New Build

[dogears]

The .022 is the CL2 cap after the plate of V1b. You have a .047uf

Tonestack needs to work! That is definately a serious issue

Not sure in wattage of trimmer...... I think you put it between the two PI plates though. See pictures..... Adjust to get a 10k difference.

Try the .01uf midcap. However, until your stack works, that won't matter.

Good luck with the stack.....

Hi dogears,

They do not work in non boost mode either.

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 ?

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

[glasman]

Mat,

Ok I looked over the voltages. They seem to be in line and similar to what I get on my amps. The PI Grid is a little off, but lets check that later.

First Thing. Stop... Fix the Bass and Mid control issue first. If you rotate the controls and nothing happens then there is a wiring problem and must be fixed before messing with any other parts..

Make sure that you have continuity between the BOTTOM of the Treble and the TOP of the bass control in NON BOOST mode.

Check that the same connection is OPEN in boost mode.

FWIW, the MID control is wired backwards to my thinking....

Check the voltage on Bass and Middle Caps. The common side should read the SAME as V1a plate voltage.

Check your ground connection for the tone stack. Make sure it is truly going to ground. Reference it to your V1 cathode ground.

Let start here and see where we get.

Gary

[glasman]

BTW, FWIW. Here are the current calculations for Mat's measured voltages.

V1ap 220000 189 0.000672727
V1ak 3300 1.92 0.000581818
V1bp 150000 202 0.0009
V1bk 2200 1.8 0.000818182


V2ap 220000 194 0.000695455
V2ak 3300 2.03 0.000615152
V2bp 150000 200 0.00098
V2bk 2200 1.92 0.000872727


These are reasonable and note that the Plate and Cathode current are close to equal, as they should be. To get more accuracy would require more decimal points in the measurements All less than 1ma.

Gary

[mat]

Mat,

Ok I looked over the voltages. They seem to be in line and similar to what I get on my amps. The PI Grid is a little off, but lets check that later.

First Thing. Stop... Fix the Bass and Mid control issue first. If you rotate the controls and nothing happens then there is a wiring problem and must be fixed before messing with any other parts..

Make sure that you have continuity between the BOTTOM of the Treble and the TOP of the bass control in NON BOOST mode.

Check that the same connection is OPEN in boost mode.

FWIW, the MID control is wired backwards to my thinking....

Check the voltage on Bass and Middle Caps. The common side should read the SAME as V1a plate voltage.

Check your ground connection for the tone stack. Make sure it is truly going to ground. Reference it to your V1 cathode ground.

Let start here and see where we get.

Gary

Gary quess what...

I did not have continuity between the pots. So I followed the hybrid A schem and really tried to follow the schem and my wiring. Amazing enough I think I found one error on Normsters layout. The blue wire coming from RJ switch should go to the other side of the bass pot. At least now the tone stack works for the first time when I changed it Also the boost of the boost switch started to be in more exceptable level

I was thinking of the PI grid. It is the only place having ecc83 in it. As dogears pointed the ecc83 is not the same as 12ax7. So maybe (hopefully) that will be better after I change it to 12ax7 ?

The mid control seems to work same way as the others.

Thanks Gary

I really can't wait till tomorrow (it's 10:20PM here) to try it with proper volumes......

[dogears]

Dogears pointed out that JJ ECC83S tubes are not really 12AX7. Real ECC83 tubes are the same! Just the new JJ is not.

Please let us know how she is sounding!!

As dogears pointed the ecc83 is not the same as 12ax7. So maybe (hopefully) that will be better after I change it to 12ax7 ?

I really can't wait till tomorrow (it's 10:20PM here) to try it with proper volumes......

[glasman]

Gary quess what...

I did not have continuity between the pots. So I followed the hybrid A schem and really tried to follow the schem and my wiring. Amazing enough I think I found one error on Normsters layout. The blue wire coming from RJ switch should go to the other side of the bass pot. At least now the tone stack works for the first time when I changed it Also the boost of the boost switch started to be in more exceptable level

I was thinking of the PI grid. It is the only place having ecc83 in it. As dogears pointed the ecc83 is not the same as 12ax7. So maybe (hopefully) that will be better after I change it to 12ax7 ?

I really can't wait till tomorrow (it's 10:20PM here) to try it with proper volumes......

Ok on to the next issue. The PI. You current looks ok but the Grid voltage is a little wacked. Your total cathode current is about 2.98mA.

Make the following DC measurements.

Measure ACROSS the 820 cathode resistor. This should read about 2.4 to 3 volts.

Measure ACROSS the 24K tail resistor. Should be around 65 volts

Measure ACROSS the 390 resistor. Should be roughly between 1 and 1.5 volts.

Double and Triple check the PI wiring, especially in the area of the Cathoode and tail resistors.

Gary

[mat]

Dogears pointed out that JJ ECC83S tubes are not really 12AX7. Real ECC83 tubes are the same! Just the new JJ is not.

Please let us know how she is sounding!!

