Plate current range for 6L6 and EL34 tubes in Mark V

[kreatorkills]

Can someone please tell me the proper plate current range for 6L6 and EL34 tubes to be used in a Mark V. The highest and lowest on each that would be safe. Thanks.

 

[Nicklotsaguitars]

450v dead on with mine full power. Regardless of where the valve type switch is set.
386v variac. Get +/- 1v drift on this mode though

Sort of explains why Mesa say to use the amp in variac mode with EL34's. 450v is maximum plate voltage for them.

 

[Nicklotsaguitars]

Saying that, of the Marshalls I've had through, I kept notes on their plate voltages. Just so if they came back I could check to see all was ok with that. I've never seen one less than 463v. My 800's run at 474 and 482v.

 

[bandit2013]

You got the plate voltage vs plate current... What the highest or typical current for the center pair of tubes should be the measurement you need (note that this will be operating extended class A push/pull and not the traditional Class A/B that is common for other brands of amps as well as the RA100, Rectifier series, and the JP2C). Unfortunately I cannot report what the plate current is as I have no means to measure it. Also note that the Mark V runs in Cathode bias (assuming the schematic that I have seen is correct) for the 10W mode vs the grid bias in 45W and 90W.

 

[kreatorkills]

You got the plate voltage vs plate current... What the highest or typical current for the center pair of tubes should be the measurement you need (note that this will be operating extended class A push/pull and not the traditional Class A/B that is common for other brands of amps as well as the RA100, Rectifier series, and the JP2C). Unfortunately I cannot report what the plate current is as I have no means to measure it. Also note that the Mark V runs in Cathode bias (assuming the schematic that I have seen is correct) for the 10W mode vs the grid bias in 45W and 90W.

Maybe i didn't make myself clear on what I'm looking for. I bought a quartet of ruby 6L6GCMSTR tubes from amazon for $49.99. I love the ruby EL34BSTR tubes and usually by them from Doug's but i wanted to try the 6L6's and amazon had them way cheaper than Doug's so i thought I'd try them. When they arrived they were marked on the socket and the box with a "PC 48" which i thought means plate current and which i also thought was extremely high. I tried them for only a couple of minutes though and there was definitely something wrong. Channel 2 and 3 sounded really distorted and channel 1 sounded awful and had no head room, so i returned them.
I don't know much about tubes and mesa tubes aren't marked so I'm trying to figure out what numbers mean what and whats recommended.

 

[bandit2013]

That is a hard call as tubes with certain markings usually may have another meaning than what may be implied.

Funny that you mentioned that as I have a quad of those I bought from Doug's Tubes specifically for the Mark V.

Doug's label states plate current of 21.9mA and Transconductance of 2400. The Ruby label indicates the PC 37 and TC 3125. The difference being how the tube was sorted and or tested and at what plate voltage was this test conducted. So the Ruby 6L6GCMSTR will sound almost identical to the Mesa Branded tube (since they are identical) but will have a slightly different tone than the Mesa Sorted tubes. In the Roadster I had a bit more treble but not much, in the Mark V they performed quite well, actually I think better than the Mesa branded tubes.

 

[ATR1]

How can I measure the plate voltage with out taking the PC board off inside that covers the tubes?

 

[user 41014]

Pin 3 is the plate. High voltage. Don't let your probe touch anything else.

The weber bias-rite is a much safer way and since they don't make them anymore you have to go used unless someone else makes one of these now.

 

[domct203]

I use the Eurotubes ‘Pro One’ bias probe. B+ and plate current in one box.

https://www.eurotubes.com/store/pc/bias probes.htm
I still have one of the Weber bias probes in a drawer somewhere. That just measures plate current using your multimeter. With the Pro One probe and my old Weber 90 degree adapter I don’t even have to pul the chassis anymore.

Dom

 

[user 41014]

I use the Eurotubes ‘Pro One’ bias probe. B+ and plate current in one box.

https://www.eurotubes.com/store/pc/bias probes.htm
I still have one of the Weber bias probes in a drawer somewhere. That just measures plate current using your multimeter. With the Pro One probe and my old Weber 90 degree adapter I don’t even have to pul the chassis anymore.

Dom

Good to know someone is making one. The weber I'm referring to is not probes but either a 1 or 2 pair digital readout from placing the test sockets between the power sockets and the tubes.

It's not simultaneous readouts but does give switched plate volts and mili-amps without pulling the chassis for a combo. Heads may not have the clearance.

 

[ATR1]

Thank you for the info.
I have a Eurotube single socket probe which I was able to find the PV. This amp is running 475v @70% approx. 44ma shooting for. I will be rolling tubes till I find a match set. this amp is 2009. Then I will test amp #2 to see if the ma matches amp #1 which is early 2001 I believe. These are combos.
Thx

 

[ATR1]

I have noticed that 8 of the MB 6L6GC tube I own measure in the high 20s ma. That seams cold for 6L6s. Correct me if I am wrong.
I just ordered 2 matched sets of JJ @ 44ma which should be 70% of my amp. Stock.

 

[user 41014]

JJ's used to be known for being able to take higher plate V abuse. I don't know where they stand now.

I believe most of the mesa tube rainbow is in the 20's-30's and you would be at the high end at 44mA. It's my understanding the factory bias is not at 70% given most of their select tubes are lower.

A bias pot or 7581A's takes care of that.