tweaker 15 running 40 ma per tube at 466volts?

[jamme61]

I know its cathode bias but isn't this way to hot for 6v6 tubes? I also tried some nos 6l6wgb tubes and they were running around 50 ma per tube, still to hot, right? I didn't check the bias until I noticed the amps tone change after it was on for some time. The tone would start to get a little mushy in the bass and just not sound as good. thinking of changing cathode resistor, stk it has a 10 watt 220 ohm resistor, was thinking going to a 500 ohm, sound right? anyone else have this problem? why did egnater bias the amps so hot? thanks for any help.

[Colossal]

Yes, 40mA is smokin' for a 6V6! Something seems amiss there.

FWIW, I ran a 6V6 Plexi with a pair of JJ 6V6Ss at 460V but biased to just 18-20mA (about 70-80% of max dissipation for a 6V6 at that voltage). NOS 6V6s did not appreciate voltage that high but the JJs do just fine and withstood the abuse without complaint. They are really more of a mini-6L6.

For 6L6WGB however, 40mA is reasonable at that voltage, 50mA running on the high side.

If your sound is getting brown and bass is lacking clarity, sounds to me like your PT is saturating. This could be due to a failing PT or a PT that is undersized to the load it is intended to handle (a typical cost and quality-cutting measure to meet a price point). So if the amp was operating correctly but now the power tubes are well above the intended bias set point, then I would look elsewhere in the amp. I don't think Egnater would set an amp up with these conditions and expect them to withstand the rigors of the consumer market.

[jamme61]

thanks I just changed the bias resistor to 500 ohms(all I had) any way got the 6v6's down in the 20's and the 6l6's in the 30 ma range. I'll have to see how that works out but what you said about the transformer is something I have to watch for. Thanks

[Colossal]

thanks I just changed the bias resistor to 500 ohms(all I had) any way got the 6v6's down in the 20's and the 6l6's in the 30 ma range. I'll have to see how that works out but what you said about the transformer is something I have to watch for. Thanks

The 20s is still quite hot for a 6V6. 20-22ma for a 6V6GT or GTA is on the high side. A JJ 6V6 can probably handle it but you are pushing the limits of dissipation. I've successfully run tubes quite hot for the tone, but never beyond their limits, new production or old stock tubes. I dunno man, you shouldn't "have" to change the stock cathode bias resistor in that amp unless they are truly running those voltages. I just can't believe that despite the encouraged tone-tweaking flexibility the amp's name implies that Egnater would run those tubes that hard, risking high probability of failure in the consumer market. Have you checked with them? They were willing to help me with sanity checks when I had a couple of their amps on my bench for repair. I am more inclined to believe that some other condition has changed in the amp that has resulted in excessive bias.

Have you taken voltages throughout, noting any asymmetry or anything else that might be blown?

[M Fowler]

why did egnater bias the amps so hot?

The amp is called a tweaker for a reason

Your getting closer to the desired bias but how does the amp sound? Colossal is on to something in the fact that something in the amp has changed since it was new to cause the bias to shift so much or plate voltage to increase?

What type of power supply is the amp running, I have no idea what this amp is based off of.

Mark

[jamme61]

Amp sounds fine but need to play it for a couple of hours to make sure. I did read online where someone was talking about tubes runing to hot in his tweaker and Bruce Egnater, chimed in and sugested he change the bias resistor. Can't find it but know I read it. when my amp turned to mush (after playing it for a couple of hours) it made me wonder about the bias. I can't imagine egnater biasing the amps so hot either? I think I'm good now but, time will tell if there's more to this.

[Structo]

Keep an eye on the power tubes when you play to be sure they aren't red plating. ( too much current!)