How safe will i be . . . (JTM-45 question)

SirJackdeFuzz

SirJackdeFuzz

New member
. . . or am i looking for trouble, when i do this :


A JTM-45 is a 30'ish watt amp, right ?

(Now i am talking about a fantastically booteek quality clone, made 100% on the very 1st schematic with KT-66 valves)

Am i looking for trouble by connecting an amp like that, to my 2X12 cab with 1974 Celestion G12H 55Hz 30watt drivers ?

The amp will not be cranked to '10' . . . but i would like to push the amp way past it's clean tone.

Thanks to all.
 
Re: How safe will i be . . . (JTM-45 question)

It can be done. Used to be in a band with a guy who used a blues breaker reissue. That was 2 25 greenbacks, without the attenuator he ran the volume about 5-6 with the attenuator taking off 3 db he was using 7-7.5. We used to practice 3 nights a week for 3-4 hours then had a steady gig 2 other nights a week for 6 and the amp never had speaker issues in the years we did that gig.
 
Re: How safe will i be . . . (JTM-45 question)

Why would there be concern for running a 30 watt amp into a cab rated for 60 watts (2X30 watts)?
Although, I believe a pair of KT-66 can deliver up to 50 watts. Guess it depends on how realistic the 30 watt rating is????
 
Re: How safe will i be . . . (JTM-45 question)

IM4Tone said:
Why would there be concern for running a 30 watt amp into a cab rated for 60 watts (2X30 watts)?
Although, I believe a pair of KT-66 can deliver up to 50 watts. Guess it depends on how realistic the 30 watt rating is????
Click to expand...


MMmmmm . . . i was under the impression the two 30watt drivers is still just good for 30watts - No More.

It is wired for an 8ohm load.
 
Re: How safe will i be . . . (JTM-45 question)

SirJackdeFuzz said:
MMmmmm . . . i was under the impression the two 30watt drivers is still just good for 30watts - No More.

It is wired for an 8ohm load.
Click to expand...

Nope the power handling would be additive it would be 60watts. You should be ok, though a pair of KT66's pushed into THD will give much more than 50watts. FWIW one time on a bench i put my 72 Marshall 50watt and cranked it scoped at 90watts. But you should still be ok.
 
Re: How safe will i be . . . (JTM-45 question)

SirJackdeFuzz said:
MMmmmm . . . i was under the impression the two 30watt drivers is still just good for 30watts - No More.

It is wired for an 8ohm load.
Click to expand...
NOPE. Doesn't matter if the two speakers are wired in series or parallel, the total power handling capability of the pair is 60 watts.
 
Re: How safe will i be . . . (JTM-45 question)

IM4Tone said:
NOPE. Doesn't matter if the two speakers are wired in series or parallel, the total power handling capability of the pair is 60 watts.
Click to expand...


BRILLIANT . . . thank you very much guys !

U guys made my day ;)
 
Re: How safe will i be . . . (JTM-45 question)

The power-handling of a speaker cab is always the multiple of the wattage of its lowest rated speaker times the number of speakers. So if you had a 4x12 with a pair of 60-watt Vintage 30s in it, and a pair of 30-watt H30s in it (like I do)... you'd have 120-watts of power handling capacity. The 4x12 that sits next to it has 4 Vintage 30s in it, so I get 240 of power handling out of that cab.

And a ditto to the point regarding tube amp output and speaker rating. If you push an identically rated power amp as your speaker rating and turn it up enough, you can blow your speakers (especially if you're boosting the signal -- as most people do). So I always prefer to have a nice pad of 25% or more between the head and the cab rating. On occasions that they are matched, I try to avoid pushing the master volume past noon. But that's easy for me as I use my pedals for OD and only use the power tubes for volume and compression (which can be had easily on amps running below their halfway point).


Btw... I'm diggin the crap out of my JTM clone these days.
 
Last edited:
Re: How safe will i be . . . (JTM-45 question)

Edgecrusher said:
Nope the power handling would be additive it would be 60watts. You should be ok, though a pair of KT66's pushed into THD will give much more than 50watts. FWIW one time on a bench i put my 72 Marshall 50watt and cranked it scoped at 90watts. But you should still be ok.
Click to expand...

this is why its a valid question. I blew a 50w speaker with a 22w amp, cannabis rex with a '66 deluxe reverb. tube amps can push a lot of juice when cranked up all the way
 
Re: How safe will i be . . . (JTM-45 question)

Red_Label said:
The power-handling of a speaker cab is always the multiple of the wattage of its lowest rated speaker times the number of speakers. So if you had a 4x12 with a pair of 60-watt Vintage 30s in it, and a pair of 30-watt H30s in it (like I do)... you'd have 120-watts of power handling capacity. The 4x12 that sits next to it has 4 Vintage 30s in it, so I get 240 of power handling out of that cab.

