About to start my 8th build. It will be my second trainwreck. How I wish I watched your grounding videos before haha. I feel like some back tracking is in order.. Great stuff Lyle !
Did a full recap, bias and gain modification to my 2205 with confidence from watching your videos. Thank you from Australia you've help me understand my Amps and they're all running so much quieter and smoother now!!
I also have a 2205 and I'm about to do the same! Well, almost the same, gonna leave the biasing to a pro. I'm just handy with a soldering iron from maintaining my guitars (have 17 now) since I was 15.
Great. I love possibilities and improvement. I’ll always choose to make thinks better over the originality. If something is a collector’s item I rather sell it to a collector and make me an improved version of it. 😁😁
I could never understand why Marshall did not twist the wires on those models. Although another well know amp builder once told me that the 800 circuit is less sensitive to heater noise. What about using a small cap from the input jack to ground to eliminate the radio station pickup? Do you have a layout diagram or a schematic showing your grounding scheme and DC heater elevation work? Thank you for this excellent video, very helpful.
The 2203/2204 is much more sensitive to heater noise than other Marshalls. But it's not about twisting vs not - it's about that unbypassed 10K cathode. See the in-video link about 2:30 for the ground scheme explanation. If you see the Germino the other day you'll see Greg does the preamp grounds more in line with my ideas than Marshall's.
Have had ceramic cap demodulate AM station before that with the ground problem make a nice little radio receiver . May not be what you are looking for . Nice instructional video as a matter of fact. Antenna theory in plat there a fine demonstration of the importance of good practices . Elevated heater reference is in the RCA RED book the reference for design of tube amplification . Vintage is the bane of great design .
LOL they kept copying the Bassman ground scheme 30+ years after Fender stopped making them. The replica amps I build have minor changes to the ground scheme and filament wiring for noise reduction. If this were my amp, I’d say fix it. Vintage collectors can stuff it. I’d rather have a properly working amp.
Very good info here. Can someone please explain on why you can ground the shield part of the the shielded grid wire of v1 to its plate? Isn’t that asking for trouble since the plate is at higher DC?
I noticed you suggested referencing the heaters to a DC supply instead of using two resistors to ground. Is this because of a Marshall 2203/2204 being higher gain than a Fender amp?
My question is about the feedback wire on the impedance selector. Shouldn’t the purple wire be moved from 4ohm tap, to 8ohm tap? This is one step that seems to be often over looked. Or, is this step unnecessary?
The 12AX7 has a maximum Rf/k of 20k so i choose 18k max to be the value for the lower divider resistor and then calcualting a top resistor accordingly. Have you ever experienced any problems with going higher? Because you mentioned 330k/100k as example in the video.
None at all. Just watch the power rating of lower value resistors when dropping that much voltage. I usually don't go lower than 47K for the bottom of the divider for that reason.
@@PsionicAudio Sure do, in general i don't use anything lower then 2W just because of voltage ratings which many people are not aware of. Lifting up heaters and how it is done properly may-be a good topic for a follow up on the excellent grounding video.
If the customer opts for better than "authentic" ground architecture you might interest him in an upgrade to stainless steel fasteners and nylock throughout as well?
That's what I would do. Two broken brass screws, it's possible the others are weakened and not far behind. I'm very much a "get on it before it gets on you" guy.
@@marshallstack1972 Although the brass mounting hardware might not actually break as the owner is transporting or using the amplifier, the bolts will probably stretch a little bit and all the grounds and mechanical connections will come loose again.
I have mixed feelings on nylock nuts. I prefer a Keps nut, or an added star washer; and black-oxide fasteners/hardware are verboten. (Although if the ground lugs have an internal star tooth on them, you can't put something else like a Keps nut or an additional star washer over it and expect to be able tighten it securely. You can, however, still put a star washer under the head of the bolt).
The connection of the pot case to the chassis through the bushing is good enough to provide shielding for the pot, but not good enough if there is current present (power supply or signal return path).
Yeah, the buss is fine to keep all the pots shielded in case one comes loose, but it is a terrible idea for the actual signal negative function of ground. I keep meaning to do a video on all the different things "ground" can be. AC negative, DC negative, DC positive (in bias), shielding. Very different functions, not interchangeable.
If the buss wire is heavy enough it'll prevent the pots from spinning around to some extent if the shaft nuts come loose 😁! (That's just me being a wise ass).
@@PsionicAudio I would be interested in seeing that video when you get around to it. I was working on my cheap SS practice amp which doesn't feature a ground strap across the back of the pots. I measured resistance from the pot cases to the earth point on the chassis and they all varied by a couple of ohms. Just a case of oxidation on the chassis I thought , so I cleaned up the chassis where the pot shafts pass through and the end result was no background hum at switch on. But is there a better or more correct engineering solution? Ian
Lyle is in the Memphis area. He said he's been having problems with his email service, and getting lots of spam, and a ton of inquiries about repairs, so he is often behind on answering people's emails or phone calls directly.
@@PsionicAudio I get that, but the coax is effectively adding a small capacitor between the plate and grid. I don't see anything good coming out of that. In fact, the high voltage across the coas might be what makes the cable microphonic.
For the humbucking Strat demo - why mention the pickup's DC resistance? I would have thought an experienced tech guy would know that DC resistance of a pickup is only very vaguely related to its voltage output. The internet is full of this piece of misinformation, why perpetuate it?
Generally I wouldn't consider any tube guitar amp built with a printed circuit board to be vintage; although, the amps made with circuit boards tend to repeat many of the mistakes of the past from when amplifiers were all handwired onto eyelet, turret and tag boards. I guess you could say that these 80's Marshall's are being built to conform to late 1950's/early 60's wiring and layout standards, but merely using more modern materials.
@@RocknJazzer , what tube-type guitar amps used PC boards in the 50's? Never seen such, specific details would be appreciated. In the 60's, Ampeg adopted use of circuit boards for tube amps, as did Japanese-made Univox amps, but I can't think of any others off the top of my head, except for solid-state amps. By the early 70's, of course, most amps had PCB'S. As for this particular Marshall amplifier in the video, I said that it looked to be built to 1950s/60s construction standards because although it has a circuit board , all of components are laid out very cleanly in a straight line, similarly to how they might have been laid out if it was an eyelet board or turret board.
@@goodun2974 having worked on so much vintage gear, from guitar to pro audio, have seen boards in much 50s stuff. look up the history of PC boards, they date back to the 40s
I’ve got a lot of noise in my JTM45 clone and everyone on the Marshall forums was telling me that it was coming from the four-hole inputs and the 68K grid stoppers. Changed the 68k resistors from carbon comps to some high dollar Vishay resistors will little to no difference. I’ll have to try redoing the grounding bus as mentioned here and possibly the elevated heaters.
