Dumble Modded Bassman Layout/Schematic

[pompeiisneaks]

Okay I've updated it to reflect the newer changes suggested as well as caught a few errors.

Things I fixed:
colors of resistors, cc/cf/mf types per the photos
Fixed messed up cathode follower tube wiring
designated connections of B+ from the different nodes
added missing 100k NFB resistor from OT Tap

If anyone sees anything else I've missed, let me know.

There are still one area I'm unsure of, if someone has insight:

1. I put the cathode follower 100k to ground on the second triode to ground right by the tube, but I can't see anywhere else it might have been put?

Oh also, the schematic I have didn't show this but I do see in this layout a cap between the anode resistors of the PI, what value would that likely be? I can't read it...

~Phil

[pompeiisneaks]

I'm seeing two types of metal film resistors in that photo. NTE metal film(4 band) and Roderstein Mk3(6 band). The fifth brown(temp) band is almost completely washed out on all of the resistors in the photo. This means there is a double band before the black band on the resistor in question. I see either a double brown or double grey and I don't find it very likely that it is 88k. So I'm voting for 110k. The carbon film 120k is a Q-Line and the 100k carbon films look like Radio Shack. This also confirms to me that the channel isolation resistors in the Bandmaster UP are 475k. Phil that wire to nowhere looks like it is the brown wire that comes from the pots through the hole under the board and to the jumper on the top of the board. The brown wire floating above the board with the yellow wire connects to the jumper and goes all the way down to the channel isolating 470k resistors. The cathode follower 100k appears to have a white wire on one end that goes down into the wire bundle that goes to the filter caps. Finally, check that switch with all the capacitors and 100k resistor on the front end. It appears to wire to the volume pot not the treble. Also notice the funky way of rolling off some high end at the first input. A 100pf or 10pf ceramic disc going from input to the shield of the coaxial. Phil I'd really enjoy hanging out with you on a live stream. I promise, I'll wear a virtual face mask.
CW

Oh man you edited this a bit, I didn't see some of the other commentary... rereading now

[Charlie Wilson]

Phil, I think disregard what I said about the cathode follower 100k. I think the white wire is actually an additional B+ supply. The 100k cathode follower cathode resistor may be one of the resistors on either side of the bypass cap next to the PI section in which case it could ground negative end of the cap.
CW

[pompeiisneaks]

... The cathode follower 100k appears to have a white wire on one end that goes down into the wire bundle that goes to the filter caps.

That actually seems to be the bass wire going from lug three to the mid pot on the back if I'm viewing it right... see here to follow my 'blue trace' over the white coax

CathodeFollower.jpg

[Finally, check that switch with all the capacitors and 100k resistor on the front end. It appears to wire to the volume pot not the treble.

Oh yeah you're right... it is the volume pot... I'll fix that. The only part that now becomes unclear is that it seems to have a 47pf, a 100k and a .005uf cap in there but they seem to be connecting to only one half of the DPDT switch like its a SPDT and I can't see how it's wired exactly? Does this look right? I know it's not 'right' because there has to be some wire coming into it from somewhere... so I'm a bit confused, but that's what I 'can' see I think in the close up shots of that wiring setup.

WiringSwitch.png

Also notice the funky way of rolling off some high end at the first input. A 100pf or 10pf ceramic disc going from input to the shield of the coaxial. Phil I'd really enjoy hanging out with you on a live stream. I promise, I'll wear a virtual face mask.
CW

So I'm looking at that and I took it as the bright cap on that first wire, connected between drive and ground for sure, but no switch so it's gonna have no 'bright switch' it's just always on. There didn't seem to be an actual switch at the front to manage that, so it seemed 'hard on' The Aaron schematic showed it as 10pF...

[Charlie Wilson]

Phil, isn't the 100k cathode follower cathode resistor on the board right next to the 33k resistor?
CW

[pompeiisneaks]

Oh you're right, I've got something screwy there, I think I need to reroute around there. I've got a jumper below the 470k and that thinking it was signal path but that's not right at all... gotta get back at that later tonight...

