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Blues custom - Biasing?


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Posted

Hey guys, I just need a bit of advice - I recently bought a pair of tube amp doctor 6L6WGC-STR's for my bc30.

After a year of playing the stock sovteks these things really took my tone from a bit sterile to sweet overdriven blues. The only problem is one of them just blew, after about 3 hours total use.

All the others a fine but after dishing out money only a couple of days ago for them I am gutted. Could it just have been a faulty tube or does the bc30 need biasing and what not to use new tubes longer than a few hours (i was under the impression the amp doesn't need to be biased manually)?

I dont really want to buy more tubes and have them blow on me whilst gigging (or blow at all for that matter).

 

Cheers,

 

Gareth

Posted

Sounds like a bad tube to me. The BC30 is cathode biased so you should be able to swap 6L6's with no bias requirements. I replaced the original nasty Sovteks with some decent NOS RCA's and have had no problems whatsoever.

Posted

Thank you, that answered my question. I dont suppose you know if the rectifier valve affects tone and would be worth replacing, or am i right thinking its to do with converting ac-dc and doesnt have a part in the tone signal?

Posted

Right. The rectifier does not affect the tone. However, the rectifier does affect the power to the other tubes in your amp. This is why when you hit chords or even use a harder attack on your notes the sound from your amp will "sag". Your tone remains the same but the power or sound of your instrument through the amp will momentarily sag. Some folks refer to this as compression (it's not). Some people like this sagging and make good use of it. Others don't like it and find no use for it. In my BC30 a 5AR4 is used as the rectifier. I like the sag. If you don't like the sag there is a device that is a solid state rectifier. It plugs directly into the rectifier tube's socket. This pretty much eliminates the sag. I am not sure if there is a solid state direct replacement for the 5AR4. Someone who knows their tubes better can tell you.

Posted

Twanger - really nicely put and well described.

 

From my very limited experience there seems to be a 'bounce' which you get with tube rectifiers which isn't there with ss. Also when I replaced the stock 5AR4 with a NOS GZ34 (in this case a used but almost perfect tesing 1959 Mullard) there seemed to be more control in the sense of how the amp responded to attack and vibrato. Almost impossible to quantify and in all possibility could be in my head as an effect of expecting an improvement but it definately made the amp feel more 'springy' (trying to find an apt description here!)

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