Finally getting around to the Rev. B board I've had for a while. This was supposed to be a Christmas present for my brother when he was visiting but there was a big hold-up on parts.
I know I'm going to need help and guidance on this so I figured I'd start a build thread here where I can constantly irritate @xtian and @JazzGuitarGimp - who've both been awesome via email!
I seem to be missing the Cliff Jacks I swear I ordered and I need recommendations on size of small parts for screws and washers for securing the new Belton sockets. I'm sure there's something else I'm forgetting but right now I'm just tracking down a drill bit for opening up the chassis for the Alpha pots I have on hand.
xtian wrote: ↑Thu Mar 26, 2020 10:51 pm
I use stainless steel #4-40 machine screws, 3/16”, and nuts with integral lock washers from mcmaster.com.
Great, thanks!
I think with those couple incidental parts taken care of I can finish the build. Honestly, I don't know anything about Dumble amps, never chased that tone. I'm building this to experience it for the first time and have the fun of a rebuild on a burned out, noisy, broken amp.
My favorite is the EV EVM 12L family. Zakk Wilde has a model, Andy Timmons, etc. I like the Eminence Wheelhouse 150 --it has a Neo magnet for light weight, and a hemp cone which is great for taming highs. Other awesome choice is the Eminence EM12N--even closer to the original EV speaker, but with a Neo magnet again.
xtian wrote: ↑Thu Mar 26, 2020 11:13 pm
My favorite is the EV EVM 12L family. Zakk Wilde has a model, Andy Timmons, etc. I like the Eminence Wheelhouse 150 --it has a Neo magnet for light weight, and a hemp cone which is great for taming highs. Other awesome choice is the Eminence EM12N--even closer to the original EV speaker, but with a Neo magnet again.
Although! I even like the stock speaker in the Hot Rod Deluxe quite a bit!
I've never tried the EVM but I've read about it many times. Heard it could be a secret weapon in DRs - I've yet to try it - but I think I'll probably grab a EM12N and give it a go!
What did you do to deal with the size disparity on the noval sockets? The Belton sockets are so small they just don't quite span the opening from the PCB-mounted original sockets. I don't want to spend money on an adapter plate if I can get away with a wide washer and lock nut.
I just center-punched the holes hard, and used a hand-held drill. It's a bitch because the chassis is steel. Anyway, got-er-done, and everything fit.
IMG_1800.JPG
I've got those same sockets; not looking forward to getting them mounted but once that's done I think all the sucky stuff is done.
Though I've never enjoyed running filament wiring...
Got the last few parts on order and I'm gonna sort the noval sockets tomorrow. Thanks much for your help - very excited to have this thing all together!
xtian, if you don't mind sharing them, I'd love having as many reference photos as you've got. Your HD images help me connect schematic to application and are great study material.
xtian wrote: ↑Fri Mar 27, 2020 3:51 pm
I have posted many photos to my build threads here on TAG. Let me know if there's a specific area of interest you want to see.
Looks like you made the heater artificial CT with the cathode one ohm to ground on the V5. Why there on the filament CT?
Any pictures you've got of the power section wiring would be great - OT, PT, tubes. The rest is very well directed from the PCB.
Where do you check the bias once it's all up and running?
The one ohm resistors should be 1% tolerance and are there to test the mV across them, and then due to ohms law you get the tube's mA of current.
A = V * R which basically means XmV * 1 = XmA
not sure I understand your question about the 100ohm virtual center tap? you can put them anywhere you want on the heater line, just one per side to ground. Or are you asking why he's doing one instead of using the center tap?
I think it's a bit of a preference thing. Many feel the 100 ohm virtual center tap is more 'balanced' than the real one, as the real one can sometimes be offset a tiny bit due to non perfect exact center tap location or imperfections in the wire itself, giving imbalanced halves.
pompeiisneaks wrote: ↑Fri Mar 27, 2020 6:31 pm
The one ohm resistors should be 1% tolerance and are there to test the mV across them, and then due to ohms law you get the tube's mA of current.
A = V * R which basically means XmV * 1 = XmA
not sure I understand your question about the 100ohm virtual center tap? you can put them anywhere you want on the heater line, just one per side to ground. Or are you asking why he's doing one instead of using the center tap?
I think it's a bit of a preference thing. Many feel the 100 ohm virtual center tap is more 'balanced' than the real one, as the real one can sometimes be offset a tiny bit due to non perfect exact center tap location or imperfections in the wire itself, giving imbalanced halves.
~Phil
Sorry if I phrased it poorly - I was just curious about whether there was a particular rationale for the CT location vs. any other possible point, that's all. I was actually just reading about the one ohm resistor biasing method yesterday on the EL84 World website, which is interesting to me as I used the OT resistance method most recently on my Fenders. This seems quicker and more accurate. I don't think I have any of those 1% resistors and I just got an order from Dave shipped to me - d'oh!
