Blues Deluxe to ODS #183 Thread

[pompeiisneaks]

of course I have none.... I'll see if I can hop over to the local electronics shop tomorrow and find some 25pF ceramic caps.

~Phil

[xtian]

hop over to the local electronics shop

Great gravy! You have one of those?!?

[pompeiisneaks]

Yup, love it, it's full of all kinds of random cool stuff, called vetco electronics. I still find some NOS mallory stuff there, but it's always way outta what I need like 100000uF at 10v or some odd crap like that. They do have a lot of older stock resistors as well, I've seen boxes full of allen and bradley but they're all one value and something I've nott usually seen in tube amps like 25ohm or some useless value like that no 1.5k or 100k etc. They also have a lot of what i think are Piher or the like the really big brownish red ones, but also in random odd values I've never needed. I've bought a few grab bags from them and it's had some cool stuff, that I can never really use

They did just close down their upstairs area that had a ton of old things like scopes, frequency counters etc. but they seemed to always have them at a pretty steep price so I never did buy any. One exception was an old scope I bought for 20 bucks that's broken to see if I can get it working again, but I can't find the service manual for it

~Phil

[pullshocks]

Yeah Vetco electronics is awesome, the only local electronics shop left in greater Seattle that I know of

[talbany]

of course I have none.... I'll see if I can hop over to the local electronics shop tomorrow and find some 25pF ceramic caps.

~Phil

Phil
In that amp I would use 2 250pF caps instead of the 25's

Tony

[pompeiisneaks]

of course I have none.... I'll see if I can hop over to the local electronics shop tomorrow and find some 25pF ceramic caps.

~Phil

Phil
In that amp I would use 2 250pF caps instead of the 25's

Tony

Good to know, thanks!

Is that because of how much you're hearing, or just because you've seen the #183 need the higher capacitance?

Cheers!

~Phil

[pdf64]

Other mitigation could be a screening plate, between V1 socket and the wiring to it, and the circuit board.
Similar to that behind the input jacks on an AC50.

Or remount the V1 socket to be adjacent to the wire points on the board.

[talbany]

is that because of how much you're hearing, or just because you've seen the #183 need the higher capacitance?

No it's because your amp is oscillating. IMO once you went with a PCB layout, put it in a different chassis style went with a 50 watt and used completely different parts types I don't really consider your amp a 183 anymore.it's another amp that shares the 183 circuits. Nothing wrong with that it just requires a different approach. Your amp is really IMO a one of a kind
"The circuit is just another piece to the sonic puzzle"
Tony

[pompeiisneaks]

is that because of how much you're hearing, or just because you've seen the #183 need the higher capacitance?

No it's because your amp is oscillating. IMO once you went with a PCB layout, put it in a different chassis style went with a 50 watt and used completely different parts types I don't really consider your amp a 183 anymore.it's another amp that shares the 183 circuits. Nothing wrong with that it just requires a different approach. Your amp is really IMO a one of a kind
"The circuit is just another piece to the sonic puzzle"
Tony

Got it.

It didn't help. I'm not sure if I got the right kind of ceramic caps, but they don't have a clear name anywhere as to what kind they are. They were like 240pF or 270pF I can't recall but they didn't have 250. I'm sure that shouldn't matter much.

So much for that fixing it I've gotta go out of town for the week so I'll not be able to do anything with it until then /sigh.

~Phil

[talbany]

is that because of how much you're hearing, or just because you've seen the #183 need the higher capacitance?

No it's because your amp is oscillating. IMO once you went with a PCB layout, put it in a different chassis style went with a 50 watt and used completely different parts types I don't really consider your amp a 183 anymore.it's another amp that shares the 183 circuits. Nothing wrong with that it just requires a different approach. Your amp is really IMO a one of a kind
"The circuit is just another piece to the sonic puzzle"
Tony

Got it.

It didn't help. I'm not sure if I got the right kind of ceramic caps, but they don't have a clear name anywhere as to what kind they are. They were like 240pF or 270pF I can't recall but they didn't have 250. I'm sure that shouldn't matter much.

So much for that fixing it I've gotta go out of town for the week so I'll not be able to do anything with it until then /sigh.

~Phil

Phil
So the amp oscillates exactly the same way it did before you installed the caps? (no change at all). This would lead me to believe it's either coming from another part of the amp or that it's so bad it rendered the snubbers completely ineffective at suppressing oscillations in the OD side (rare)
BTW. If a 240 does nothing I doubt a 270 will fix it. IMO
Good Luck!

