I finished the amp Friday. It wasn't till late Saturday that I got to test it. I hooked up my light bulb current limiter and got a bright light. Major current being drawn, not good. I found the B+ was shorting to ground from a torn wire (wire was torn by a grounding lug). After replacing the wire the amp was running properly and not drawing excess current.
The OD initially wasn't working. Soon found two reversed wires coming from level/ratio, OD was then working. The PAB (pre-amp-boost) relay switch wasn't working either. Found an error in the schem/layout that stopped the switch from working. Fixed that little issue and the PAB was working as well. So basically the amp was fully 100% functional.
Originally the sound wasn't anything to write home about. The clean was ok and the OD was bad. The OD was crunchy and had too much highs, not smooth. I figured I was in for a long haul of tweaking, Dumble's are notorious for taking a long time to tweak....I played around with the OD input trimmer and found my sweet spot. OD was a little better. Still overall the amp lacked though.
The voltages are critical in these amps. V1 must be 190V, V2 200V and V3 280V/290V for this particular build. It took a long time of tube swapping and resistor string changes to get the voltages spot on. Different brands of 12AX7s draw different amounts of current so the plate voltages change. In the end I found three perfect tubes that got me the voltages I need and had a really great tone.
V1 - I used a really old 12AX7 I pulled from a radio. It is definitely vintage, no noise issues though. It is clear and articulate, good punch.
V2 - Mullard Reissue. This tube really smoothed out the OD channel. It is a dark smooth tube so it did the perfect thing to the OD. The OD is very smooth now.
V3 - A lot of "D" owners and builders like the Sovtek LPS here. It seems to do the job well. I balanced the plate voltages using the PI trimmer. The harmonics are great, lots of second order.
Anyways...if you have read up to here, props! The amp is so amazing! My favorite to date for sure. The sound is great, it is very much a blues/jazz/rock amp. Yet it is very versatile and can get a range of sounds for these genres. Very sensitive, controls and switches are very effective.
Sorry no soundclips. I literally finished the amp up days before I had to leave to go off to university. No the 50W amp did not travel with me to my dorm room . All I got is a little modded Valve Jr.
I ordered the Overtone Special from Ceriatone last month. I am not building it as this is over my head and am patiently awaiting it's arrival. I have been looking at these for about 4 or 5 years now and finally decided to get one. I love the tones I have heard by Marinblues, Zucker and others that I have heard demo the amp. I really wanted to build it but shied away as it looks to complicated for a first amp build.
if you really want your amp to shine, you should use metal film rn65 resistors for the plates and the right caps. if you want hours of reading, but everything you need to know for a good tube sound, go to ampgarage.com dumble amps. it's all there. i've built lots of amps, usually d type of amps, and they all sound great.
. All I got is a little modded Valve Jr.