JCM800 and 900 on stereo

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DesertRose

New member
Hi guys

I'm intending to run the above mentioned 2 amps on stereo.
However, the JCM800 is 50w while JCM900 is 100w
Currently the volume of the JCM900 at 2.5 is overpowering the JCM800 even at 5. Preamp volume of 900 is 5 while the JCM800 is like 7.

Preamp tubes for the 900, V1-3 are 12AX7
Preamps tubes for the 800, V1-4 are 12AX7, V5 Mullard 12AU7

Any ideas how to better balance the volume up?
Like perhaps plucking out 2 power tubes from the 900?
or change the preamp tubes for the 900 to 12AT7 or 12AU7?

Or just let it be ....
Thanks ...

PS: both amps are 1 x 12" celestion
 
Re: JCM800 and 900 on stereo

That 12AU7 in the phase inverter of the 800 really cuts down on the output level. You could try swapping it to the 900 and putting the 12AX7 from the 900 in V5 of the 800 to see if it balances the power output of the two amps. A 12AU7 in a 100 watt 900 really tightens up the bass and gives it a bit more of a nu-metal tone and response.
 
Re: JCM800 and 900 on stereo

Beer$ said:
Turn the master of the 800 up even further.
Click to expand...

haha
Thats the last resort bro.

tonefreak1527 said:
put an eminence wizard in the 800, more efficent speaker=more volume
Click to expand...

That could be another solution.
I'm trying to keep it cost efficient first.
I think a eminence wizard speak would be like $300?

glassman said:
That 12AU7 in the phase inverter of the 800 really cuts down on the output level. You could try swapping it to the 900 and putting the 12AX7 from the 900 in V5 of the 800 to see if it balances the power output of the two amps. A 12AU7 in a 100 watt 900 really tightens up the bass and gives it a bit more of a nu-metal tone and response.
Click to expand...

Hi bro, thanks for the rescue again.
Did I hear you say a 12AU7 gives it a bit more of nu-metal and response?
Wow ...
Here is a pic of the JCM900's V1-3. Left of it is near the input jack. Right is towards the rear where the fx-loop is located.
If its similar to the JCM800, the PI should be V3 1st from the right?

29122008313.jpg


Thanks
 
Re: JCM800 and 900 on stereo

weird I thought all 900's had the half power switch. I'm real surprised that your 100 watt 900 is overpowering the 50 watt combo, My friends 2204 was louder than any amp I've ever heard. Turn the presence down on the 900 a bit and the master up on the 800
 
Re: JCM800 and 900 on stereo

Pull a pair of the output tubes (either both the outside or both the inside tubes) from the 900.
 
Re: JCM800 and 900 on stereo

The reason the 800 isn't as loud is because of the 12AU7 in the PI.

Try Glassmans suggestion and see what happens.

The 900 high/low power switch doesn't say Pentode/Triode. It just says "Mode" above a little slider selector that selects between low and high. But maybe they couldn't make room for it on the 1x12 combo format?
 
Re: JCM800 and 900 on stereo

You have an 800 with 5 pre amp tubes ? I've never seen such a thing. How did you do that ?
 
Re: JCM800 and 900 on stereo

Invader09 said:
You have an 800 with 5 pre amp tubes ? I've never seen such a thing. How did you do that ?
Click to expand...

Its one of the oldies bro.
It actually sounds more crunch compared to the JCM900 to me.
It runs on EL34s while the JCM900 is 6L6GC. Both are wing =C=.

If I could get my hands on the schematics I would wanna standardize both to EL34s.

Lake Placid Blues said:
The reason the 800 isn't as loud is because of the 12AU7 in the PI.

Try Glassmans suggestion and see what happens.

The 900 high/low power switch doesn't say Pentode/Triode. It just says "Mode" above a little slider selector that selects between low and high. But maybe they couldn't make room for it on the 1x12 combo format?
Click to expand...

I could do that.
I think I will try swapping the AU7
It does sound sweet if not for hard rock.
 
Re: JCM800 and 900 on stereo

I have an 800 from 1985, So I know oldies too ;) I just didn't know the 2205's had 5 preamp tubes. Mines a 2204.
 
Re: JCM800 and 900 on stereo

DesertRose said:
Hey bro,
Mine is a combo.
The only switch I see is the impedance selection of 8 or 16ohm and hi/low of this impedance.

Apart from that, there ain't any pentrode/triode switch.
Click to expand...

The Hi/Low switch is the power mode. High being Pentode and Low being Triode. It has nothing to do with the impedance. Also, since this is a combo, the 16(4) impedance selection is 4 Ohms, not 16.
 
Re: JCM800 and 900 on stereo

Also, please don't pull any tubes. There is a risk of impedance mis-match which can be fatal to your Output transformer. The output difference from 50 to 100 watts is a mere 3db, so not really worth the risk of blowing up the amp.
 
Re: JCM800 and 900 on stereo

GET THE 12AU7 OUT OF THE PHASE INVERTER. it only has a gain factor of 18, a 12ax7 has a gain factor of over a hundred
 
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