Ah, sorry dogears - I didn't know that one

[mat]

Ok on to the next issue. The PI. You current looks ok but the Grid voltage is a little wacked. Your total cathode current is about 2.98mA.

Make the following DC measurements.

Measure ACROSS the 820 cathode resistor. This should read about 2.4 to 3 volts.

Measure ACROSS the 24K tail resistor. Should be around 65 volts

Measure ACROSS the 390 resistor. Should be roughly between 1 and 1.5 volts.

Double and Triple check the PI wiring, especially in the area of the Cathoode and tail resistors.

Gary

Gary, I will measure them in couple of hours and report back. I will also put the trimmer on the 'left PI resistor'.

[mat]

Ok on to the next issue. The PI. You current looks ok but the Grid voltage is a little wacked. Your total cathode current is about 2.98mA.

Make the following DC measurements.

Measure ACROSS the 820 cathode resistor. This should read about 2.4 to 3 volts

.

With 811R resistor it give 2.12V.

Measure ACROSS the 24K tail resistor. Should be around 65 volts

With 24k9 (two resistors in series) it gives 65V.

Measure ACROSS the 390 resistor. Should be roughly between 1 and 1.5 volts.

With 390R it gives 0.94V.

Double and Triple check the PI wiring, especially in the area of the Cathoode and tail resistors.

They are as on the layout, I'll compare it to Hybrid A schem and study more.

Do You think it could be the JJ ecc83s in there? I try to get the 12ax7's today but I might not get them until tomorrow.

Thanks again,

[glasman]

Ok on to the next issue. The PI. You current looks ok but the Grid voltage is a little wacked. Your total cathode current is about 2.98mA.

Make the following DC measurements.

Measure ACROSS the 820 cathode resistor. This should read about 2.4 to 3 volts

.

With 811R resistor it give 2.12V.

Measure ACROSS the 24K tail resistor. Should be around 65 volts

With 24k9 (two resistors in series) it gives 65V.

Measure ACROSS the 390 resistor. Should be roughly between 1 and 1.5 volts.

With 390R it gives 0.94V.

Double and Triple check the PI wiring, especially in the area of the Cathoode and tail resistors.

They are as on the layout, I'll compare it to Hybrid A schem and study more.

Do You think it could be the JJ ecc83s in there? I try to get the 12ax7's today but I might not get them until tomorrow.

Thanks again,

Ok very good, the slight differences are due to the actual component values that you used. The voltages are very good.

And no, unless you have a very leaky JJ, I do not think this is the reason for the low grid voltage.

Ok so lets take a little deeper look into the circuit.

1. The grid should be drawing very little current if any current.

2. Given this, the voltage on the grid should be the same as that measured at the junction of the 811 and 24K9 resistors. ~65v.

3. Things that could cause this issue would :

- Leaky tube
- Leaky coupling caps
- Mis-wiring

4, Things to test.

- Measure the voltage between the Cathode and the grid pins.
- Measure the voltage across the 1M grid resistors
- Try lifting the coupling caps and make the same measurements. This means both the .02uf and .1uf on the PI inputs.

These might point to where the issue may reside.

Gary


PS> If anyone has any other ideas, please chime in....

[mat]

Ok very good, the slight differences are due to the actual component values that you used. The voltages are very good.

Nice to hear

And no, unless you have a very leaky JJ, I do not think this is the reason for the low grid voltage.

Ok.

Ok so lets take a little deeper look into the circuit.

1. The grid should be drawing very little current if any current.

2. Given this, the voltage on the grid should be the same as that measured at the junction of the 811 and 24K9 resistors. ~65v.

3. Things that could cause this issue would :

- Leaky tube
- Leaky coupling caps
- Mis-wiring

4, Things to test.

- Measure the voltage between the Cathode and the grid pins.
- Measure the voltage across the 1M grid resistors
- Try lifting the coupling caps and make the same measurements. This means both the .02uf and .1uf on the PI inputs.

These might point to where the issue may reside.

All right, I will measure them as You suggested the first thing on the morning (it's again evening here..).

I bought today few 12ax7's. Two Tung-Sol's, one Svetlana and one Sovtek 12ax7wb. With the sovtek I get 195V on the V1a plate. The clean sound is actually very nice The OD channel lacks the 'glassy' sound and is a bit harsh.

dogears: I haven't yet changed the clean cap from .047 to .022 but will do it also in the morning. Do You think it could tame the harshness from the OD channel ? Lots of harshness went away with the Weber C1265.

OT:
I also bought today red&white and blues speaker and WOW What a difference between that and Weber C1265. The sound is much more livelier, open and tighter. I'm _very_ pleased with the RWB.

OT2: I will go tomorrow to see George Thorogood and Gary Moore (my neighbour insists..). And after the gig our family will travel to me and my wife's home town where My father in law's guay (did check from dictionary) has collapsed, so we have to build it again. How can I leave when my clone is just finishing with the help of the pros and it starts to remind me of the Fuchs I tried in Frankfurt ... Well got to keep the father-in-law happy tho'.
So after tomorrows measuring and reporting I'll be gone for two days.

