JCM900 with power brake

[jcm900]

Hi guys, I just want to know if is the power brake necesary for the jcm900 head? I have a dual reverb 4100 head with a 1936 (2x12) cabinet, but, I think it could sound better with the attenuator becouse, you know, the tube amps works better like this way...VOLUME 10!!
-Has someone any experience with this attenuator?
-Is it necesary with this kind of amp?

Thanks for any advice!

 

[Guv'nor]

Hi again

There are many ways to reduce the power

There are different attenuators you can use. Power Brake, THD Hot plate, Ted Weber... They all have their advantages and disadantages but all of them will affect the overall tone. They are all pretty expensive too

Some people use yellowjackets to convert the EL34s into EL84s

You can also withdraw the 2 outsider power tubes leaving only 2 of them.

Some other people is ok using a Tubescreamer or similar

Less efficient tubes and speakers would drastically affect the power too...

It's a matter of trying yourself and choose according to your taste.

 

[Guv'nor]

You can also withdraw the 2 outsider power tubes leaving only 2 of them.

I have received a mssg in my mailbox asking to explain how to do so. I think it is a very good question because it is important to follow some procedures.

You can reduce the power from 100w to 50w by withdrawing the 2 outsider tubes leaving the 2 in the middle ---> XOOX

When you do so, you have to run the amp at half of the cab's load. I mean if you are running a 16 ohm cabinet you'll have switch your amp to 8 ohms. This is VERY imporant

Enjoy!

 

[superleadfixer]

+1

You could also remove the two inner tubes, same thing will happen

 

[jcm900]

thank you very much. I'm going to try this configuration. If I can save no buy a power brake, great!

 

[superleadfixer]

You will lose headroom but it still will be loud, less a little but loud still...

Good luck!

 

[jcm900]

Ok, if I set to "low" in the rear I'll get the half of power, so with 2 tubes, I'll get 25 Watts? Is it true?

 

[superleadfixer]

Ok, if I set to "low" in the rear I'll get the half of power, so with 2 tubes, I'll get 25 Watts? Is it true?

No no no.........

When you pull two tubes your amp output impedance changes to a higher value automaticly, you have to correct that mismatched by lowering the impedance selector one step lower (ex. if at 16ohms go 8ohms, if at 8ohms, go 4ohms.....), you will have haft the power in all cases around 50w......

Make sure you unserstand that or you will damage your OT

 

[jcm900]

I'll try this:
-remove 2 power amp 5881 tube -> XOOX
-set the impedance selector in 16(4) ohms

My cab is a jcm 900 1936 (2x12) which it has 2 input:
-mono 8 ohms
-stereo 16 ohms

here is a picture of the cab:
http://cgi.ebay.com/ws/eBayISAPI.dl...ndexURL=1&photoDisplayType=2#ebayphotohosting

Have I connect in stereo mode with the amp in this case?

Thank you very much

 

[superleadfixer]

I'll try this:
-remove 2 power amp 5881 tube -> XOOX
-set the impedance selector in 16(4) ohms

My cab is a jcm 900 1936 (2x12) which it has 2 input:
-mono 8 ohms
-stereo 16 ohms

here is a picture of the cab:
http://cgi.ebay.com/ws/eBayISAPI.dl...ndexURL=1&photoDisplayType=2#ebayphotohosting

Have I connect in stereo mode with the amp in this case?

Thank you very much

Nothing is connected on your pic??!!

Normally in mono one jack is needed and both speakers will play, just stick in the proper mono jack input..For stereo you'll need two jacks in the cab normally, and you must put the selector on stereo at the cab...I can't see on your pic......

-If you play mono and your cab is in 8 ohms/mono put your amp on 4ohms with two tubes pulled...

-If you play stereo and your cab is in 16ohms/stereo put your amp on 8ohms with two tubes pulles...

 

[superleadfixer]

-set the impedance selector in 16(4) ohms

?????? What do yo mean here????

Have I connect in stereo mode with the amp in this case?

????????????

Thank you very much

 

[Guv'nor]

Yep, it is difficult to undersytand what you mean.

Ask me in Spanish if you think you'd explain it better.

 

[jcm900]

Ok, sorry if I coudn't explain well... :roll:

I want to be sure which impedance have to set and how connect the amp to de cab.

I think superleadfixer wrote my answer:
"If you play mono and your cab is in 8 ohms/mono put your amp on 4ohms with two tubes pulled..."

'couse I play in mono.

The pic is just an illustrative picture of the rear of the cab (ebay). I did not take a photo of my equipment...

Thank you very much friends!

 

[Perry_PRS]

"You can reduce the power from 100w to 50w by withdrawing the 2 outsider tubes leaving the 2 in the middle ---> XOOX"


Interesting! Would this also work on my 1986 JCM 800 Lead Series 50 watt combo 1x12? I only use this for practicing in the house now and would love to reduce it's output.

 

[jcm900]

I don't experiment this yet, 'couse I don't have time.
I think it will work in your amp too.

Good luck

 

[superleadfixer]

"You can reduce the power from 100w to 50w by withdrawing the 2 outsider tubes leaving the 2 in the middle ---> XOOX"


Interesting! Would this also work on my 1986 JCM 800 Lead Series 50 watt combo 1x12? I only use this for practicing in the house now and would love to reduce it's output.

Don't try to play your amp with only one tube......this won't work and will damage your OT (for a 50w)

 

[Erim]

I have a JCM 900 SLX Model 2100 - 100w/50w - If I am running it on power drop (50w) do I also need to switch the Impedence? Or is that only if I actually am removing tubes?

 

[PTV]

A PB100 in a JCM900 head with the clean channel cranked is a very good tone, but I found mine did hum quite a bit!

 

[stryker59]

imo, the pulling of the tubes will work if u do the steps given here, however i think that affects the tone to much! i can hear the difference in tone between a 100 watt amp and the same amp in a 50 watt version. personally i like the 100 watt sound better. i would go w/ a thd hot plate or similar(weber) attenuator. the power brake is not a very good attenuator in my opinion, it changes the tone to much. however on the flip side, if u pull the tubes u may like the sound better, so its trial and error, just make sure u understand how they are telling u to do it!