First Stage Filtering

[Funkalicousgroove]

What are you guys liking for your first filtering stage 50uf, 100uf or 150uf? I usually like 50 (2x100uf caps) but I played in a place with dirty line voltage the other night (like 109 coming out of the wall at GOD KNOWS what frequency) and I was getting ghost tones like an underfiltered amp, I am wondering how much "Stiffer" the amp would be if I went up to 100-150uf to try and correct that possibility?

[dogears]

Was it a 100 watt amp?? I would go with 50uf on the 50 watters and 110uf on the 100 watters.

I have seen Dumbles with 50uf to 150uf (2X100uf or 2X300uf) on the first bank. Many later amps had 2X200uf......

I like the 2X220uf on my 100 watter fwiw.

[tonelab2]

Often thought why I'd seen many pro road crews luggin' around those dirty ol' variacs, perhaps they do work in some situations.

[v00d00blues79]

What would the detrimental effects be of running 40uF on B+1? I only have 2-80uF's to use at this point in my 50w...

Thanks,

Andy

[Bob-I]

What would the detrimental effects be of running 40uF on B+1? I only have 2-80uF's to use at this point in my 50w...

Thanks,

Andy

I used 40uF on one build and now I have 50uF. I can't tell the difference myself. I tried 220uF at one point because I had a big mother 220uF/500V cap and a 275-0-275 PT. The amp was as stiff as an old man overdosed on viagra.

[Funkalicousgroove]

I think I'm going to tack a couple of 200uf's across the 100's that are already there and see how it is at 150uf. It's a 100 Watter, but I wanted to make sure it has plenty of sag.

[Normster]

I've only built 50 watters and always use 50uF filtering (2 x 100uF). However, I may try the 110uF filtering on my 100 watt build.

Speaking of sag, has anyone tried a 100 ohm resistor in series with the choke? I recall seeing this mentioned as a "sag" resistor mod on the Blues Deluxe. I run a resistor in place of the choke on my Bassman and like it, but was just curious if anyone has tried both.

[BobW]

I have two 100's in series = 50uF in my 50W bassman clone, and wasn't able to SEE with a scope any reasonable difference in ripple or sag voltage across the caps from zero to full volume into a dummy load. I agree with dogears, 50uF in a 50W, and 110uF in a 100W.

fwiw, I plan to redraw the present values of my basman clone and post the results, all in all I'm now very happy with the tone...too bad I still don't have sound clip capability, maybe soon.

[ayan]

I have two 100's in series = 50uF in my 50W bassman clone, and wasn't able to SEE with a scope any reasonable difference in ripple or sag voltage across the caps from zero to full volume into a dummy load. I agree with dogears, 50uF in a 50W, and 110uF in a 100W.

If you're inclined to pursue this further, try the same experiment with the amp in OD mode and with the PAB engaged. The thing is that you need to take the amp out of its "comfort zone" to see anything interesting, so I suggest you tune the input signal level to where -- at full tilt -- the power supply begins to crap out. At that point, you will see a few things happen: the negative feedback loop around the power amp will go apeshit and the PI will begin to clip completely asymmetrically. Also, the ripple in the power supply will go up because of the power demand on it (the PS) is too great. That is the point where you'd hear the note ghosting phenomenon. As everyone already knows, the higher the capacitance of the PS, the more insurance against that happening.

Cheers,

Gil

[Funkalicousgroove]

It only did it with the amp cranked on the clean side with the PAB engaged, the other thing I noticed was the "Light show" in the back of the amp, you could actually see the blue light in the tubes go brighter and darker side to side, and it changed with playing dynamics. With the OD on they didn't change at all.

I mostly use the amp in the OD mode, and I'm torn as to whether I should risk the current "Feel" of the amp or just use my Lehle box and my Rocket for clean-Decisions!

[ElectronAvalanche]

Hi there,

most of the pics I have seen of grail era 100W Dumbles had two 100uF caps as the first B+ Filter cap giving 50uF in sum.

