AmpTalk.com

[renegade731]

I'm about to replace the tubes in my amp. I have a JCM800 (model 2210) 100watt dual channel w/reverb head. Which tubes should I get to give me a full thick tone rich sound? However, I don't want my sound to end up being muddy, but I really want to get a thicker sound. I hate to admit this but I bought the amp about 10 years ago and never have changed the tubes. I bought it used and there's no telling how long it had been since the tubes were changed before I bought it if they were ever changed.
One other thing, I've just recently heard that my ohm setting on my amp should match the ohms on my speakers. I have a KMD cabinet with Celestion (sp?) speakers. However, I have no idea what ohms the speakers are. Should I just try to change the ohms on my amp and see if it affects the tone and go with what I think sounds best? Or does the ohms have to match?

[1911]

Renegade:

Generally JJ ECC83/12AX7 tubes will darken and thicken your sound without muddiness. EI ECC83 tubes will usually give you harder drive but keep their edginess. The SovTek tubes usually sound a bit nasally and boxey in a Marshall. For power tubes the JJs are excellent. The EIs are a bit hit and miss due to uneven quality control (I have been told they are going out of business-sad day!). I haven't tried the Electro Harmonix, but I understand they are good (I didn't have luck with EH in my Fender).

As to your cabinet, there are a couple of different ways to find your cab impedance. First, if the back is removable, open it up and see if the speakers have labels which tell their impedance. Then note how they are wired (series will be one speaker's + to the next speaker's - and the impedances of the speakers will be the first plus the second. Parallel will be one's + to the next one's + and - to - and the individual impedances will half). If you have a multimeter, the easiest way is to plug the speaker lead into the cab and measure the impedance. The measured reading will be about 70% of the actual cab impedance (i.e. 4 ohms will read about 2.6, 8 will be about 6 and 16 will read about 11-12). Hope I have helped.

[renegade731]

Thanks allot. I really appreciate your help. Does matching the ohms on the amp and cabinet affect the tone any? What other importance is there to matching them? I know that may sound dumb, but in all of my 19 years that I've been playing, I never really learned the importance of any of this. Wish I had now... lol.

[1911]

The biggest worry with mismatching impedances is that the output transformer can often heat up and may fail over time if the impedance is extreme. Mismatches can also tube life as well. The age old rule is :With a tube amp, you can safely use a cabinet with an impedance AT OR LESS than the amplifier's rated impedance. The opposite is true for solid state amps. Generally, for most efficient power transfer, you want amp and cab to match. I have known players who mismatched on purpose, saying the mismatch punished the amp and helped make their sound. These were the same guys using variacs and such and-perhaps as a side effect-replacing transformers as well. They saw it as a necessary evil, but I don't like to punish the amp if I can help it. Luck, Bill.

[Goes_To_Eleven]

Your head would sound better just by re-tubing it in the first place, but I'd recommend the Electro-Harmonix tubes. I have them in my Super Lead and Jubilee 50-watt and they sound great. Nice, rich distortion without muddiness, and they're pretty quiet too. I use the high-gain 12AX7 EH tubes and EL-34 power tubes and have been very happy with the results: rich, clear, and very musical.

[arclight05]

HI math time ... with a quadbox generally you have two speakers in series conected to another pair in series and thesre two pair then conected in parralel eg 8+8and 8+8which is 16 in parrale with 16. to calculate spekers in series / parralel its 8x8 divided by 8+8 .......or 64divided by 16 which equals 4 ohms ... for 16 ohm speakers its 16x16 divided by 16 plus 16 which is 256 over 16 which equalls 8 ohjms now you know