Tony

[JD0x0]

Get a whole bunch of value caps from 180p to ~680p (Make sure they're high voltage, too). The snubbers are great for tuning out any overdrive 'fizz'
You can also use many of those values for 'treble caps' in tonestacks, bright caps and treble peaking networks (grid stopper bypass caps), so they do come in handy.

FWIW I have a higher gain ODS* that remained very stable even before I added the snubbers, and the stock grid stoppers should also help with stability, so personally, I don't think these circuits should really require the snubbers to be stable. Did you confirm your voltages?

*Just to expand, this ODS has more gain than any high plate, and uses a high voltage FET stage using an LND150 that further increases gain. It's a gain monster, IMO, but remains stable even with my admittedly slightly sloppy hand wiring and additional mods I tried to stuff into the amp.


BTW, (and not to doubt the PCB builder, but flaws and QC issues do happen) have we confirmed this revision of the PCB is stable? I know this is kind of an 'in development' product, so there may be kinks that need to be worked out still.

[pompeiisneaks]

Get a whole bunch of value caps from 180p to ~680p (Make sure they're high voltage, too). The snubbers are great for tuning out any overdrive 'fizz'
You can also use many of those values for 'treble caps' in tonestacks, bright caps and treble peaking networks (grid stopper bypass caps), so they do come in handy.

FWIW I have a higher gain ODS* that remained very stable even before I added the snubbers, and the stock grid stoppers should also help with stability, so personally, I don't think these circuits should really require the snubbers to be stable. Did you confirm your voltages?

*Just to expand, this ODS has more gain than any high plate, and uses a high voltage FET stage using an LND150 that further increases gain. It's a gain monster, IMO, but remains stable even with my admittedly slightly sloppy hand wiring and additional mods I tried to stuff into the amp.


BTW, (and not to doubt the PCB builder, but flaws and QC issues do happen) have we confirmed this revision of the PCB is stable? I know this is kind of an 'in development' product, so there may be kinks that need to be worked out still.

Thanks both to Tony and you JD0x0, I haven't confirmed yet that it's related to the PCB, but xtian built several including a #183 component based build on the older rev with no issues. He's building one now as well. when I get back this weekend, I'll try tracing the oscillation on my scope to see if I can narrow down where it's appearing. I was first looking for obvious component problems by chopsticking or anything else I'd missed. it's so odd that it works so well all the way up to the top end of the drive then starts oscillating.

xtian is about to build one with this REV B board so maybe he'll have some insight after? It does seem to be, on the clean side w/o OD engaged I have a lot of gain already. Like maybe somethings setup so that the first triode is just really strong? not sure? I've tried swapping around a few tubes though with no change either... Next maybe is just a component level check to make sure I didn't do something silly there as well.

the 183 is a high plate model, I thought high plate meant cleaner tone and less gain on the clean side of things no? or is it expected to be pretty driven at no OD and volumes up near the top end?

That's where I keep thinking things may be too 'hot' is the first stage...


~Phil

[JazzGuitarGimp]

If my understanding of High Plate is correct (and it may very well not be), the High Plate models have higher values of plate load resistors in the preamp stages (when compared to the standard Fender value of 100K). This increases gain in the preamp stages.

[pompeiisneaks]

If my understanding of High Plate is correct (and it may very well not be), the High Plate models have higher values of plate load resistors in the preamp stages (when compared to the standard Fender value of 100K). This increases gain in the preamp stages.

Although I think increasing the anode resistor changes the point in the curves where it is active, the gain of the stage is more impacted by the cathode resistor which is raised up to say 2.2k or 3.3k instead of the stock/common values of say 820 ohms to 1.5k. Or am I misunderstanding the way that works? I know if you keep the 100k anode and lower the cathode it definitely increases gain, and raising it decreases gain.

~Phil

[JazzGuitarGimp]

I think it’s more about the ratio of the anode resistor to cathode resistor. Taking the anode resistor up to 330K would bring the cathode resistor up to 5K to maintain the same ratio of 100K:1.5k. Any cathode resistor lower than 5K (with a 330K anode load) will increase gain. Someone, please stop me in my tracks if I am upside down. And, of course, bypassing the cathode resistor with 4.7uF cap will effectively lower the value of the cathode resistor (thus increasing the gain) from DC up to the cutoff frequency specified by the parallel combination of the two. And the cutoff frequency increases as the cathode resistor increases. So a 4.7uF cap across a 2.2K resistor will extend the low frequency gain further up toward the midrange frequencies than a 4.7uF cap across a 1.5K resistor.