Svetlana 6L6 Bias BDRI

[Jon Barr]

Hello all,

I switched tubes in my BDRI. Jan Phillips 5771 (v1), tungsol ax7 (v2) and tungsol AT7 (v3). Power tubes are Svetlana 6L6gc. After playing for an hour the bias is reading 92.3V. Is this too high?

The Svetlanas are orange and a slight blue colour. Pre amp tubes are orange. No red. It’s a nice sound and I’d like to keep it around this setting, just don’t wanna cook the tubes out too fast. I’m on a poor mans budget lol. If anyone could chime in, that’d be great, special thanks!

Jr

 

[Gtrjunior]

Re: Svetlana 6L6 Bias BDRI

What’s your plate voltage?

 

[Jon Barr]

Re: Svetlana 6L6 Bias BDRI

With the amp in standby the reading is 58V. With the amp fully on, the reading is 92.3V

 

[Gtrjunior]

Re: Svetlana 6L6 Bias BDRI

Plate voltage is typically +\- 500v. I’m not familiar with your particular amp but all 4 of my tune amps read somewhere in that region (el34).
I suspect your not reading the voltage correctly.

 

[Lake Placid Blues]

Re: Svetlana 6L6 Bias BDRI

What is a BDRI?

 

[Gtrjunior]

Re: Svetlana 6L6 Bias BDRI

Not your exact amp but I’ll bet it tells you what you need to know.

https://youtu.be/19IUadZJf-c

 

[Gtrjunior]

Re: Svetlana 6L6 Bias BDRI

What is a BDRI?

Blues deluxe reissue I’m assuming.

 

[Gtrjunior]

Re: Svetlana 6L6 Bias BDRI

More info backing the setting in the video.

https://forums.fender.com/viewtopic.php?t=41432

 

[Lake Placid Blues]

Re: Svetlana 6L6 Bias BDRI

After looking up some information, the test point is for both tubes. The plate voltage is about 410v. With 6L6GCs, 92ma (mv = ma in this case) is 46ma per tube which is 63% of the plate dissipation. That's safe and not too hot or too cold.

 

[JMP/HBE]

Re: Svetlana 6L6 Bias BDRI

Pretty clear you don't know what you're doing.

Take your amp to someone who does.

 

[Jon Barr]

Re: Svetlana 6L6 Bias BDRI

Thanks for the help guys! The bias at 92ma seems hot but no cherry red. My strat sounds fuller. The 59 humbuckers in my sg really push the amp at this bias. There’s lots of distortion and overall much louder. Is this normal?? I’m thinking it’s just the hotter output of the Hums and there breakin up. Please correct me if I’m wrong.

Jr

 

[Gtrjunior]

Svetlana 6L6 Bias BDRI

Thanks for the help guys! The bias at 92ma seems hot but no cherry red. My strat sounds fuller. The 59 humbuckers in my sg really push the amp at this bias. There’s lots of distortion and overall much louder. Is this normal?? I’m thinking it’s just the hotter output of the Hums and there breakin up. Please correct me if I’m wrong.

Jr

Your bias is waaaaaaay too hot man. 60mA
Didn’t you watch the video I posted?

 

[JMP/HBE]

Re: Svetlana 6L6 Bias BDRI

"She was sounding really good just before the smoke & flames."

 

[Lake Placid Blues]

Re: Svetlana 6L6 Bias BDRI

It depends on the actual plate voltage of the specific amp. And if the power tubes are a matched pair. Reported plate voltages vary quite a bit from around 400v to 455 volts. So take it to some one that can safely measure the plate voltage of your specific amp.

 

[Lake Placid Blues]

Re: Svetlana 6L6 Bias BDRI

Don't scare the OP. 30 ma per tube is only 60% if the tubes are 5881s and the plate voltage is as high as 455. If the tubes are 6L6GC then it's less than 50% plate dissipation, even at 455 plate volts. That's pretty cold. But the tubes are more likely to last past the warranty. As the current increases the plate voltage will drop some too.

 

[Gtrjunior]

Re: Svetlana 6L6 Bias BDRI

Don't scare the OP. 30 ma per tube is only 60% if the tubes are 5881s and the plate voltage is as high as 455. If the tubes are 6L6GC then it's less than 50% plate dissipation, even at 455 plate volts. That's pretty cold. But the tubes are more likely to last past the warranty. As the current increases the plate voltage will drop some too.

