preamp tube temperature differences - triple giant and jmp-1

[shawn]

in my jmp-1, the preamp tubes get warm, but not hot. *in the bogner/hafler triple giant, they all get quite hot. *why is this?

[bammbamm]

It could be a one or more of a few things that can affect the temp. one being the voltages used to bias the tubes and or power the heater elements. If one unit is running a hotter plate voltage it may generate more heat. Another is the unit's ventilation layout. how well vented to the outside is each unit? can air flow inside ?

Since these are both preamps, you are most likely using 12AX7a's in each, so the best guess is just the units' respective layouts. Not to mention the number of tubes in each unit.

Bamm

[shawn]

well, when i noticed and was comparing temperature differences, the tops of both units were off and had free air flow. *as far as the number of tubes -- the triple giant has 7 tubes, but only two run per channel with one as an output stage, and they are spaced out enough on the circuitboard that they wont affect one another. *another point: *i was also under the impression that the jmp-1 lacked more "tube sound" because it only had 2 12ax7's, but this was disproved when i looked at the circuitboard of the triple giant -- only 2 per channel and 1 output. *so what is it that give the triaxis, the triple giant, and every amp head that ive ever heard more thick "tube tone" than the jmp-1. * i love the jmp-1 as far as controllability and the fundamental structure of the tone, but it just needs more of what the others have. * any help there?

[rgr]

Bamm probably already answered your question, they are probably running the tubes at a higher plate voltage which makes them more dynamic. *The fact that they are putting off more heat is an artifact of this. *

[davenit]

I have noticed this in the SAME preamp, but just switching tubes. NOS and Telefunkens RIP with heat while some of the newer cheaper tubes run real cool. The hotter the warmer the tone. At least that's what I have noticed, maybe I'm screwed up...

Dave

[shawn]

hmmm, nifty observation. *my tube temp differences were observed using the exact same tubes-----not same brand or type, but actually switching out the same tubes. *but youre right, the hotter the tube, the warmer the tone.

i guess this brings about another question:

would it be possible to raise the voltage that the jmp-1 is sending to the tubes? *change out something on the circuitboard? * now that would be cool.

[bammbamm]

I wouldn't attempt it unless you intimately understand what you are doing with the values.
By changing the Plate voltages, you must then alter grid potentials as well, then you need to introduce new componants to allow these changes to occour.
I have been modding amps off and on for about 7 years and I wouldn't even want to do what you propose.
Your idea means taking a system designed specifically for a set range of voltages and pushing that out the window on to the Caddilac down below.
you also must take into consideration that Marshall spent TONS of time and money developing the system to sound like it does so they also made specific voltage curves and adjusts in the software, and by changing one seemingly simple variable you affect the entire system.

Translation, youre gonna hear something when you fire it up and you won't like it.
The solder runs in your Marshal most likely cannot handle the increase in power. Thats where point to point wired amps excel in my opinion. You can mod the heck out of them and make most of the changes fairly easily.


As for why the boogie sounds thicker?
According to the schematics I have from Mesa, they typically have at least 3 of the 5 tubes running at any given time.
Also with your Hafler you have 7 tubes that are ALWAYS running weather youre using them or not, the heaters are still on inside them even though they only run through 2 tubes at a time.

Bamm

[Purplehaze]

I've owned a JMP1 since '94 and love the tone, I have never been able to understand the criticism it has received for not enough gain, not warm enough, not fat enough etc. *Then I noticed something, most of the 'not enough' comments were from people Stateside, so I am wondering if somehow the US JMP1s kinda lost something in the process. *I guess when you think about it an EC83 in a 240v unit has got to have some differences to a 12AX7 on 110v? *Just a thought.

[bammbamm]

Actually Purple, it doesn't make any difference.
The unit has a built in transformer to knock the voltage down to the needed operating voltage. Odds are around 12-24 volts and 3-5 volts on the processor side. *I have heard people knock Boogie tone which to my ear can be VERY Phat and people say it lacks density or whatever, I think its just in the ear of the beer holder.

Bamm

[J Todd Beachler]

I'd just like to point out that the Marshall JMP-1's distortion does not come from the tubes! *The distortion comes from solid state devices. *The tubes are in the unit to provide warmth to the overall sound. *One tube is used for the clean channels and the other tube is used for the distorted channels. *

I have also been inquiring, for a few years now, about the gain levels on my JMP-1. *I just want more gain! *Is that so bad?

Purplehaze, you bring up a good point. *Maybe Marshall used different op amps in the stateside JMP-1s. *Or maybe they used different op amps in different batches of JMP-1s. *Who knows? *

[Purplehaze]

Some interesting comments there, and I totally aggree, Bamm, that tone is a subjective thing.
I own/have owned a Piranha, GX700 and Soldano and by comparison the JMP does not lack in the gain dept. *I have always used it straight, ie no stompbox in front to beef the signal and with the aid of a Rocktron ProQ (purely to scoop the mids a little more) was able to get a pretty good Metallica 'Sad but True' tone.
My earlier comments were simply an observation that most of the criticisims I have seen come from the US, so I'd be keen to hear the two versions side by side to see if there really is a difference.

[jay ratkowski]

I thought ALL Marshall amps these days have distortion that comes from solid state devices. *No? *(Maybe the reissues are still true tube amps...). *