Quote:
Originally Posted by Nilzon
OK Thanks, theres no marking of the tubes at all seen from the back.
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Hey welcome aboard. No matter what, all of your small tubes are 12AX7's. These are high gain dual triodes. V1 like SolarBurn has stated is the tube farthest away from the power tubes. It should have a polished metal shield covering it. To remove the shield, carefully twist the metal cover in either direction until the tabs on the cover match up to two slots in the chassis. The cover will now come off.
You will get the most gain change in V1 and V2. If you are changing the power tubes, the power tubes need to be biased. The JTM-60 is moderately difficult to bias and if you haven't done it, I would recommend taking it to a tube shop.
Also, try this thread for info on preamp tubes:
Preamp Tubes? - Who, What, When, Where, Why, and How?
Marty