Roadster - BIAS - Results - Facts 6L6 and EL34 readings

[sfx70]

Hey guys
So here it is: i've measured voltages on my roadster with both the original Mesa 440STR 6L6 (rated 10 by Mesa) and EL34 (RUBY).

Here are my findings I wanna share with you guys: note the readings are PER TUBE (not all 4). I'm using bias probes.
NOTE: the bias voltage was measured about 1 minute after I powered my amp. The readings do go up about 5mV PER tube or so once things get hot. For the proper bias reading I used the Weber VST bias calculator at 70% dissipation (on the hot side) class AB.

RESULTS:

MESA 6L6 440STR - bias switch to 6L6

------------------ Bias (mV) ----- Proper Bias (mV) (70%) --- Plate Voltage (V)
----------------------------------------------------------------------
Bold ----- Diode --- 24 -------------- 46 ----------------------- 450
Bold ----- Recto --- 16 -------------- 50 ----------------------- 420
Sponge -- Diode --- 18 -------------- 57 ----------------------- 366
Sponge -- Recto --- 12 -------------- 61 ----------------------- 340



MESA 6L6 440STR - bias switch to EL34

------------------ Bias (mV) ----- Proper Bias (mV) (70%) --- Plate Voltage (V)
----------------------------------------------------------------------
Bold ----- Diode --- 58 -------------- 46 ----------------------- 450
Bold ----- Recto --- 39 -------------- 50 ----------------------- 420
Sponge -- Diode --- 42 -------------- 57 ----------------------- 366
Sponge -- Recto --- 28 -------------- 61 ----------------------- 340



RUBY EL34 BHT (PC 40) - Bias switch to EL34

------------------ Bias (mV) ----- Proper Bias (mV) (70%) --- Plate Voltage (V)
----------------------------------------------------------------------
Bold ----- Diode --- 41 -------------- 38 ----------------------- 450
Bold ----- Recto --- 25 -------------- 41 ----------------------- 420
Sponge -- Diode --- 29 -------------- 47 ----------------------- 366
Sponge -- Recto ---18 -------------- 51 ------------------------ 340


So to me without modding the amp you got a few options:

1. Run 6L6s on Bold - Recto with the EL34 bias switch on - that'll give you 39mV which will eventually will go up to 45ish - pretty close to proper 50mV (70% dissipation)
2. Run EL34 with PC reading maybe around 30 - 35 (earlier distortion) on Bold Diode - EL34 bias switch on
3. Run EL34 with PC reading around 50 (if you can find them) on Bold Recto - EL34 Mode
4. Depending on your preference if you do choose a tube that will work in one mode it's likely that it won't be properly biased in the other modes - which is super weird to me. No sure why Mesa did that...

Anyways, the amp is biased way too cold.

What I also did is I plugged in 2 6l6s and 2 EL34s on the EL34 mode and HOLY SMOKES!! The tones was awesome - no more fuzz just super amazing punchy warm tone - the issue with this setup is that the 6L6s are running too hot ,and the EL34s a bit cold.. I don't think you can damage the amp if you do this - the 6L6 tubes will go faster.

WHAT DO YOU GUYS THINK of all this?
Thanks

 

[fluff191]

Good read!

Its common knowledge that one of the only faults of Mesa is having their amps biased VERY cold, which is way alot of people (including myself) modify their own amps to bring the voltages up to where they should be.

 

[thejay]

Running two 6L6s and two EL34s at the same time... hmmmm I might try this. Does it matter in which order you place them? Possibly a stupid question - but hey you never know.

 

[paytojt]

And none of this would cause damage? What are some differences in tone with cold vs hot biases?

 

[sfx70]

Running two 6L6s and two EL34s at the same time... hmmmm I might try this. Does it matter in which order you place them? Possibly a stupid question - but hey you never know.

I wouldn't because the 6L6s will run way too hot and the EL34s a bit cold - u have to make sure that tube 1 and 4 are the same type of tube and 2-3 are the same type of tube..so

EL34 - 6L6 - 6L6 - EL34

Again, based on my bias readings I would NOT recommend this settings unless u find tubes that are running within decent bias parameters, otherwise you'll kill your tubes faster.

But I'll tell u this:the EL34s sounds waaaaaay better than the stock Mesa STR440 6L6s.It's like night and day - way smoother less fuzz.

 

[droptrd]

I had simular readings when I metered (bias probe) my rev G (sold). I used to run it with 6L6's in EL34 mode. less fizz and more warmth. I did notice the tubes were burning up a bit faster. normally would get 12 months of use - wnet down to about 10-11 months.

Hey guys
So here it is: i've measured voltages on my roadster with both the original Mesa 440STR 6L6 (rated 10 by Mesa) and EL34 (RUBY).

Here are my findings I wanna share with you guys: note the readings are PER TUBE (not all 4). I'm using bias probes.
NOTE: the bias voltage was measured about 1 minute after I powered my amp. The readings do go up about 5mV PER tube or so once things get hot. For the proper bias reading I used the Weber VST bias calculator at 70% dissipation (on the hot side) class AB.

