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carvin tube 100 tried 6L6's

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davidfugler:
I tried some 6L6 tubes in a Carvin tube 100, and the lowest bias I could get was 48 milliamps . I'm wondering if there's a resister I can change, to get that lower? I read a lot of really good reviews on the Tung-sol 7581A, so I'm trying those. Also, I'm wondering how short the life of the tubes would be if I try leaving it as is? Thanks

rnolan:
Hey David, I have a Carvin TS100, I bought it when my B200s was playing up.  It has 6L6 tubes, they can also take EL34s (I'd try the Mullards, they sound nice in my 1972 Marshall 50w), there's a switch for each channel inside it, you can also run one channel with 6L6 and one with EL34 (but not in bridged mode), although not something I'd bother with, although you could change one channel to EL34s and then compare.  The TS100 is a very clean tube amp e.g. you can run studio monitors off it.  I like it, and have no need for the presence knobs at all so I leave them off.  You said on the other post that you find it a bit top heavy, it's a very flat clean amp so maybe try a bit less tops and more bass on your patch  :dunno: .  With your MP2, just turn the room eq knob counter clockwise, the further you go the more bass you'll get.  The bias topic is interesting, my understanding of bias in a tube push pull output circuit is it's about limiting cross over distortion at the point where one tube takes over from the other as in one tube does the +ve side of the signal and the other the -ve (think a sine wave).  The amp manual (all 4 pages of it) explains how to set the bias, it's not about getting it lower or higher (unless you are trying to get output distortion or some such), it's about getting it right so the 2 tubes produce the signal correctly and cross over seamlessly.  BTW Carvin recommend 50mA not 48mA or lower (which will introduce cross over distortion).  The Tung-sols should be nice as a 6L6 equivalent.  As (if) you are not trying to get output tube distortion and pushing them hard (i.e. you can get 100w out of a pair of EL34s or 6L6s (50w each) but they are working hard), the tubes should last quite a long time.  I have GT 6L6s (the ones it came with) and they are still fine after quite a few years.The TS100 has 4 12AX7 tubes, 2 per channel.  The first is a buffer tube (and a lower gain 12AU7 would probably be better  :dunno: ), the second is the phase splitter (one triode does +ve side, the other the -ve side) which just splits the signal so the +ve goes to one power tube and the -ve to the other for the push pull output.  12AX7s are not great phase splitters, it's not their DNA, probably better to go with a 12AT7, lower gain but higher current, you don't want gain from a phase splitter but more current will push the output tubes harder.  Then this is suited to say an older Marshall (pre master volume control models) when/if you want to add output tube distortion and not so much for a really clean amp like the TS100.

MarshallJMP:
You can even go to 60mA, don't forget this is for 2 tubes so if you have matched tubes each one will draw 25 or 30 mA

davidfugler:
this is with a bias probe, under one tube, but these tubes are rated at 35 watts each. I wonder if that gives me a little more to play with. Also, I'm thinking the bias pot is 20K. maybe 25 or 30K for the pot?

MarshallJMP:
If that tube is rated for 35w 48mA will still be safe for the tube (around 68% of max power) but it will stress your power supply a bit more.
Is you bias pot maxed out? Can you measure the negative grid voltage? Changing the pot won't help if maxed out.
Could also be a leaking decoupling cap, do you have the same reading for all the tubes?

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