[Stone]

Hi

If the grounding of the fx loop does not change anything and the resistor tied to fx return is 1 Meg and not 1k, then I would assume a problem within preamp.

Stone, the fx/send is in ordnung. Can you please tell me which setup to make?
Both amps on Normal channel
Send SLO50 to return SLO100
Guitar in SLO50
And then?

Speaker connected to SLO100 - I think this is obligatory to say, but ... ;-) If you play your guitar then it should sound like "normal" (clean more or less) channel with standard volume.

Is there any change in sound if you switch to lead channel on the SLO50?

If I should judge by the soundfile then I would assume you have a problem with the amount of distortion - sounds like a Marshall SLP ... which has only 2 stages of distortion generation - and it has e.g. a 2n2 coupling cap.

So we are left with check of VTL optos, checking resistor values and capacitor values - and more important - checking right connection of cathodes and anodes etc., does the preamp really switch from normal to lead (or are we hearing the normal channel boosted?), etc.

Regards, Stone

[_peter]

Hi,

you said the voltages are ok - which voltages did you mesure? Could you post them, please?

If you are right and the amps dc path and the tubes are ok then you shold check the ac path,
which means especially capacitor values and the circuitry after the coupling caps of each stage.

But please go step by step and report the results so you don't generate unnecessary work for
yourself and us. That is, check the value of said resistor at the fx return and follow the divide
and conquer strategy as Stone pointed out (from one amps fx loop into the other ones and
vice versa).

Cheers, Peter

[Stone]

Hi

I listened to the sample again because I needed to be at home to have a better pair of speakers available; the second half is not that much different to the first one, except of missing bottom end (as far as I can hear through the speakers available).

It sounds like bass potentiometer turned to zero, so I would suggest beside all the other checks to have a look to the bass cap and potentiometer values.

Regards, Stone

[Guile]

Hi

If the grounding of the fx loop does not change anything and the resistor tied to fx return is 1 Meg and not 1k, then I would assume a problem within preamp.

Speaker connected to SLO100 - I think this is obligatory to say, but ... ;-) If you play your guitar then it should sound like "normal" (clean more or less) channel with standard volume.

Is there any change in sound if you switch to lead channel on the SLO50?

If I should judge by the soundfile then I would assume you have a problem with the amount of distortion - sounds like a Marshall SLP ... which has only 2 stages of distortion generation - and it has e.g. a 2n2 coupling cap.

So we are left with check of VTL optos, checking resistor values and capacitor values - and more important - checking right connection of cathodes and anodes etc., does the preamp really switch from normal to lead (or are we hearing the normal channel boosted?), etc.

Regards, Stone

Signal is clean, but as I said, very low volume (not standard).
I think the amount of distortion is not the problem. The recording is every pot at 12:00 (not preamp and master). It switches normally from clean to lead.

I checked every resistor and cap visually and tested resistors with multimeter and (unfortunately) all is according schematic/layout.

I'm beginning tot get tired of this amp. I rewired most of the spaghetti and believe it or not, it sounds even more shrill then before.

Anyone wants to buy this piece of shit?

[_peter]

Dude,

you need to operate more systematicly when troubleshooting.

How about the voltages - are they still in place? What are they? If you don't give us the necessary information
we're just guessing. Looking at the burnt resistor on the power amp board I start to believe that it's more than
an error in the singal path. Something is drawing too much current or the resistor is weak.

Cheers, Peter

[Stone]

[...]
Anyone wants to buy this piece of shit?

It depends on the price you try to get.

Basically I am interested.

If you have checked all resistors, caps, etc. there must be a problem with the wiring - if you have shortened some wires and the problem increased I guess the error / fault is located somewhere next to the changed cabling.

On the other hand side - and I am far away from being a wiring and layout expert - it is important e.g. to have heater wires installed accurately otherwise you will get all sort of noise, first of hum, keep wires to grids and anodes as short as possible, some people recommend to tie them together, shielded cable for input, fx loop,  first stages grids, correct connection of shield and so on.

Sometimes - to get away a little bit of the wiring - it is a pretty little error you have overseen or an effect you did not think about in any way and most times their reason is pretty simple.

What I remember if it comes to low volume and less bottom is a Marshall 2210 I got some years ago for repair - one of the B+ resistor (10k) was faulty. After 2 or 3 minutes the amp became quiet, the sound was close to your sound sample. It turned out that the resistance of the faulty resistor increased during operating time - took around 10 minutes to find it, because I started measuring voltages.

