe.

[mat]

Hi Bob,

I'd find out where the voltage is being dropped. Measure the voltage drop across the power supply resistors and see if perhaps you have a bad cap or something else dropping voltage.

Thanks for the tip I'll do _that_ first thing in the morning !

For example you're seeing 331 at B+5 and 178 at B+4. That means that the resistor between the 2 must be dropping 153V. That's not likely so you need to determine what's dropping that voltage.

B+4 tap on PS board shows 341V but after 180k on plate 1 (V2) and 150k on plate 2 it gives both 194V ?? Very strage indeed..

Disconnect everything from the power supply and you should see the same voltage at every node. No current, no voltage drop. Then add things back in one at a time and observe.

You mean I disconnect B+2 to B+5 ? And then there is same voltage on the pins B+2 to B+5 ? If soI'll try it but I'll wait for Your confirming.

Thanks Bob !

[glasman]

I'll see if Glasman can chime in.........

You can measure the cathode resistors to ground in circuit.

DING DING (you did say chime right!)

Mat, can you list the current configuration for the amp. What I would like to see is the following..

Plate Resistor and Cathode Resistor Values for V1 and V2 and PI
Plate Resistor and Cathode Resistor Voltages for V1 and V2 and PI.

For the PI, measure the Grid voltage as well.

Measure your current string voltages from Plate supply down to V1 supply.

it is hard to tell from thread exactly what the current values are....

Also , I like a AX7 for the reverb. makes it sounder a little better, just my 2 cents.

Maybe with this information, I can give you some places to look.

Gary

[Bob-I]

B+4 tap on PS board shows 341V but after 180k on plate 1 (V2) and 150k on plate 2 it gives both 194V ?? Very strage indeed..

that's like 9 AMPS!!!

You mean I disconnect B+2 to B+5 ? And then there is same voltage on the pins B+2 to B+5 ? If soI'll try it but I'll wait for Your confirming.

Thanks Bob !

Exactly. somethings throwing your current off. This'll tell you what's drawing all that current.

[Normster]

Mat, I don't know if it matters, but try swapping the leads on your reverb tranny. Every schematic I've ever seen has the blue wire to the plate and the red wire to B+. Also, the input side of the tank should be grounded. You have both RCAs insulated from ground. (Actually, I have both sides grounded and it seems OK.)

Your PI voltages still seem out of range for pins 2 and 7. With 69V on the cathodes, I would expect to see something in the range of 45-50V. Maybe that's normal for a 12AT7?

[mat]

I'll see if Glasman can chime in.........

You can measure the cathode resistors to ground in circuit.

DING DING (you did say chime right!)

Mat, can you list the current configuration for the amp. What I would like to see is the following..

Plate Resistor and Cathode Resistor Values for V1 and V2 and PI
Plate Resistor and Cathode Resistor Voltages for V1 and V2 and PI.

For the PI, measure the Grid voltage as well.

Measure your current string voltages from Plate supply down to V1 supply.

it is hard to tell from thread exactly what the current values are....

Also , I like a AX7 for the reverb. makes it sounder a little better, just my 2 cents.

Maybe with this information, I can give you some places to look.

Gary

Hi Gary, Thanks for joining this thread

Here are values measured with 12AX7 on V1, V2 and V3 (reverb):

V1 plate 220k, 150k V1 cat 3k3, 2k2
V2 plate 180k, 150k V2 cat 2k7, 2k2
PI plate 100k, 100k PI cat 820R

V1 plates 189V, 202V cat 1.92V, 1.8V
V2 plates 194V, 200V cat 2.03V, 1.92V
PI plates 284V, 290V cat 69.2V

PI pin2= 23.8V, pin7=25V, pin8=70V

B+1=456V
B+2=455V
B+3=436V
B+4=347V
B+5=337V

V3 (reverb) pin1=450V, pin6=195V

Layout is Normsters Bassman layout:
[img846]http://bad-domain/Pics/Bassman_Dclone_LayoutV3.jpg[/img]

And PS board is also Normsters:
[img:400:303]https://tubeamparchive.com/files/thumbs ... v3_154.jpg[/img]

With from B+ choke,2k2,17k5,3k3, last (B+6) resistor is disconnected. The resistors going in parallel are 325K ones.

Bob-I:

I was little unsure to know how to do the following:

Measure the voltage drop across the power supply resistors and see if perhaps you have a bad cap or something else dropping voltage.

With the 12ax7's the voltages seems to be +10V. Maybe my build dislikes the JJ's ?

When measuring the plate voltages the amps reverb strings could be heared clearly every time I connected the probe to plate, this might be normal.. The reverb seems clearer now and reverb at 1 or 2 is same as it was earlier at 5 or 6.

The amp does not sound bad at all, but I would like to get it closer to THE sound.

The not working bass and middle pots (wired as on the layout) + the huge amount of the boost with the boost switch bothers me also a little.

Big Thanks to all helpers

[mat]

Mat, I don't know if it matters, but try swapping the leads on your reverb tranny. Every schematic I've ever seen has the blue wire to the plate and the red wire to B+. Also, the input side of the tank should be grounded. You have both RCAs insulated from ground. (Actually, I have both sides grounded and it seems OK.)

Your PI voltages still seem out of range for pins 2 and 7. With 69V on the cathodes, I would expect to see something in the range of 45-50V. Maybe that's normal for a 12AT7?

Hi Normster,

The sheet that came with the tranny shows blu + brn on otherside and black(common) and grn(4ohms) on the other. The tranny actually has blue and RED wires on it. I will try later how it affects to the sound if swap the blue and red wires.

I have also both sides grounded. I did it just after I took the photo.

I don't have 12at7 on PI. It has ecc83s (similar to 12ax7) in it.

The reverb with 12ax7 has now 195V on pin6 (plate) which is now closer to what You told it should be

I have to buy few fresh 12ax7's to try it also on PI.

Thanks Normster,

[dogears]

Hi Mats,

So your bass and mid pots don't work in normal, non boost mode?

In any event, try these tweaks... Lower the 220k that feeds the 100k od trim to a 180k. Change the midcap to a .01uf Lower the CL2 cap to a .022 Measure the OD drive and level pots. If they are low, raise the series resistors that feed them by the same amount. For example, 95k drive pot gets a 105k resistor. Lastly, no Dumble ever had an audio taper OD level pot. That is bad and wrong IMO. Makes it hard to level match. No tone issue, just practicallity. Switch to 100kb. Make sure you have about 10k difference in the PI plate resistors. 100k/100k is not good unless there is a balance trimmer. Try 110k/120k if you have no trimmer.

Let me know how it works!

[mat]

Hi dogears,

So Your bass and mid pots don't work in normal, non boost mode?

Yes, I know they are bypassed in boost mode. They do not work in non boost mode either.

In any event, try these tweaks... Lower the 220k that feeds the 100k od trim to a 180k.

I have done many tweaks at the beginning of the build by Your suggestions.

Change the midcap to a .01uf Lower the CL2 cap to a .022

You mean the one that is going to viper of the volume pot ?

Measure the OD drive and level pots. If they are low, raise the series resistors that feed them by the same amount. For example, 95k drive pot gets a 105k resistor.

OD level = 97.2KB Drive = 98kB

Make sure you have about 10k difference in the PI plate resistors. 100k/100k is not good unless there is a balance trimmer. Try 110k/120k if you have no trimmer.

I'll put 10K trimmer in series with the left resistor. Any power ratings for that one ?

Let me know how it works!

Ok