Talk about tubes and their effect on your tone

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Mark III
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Post by jnoel64 » Thu Aug 03, 2017 1:36 pm

Not sure whether to post this here or in the Mark V section, but....

Has anyone tried the TAD 6L6WGC-STR in their Mark V? I have been using TAD 6L6GC-STR until one of the plastic center pieces broke off one one tube. I am thinking of putting the WGCs in the middle pair and wondered if anyone has tried this or something similar.
TC-50, Mark V, Electra Dyne, Road King I
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Triple Recto
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Post by bandit2013 » Sun Aug 13, 2017 11:33 am

If you did not break off the glass tip that is protected by the plastic boss you can still use the tube. I have done the same thing with the TAD 6L6GC-STR tube. I even glued the plastic part back on but that did not work for long. I did mark where the guide pin should be on the plastic bass with a silver sharpe pen so I do not index the tube improperly when inserting it. I had to mark the ceramic sockets on the RA100 head as the original owner chipped out the center section to use other tubes in that amp. I can easily place tubes in that amp indexed incorrectly so I check to verify the heaters turn on with the amp in standby first after inserting the tubes. If the heaters work the tube is inserted properly. I am not sure if the inner and outer pair of tubes need to match and it may be possible to run a tube with early distortion in the outer pair vs the inner pair. However, 10W mode may or may not be ideal. Note that the outer pair of tubes has a different signal strength than the inner pair of tubes due to the resistors on the control grid and voltage divider network so the inner and outer pair need not match when running the amp in 10W mode (uses cathode bias on the two tubes closest to the rectifier tube and the other tubes remain connected to the grid bias but are not used to amplify the signal hence they operate as dummy loads as they will use the them similar to a current mirror effect, or it could be used to turn the OT into a saturable reactor, not really sure what is going on. Just some thoughts on how it may be operating in 10W mode but that would effectively reduce the output level).

That could be interesting if you place more sensitive tubes in the outer pair ( Cold bias) and tubes of different gain characteristic on the inner pair (best suited for hot bias class A) that would sound great. I have done this with the Mark IVb using the TAD 6L6GC-STR after I killed one of the quads. The simul-class circuit was very similar to the Mark V but not as hard on tubes. I still have two TADs that are good and will have to give it a try again. I just could not replicate the sinister tone I got from the Mark IV with TADS and =C= tubes. Tried that in the Mark V but may have had the tubes reversed as the outer pair was the class A push pull and the inner pair was the Class A/B on the Mark IV.

It should work. As a reminder with the TAD tubes, the plastic base keyed post may be a bit thicker than it should be so mark the base of the tube where the key is located so you can still use the tube if the post breaks off on the other tubes.

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