I agree. I was referencing the video I posted as well as the forum link. 30mA/side is definitely a safe albeit possibly cold bias.
I say possibly because some amps (like my quickrod ) actually sound better with a colder bias and because according to the forum post 30/side (60) is factory recommendation.
I think somewhere between my suggestion and your suggestion is probably perfect for the amp.


But yes....let’s help the op and not be harsh. This is how we learn.

 

[Jon Barr]

Re: Svetlana 6L6 Bias BDRI

The bias at 92ma does seem quite high at 46ma per tube. Although lake placid did do the research and you confirm this to be fine. I appreciate that. I’m going to drop it down to 64ma to 80ma altogether ( so 32ma to 40ma per tube) and see what sounds the best to my ear. I’d rather be safe than sorry. I’ll take it in to get it properly diagnosed. I need to find a tech here in the city (Ottawa).

Lake placid and minion. You both share the same picture. Appears to be Duane allman and Clapton? Very cool. The recorded sessions they did are on YouTube by the way. Which you likely already knew or you have vinyl. In which case I’m very jealous of that lol. Anyways, thanks for helpin me out. Special thanks,

Jr

 

[Lake Placid Blues]

Re: Svetlana 6L6 Bias BDRI

The bias at 92ma does seem quite high at 46ma per tube. Although lake placid did do the research and you confirm this to be fine. I appreciate that. I’m going to drop it down to 64ma to 80ma altogether ( so 32ma to 40ma per tube) and see what sounds the best to my ear. I’d rather be safe than sorry. I’ll take it in to get it properly diagnosed. I need to find a tech here in the city (Ottawa).

Lake placid and minion. You both share the same picture. Appears to be Duane allman and Clapton? Very cool. The recorded sessions they did are on YouTube by the way. Which you likely already knew or you have vinyl. In which case I’m very jealous of that lol. Anyways, thanks for helpin me out. Special thanks,

Jr

Yep, I'm a ABB fan boy. love em. All eras.

This is the reason knowing your plate voltage is helpful.

If it's 455 then the math is:

30 (watts plate dissipation of 6L6GC)/455 = 66ma (100% plate dissipation current.) 46 ma = 70% plate dissipation. 70% is considered the high end of safe and many like it there. Therefore many techs set it there.

If it's 475 volts however:

30/475 = 63ma. 46 ma = 73% PD. It might not be red plating but it is getting beyond the safe zone. It might have shrill highs and muddy lows too.

If it is 410 volts as reported in some articles:

30/410 = 73 ma. 46 ma = 63% PD

 

[Darg1911]

Re: Svetlana 6L6 Bias BDRI

Does anyone still make a 6L6/6L6G/6L6GB anymore? I think those were all 20 - 25 watt tubes (or thereabouts, depending on the suffix) with max plate voltage ratings of 350-400V or so (again, depending on the suffix letters). The 6L6GC is rated for 500V on the plates and a max dissipation of 30 watts. I thought that I read that all current production 6L6's were 6L6GC's regardless of the suffix letter they tag on the end. But I could be wrong. That said, Fenders recommended 30ma per tube (60ma total) may be an attempt to more approximate the tone of the original BD's. Or, it may be a way to add some longevity to the tubes. Or, maybe a bit of both. Just a guess.

I would experiment with the bias. The amp may sound better with a colder bias. Or not.

 

[Jon Barr]

Re: Svetlana 6L6 Bias BDRI

Safe to say if I’m in the low 40ma per tube I should be safe. That’s good to know. Do the humbuckers push the power tubes harder than single coil?

Yes the allmans are a favourite of mine too. What’s not to love about em. The good old boys from down south, straight rock n rollers with country and jazz influences. Likely get in sh!t for sharing this, seeing as it’s off topic but ABB songs that stand out to me.

“Dreams” with the organ (Leslie) opener off the flrst album
“High Falls” - 11 minute instrumental by Dickey off Win,lose,draw
“No one left to run with” - where it all begins album

Marshall tucker band too!

Peace