Marshall JTM Studio Series

[blackstratblues]

Not sure about this one but the originals were tube rectified with kt66? They sag a lot more than a Plexi and have a lot more bass, beautiful cleans through to breakup but fall apart under higher gain settings. Plexi is tighter.
I love both!

While I was referring to the Studio versions, it's true that the very first Marshalls did have 5881s in line with their Bassman heritage. They quickly changed to KT66s as they were more cost effective.

[goldtop0]

The old 45s were KT66 with a GZ34 rectifier, this JTM20 is tighter.
I talked with Clarry Schollum yesterday re, could a rectifier tube be added to the JTM20, to which he said that it could be possible so I'll get one and take it to him for a look see.
It entails a rewind of the PT and a number of other variables around the whole process that would be 50/50 as to whether it'd be possible or not.
We'll see.

[godgrinder]

These Studio series have really low plate voltage (~200V IIRC) so they are probably saggy enough in the first place even with SS rectifier.

[goldtop0]

I seem to remember Clarry saying when he worked on my SV20 that the voltage was around 220 or so and he took it down to around 210 so I could swap KT66s in and out.

[RectifiedAmps]

If you want more sag just get Clarry to add some series resistance to the power supply. A GZ34 has an internal resistance of about 175ohms, so a resistor in the same ballpark will produce similar response. It’s way cheaper than rewinding a transformer, installing another valve socket, buying a rectifier, etc - and more importantly it’s reversible if you decide you don’t like the result!

[calling card]

How hot would it get? the resistor.

[RectifiedAmps]

If it was properly rated (maybe 10W?) it shouldn’t get too hot to touch. Certainly not as hot as a rectifier tube!

[MikeC]

How hot would it get? the resistor.

You'd need to know the current, voltage drop & the resistor's value to calculate how many watts it would dissipate when the amp is at full volume. Then purchase a suitably rated resistor. I'd say "probably pretty hot" but as long as it's rated for it then no worries.

[goldtop0]

If you want more sag just get Clarry to add some series resistance to the power supply. A GZ34 has an internal resistance of about 175ohms, so a resistor in the same ballpark will produce similar response. It’s way cheaper than rewinding a transformer, installing another valve socket, buying a rectifier, etc - and more importantly it’s reversible if you decide you don’t like the result!

That sounds like a cunning plan. I love sag in an amp, it's a lost tone/sound these days.
I'll broach the subject with him when I get the thing and see what magic can be conjured up.......cheers.

[StrummersOfThunder]

Anyone wind up with one of these?
Whats the general consensus in terms of utility as an 'at home' amp with some chewy flavour ?
Ticks a few boxes in terms of aestehtic, size, weight, power scaling and use of large glass toobs). Plus the cream back loaded cab is appealing.

[goldtop0]

Anyone wind up with one of these?
Whats the general consensus in terms of utility as an 'at home' amp with some chewy flavour ?
Ticks a few boxes in terms of aestehtic, size, weight, power scaling and use of large glass toobs). Plus the cream back loaded cab is appealing.

Yep, picked one up in September and it's different in sound to the plexi SV20 as you'd expect, not as strident. Mind you I'd tamed the SV20 with a 100pf Bright cap to take that raspy hiss out of the High Treble channel at lower volume, which if you're playing it at home just makes sense, even the neighbours agreed !!
Got Clarry to do some work after a month or so, and it now takes KT66s and EL34s as well.
I like it as it's very much a junior JTM45, hasn't got the grunt of it's big brother but it has the sound and tonal characteristics you'd expect, crank it and the compression is there, harmonics abound.
And for example, if you were to go 1974X and ST20 side by side, the ST20 would stand out as does the SV20, just different circuitry and valves.
Merry Christmas y'all.