I will have a look to the pictures again - maybe I can find some things more; updated pics would be fine. But if you like, you can make me an offer for the 50 one.

Regards, Stone

[Guile]

Dude,

you need to operate more systematically when troubleshooting.

How about the voltages - are they still in place? What are they? If you don't give us the necessary information
we're just guessing. Looking at the burnt resistor on the power amp board I start to believe that it's more than
an error in the signal path. Something is drawing too much current or the resistor is weak.

Cheers, Peter

I appreciate the comments guys.

Resistor is not burnt. What you see is the residue of my capacitor discharger that got burnt when I forgot to take it out. The amp sounded already bad when that happened.

These are the voltages:
V1
1 228
2
3 2
4
5
6 159
7
8 1.4
9

V2
1 228
2
3 1.9
4
5
6 300
7
8 4.4
9

V3
1 360
2 173
3 193
4
5
6 174
7
8
9

V4
1 360
2 153
3 158
4
5
6 141
7
8 2.4
9

V5
1 227
2 13
3 40
4
5
6 237
7 12.3
8
9


In general the tone stack acts weird:
Bass: does not add bass but adds mids
Middle: adds more fullness and bass
Treble: adds highs
Presence: adds (earpiercing) highs but only after 15:00
Depth: adds depth, but not much.

I will now measure all of the resistors of the SLO100 and compare with the SLO50 (again)

Hopefully this information helps to find something!
Thanks in advance.

[Stone]

Hi

Check the resistor and ground connection of that at V3b, pin 8. You wrote down any value, but you should have something around 1,5 volts and 2,0 volts. There must be current flowing through the triode, because you have a voltage on pin 6, which is lower than B+, but no value indicates a rather high value (and multimeter was set to low) or another fault.

Also have a closer look to V4b - pin 6 and pin 8. Measured value for pin 6 is a little bit low, also value for pin 8 seems to be a little bit.

If the tonestack is not behaving the way we expected it to do, check the wiring of the potentiometers and also their values and type (mixing up linear and log type is a common fault).

[Stone]

[...]
I will now measure all of the resistors of the SLO100 and compare with the SLO50 (again)
[...]

This must be more detailed ... if you are measuring cathode resistors, e.g., you need to measure resistor to ground (chassis) because this will tell if the resistor has a ground reference.

What I cannot figure out on the pictures: how are the speaker jacks connected to ground? (<= and this is pretty important!)

Regards, Stone

[_peter]

Hi,

Resistor is not burnt. What you see is the residue of my capacitor discharger that got burnt when I forgot to take it out. The amp sounded already bad when that happened.

ok, I understand.

There is a 20V difference between the grid and the cathode of V3A -> there must be something wrong
or the measurement is incorrect.

At V4 you measured 153 at the cathode followers grid but 141 at the feeding anode. 

Are your voltages jumping up and down during measuring?

Cheers, Peter

[Stone]

[...]
At V4 you measured 153 at the cathode followers grid but 141 at the feeding anode. 
[...]

That 's what I had in mind ... thanks for clarifying.

Regards, Stone

[Guile]

Hi

Check the resistor and ground connection of that at V3b, pin 8. You wrote down any value, but you should have something around 1,5 volts and 2,0 volts. There must be current flowing through the triode, because you have a voltage on pin 6, which is lower than B+, but no value indicates a rather high value (and multimeter was set to low) or another fault.

Also have a closer look to V4b - pin 6 and pin 8. Measured value for pin 6 is a little bit low, also value for pin 8 seems to be a little bit.

If the tonestack is not behaving the way we expected it to do, check the wiring of the potentiometers and also their values and type (mixing up linear and log type is a common fault).

You are correct
V3b - pin 8: 1.4
V4b - pin 6: 252
V4b - pin 8: 1.4

I checked the wiring of pots and their values and did not find errors.

The speaker jacks are connected to ground on the chassis.

[Guile]

V4 looks problematic:

1: 352
2: 184 to 177 to 172
3: 208 to 198 to 194
4/5:
6: fluctuated a lot 222, 214, 189 and 130 so I put a new tube in. Started at 170 then 188 then 173. Standby switched off and on 209
7:
8: 1.5
9:

[_peter]

Do the dc voltages at V3 and V4 change when you toggle the fx bypass switch?
(Then you have a faulty capacitor in the tone stack.)

Cheers, Peter

[Guile]

They definitely do, all of them drop to zero when bypass is to 'off'