Played Gig #2 with the JVM this past Saturday...

Gainfreak

Gainfreak

New member
The JVM is quickly becoming one of my favorite amps of all time and I haven't said that since 1992. I even like the powerball but the JVM smokes it in features.
 
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SgtThump":66f28 said:
Sounded even better this time around. I imagine it's a combination of the following:

- Bogner cab breaking in more
- New pickup in bridge of LP (Duncan '59 Model)
- We turned up louder at this gig

Also, I biased the JVM up to 80mV (or mA, whatever it is) per side. I suppose that's around 40 per tube. On the www.jvm410.com forum, Santiall said that a good balance of tone vs tube life was something like 30-35 per tube. He also suggested going no higher than 45 per tube. I decided to go for 40 and I think that may be why the amp sounded better to me (but it could be one of the above things too.)

It was smoother and the distortion seemed to be more under control? I don't know if I'm just getting used to it or if there indeed was a wider sweep on the preamp gain knob for the OD1/Orange channel/mode. But dialing in the preamp distortion at 10:00 o'clock just seemed better to me at this past gig than before.

Also, I don't remember what the amp was biased at from the factory, but it was colder than 80 per side. Maybe it was at 60 per side or something? I think so...

So anyway, it won me over even more this past weekend. I used the "Crunch/Red" and "OD1/Orange" channels/modes 99% of the time with an occassional jump over to the "Clean/Green" channel/mode.

At one point, I was confused, because the distortion seemed waaaaay too high and the guitar was feeding back and stuff. I then realized I switched it to "OD1/Red" by accident. The Orange and Red lights on the footswitch look similar at times and I didn't realize the mistake. Once I figured that out, I was back to rocking good. :)

Great amp for sure!
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I've noticed that as well (orange/red)...

Have you tried rolling the volume on your guitar? It takes to it surprisingly well, IMO.
 
You sunbitches keep talking about these and I keep drooling. I'm on vacation in a few days. When I get back I'm going to have to bite the bullet.
 
I've not touched mine yet, but I'll likely set mine to 60% and see.

With Marshall's "recommendation" for the TSL/DSL being 90% idle dissipation, I take anything they say with regards for bias with a grain of salt! :)
 
Nice...
chris did you change the tubes also ?
I just ordered some winged C and tung sol preamp tubes . I love the amp . I also use a Duncan '59 in the bridge , probably my favorite pup to date .
JB
 
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chobley":10811 said:
Nice...
chris did you change the tubes also ?
I just ordered some winged C and tung sol preamp tubes . I love the amp . I also use a Duncan '59 in the bridge , probably my favorite pup to date .
JB
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I think the stock power tubes are =C='s :)
 
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kannibul":95c65 said:
I've not touched mine yet, but I'll likely set mine to 60% and see.

With Marshall's "recommendation" for the TSL/DSL being 90% idle dissipation, I take anything they say with regards for bias with a grain of salt! :)
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Well there is a differance in taking what marshall says with a grain of salt vs what the actual amp designer says! That's the HUGE plus side of having Santiall post here and on the JVM site ;)
 
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kannibul":00d07 said:
I've not touched mine yet, but I'll likely set mine to 60% and see.

With Marshall's "recommendation" for the TSL/DSL being 90% idle dissipation, I take anything they say with regards for bias with a grain of salt! :)
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It is/was less. Those amps are running at lower plate voltages like 440V (at least those I've biased - DSL100s), which then calculates to 75% or so.
 
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SgtThump":4bae0 said:
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I stuck 5 newer Tung-Sol 12AX7's in it, but they were super noisy. I like the tones from those Tung-Sols, but I've had nothing but bad luck with them. So I pulled them and put the stock tubes back in for the weekend.
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I haven't been lucky with the tung-sols either.
 
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Gainfreak":bc111 said:
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Well there is a differance in taking what marshall says with a grain of salt vs what the actual amp designer says! That's the HUGE plus side of having Santiall post here and on the JVM site ;)
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The designer posts on here?

How fucking cool is that!
 
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duesentrieb":c9e9b said:
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It is/was less. Those amps are running at lower plate voltages like 440V (at least those I've biased - DSL100s), which then calculates to 75% or so.
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I remember doing the calculations having measured my plate voltage, and it coming out to something like 90% idle.

Then again, this was before I knew that the plate voltage would shift when you change the bias - I don't know why I didn't think of that at the time...

wattage = current x voltage, you have the same power (wattage) being consumed, but you're changing the amount of current, therefore the voltage will flux.
 
Since my guess is that it has the same transformers as the DSL - sounds good to me, but in the end it depends on the plate voltage (PIN 3).

25W*x/440V = 0.04A
x = 0.04 x 440V/25W => 70%

if the plate volatage should be higher --> safe
if it should be lower (I don't think so) --> too hot

I've also set the DSL to 40mA (80 per pair) per tube btw ;)
 
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SgtThump":0ad25 said:
So what do you guys think of me running each tube pair at 80 whatever? Does that sound high?
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I guess it depends on the plate voltage. I'd take a measurement of the plate voltage with it at 80, and see what it works out to be.

I think (if I remember correctly from last night) you can easily read the plate voltage from the white wire leading to the OT (and ground the other lead)

I will likely make a pop-noise when doing so...
 
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duesentrieb":c3a0a said:
Since my guess is that it has the same transformers as the DSL - sounds good to me, but in the end it depends on the plate voltage (PIN 3).

25W*x/440V = 0.04A
x = 0.04 x 440V/25W => 70%

if the plate volatage should be higher --> safe
if it should be lower (I don't think so) --> too hot

I've also set the DSL to 40mA (80 per pair) per tube btw ;)
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I know the transformers are different than what's in the TSL.
 
I've never opened a TSL - but some DSLs and from the pics I've seen from the JVM . . . but as I've said: I'm just guessing here . . .

Chris needs to read the plate voltage - and he owns a bias rite with the VI option, so its not a hard thing to do for him - with tubes installed.

Btw to avoid the pop by measuring the PV or even shunt-bias it: just hook the wires with croco leads to the OT and THEN switch on ;)
 
I played a JVM at George's shop on Saturday and I was real impressed with it. Even played through a cab with new 75's it still sounded great! Now I want one as well. Gotta love the "no boost pedals needed" thing too. Wow.......think it has enough gain???......holy cow! I really liked OD1 orange. Neat amp.
 
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duesentrieb":bfeb0 said:
I've never opened a TSL - but some DSLs and from the pics I've seen from the JVM . . . but as I've said: I'm just guessing here . . .

Chris needs to read the plate voltage - and he owns a bias rite with the VI option, so its not a hard thing to do for him - with tubes installed.

Btw to avoid the pop by measuring the PV or even shunt-bias it: just hook the wires with croco leads to the OT and THEN switch on ;)
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All I got is the standard probes that came with mine - but some clips would be nice - just I use my meter so rarely outside of building amps, and really I doubt I'll be doing it much any more.
 
Glad to hear its working out well Chris. I was supposed to gig with mine last friday but we got snowed out. Now I have to wait until this friday to gig test it.
 
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