Blues Deluxe to ODS #183 Thread

[sluckey]

If you want to eliminate everything on the input, just put a ground clip directly on the tube grid pin.

I think you overlooked this part. If the ground clip does not kill the oscillation, then look elsewhere.

[pompeiisneaks]

If you want to eliminate everything on the input, just put a ground clip directly on the tube grid pin.

I think you overlooked this part. If the ground clip does not kill the oscillation, then look elsewhere.

Isn't that the same thing as having a switched jack that works? If I have the switched jack in and it works (I just replaced the jack, and there's no oscillation with input grounded) then that's the same no?

or is there something else that directly grounding the grid pin does that I'm not?

I have also verified grounds are good and signal is back in operation, and I'm definitely getting the oscillation/squeal with any guitar and with two different cables. So it seems to be getting worse.

Not sure what's next... I've continued trying moving wires, tapping things etc to see if anything changes it, nothing does, with one exception, when I was touching the input wire that connects into the grid, it does make a slight amount of change to the noise, but just changes it, not removes, make it better or worse, etc, just a change in tone slightly. All the pots/switches etc will impact it's tone a bit, except bass but I think it's too high for bass to be involved.

W/O drive, though its super clean...

~Phil

[pompeiisneaks]

okay, maybe I've been overthinking this too much...

I have the normal volume at max, drive at max and drive master volume at max and am getting this issue. I wasn't thinking too much about it at first, but the normal clean tone, at max volume and at decent master volume is really driven already... maybe this is just expected?

If I dial the clean volume down to about 9, and the drive to 9 and the master up quite a bit, it works great. Am I just giving it too much from the first gain stage?

~Phil

[JazzGuitarGimp]

Hi Phil,

I’m curious where the od entrance trimmer is set. With power off & caps discharged, can you measure the resistance from the center pin of the trimmer to ground?

[pompeiisneaks]

Hi Phil,

I’m curious where the od entrance trimmer is set. With power off & caps discharged, can you measure the resistance from the center pin of the trimmer to ground?

I'll see if I can get that, but basically I get the oscillation shortly after I start getting sound if I turn the trimmer down so low that the sound cuts out. Once I get volume out, the drive is pretty weak, then it goes into 'here's some drive AND a heap ton of oscillation for you' as soon as I get maybe 1/3 of the way up the pot. There were none of your type of pot available, so I'll have to see if I can find the connected components for the reading, the pots I have cover the solder points very well.

~Phil

[pompeiisneaks]

I've set it when connecting one end of my DMM to ground and the other to R15 so that I get about 22K right now. I can't play it tonight, as it's late enough that I'd wake someone I'm sure.

I'll check it tomorrow at that point.

~Phil

[pompeiisneaks]

Okay I was able to fire it up. If I keep the clean volume below 10, say 9 (this is a fender with 12 being max volume) I can push the drive volume up to also about 9 before the oscillation starts. If I dial the clean volume back to maybe 6 I can almost go to 12.

If I dime the drive, I have to turn the clean volume down to about 3 to keep it from oscillating and it still has a pretty heavy buzz.

if I dime the clean, I can't turn the drive over about 9 before it starts to buzz and goes into oscillation.

If this is basically 'expected' for a 183, then maybe that's fine.

This is, with the resistor set as my last post.

I did have a side question, I think I asked before, but can't recall now. I used the EL34 based NFB values and the EL34 grid stoppers on these 5881's (and for future potential 6L6's) is that okay? Should I adjust the NFB resistor to say 820ohm like the other 50W styles of the dumble or is 4.7k fine? I'm guessing it just means it has a bit 'less' negative feedback with the higher resistor inline? And for the grid stoppers, I think they more commonly used 2.2k in those, is 5.6 still fine?

~Phil

[xtian]

If this is basically 'expected' for a 183, then maybe that's fine.

It's not. I have built three, and still have one hand-wired 100w EL34 #183 in the house, and my HRD conversion using 6L6 built with Rev A of the PCB. On all amps, I can dime all the controls (keeping master volume low) and get no oscillation.

I did have a side question, I think I asked before, but can't recall now. I used the EL34 based NFB values and the EL34 grid stoppers on these 5881's (and for future potential 6L6's) is that okay? Should I adjust the NFB resistor to say 820ohm like the other 50W styles of the dumble or is 4.7k fine? I'm guessing it just means it has a bit 'less' negative feedback with the higher resistor inline? And for the grid stoppers, I think they more commonly used 2.2k in those, is 5.6 still fine?