And a ditto to the point regarding tube amp output and speaker rating. If you push an identically rated power amp as your speaker rating and turn it up enough, you can blow your speakers (especially if you're boosting the signal -- as most people do). So I always prefer to have a nice pad of 25% or more between the head and the cab rating. On occasions that they are matched, I try to avoid pushing the master volume past noon. But that's easy for me as I use my pedals for OD and only use the power tubes for volume and compression (which can be had easily on amps running below their halfway point).


Btw... I'm diggin the crap out of my JTM clone these days.
Click to expand...



Hence my question . . . i might go that direction myself ;)
 
Re: How safe will i be . . . (JTM-45 question)

SirJackdeFuzz said:
Hence my question . . . i might go that direction myself ;)
Click to expand...

DO IT!!! You know you want some! :D

Mine's a JTM45 clone, but it's rated at 50 watts though. 2x6L6 (was KT66s).

20140612_172819_resized_zps75ce68b9.jpg
 
Re: How safe will i be . . . (JTM-45 question)

One more thing... if you find yourself wanting to play a head that's rated at higher power than your cab, get an attenuator. I was playing my 100 watt JCM800 2203X into my 60 watt Laney LT212 cab. It had two Heritage 30 speakers rated at a strict 30 watts each. No issues. Just had to make sure that I always had my attenuator in between the Marshall the the cab.
 
Re: How safe will i be . . . (JTM-45 question)

Red_Label said:
DO IT!!! You know you want some! :D

Mine's a JTM45 clone, but it's rated at 50 watts though. 2x6L6 (was KT66s).

20140612_172819_resized_zps75ce68b9.jpg
Click to expand...



YOU SIR . . . are NOT helping my bank balance :laugh2:

Any tonal diffs in the 6L6's that you prefer over the 66's ?
 
Re: How safe will i be . . . (JTM-45 question)

SirJackdeFuzz said:
YOU SIR . . . are NOT helping my bank balance :laugh2:

Any tonal diffs in the 6L6's that you prefer over the 66's ?
Click to expand...

Well... I like to share my own bank-balance-woes with everyone! :D

So far, the 6L6s seemed to really tighten things up over the KT66s that came in it. But I'll admit that I removed them before I'd really learned to dial this amp in tonally. So one of these days I'm going to slip the 66s back in there and do some tweaking. Because I do hear a lot of people go on about 66s and want to hear what they're hearing. Plus, it probably wouldn't hurt to try a new pair of 66s. The pair that came in it are nice-looking Gold Lions... but I have no idea if there's any life left in them or not. I don't think I even checked the bias before I ditched them. Maybe they weren't set optimally.
 
Last edited:
Re: How safe will i be . . . (JTM-45 question)

SirJackdeFuzz said:
YOU SIR . . . are NOT helping my bank balance :laugh2:

Any tonal diffs in the 6L6's that you prefer over the 66's ?
Click to expand...

They sound pretty different, especially if you push them into power tube distortion. IME KT-66s have deeper bass and smoother highs that have a really glassy breakup as opposed to the harsh/gritty breakup of 6L6s. Regarding amp wattage, remember that a JTM-45 is tube rectified as opposed to solid state; the decrease in rectifier efficiency will reduce peak wattage somewhat. I've heard that a JTM-45 puts out 30-35W at onset of power tube distortion compared to 50ish watts for a SS-rectified model 1987.
 
Re: How safe will i be . . . (JTM-45 question)

dystrust said:
They sound pretty different, especially if you push them into power tube distortion. IME KT-66s have deeper bass and smoother highs that have a really glassy breakup as opposed to the harsh/gritty breakup of 6L6s. Regarding amp wattage, remember that a JTM-45 is tube rectified as opposed to solid state; the decrease in rectifier efficiency will reduce peak wattage somewhat. I've heard that a JTM-45 puts out 30-35W at onset of power tube distortion compared to 50ish watts for a SS-rectified model 1987.
Click to expand...


Great - good to know !

Thank you very much !
 
You must log in or register to reply here.
Back
Top