I miss the telefunkin el34's of 30 years ago my marshall 's really came alive the new reissue tubes are not made in germany and not the same thing nor are the mullards the same bo hoo.
I have to admit, the intro was pretty awesome... the reverb was a nice touch. ;) Utterly fascinating dissection of this mod and the consequences of how it was done.
This is great! I owned a 1959RR, noisy as it could be. I had to reach out to Marshall and Jam Industries had me send it to a service center where they rebuilt the hum balance. Sounded much better after that, but still a wild animal of an amp and tough to tame.
Lyle that intro is an instant classic! You have listened to the amp hype channels! And then straight into a level headed breakdown of the circuit, fantastic! Click BAIT then switch!
Another great video ! I'm lucky enough to have a great tech that is also an electronic engineer and every time I bring him a Marshall , it always gets back better quieter. I phone him back and say what the heck did you do ? He says , I fixed Marshall mistakes ! You remind me of him in a knowledgeable and intelligent way .
About to handwire a 1987 in an origin 50 donor. So this was very helpful ! Great stuff as usual. I want to use the one wire mod and this made it clear. I looked at the robinette page and it was done differently and left me with questions...
This is great, very interesting stuff! Appreciate you sharing your knowledge. I built an amp about 10yrs ago. It was going to be a 1959 preamp with a 5watt 6V6 power amp. But I decided to go for a JCM800 preamp for a higher gain sound. Somewhere along the lines I got the two mixed up. It looks like a It has the same first stage as a JCM800 with the 2.7k/0.68u, or you could call it a 1959 bright channel. and the second stage is the jcm800 cold clipper with the 10k unbypassed cathode resistor, 22n on the output into a 470k/470k attenuator and the 3rd stage is the 820R/100k. What I can't figure out is why the output from the first stage, is more like a 1959. It goes to the 22n, then to the 1M vol pot, then through a 470k res (bright cap removed). As the rest is a JCM800 schematic it should have gone from 22n into the 470k/470p, to the 1M pot and then to stage 2. It has a kinda plexi sound but eq balance is all wrong. I think I forgot I went for jcm800 and partially wired it as a 1959 lol
Great video as always. Interesting stuff about the effect loading has on pickups. I wired my Tele to '50's Gibson spec (tone pot wired to vol pot wiper) and found that I didn't need a treble-bleed to compensate for high end loss. I guessed this was due to the reduced load on the pickup when the volume pot was turned down
I have tried adding 1Mohm resistor from 3rd triode stage grid to ground, right after the paralleled 470pF 470k because it creates a real voltage divider with 470k to lower frequencies. It sometimes makes the sound better especially if the cathode bypass capacitors or coupling caps of the circuit are a bit too big. Of course it loads the earlier stage triode output a bit more too.
Would u consider doing a second video regarding the guitar pickup loading with regards to a buffer? Most guitar players have a pedal board and I am curious how the calculations change after running thru a boss pedal for example
What are the 1k grid resistors? Is this something marshall did on these amps? And cant you lower the V1a cathode bypass cap by inserting a .68 on the tube socket? You will be stuck with the 820 resistor still. But this would lower some gain and bass from V1a. Also, if you plug into normal channel and the put a cable or just a jack into bright channel input low or high, you will get so much gain that you have to turn both down to 5.
One of the most bizarre things to me about Marshall circuits (which I love) are the 250 or 320/330 uF cathode bypass caps on V1(a). So many frequencies are being amplified that are unnecessary, especially below 80 Hz or so. What value cap would you put there for a good, normal channel Marshall clean?
@@PsionicAudio LoL, I will have to go and double check the schematics. Thanks for showing the one wire mod schematic, finally have something in print to compare to.
You mentioned a problem with the "faulty heater balance circuit" at the beginning of the video but as far as I can tell you never talked about it again.
The biggest problem that I see is the "guitar volume" pot wiring. At low settings it will absolutely cause all sorts of tone suck. I suggest disconnecting the wiper from its existing configuration and connecting it to the grid of the input tube. That way, the guitar pickup will see the same impedance regardless of the pot's position.
That's not how it works. Unless you put in relays the ch 1 connection will always load down an instrument plugged into ch 2. Limitation of the one wire mod.
@@PsionicAudio My comments were based on your simplified schematic. I just looked at the full schematic and see what you mean. VR1 (volume 2) is very unusual. In retrospect, I would probably replace it with a ganged dual pot to allow the same functionality while presenting as constant impedance as possible to the guitar pickup. But then, that's substantially bigger than a 1 wire mod. I've even built JFET buffers on a small board to ensure high input impedance for situations like this.
