Picked up this stack just before Christmas in mint condition and have been tinkering with it given that it's 20 watts and EL34 loaded, haven't owned an EL34 M for a few years now.
It's a very good sounding amp but is somewhat strident and piercing at volume(with the Treble High channel) so might change the Bright cap to 100pf which should relieve any of the harshness. With cathode biased amps like this you can change valves in and out so will check out with Clarry Schollum just to what extent that is possible, I'm no tech so proceed with caution with anything like this.
Have hunted for a used one of these for a while.
All the best for 2023 you guys
jeremyb wrote: ↑Sun Jan 01, 2023 9:18 am
Score dude, love the colour too!
Cheers matey, yep burgundy snakeskin, however if I'd had a choice I would always go with the maroon/cream finish, just love the old art deco look that M do so well.
Looks great. That piercing treble really smooths out at higher volumes, once the tubes start compressing. Otherwise you can go for a speaker with a little top-end roll-off. Creamback or similar.
Jops wrote: ↑Sun Sep 18, 2022 7:46 am
Spring is the comic sans of reverbs anyway.
robthemac wrote: ↑Sun Jan 01, 2023 9:57 am
Looks great. That piercing treble really smooths out at higher volumes, once the tubes start compressing. Otherwise you can go for a speaker with a little top-end roll-off. Creamback or similar.
Yep, will put a Gold in the cab and that'll add to the overall smoothing out for sure.
robthemac wrote: ↑Sun Jan 01, 2023 9:57 am
Looks great. That piercing treble really smooths out at higher volumes, once the tubes start compressing.
The higher the volume is on the bright channel, the lesser the effect the bright cap has. I imagine it is quite spanky right out of the gate once you barely crack the volume control? I wonder what the actual value of the bright cap is? 4700/5000pf is a typical value.
robthemac wrote: ↑Sun Jan 01, 2023 9:57 am
Looks great. That piercing treble really smooths out at higher volumes, once the tubes start compressing.
The higher the volume is on the bright channel, the lesser the effect the bright cap has. I imagine it is quite spanky right out of the gate once you barely crack the volume control? I wonder what the actual value of the bright cap is? 4700/5000pf is a typical value.
That's really interesting. I thought it was the signal compressing in the preamp section that caused the brightness to relatively roll off at higher volumes.
Jops wrote: ↑Sun Sep 18, 2022 7:46 am
Spring is the comic sans of reverbs anyway.
robthemac wrote: ↑Sun Jan 01, 2023 10:56 amThat's really interesting. I thought it was the signal compressing in the preamp section that caused the brightness to relatively roll off at higher volumes.
It works pretty much like a treble bleed on the volume pot in a guitar; maintaining some high-end when rolling back on the volume.
But in this case, on steroids depending on the value of the bright cap. The bigger the cap value, the brighter the amp will be at lower settings on the volume control. Marshall used anything from 100pf in the early days to the forementioned 4700pf/5000pf in latter Super Lead design. 470pf/500pf is also pretty common.
I have read that It does take some of the magic away reducing the value of the bright cap but I guess it comes down to personal preference and how you are using the amp. For example, jumping the channels or not.
With these 4 input Ms I tend to jump the channels and playing at high volume is not generally not the norm for me these days so relief at medium to lower volume playing is what I look for now.
The Bright cap on this one is 4.7nf apparently.
goldtop0 wrote: ↑Sun Jan 01, 2023 11:28 am
With these 4 input Ms I tend to jump the channels and playing at high volume is not generally not the norm for me these days so relief at medium to lower volume playing is what I look for now.
The Bright cap on this one is 4.7nf apparently.
A 470pf/500pf might be what you are after if you blend the channels. It will still give you a bit of bite without the that super aggressiveness of the 4.7nf/4700pf.
After doing some research, the bright cap is soldered to the PCB that the pots are attached to so it would be a relatively simple mod. Famous last words; desolder the old cap and install the new one. I don't know how labour intensive removing the PCB from the chassis would be however.
The cathode arrangement on the bright channel, if what I read was true, is a 820R resistor bypassed by a 680nf cap. This also will thin things out a bit more than the 2.7k/680nf arrangement.
goldtop0 wrote: ↑Sun Jan 01, 2023 9:03 am
Picked up this stack just before Christmas in mint condition and have been tinkering with it given that it's 20 watts and EL34 loaded, haven't owned an EL34 M for a few years now.
It's a very good sounding amp but is somewhat strident and piercing at volume(with the Treble High channel) so might change the Bright cap to 100pf which should relieve any of the harshness. With cathode biased amps like this you can change valves in and out so will check out with Clarry Schollum just to what extent that is possible, I'm no tech so proceed with caution with anything like this.
Have hunted for a used one of these for a while.
All the best for 2023 you guys
FuzzMonkey wrote: ↑Sun Jan 01, 2023 11:52 am
The cathode arrangement on the bright channel, if what I read was true, is a 820R resistor bypassed by a 680nf cap. This also will thin things out a bit more than the 2.7k/680nf arrangement.
The 820R value is thicker/more bass/less treble shelving than the 2k7 but yeah
Optical wrote: ↑Sun Jan 01, 2023 12:31 pmThe 820R value is thicker/more bass/less treble shelving than the 2k7 but yeah
I believe the 820R/680nf was featured in the early Marshalls with the split cathode arrangement before they went to the more common 2.7k/680nf arrangement. The 820R/680nf rolls off the lower frequencies from 285Hz downwards and 2.7k/680nf from around 86Hz.
