Blues Deluxe to ODS #183 Thread

[JazzGuitarGimp]

Additionally, the bias point of the preamp stages will have an impact on the perceived headroom, or cleanliness. If the bias point sits either hot or cold of center, the stage will break up into distortion earlier, or at a lower signal voltage. If the design intent is for a high headroom, clean sound, all the preamp stages in the clean channel should be biased very close to the center point of the load line.

[xtian]

Phil, in the several #183s I've built, including the Rev A ODS->HRD build, the clean channel barely reaches "crunch" territory with the Volume control maxed, even when playing humbuckers. So if you're getting a high gain sound on the clean channel, that would be very out-of-spec.

Definitely check and re-check your anode and cathode resistors for V1 stages.

[JD0x0]

Phil, in the several #183s I've built, including the Rev A ODS->HRD build, the clean channel barely reaches "crunch" territory with the Volume control maxed, even when playing humbuckers. So if you're getting a high gain sound on the clean channel, that would be very out-of-spec.

Definitely check and re-check your anode and cathode resistors for V1 stages.

Interesting, I have a high plate (albeit not 183 spec), skyliner that I thought got pretty saturated on the clean channel with the LNFB lifted. I do tend to run the mids high and mid boost on, in 'rock' setting, so the stack is a bit less lossy, and it has the gainier PAB. I ended up going to a more 'mid plate' biasing and kept the LNFB to keep the clean channel from breaking up so much. The high plates seemed to have more harmonic distortion and compression compared to the low plates, IME. If I'm not mistaken 100k/1.5k it's supposed to be fairly close to center biased with the B+ voltages typically seen in D and F style amps. The higher plate load gives a more horizontal load line, if I'm not mistaken.

Something is definitely afoot in Phil's amp because even with all the gain and clipping these things produce when dimed, I've never had the amp oscillate, like that. Just a note, if someone were to accidentally use a 33k or 22k cathode resistor in place of a 3.3k or 2.2k that'd create one gnarly cold clipper stage, which has its cathode more or less fully bypassed, which is likely to oscillate, but might sound ok at more tame settings.

[xtian]

Should have specified in my post: clean channel with no mid boost, no PAB boost, Rock tone stack. This is what I would call "default" state for the clean channel. Certainly there is some harmonic warmth when you crank the Volume in this mode, but not what I would call AC/DC overdrive, and certainly not high gain.

Actually, the Low input on my '83 JCM 800 is similar. Crank the Volume and you've got nice round warmth, but no crunch.

[pompeiisneaks]

all great info, thanks! yeah JazzGuitarGimp, that's pretty much how I understood it too. I think the High Plate does increase the anode AND cathodes pretty much equally to just get the tube into a different but similar region on the tube curves.

I'll triple check all the V1 components, make sure I've not done something bone headed there as well, because I mean it's got some strong drive (not quite AC/DC levels) on V1 in rock mode etc. crunchy to say the least!

~Phil

[pdf64]

Is a schematic and pcb layout/overlay available? No luck tracking them down after trying for a while.

[pompeiisneaks]

Is a schematic and pcb layout/overlay available? No luck tracking them down after trying for a while.

There are, yes, JazzGuitarGimp has made them, not sure if they're being readily shared or if, due to the fact that they're still mid design, he's waiting until a more solid version is ready... but it IS based off the BluesMaster as far as I recall, but I changed the bulk of the signal path stuff to mirror the #183. Of course it has HRM, which the #183 didn't have, and a mid pot on the PAB switched ground area, but otherwise it's almost a #183. Another major difference of course is the use of 6L6GC/5881 in the output section instead of EL34's.

JazzGuitarGimp are you planning on sharing the docs for these?

~Phil

[xtian]

The power tubes and grid stops are off-board, so it’s up to you what power tubes you use.

[pompeiisneaks]

The power tubes and grid stops are off-board, so it’s up to you what power tubes you use.

Agreed, but the output transformer was setup for the tubes I have. I don't know that it could handle el34's in the blues deluxe.

Phil

[JazzGuitarGimp]

I can’t figure out how to post the schematic from my iPad, but I will post it here when I am home later tonight.

Latest schematic is attached. Page 1 represents the PC Board only and Page 2 details the chassis power amp wiring.

Cheers,
Lou

[talbany]

Is a schematic and pcb layout/overlay available? No luck tracking them down after trying for a while.

There are, yes, JazzGuitarGimp has made them, not sure if they're being readily shared or if, due to the fact that they're still mid design, he's waiting until a more solid version is ready... but it IS based off the BluesMaster as far as I recall, but I changed the bulk of the signal path stuff to mirror the #183. Of course it has HRM, which the #183 didn't have, and a mid pot on the PAB switched ground area, but otherwise it's almost a #183. Another major difference of course is the use of 6L6GC/5881 in the output section instead of EL34's.

JazzGuitarGimp are you planning on sharing the docs for these?

~Phil

Phil
Does your amp have seperate masters for clean and overdrive ala Bluesmaster and did you use the OD entrance network for 183 or the stock Bluesmaster low gain network?

Tony

[pdf64]

Sorry if you’ve answered this already but do any of the tonestack or the VR4 vol control settings affect the whistle?
Are C31 and R10 values as per the schematic?
Sorry, I’m using my iPhone and am having trouble finding photos showing V1 wiring and the pcb together; please could you include a link directly to the photo or the post that includes a photo link?

[pompeiisneaks]

I'm still out of town, so I'll have to get more detail when i get back this weekend.

The amp has a 'volume' and a 'master volume' and a 'drive volume'. I'll have to double check what I used for the OD entrance. I think I kept that the same as the #183 and just added in the components for the HRM as the bluesmaster called for them (where they didn't exist in the #183) but I can look and let you know soon.

As for the photo's of hte V1 I'll get some more specific photos that show the leads and components etc, well lit all that.

Sat or sunday.

~Phil

[pompeiisneaks]

Okay haven't had time to power it up and do scope stuff, but I did just measure the resistors.

They all read as follows, matching the #183 precisely.
V1a
A: 220k
C: 3.3k
G: (33k I swapped this due to breaking the 22k lead, but that should just attenuate signal a bit more right?)

V1b
A: 150k
C: 2.2k
G: 220k couple4d with the 500p Ceramic in parallel

I also have the expected 150k for the entrance to the tone stack and all the caps there toherwise seem right. I have the 100k to the jazz switch side as well.

So no clear reasons there why I'd have higher gain on that first triode... hmm, I wonder if it could be at the PI?

Does anyone know, when I get to the scope, what say a 4-500mA 1000Hz signal shoudl be at in VAC when it gets out to the section just before the switch to OD/Direct to PI?

~Phil

[pompeiisneaks]

Here are the pics of the input section and board components:

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20191207_171233.jpg

20191207_171247.jpg

20191207_171243.jpg

20191207_171238.jpg

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20191028_141617.jpg

20191028_141608.jpg

Edit: the lower pictures are of the whole thing when I took them before any attempts to mod it, the top few are as it is now.

~Phil