Need help buying NOS power tubes!

[BigKD]

I want to buy some NOS power tubes for my mark III and mark IV. Problem is that most of the online vendors who are familiar w/ the mesa bias range either don't have the NOS tubes I want or are charging way too much. I found a guy w/ a real nice selection of NOS 6v6s that I want to try in my mark IV. Unfortunately, he's not much of a guitar guy...so we couldn't come to any conclusions regarding the tubes I want. Are there any specs I could provide him so that he can pick out some tubes from his stash that will function properly in my mark IV? I also want to buy some tesla el34s from him for the mark III.

Thanks in advance! This is my first post and this board is an amazing resource for boogie owners.

 

[stokes]

Unless you can find a vendor who is willing and able to put some tubes in a MKIV and see where they sit as far as idle current goes,you will have to add an adjustable bias pot to your amp and learn to set your own bias.If you are a half assed solderer and know a minimal about circuits,its quite easy and inexpensive.Its a very valuable mod,you can then buy any matched tubes and set the bias where you want.I wouldnt recommend using 6V6's in a MKIV,by the way.

 

[BigKD]

Unless you can find a vendor who is willing and able to put some tubes in a MKIV and see where they sit as far as idle current goes,you will have to add an adjustable bias pot to your amp and learn to set your own bias.If you are a half assed solderer and know a minimal about circuits,its quite easy and inexpensive.Its a very valuable mod,you can then buy any matched tubes and set the bias where you want.I wouldnt recommend using 6V6's in a MKIV,by the way.

Why no 6V6s in the mark IV? There are lots of positive reviews on this forum for mark IVs w/6V6s. Mesa states that it's ok as long as you flip tweed power, simul class, and connect an 8 ohm cab into the 4 ohm jack. I started another thread asking if a lonestar might be a better choice for the 6V6/deluxe tone I seek. We'll see what people think.

I can tell some venders when I'm ordering, "hey this is for a mesa" and they know which "range" of tubes to send me. So why can't I find out this range and use it to buy NOS tubes that I can just pop into my amp? That's my question.

As far as the bias mod goes...I'm pretty much a newb when it comes to circuits and soldering, but I want to learn. I'm going to start by learning to solder up my own cables. I could probably find a tech around here to do the mod.

 

[stokes]

Why no 6V6's?Because the amp is designed to use 6L6GC's or EL34's.If you have to keep the amp switched to a lower power mode to make it safe to use the 6V6's what happens if you mistakenly have it set to full power or some inquisitive nimrod touches your amp when you aint looking?You blow something up,maybe the tubes,maybe your PT.I'm old school when it comes to amps and using an amp for something it wasnt designed for is not good.
What Mesa says is acceptable bias range for tubes isnt always the optimal bias setting,it is "safe",but not always the best.It is always very cold.I have seen 2 sets of tubes that are supposedly the same bias range vary by 10 to 20ma's,there are economical reasons for this,as well as Mesa's whole scheme with their "fixed" bias scam.Why spend the premium price for NOS tubes if they are gonna sound like *** at a cold bias setting?I suspect this is why NOS vendors dont want to get involved with Mesa'a scheme.I would not recommend using NOS tubes without the bias mod.I have worked on hundreds of Mesa amps over the years and cannot remember not doing the mod on any I have had on my bench.Even when using current production tubes it is quite beneficial.If I am doing a cap job on a Boogie,I do the mod for free,it is that easy and the part is about $2.

 

[BigKD]

Why no 6V6's?Because the amp is designed to use 6L6GC's or EL34's.If you have to keep the amp switched to a lower power mode to make it safe to use the 6V6's what happens if you mistakenly have it set to full power or some inquisitive nimrod touches your amp when you aint looking?You blow something up,maybe the tubes,maybe your PT.I'm old school when it comes to amps and using an amp for something it wasnt designed for is not good.
What Mesa says is acceptable bias range for tubes isnt always the optimal bias setting,it is "safe",but not always the best.It is always very cold.I have seen 2 sets of tubes that are supposedly the same bias range vary by 10 to 20ma's,there are economical reasons for this,as well as Mesa's whole scheme with their "fixed" bias scam.Why spend the premium price for NOS tubes if they are gonna sound like *** at a cold bias setting?I suspect this is why NOS vendors dont want to get involved with Mesa'a scheme.I would not recommend using NOS tubes without the bias mod.I have worked on hundreds of Mesa amps over the years and cannot remember not doing the mod on any I have had on my bench.Even when using current production tubes it is quite beneficial.If I am doing a cap job on a Boogie,I do the mod for free,it is that easy and the part is about $2.

Very good advice. I will definitely look into getting the bias mod. Does the new bias pot affect both the inner and outer sockets or do you need a pot for each set of tubes? I'm no amp tech at all, but couldn't having only one pot cause issues if you are running 6L6s and eL34s in simulclass?

And finally, in all of those amps you have worked on, did properly biased NOS power tubes bring some extra tone to the table?

 

[stokes]

Doesnt cause any more problem than having just one resistor setting the bias voltage,but you do have to be mindful of which pair you target when using 6L6/El34 in combination.

 

[BigKD]

Doesnt cause any more problem than having just one resistor setting the bias voltage,but you do have to be mindful of which pair you target when using 6L6/El34 in combination.

Rather than only measure one tube, do you take measurements on both tube types and then adjust the bias to where both are in a good range? As I said, I'm learning about this stuff so maybe it's not possible to measure two tubes at once?

 

[stokes]

Yes,it is a sort of balancing act.You have to monitor both sets of tubes and find a safe middle ground.I did work on one MKIV where the owner wanted to use 6L6 in all four slots and we tried to "balance" things by adjusting the resistors feeding the tube grids in the bias circuit,because of the OT configuration,we couldnt get it dead on,but it was closer.

 

[BigKD]

Yes,it is a sort of balancing act.You have to monitor both sets of tubes and find a safe middle ground.I did work on one MKIV where the owner wanted to use 6L6 in all four slots and we tried to "balance" things by adjusting the resistors feeding the tube grids in the bias circuit,because of the OT configuration,we couldnt get it dead on,but it was closer.

So there is no way to do a bias mod that includes a separate pot for inner and outer tubes?

 

[stokes]

You could but it would be complicated,dont know if you could find room for an entire seperate supply.

 

[talltxguy]

In a month or two (depending on $), I will have my tech put adjustable bias with test points on my Lonestar so that I can control the inner two tubes with one pot & the outer two tubes with another pot. And my tech confirmed what Stokes said...it is complicated.

I realize you don't have a Lonestar, but the idea is the same. I too would like to run some NOS output tubes!