RESULTS:

MESA 6L6 440STR - bias switch to 6L6

------------------ Bias (mV) ----- Proper Bias (mV) (70%) --- Plate Voltage (V)
----------------------------------------------------------------------
Bold ----- Diode --- 24 -------------- 46 ----------------------- 450
Bold ----- Recto --- 16 -------------- 50 ----------------------- 420
Sponge -- Diode --- 18 -------------- 57 ----------------------- 366
Sponge -- Recto --- 12 -------------- 61 ----------------------- 340



MESA 6L6 440STR - bias switch to EL34

------------------ Bias (mV) ----- Proper Bias (mV) (70%) --- Plate Voltage (V)
----------------------------------------------------------------------
Bold ----- Diode --- 58 -------------- 46 ----------------------- 450
Bold ----- Recto --- 39 -------------- 50 ----------------------- 420
Sponge -- Diode --- 42 -------------- 57 ----------------------- 366
Sponge -- Recto --- 28 -------------- 61 ----------------------- 340



RUBY EL34 BHT (PC 40) - Bias switch to EL34

------------------ Bias (mV) ----- Proper Bias (mV) (70%) --- Plate Voltage (V)
----------------------------------------------------------------------
Bold ----- Diode --- 41 -------------- 38 ----------------------- 450
Bold ----- Recto --- 25 -------------- 41 ----------------------- 420
Sponge -- Diode --- 29 -------------- 47 ----------------------- 366
Sponge -- Recto ---18 -------------- 51 ------------------------ 340


So to me without modding the amp you got a few options:

1. Run 6L6s on Bold - Recto with the EL34 bias switch on - that'll give you 39mV which will eventually will go up to 45ish - pretty close to proper 50mV (70% dissipation)
2. Run EL34 with PC reading maybe around 30 - 35 (earlier distortion) on Bold Diode - EL34 bias switch on
3. Run EL34 with PC reading around 50 (if you can find them) on Bold Recto - EL34 Mode
4. Depending on your preference if you do choose a tube that will work in one mode it's likely that it won't be properly biased in the other modes - which is super weird to me. No sure why Mesa did that...

Anyways, the amp is biased way too cold.

What I also did is I plugged in 2 6l6s and 2 EL34s on the EL34 mode and HOLY SMOKES!! The tones was awesome - no more fuzz just super amazing punchy warm tone - the issue with this setup is that the 6L6s are running too hot ,and the EL34s a bit cold.. I don't think you can damage the amp if you do this - the 6L6 tubes will go faster.

WHAT DO YOU GUYS THINK of all this?
Thanks

 

[thejay]

But I'll tell u this:the EL34s sounds waaaaaay better than the stock Mesa STR440 6L6s.It's like night and day - way smoother less fuzz.

Yes, I am currently using EL34s and I think they sound much better than the 6L6s.

 

[KH Guitar Freak]

I'm happy with my Winged C 6L6s in my Roadster, but them stock Mesa valves are actually not far behind in tonal awesomeness IMHO...

 

[sfx70]

It also depends a lot on what speakers you are using... I found the V30s to be a bit too ice picky for mesas in general - I believe the C90s (Black Shadown), or Eminence Legends are much nicer - less highs, tamed mids and more warmth - you crank as much highs as you want through the amp, but can't take'em out from the speaker.

Well for now, I will stay with EL34s in BOLD - DIODE (a bit on the hot side for me which is fine) or BOLD - RECTO (a bit on the cold side but not as bad as the original 6L6s).

BTW: what preamp tubes are you guys happy with? I found the original MESA Russian-1 weren't that great - I now have 4 TungSols 12AX7 and 2 Ruby 12AX7AC5

 

[KH Guitar Freak]

It also depends a lot on what speakers you are using... I found the V30s to be a bit too ice picky for mesas in general - I believe the C90s (Black Shadown), or Eminence Legends are much nicer - less highs, tamed mids and more warmth - you crank as much highs as you want through the amp, but can't take'em out from the speaker.

Well for now, I will stay with EL34s in BOLD - DIODE (a bit on the hot side for me which is fine) or BOLD - RECTO (a bit on the cold side but not as bad as the original 6L6s).

BTW: what preamp tubes are you guys happy with? I found the original MESA Russian-1 weren't that great - I now have 4 TungSols 12AX7 and 2 Ruby 12AX7AC5

I use a Mesa Stiletto 4X12 straight cab with V30s as stock, no issues with them...

 

[Kyemack45687]

Ok, so what happens if I run 6L6's in EL34/Diodes and the bias is a bit higher than suggested? Is it safe? If so, how much is that going to affect tube life?

 

[Jmcthe3rd]

I run 6l6's in my Triple recto set to spongy+recto. It looks like it would be totally safe to run this in EL34 mode. (The tubes will just wear out quicker) Am I correct in reading the chart this way? Thanks.

 

[sfx70]

Well Spong+Recto in EL34 mode on 6L6s are running this way

------------------ Bias (mV) ----- Proper Bias (mV) (70%) --- Plate Voltage (V)
Sponge -- Recto --- 28 -------------- 61 ----------------------- 340

That would still be pretty cold in my opinion.
Thanks

I run 6l6's in my Triple recto set to spongy+recto. It looks like it would be totally safe to run this in EL34 mode. (The tubes will just wear out quicker) Am I correct in reading the chart this way? Thanks.