Thanks again Gary

[mat]

Hello Gary,

Here are the measurements:

- Measure the voltage between the Cathode and the grid pins.

pin3-pin2= 1.08V pin3-pin7= 1.07V

- Measure the voltage across the 1M grid resistors

left= 0.01V right= 0.01V

- Try lifting the coupling caps and make the same measurements. This means both the .02uf and .1uf on the PI inputs.

pin3-pin2= 1.07V pin3-pin7= 1.08V
left= 0.00V right= 0.01V

This is how I have the PI section \ bias soldered (there is no connection between the two 200K resistors..:

[img:617:594]http://www.pichotel.com/pic/16028B31e/41616.jpg[/img]

I looked at the HybridA schem and noticed that the trimmers viper should be connected to B+3. What kind of power rating should the trimmer have ?

How does the bias affect to the clones sound ? If it would be closer to -35mA and not the -39mA I'm having now ?

Thank You, I'll be back after two days,

[glasman]

Hello Gary,

Here are the measurements:
pin3-pin2= 1.08V pin3-pin7= 1.07V

I looked at the HybridA schem and noticed that the trimmers viper should be connected to B+3. What kind of power rating should the trimmer have ?

How does the bias affect to the clones sound ? If it would be closer to -35mA and not the -39mA I'm having now ?

Thank You, I'll be back after two days,

Hi Mat, ok very good. Conclusion is that your PI is OK. The measured delta between Grid and Cathode seems reasonable. The reason for measuring such a large delta from the grid to ground is probably due to loading from the voltmeter. This is a guess. But based on your latest mesurements the delta between cathode and grid is about volt or so. This should be fine.

As far as the bias, normally I set to a point where I am around the 70% dissipation point and adjust for the best tone. Usually with 6L6's this is somewhere between 33 and 38 ma or so.

The trimmer can be a .25W for the PI adjustments.

So, how does the amp sound?

Gary

[mat]

Hello Gary !

Hi Mat, ok very good. Conclusion is that your PI is OK. The measured delta between Grid and Cathode seems reasonable. The reason for measuring such a large delta from the grid to ground is probably due to loading from the voltmeter. This is a guess. But based on your latest mesurements the delta between cathode and grid is about volt or so. This should be fine.

Very releaved to hear that Thanks very, very much for You to walk me trough this !!

As far as the bias, normally I set to a point where I am around the 70% dissipation point and adjust for the best tone. Usually with 6L6's this is somewhere between 33 and 38 ma or so.

Ok, I will then trust to my ears (within the borders). The bias circuit seem to be ok to You ?

The trimmer can be a .25W for the PI adjustments.

All right.

So, how does the amp sound?

I like it very much I run it trough Red,White and Blues - speaker on a wooden enclosure I've built. I'm going to build 2 x 12'' box for it with matching looks.
The clean sound is very nice. Od channel starts to work better when pushed a little (tried it today on reherseals). On neigbourfriendly level it is a bit harsh. The 'glassy' sound becomes when playing louder. I would like to get it bit more 'clear' on the bass side- I will remove the shielded wires one by one and see if I can live without them.

The reverb pan is giving noise when the chasis is on the enclosure. When chasis is outside (while modding) the amp has no noise.Turning the reverb to zero, the amp is very quiet.

I was wondering how would I get more of that percussiviness to the sound, how to increase the compression of the amp ?

Very nice percussive sound (video):
http://www.fuchsaudiotechnology.com/bermanbriggs4.mpg

Very nice (big) feedback (video) without so much volume (I presume.. ) ?
http://www.fuchsaudiotechnology.com/fuc ... indemo.mpg

Also everything dogears has recorded is an inspiration to me how the amp should sound

dogears: I tried .022 as the clean cap, but it sounded 'harsher' to me so I went back to .047. I will put some caps on switch and use it to be able to swap the _middle_ cap.

I have to study the mid-boost wiring also. It is not so good as it was earlier- don't know the reason why ?

I might also try changig the PS resistor string a bit to optimize the V+'s.

Here is how it looks:
[img544]http://www.pichotel.com/pic/16028B31e/42513.jpg[/img]

I will record sounds also soon, anyone any idea where to upload them ?

Big Thanks to Normster, dogears, glasman, jazzyjoepass, Bob-I..

[mat]

Hi,

I did put 170k to ground from B+5 and noticed that the sound was better than earlier. The V+'s dropped as expected. I lovered the B+4 resistor first from 17k to 14k7 and b+5 resistor from 3k3 to 2k2. The V+'s vere still around 180V so I dropped the B+4 resistor into 12k5 and here are the plate results:

V1 193V, 203V

V2 203V, 213V

V3 452V, 192V (reverb)

PI 296V, 300V

B+1 459V
B+2 458V
B+3 435V
B+4 348V
B+5 338V

After tweaking the V+ voltage higher to me the sound appeared a little bit harsher. Should I not try to reach the 200V with the V1 plate ? (with the reverb tube and now the 170k loading down the B+5). I mean is it somehow bad for the amp to lower the dropping resistor so much ?

Thanks,