Other Amps

JTM45, 1974x, Bassman Circuit comparisons.


Im looking for a bassman style amp and considering one of the older Marshalls but I had some questions. My understanding is the JTM45 (same as the Bluesbreaker) was based on a 1959 Bassman. How does the 1974x 18 watt model compare to the bluesbreaker and bassman? Is the 1974x a similar circuit to the bassman (like the bluesbreaker is a similar circuit to the bassman) and does the 1974x sound similar to a bluesbreaker? Thanks


No. What makes the Bassman/JTM45 circuit unique (among other Fender circuits) is the cathode follower driving the tone stack. This minimizes signal loss through the tone stack and provides a unique brand of distortion that really makes those amps sing.

The 18 watt circuit has a fairly generic preamp stage driving a simple passive tone knob. It's basically a Tweed Deluxe with British tubes and tremolo.

One could certainly build a Bassman preamp with a lower wattage power amp, but I'm not aware of any commercially available.

You might be better off putting JJ 6V6S in a Bassman or Bluesbreaker.


What does surprise me is how "Marshall" an 18W can sound. The circuits are, as you may have gathered, completely different!

You can build a 5F6-A or JTM45 amp and run 6V6s in it. You can even just put 6V6s in a plexi with a rebias. I have done that with surprising results. 6V6s do have some of the sound of EL34s but you do lose a little aggression/brilliance. The volume drop with 6V6s in a Marshall 1987 is significant.


The 18W is a copy of Watkins Dominator.


Also note that a JTM45 really only outputs about 30 watts or so, and the difference between that and the 1974's 18 watts is not that substantial. Putting JJ 6V6S in the JTM45 would probably bring it down to about 20 watts, and in my opinion would be a much better amplifier than the 18 watt.

This thread has me seriously considering putting my 6V6S in my modified JTM45. I don't know how to feel about having a 20 watt half stack though.


I have a plexi superlead circuit running on 6v6 tubes rated at 25 watts through a half stack. Sometimes just a 212. But I feel great about it.

(insert smiley face)


Well by some strange coincidence, when I put 6V6s in one of my EL34 amp I find the bias is not very far off already. I tend to use JJ EL34s or KT77s and also JJ 6V6s. Even though the bias voltages needed are very different, it just happens that I could almost just swap the tubes with biasing because they are so close.

So trying 6V6s in your JTM45 might be easier than you think. It does drop the volume a significant amount, and sounds pretty good too.


Those JJ 6V6S really are wonderful tubes, aren't they? I had a quad of them in my old Twin Reverb for years.

As far as I can tell, you could put them in everything short of an SVT, and even the SVT would sound amazing just before it explodes.


Agree. Great tubes. I see little reason to use anything but JJ 6v6s or wafer-base Russian "5881" in my daily used amps these days. I run an attenuator pretty hard, and I'm not sure you can even wear out the Russians. I did get a couple screen shorts on a 7-year old pair of JJs finally...That pair of tubes kicked out a lot of jams.

I'd like to check out a JTM 45 one of these days.


I have a JTM 45 that I absolutely love. It is the most impractical amp I own. The thing is ridiculously loud, but man is it a gorgeous sound, clean or cranked, especially cranked. Having never played through a 59 Bassman I can't tell you how it compares, but I play 6120s and a White Falcon through it and they sound fantastic. It's just a rich sound I don't get from any other amp. I did get an attenuator to tame it, otherwise the windows in the house rattle before it gets dirty.


Rogers, you can run JJ 6V6s tubes in your JTM45 to bring the volume down, will still need an attenuator for playing at home though! It is not a straight swap though, will need a bias adjustment and possibly other considerations depending on which amp you have exactly. JTM45 is very similar to a bassman. If you look through this thread there is obviously alot of love for JTM45 with JJ 6V6s tubes, thanks for all your posts guys.


The impedance of 6V6's is more than double EL34's, so if you do that, it'll sound a lot better if you run a 16 ohm speaker on the 8 ohm setting or an 8 ohm on the 4 ohm setting, etc.

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