On my 100w EL34 hand-wired #183, I have 5K6 grid stops and 4K7 gNFB off the 8-ohm tap, which matches the #183 schematic by "jaysg" rev 1.3 dated 12/02/2010.

On my 40w 6L6 Rev A PCB #183, same 5K6 grid stops, and gNFB is taken from the 4-ohm tap, with the Bluesmaster gNFB arrangement shown in "100W HRM in BluesMaster Style" schematic by "mdroberts1243" rev 0.99 dated 12/20/2007.

I never gave a second thought to the gNFB, just followed the schematics.

[pompeiisneaks]

The final video... first power on, and demo.




If you want to skip to the demo, the skip to 14:39

Also, I'm still open for other troubleshooting ideas on the oscillation

~Phil

[didit]

Also, I'm still open for other troubleshooting ideas on the oscillation

Post some close up photos? Often easier to spot any err wires etc what make for the unwanted signals.

Best .. Ian

[pdf64]

I’ve already put forward my thinking that the layout, specifically the proximity of the tube socket (and the associated wiring) that deals with the 1st 2 stages to later stages, is the cause of the oscillation issue.
Look at how it differs to the HRDeluxe that the board was designed around.
I suggested some measures that may help to mitigate this.
It would be the work of a few minutes to try them out

[pompeiisneaks]

I’ve already put forward my thinking that the layout, specifically the proximity of the tube socket (and the associated wiring) that deals with the 1st 2 stages to later stages, is the cause of the oscillation issue.
Look at how it differs to the HRDeluxe that the board was designed around.
I suggested some measures that may help to mitigate this.
It would be the work of a few minutes to try them out

I must have misunderstood them, because i tried them and it didnt' change anything, I also asked a question about it and you didn't clarify.

Please do help me understand.

I tried adding a 33k resistor at the jack instead of the tube grid, that changed nothing
I didn't desolder the grid wire and wrap it around the anode wire, but i tried wrapping them around one another with the amount of free lead I have available, to no change.
I didn't understand why swapping the leads of V1a and V1b would help since that would require crossing the leads over one another (the preamp V1b section is the first input stage and is closer to the right half of the triode). Won't that add cross triode noise? Is there a benefit/detriment of having V1a or V1b as the 'first stage'???

I've connected a screenshot of the board with my super powers of microsoft paint to show how it's currently wired, and to understand how crossing two triodes leads over one another 'reduces noise' I'm also very new to the idea of twisting the grid with the anode for noise rejection, but i can desolder and try, except that my wires may be too short for this. (Also for the first stage the shielded wire may make that somewhat pointless no?)

CurrentConnections.png

Again, I'm probably misunderstanding your requests, but I did try to do some level of attempting them.

maybe xtian can confirm if he's seeing the same issue on his build?

Or are you just saying I have the first two triodes too far away from the actual board wire connection points?

At any rate, please do help me understand what I've missed.

Post some close up photos? Often easier to spot any err wires etc what make for the unwanted signals.

Best .. Ian

I've got some one or two pages back when I first was asking about this, are those not close enough or the right area? https://ampgarage.com/forum/viewtopic.p ... 50#p405333

~Phil

[talbany]

Phil
Given that your amp is laid out differently and on a PCB board and in that smaller tweed style chassis god knows where it's coming from . A few questions?. Did you put the snubbers on the tube sockets on V2 or did I miss that? You can also put a snubber across the PI plates up to 100 pF and try to kill it there.Without detailed shots of your lead dress and a layout of your PCB board it's really hard to tell IMO..

BTW. Although that amp sounds nothing like the 183 the video was fun to watch

Tony

[pompeiisneaks]

OH OH OH!!!

That's it! (or so I hope). There are no snubbers on V2! There's a 47pF across the PI anodes yes. I'll see if I haev any ceramics of that in stock and give it at try!

~Phil

[xtian]

maybe xtian can confirm if he's seeing the same issue on his build?

No, no oscillation at all in my HRD > ODS build, though that's using the Rev A board.

I've just received my donor Carvin 100w, so will be working on a new build using the Rev B board next week.