I have a Marshall DSL 40, I changed the main tubes with some new Tung-Sol EL34 Tubes. The highest I could get them to bias was around 24. Did I get some bad tubes? I bought them off Amazon.
As far as that easy access Bias feature, is that on the Head versions as well. thanks for this video. There is no info anywhere that that Bias feature is even on those amps
Lol I was wondering if anyone would catch that! I had stopped filming and did it off camera without thinking about it. I was going to recreate it but I figured folks would get the idea. I should have redone it on camera, that was a learning moment for me haha.
The tube with the metal cover, (on the far right) is the V1 Valve/tube position on this amp. V1a is the input buffer for both channels of the amp. V1b is the first gain stage of the Ultra Channel. V1B is bypassed for the Classic channel. V2 is strictly a cascaded gain stage tube, the output of V1 feeds V2a, and that output feeds V2b. This is essentially the difference between Classic and Ultra, Classic goes V1a->V2a->V2b and Ultra goes from V1a->V1b->V2a->V2b. Follow me so far? From V2 onward, both channels go thru basically the same path, with only slight variations. V3 is what some call the 'tone stack' as the EQ controls are located right after the circuitry of this tube. It essentially is yet another 2 gain stages, as the output from V2b feeds V3a, which in turn feeds V3b. The EQ controls come next, and then the reverb circuitry. After this is the Master Volume (MV) for each channel. Yhen, just before V4 is the FX Send and Return. V4 is actually NOT a preamp tube, it is part of the power section. Commonly referred to a the Phase Inverter (PI) it is what allows the signal from the preamp to push the power tubes in a Class A/B (Push-Pull) operation. It splits the signal into 2, and then flips one side out of phase to feed the finals.
I noticed 2 preamp tubes in my DSL40CR are not lighting up .. does that mean I need to change them ? Its a new amp and I guess they were working fine till last week
@@preciseaudioblog There are 4 preamp tubes, I did one off camera. There is a shield (metal cylinder) over the 4th one that you have to remove to get to it. It’s easy to do, if I could do it over again I would have recorded that part, my mistake. But no you don’t need matched preamp tubes, as long they are the right model for the amp you’re good.
Valve/tube "V3" is your problem child. V3 being a cathode follower pushes the most current. It has more current running throught it that all of the other tubes on the DSL40CR. It's the 3rd Pre-amp tube from right to left. @@onemoreguitarchannel
