Half power switches

Iron_Man · Post by **Iron_Man** » Fri Jun 06, 2003 4:14 pm

Hi again folks,
I've come across various amps in my browsing, that have a switch to run them at half power, namely JCM900 Marshalls and Fender Dual Reverb(i think).

I was just wondering if this could be done as a mod to an amp? Namely an AD15 as I'm planning on buying one, and with a half power switch I'd be able to crank it 100%.

Thanx for any help guys <img src=icon_smile.gif border=0 align=middle>

Smoke me a kipper, I'll be back for breakfast...

Post by **bclaire** » Fri Jun 06, 2003 9:27 pm

Hmmm... I'm no amp tech, but the way those half power things usually work is they cut out two power amp tubes when there are four.... that's how my Marshalls worked. Billy

Iron_Man · Post by **Iron_Man** » Sat Jun 07, 2003 4:13 pm

Ah, so if the AD15 runs on 2 tubes I just bypass one of them? Or does it have to be 2 tubes at a time or something?

I don't fully understand all the electronics and biasing technology etc, that's why I'm unsure.

Thanx for the reply!

Smoke me a kipper, I'll be back for breakfast...

Gladmarr · Post by **Gladmarr** » Fri Jun 27, 2003 7:49 am

I think marshall used the switch as a Triode/Pentode switch. When the tubes are in triode mode they put out about (?) half the power. Fender probably did a power supply switch, so that half power was half the voltage going to the plates of the tubes. Mesa/Boogie and Acoustic did the thing where the 1/2 power option was to lift the ground from the cathodes of two of the tubes - no ground means no source for electrons, so the tube won't conduct. I know this doesn't help you with your mod per-se, but you could look into hooking up those power tubes as triodes - not easy, but if you're feeling adventurous....

Gladmarr Audio Laboratories

Post by **bclaire** » Fri Jun 27, 2003 3:36 pm

<BLOCKQUOTE id=quote><font size=1 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>
Ah, so if the AD15 runs on 2 tubes I just bypass one of them? Or does it have to be 2 tubes at a time or something?

I don't fully understand all the electronics and biasing technology etc, that's why I'm unsure.

Thanx for the reply!

Smoke me a kipper, I'll be back for breakfast...
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>
I don't think a half-power mod would work on an AD15.... it shouldn't even be necessary... that would make it a 7.5 watt amp then.... and 15 is pretty low to begin with. Most half power mods that I've seen are only for amps with four power tubes- Billy

Half power switches

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