~Phil

[pompeiisneaks]

Hmm so no, not sure that's right. The resistor next to it has a blue wire between it and the 470k resistor on the other side, which both lead to ground (see my layout) my one slightly visible picture I can see is that a 100k is on the actual socket for the tube which would be the anode connection for the lower half and then jumpers via that 100k to V2a anode. The cathode resistor you're seeing there is the 820 ohm for the first half V2B if I got that right... no? ( I edited it recently to 'fix' it and made it worse... got to sort that all out again

CFStuff.png

~Phil

[Charlie Wilson]

Phil, the pin 8 cathode follower cathode resistor is on the board and grounds with the 475k. The 820 ohm is not on the board and runs from pin three to ground on the chassis behind the socket. The 100k plate resistor is mounted on the pins of the socket. Oh yeah, the mystery resistor. I'm now leaning towards 150k which goes along with the 2k2 cathode resistor. I think I can see the second green band. The cathode resistor for the 120k plate load. Hmmm, a JCM 800 has a 100k plate load and a 10k cathode resistor.
CW

[pompeiisneaks]

Ok fixed both, I'm still not sure what is going on with the 'jazz/rock switch area, I've moved a few components around how I 'think' they work but if anyone has suggestions on how to finish that wiring, I'd appreciate it.

~Phil

[pompeiisneaks]

The more I look at that switch, the more I think it I see the 47pF cap going from volume input to the bottom right lug of the switch, the 100k goes between the same location and the top right lug, the blue cap goes from ground to the bottom lug of the switch. I just can't see what's on the left side at all.

I've mocked up what I 'think' I'm seeing, but don't know from there how it would route to actually do something. I don't seem to see any wires coming into it that would help here..

Thoughts?

What.png

~Phil

[didit]

Hello Phil -

Your current layout is a bit misaligned. Looking at the the original thread photos, from the front panel the "bass" channel has a pot in place of rightmost input jack. Repurposed "deep" switch presumptively now "rock/jazz" comes between that pot and the original volume. No terminal strip visible around the input. Speculate grid "stopper" resistor perhaps for both halves of V1 captive in shrink-wrap at the tube socket end of the coax, certainly stage one is clearly visible. Hence value at best is just a guess. Recommend building/layout as built. Less chance of instabilities. Though, that said, bringing the mid control to faceplate recommended. Drawing from Aaron's provided schematic is constructive for analysis. It may need double-checking values but overall makes sense reading with the photos. Those missing connections lurk in shadows around the pots. Perhaps Jelle might offer guidance as he built that OD channel standalone.

Best .. Ian

[pompeiisneaks]

So there are two volume pots in Aaron's schematic for the first channel(bass), the red knobbed one and the original one. Is that what you're referring to? I have that in my layout no? (Agree mid will be on the front of the amp in the build) Not sure I understood what you mean?

One volume seems to control the drive of that first channel (thus why I called it "Drive Vol" but maybe Drive Level?) the second is more like a real volume if I'm understanding the topology no?

or maybe I've misunderstood what you were trying to convey?

~Phil

[didit]

Hello --

Attempting just a few thoughts to recommend.

Stay close to Dumble's actual design. Use the single input jack directly connected via coax and a reasonable grid "stopper" (24-33K personal preference) captive within the cable end directly on V1 pin 2. Keep the "drive" control where it was relative to the switch, putting "volume" directly to the left at least until the basics are sorted. Perhaps ultimately rearrange the controls as "drive", "treble", "mid", "bass", "rock/jazz", and finally "volume". Use the schematic to help fill in the missing connections on the switch. Check out some dim but visible wiring details in the shadows in this photo.

shadow wires.jpg

Nothing more to add for the moment.

Best .. Ian

[alkuz1961]

I did some work with the photofilters. I hope this can be useful

1.JPG

2.JPG

3.jpg

4.JPG

[Charlie Wilson]

Ugh, my head hurts after this. I couldn't figure out how the 47pf ceramic fit in and then I realized it might be a snubber.
CW