I have never looked how the amp breaks up in the PS under heavy load with my scope. Maybe I will have to do that, but on the other hand I have yet to hear the ghost-noting in my amps.

I found that the stiffer 2*220uF filtering does something to the sound I personally do not like. Makes the amp a tad too stiff.

I think that the "light show", which is a sign of high electron emission is fairly normal, most amps do that under heavy load.

If the "light show" ends with the OD engaged, maybe there is a very high-freq oscillation going on, thus the current through the tube would then not fluctuate as much as in the Clean, thus less "light show". Rather a steady electron emission independend from the audio signal....

FWIW,

Dominik

[dogears]

Hi Dominik,

The best sounding Dumble that Gil ever played (correct me is I am worng Gil...), had 2X300uf caps in it. There are pics...

The later HRM amps all seem to have 2X200uf.

Hi there,

most of the pics I have seen of grail era 100W Dumbles had two 100uF caps as the first B+ Filter cap giving 50uF in sum.

I have never looked how the amp breaks up in the PS under heavy load with my scope. Maybe I will have to do that, but on the other hand I have yet to hear the ghost-noting in my amps.

I found that the stiffer 2*220uF filtering does something to the sound I personally do not like. Makes the amp a tad too stiff.

I think that the "light show", which is a sign of high electron emission is fairly normal, most amps do that under heavy load.

If the "light show" ends with the OD engaged, maybe there is a very high-freq oscillation going on, thus the current through the tube would then not fluctuate as much as in the Clean, thus less "light show". Rather a steady electron emission independend from the audio signal....

FWIW,

Dominik

[ayan]

Hi there,

most of the pics I have seen of grail era 100W Dumbles had two 100uF caps as the first B+ Filter cap giving 50uF in sum.

Dominik

The photo below if from an amp I played and it happens to be probably my favorite amp ever. Originally built in 1983, I think, the amp has a choke and the same cosmetics as RF's old amp (i.e., script logo). Note that the power supply 1st cap bank is two (you can only see one) 300uF Spragues. I've also seen an 1982 amp that looked identical to this one, and that belongs to a friend who ordered his Dumble after Robben got his in 1982. This other guy's amp also has 300uF caps, so I am inclined to believe that's the way Robben's amp started, since they are all from the same era.

This amp was "updated" by Dumble in 1986 and given the Skyliner preamp -- you can see the cap across the bass pot, and that the middle switch on the front panel has been converted to a MID switch (the panel reads "Deep," however), for example. Unlike the 90s amps, however, this amp still has the V1B feedback and the same dropping resistors as the older Dumbles. A 15pF brightness cap was added to the overall master volume.

I am personally not a fan of the Skyliner EQ (as implemented by me, in my amps) because I think it sounds too boomy, and some of you think two 220uF caps sound stiff. Interestingly, what I liked about this particular amp is that it was perfectly balanced... not bassy, not boomy, and very "unstiff" sounding. It gave up the goods very easily.

This is an example of one of the few amps that hasn't been messed with by folks other than Dumble. For the record, all that was done to this amp when I took the pictures was put new tubes in it.



Cheers,

Gil

[ElectronAvalanche]

Hi Gil,

thanks for the pic.

What OT did this amp have? What was the B+?

I see that the amp in the pic you posted had the same preamp can filter cap as the Kimock amp. Is that a 15uF or 20uF can cap?

I see the NFB is 4k7 in this amp. Did you measure the NFB cap? Oddly enough that is a Tantal cap not the usual electrolytic. I wonder how that changes the character of the NFB and Presence sound.

I wonder why Dumble went up to 150uF (in sum) on the 1st filter section.

Cheers,

Dominik

[Funkalicousgroove]

There are no oscillations, the scope is clean throughout, and it only ghost noted plugged into the dirty power outlet, I was just wondering how to correct for all possible situations.