Great video. I notice that the black wire that you desoldered in Part 1 was reconnected in a different place (on top of one of the big caps). I don't know of that makes a difference but I thought it was worth mentioning.
Hmm, not sure. I don't have time to review the videos. There can be more than one way to correctly wire a circuit in a way that doesn't make a difference.
Very instructive. I wish you would develop more the reasoning behind why if the preamp ground through the shielded cable is lost, it is grounded hot and becomes a shock hazard for example. Or the others ground reasoning. Learning amp circuits through your videos and other’s. Thanks bud.
Well, a circuit needs both + and - power to work right, this we know. The - Power is being passed thru that shield, but also, internally - is tied to ground, and therefor to the chassis, therefor any metal surface of the amp. If the wire breaks, the preamp will loose - power, but you are connected to the preamp ground via your guitar, so if you are holding the guitar, and touch a metal surface of the amp, or, any other ground source, like a microphone, you become the wire, and the preamp will try to power up via that path.
May have ghosts in the blood and the designers at Marshall sure did cocaine about it.. I read from multiple sources so far that the power supply design on a fair few models is very iffy. Basically, when turned off, V-bias discharges faster than B+. If you turn it back on too fast or have a power outage, the bias voltage is way too low for the B+ at that moment. So until the voltages are stabilized the output tubes conduct hard and essentially self destruct by red-plating. Dunno if this model is one of those but better be safe than sorry.
Heh, I wonder if this is another incentive to use the standby switch. I do recall commenting that this PSU didn't have the usual discharge resistors on the caps that I'm used to seeing. I guess that might be another reason for those resistors.
Great video. I notice that the black wire that you desoldered in Part 1 was reconnected in a different place (on top of one of the big caps). I don't know of that makes a difference but I thought it was worth mentioning.
Hmm, not sure. I don't have time to review the videos.
There can be more than one way to correctly wire a circuit in a way that doesn't make a difference.
Nice switching analysis. About to tackle one myself. Now with relays you have a ton of to-92 packaged muting jfets you gotta check.
Thanks ! With Relays ?
I miss my old 2205, for all its quirkiness it rocked like no other.
Yeah, I did quite like the overall sound of this one.
Very instructive. I wish you would develop more the reasoning behind why if the preamp ground through the shielded cable is lost, it is grounded hot and becomes a shock hazard for example. Or the others ground reasoning. Learning amp circuits through your videos and other’s. Thanks bud.
Well, a circuit needs both + and - power to work right, this we know.
The - Power is being passed thru that shield, but also, internally - is tied to ground, and therefor to the chassis, therefor any metal surface of the amp.
If the wire breaks, the preamp will loose - power, but you are connected to the preamp ground via your guitar, so if you are holding the guitar, and touch a metal surface of the amp, or, any other ground source, like a microphone, you become the wire, and the preamp will try to power up via that path.
May have ghosts in the blood and the designers at Marshall sure did cocaine about it..
I read from multiple sources so far that the power supply design on a fair few models is very iffy.
Basically, when turned off, V-bias discharges faster than B+. If you turn it back on too fast or have a power outage, the bias voltage is way too low for the B+ at that moment. So until the voltages are stabilized the output tubes conduct hard and essentially self destruct by red-plating.
Dunno if this model is one of those but better be safe than sorry.
Heh, I wonder if this is another incentive to use the standby switch.
I do recall commenting that this PSU didn't have the usual discharge resistors on the caps that I'm used to seeing. I guess that might be another reason for those resistors.
😬 P r o m o s m
What ?