SLO-50 clone 100hz hum on OD channel?

Spenzer Lee Horton said:
tapping pin 7 which has 33k resistor from input results in squeal city!!!
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Swap in another tube in there. Rule out a bad tube!

Spenzer Lee Horton said:
voltages are as follows:
V1
pin1= 255v
pin3=1.87v
pin6=179.3v
pin8=1.3v

V2
pin1= 247.9v
pin3=1.76v
pin6=334v
pin8=3.81v

V3
pin1= 362v
pin3=193v
pin6=190v
pin8=1.39v

V4
pin1= 198.2v
pin3=198v
pin6=195.6v
pin8=1.66v

V5
pin1= 235.6v
pin3=41.7v
pin6=239.4v
pin8=41.5v
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Lot of your posted voltages are OK, but you're missing some voltages...: Pin 2 of V3, pin 2 of V4, and remeasure pin 1 of V4: It should measure around 370v.

Voltage chart from C3 Amps:
SLO50 Operating Voltages.jpg
 
Spenzer Lee Horton said:
No im fine with pdf files
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Ok, I'm going to PM you some stuff in a while.
.
Spenzer Lee Horton said:
im wondering whether its the output txf primaries that need swapping? but i remember this being a lower sound before?
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I just noticed this part of your post. Out of phase OT primaries can definitely produce an insane high-pitched squeal

Spenzer Lee Horton said:
Jack input socket and fx loop socket should be isolated from chassis right?
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Instrument input jack, and the In and Out fx loop jacks need to be isolated.
The Slave jack, Footswitch jack, and the speaker jacks need to be grounded at the chassis.
 
i swapped the output txf primaries and then turned on, a huge squeal of epic proportions erupted as soon as the master was turned, so i had it the right way.

will test all the voltages again and check its all about right
 
at the moment i have grounded the fx loop shielded cable to the 10uf gnd cap leg, i will move this to the shield of the send cable on the main board where it is shown on the diagram, i dont think this is a major problem but might make a difference.

quick question: on OD channel with master at noon, should i be able to have guitar fully turned up and be about 6 foot away and turn gain up to 3pm without it squealing?
 
100Rs gnd on heaters.jpg

i noticed two extra resistors and a cap on the 100Rs on the heaters to gnd?
whats the values here and what is going on?

looks like a 100k and under the blue cap could be 100k or a 1meg?
 
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Have check all preamp valve voltages and are all pretty close to voltage sheet.

II had NFB to 4 ohm but on the line out, I had a 470k off the 8 ohm tap which I’m using to the line out rather than 47k and connected to the 4 ohm!

Now I’m not getting the squeal when I turn up but, i can’t change channels now? And there is a huge hum!!!
Sounds like a gnd issue.

Where exactly on the main board should I take the gnd from the fx loop?

Right tested which are gnd points and put everything back and apart from the hum both channels are working.

When unplugging the jack from the input the hum goes and just a little hiss remains.
If I turn up the normal channel master volume I get to about 7 then it starts to squeal?
Worse on OD channel?
 
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V1 and v2 sound microphonic so Ive swapped them for another pair, now all preamp valve when tapped are not microphonic but squeal still happens on both channels without guitar or anything on input?
 
fired up my Jose Plexi and put Quad Cortex through the FX loop and pedals in the input and no hum or buzz, sounds great!!!

Potential Internal Issues
If the problem persists and is not external feedback or a simple bad tube:
  • Parasitic Oscillation: This is an internal circuit issue caused by unintended signal paths or bad wiring layout. The signal loops back on itself for further amplification, leading to a high-pitched whine.
  • Bad Filter Capacitors: Failing filter caps in the power supply can cause various noise issues, including squealing, as they can no longer properly smooth the voltage.
  • Potentiometer (Pot) Cleaning: While a squeal is less common for a dirty pot (they usually produce crackling or static), a serious issue with the master volume pot's internal workings could contribute to noise.
  • Grounding Issues: Faulty grounding can lead to various hum and noise problems.
 
so back to the SLO-50, now when i wiring in the quad cortex to the SLO-50 fx loop, when i put a loop in on the QC the level changes as i change channels, i think i need to put the FX loop in a different place, or the wiring is wrong?

im going to trace the signal path now and see whats actually going on!!
 
Spenzer Lee Horton said:
Yep jack wise everything is correct, where do you take your gnd for the fx loop jacks?
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Look at the Effects Loop file and the Component Layout file that I sent you. The ground of both shielded wires and both effects loop jacks will be grounded at a single point in a grounding plane that’s in the middle of the main circuit board.

Spenzer Lee Horton said:
quick question: on OD channel with master at noon, should i be able to have guitar fully turned up and be about 6 foot away and turn gain up to 3pm without it squealing?
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I’m going to have to try this myself, but even with the master volume at 50%, the amp is going to be outputting maximum volume. And with the gain control set that high and the guitar only six feet away, I’m expecting mayhem!

Spenzer Lee Horton said:
View attachment 108350

i noticed two extra resistors and a cap on the 100Rs on the heaters to gnd?
whats the values here and what is going on?

looks like a 100k and under the blue cap could be 100k or a 1meg?
Click to expand...
That’s a known Elevated Heater’s mod for the Soldano SLO circuits. Its minor purpose is to reduce AC heater hum. Its main purpose is to lessen the stress of the preamp tube that operates a cathode follower circuit with high voltages at its cathodes. That would be the V3 and V4 tube in this circuit.

Spenzer Lee Horton said:
Parasitic Oscillation: This is an internal circuit issue caused by unintended signal paths or bad wiring layout. The signal loops back on itself for further amplification, leading to a high-pitched whine.
Click to expand...
My money is on this! Well engineered lead dress on a high-gain amp is crucial. Your wiring on your amp is a bit ratty, and it could be the cause of parasitic oscillation if it’s occurring in your amp.
 
yes all sounds really good now apart from when i put on the looper with the quad cortex, where the loop is effects what channel im on, say if i put a clean loop in, then try and play some lead over it, when i change from clean to OD, the loop is then distorted and sound mushy and lower in volume.
 
Spenzer Lee Horton said:
I think ive just realised whats wrong!! speaker jacks are isolated rather than to chassis!!!??
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You probably had them grounded with a wire towards the power supply area. I see a wire connected to the sleeve of the extension speaker jack, and it seems to disappear somewhere by the power supply board.
 
yes it was grounded to the heater gnd!!
its just a bit hissy now, pretty sure this is how its going to be with overall situation with it, next i will change filter caps, lead dress is a bit better.
Also will change the 1N5408 to UF5408 as they are meant to be a little better.

whats a good tube to have in V1 as this seems to the one on edge, is there less microphone prone 12AX7 variant? ive got JJ's whatever i put in V1 ends up being quite microphonic.
 
Spenzer Lee Horton said:
whats a good tube to have in V1 as this seems to the one on edge, is there less microphone prone 12AX7 variant? ive got JJ's whatever i put in V1 ends up being quite microphonic.
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Whether you like to go with New Old Stock tubes or modern production tubes, you need a dependable and honest vendor that properly tests its inventory and can provide you with what you’re looking for. I’m as(s)uming you’re located in the United Kingdom. Do you know of a vendor that you can trust?
 
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