bias question

[Woodsie]

I bought a bias probe from Eurotubes. i wanted to be able to check and bias my amp on my own. my local tech charges at Least $60. The directions that come with it say that you should only have to check one tube because they should be matched, therefore the same. I checked the bias on one tube and it was right around 44, as it should be. i decided to check the other one and, it was considerable lower. like 38. Is this a sign of poorly matched tubes? I just bought a new set of Winged C's from Tube Depot. They're supposed to be matched.

 

[LP Freak]

If they're within 5 mA they consider them matched. And you should always check all the tubes. If it's a 100w head you can add the mA of V4 and V5 and compare to V6 and V7. Swap the tubes around to get the closest match of the two pairs.

 

[Woodsie]

It's a Rockerverb 50 MKII. Two EL34s. They're at least 5, maybe 6mA apart. So it may not be a problem. Should I average them out? 1 at 40, one at 46, for example. Will that even make a difference?

 

[steve_k]

It's not a problem. When new they will likely be closer, but they will come out of their current matched state at different rates as the filaments wear. One tube in a 50 watt and 2 tubes in a 100 watt are usually doing a little more work than the others too even in a well balanced circuit.

 

[Anonymous]

You can also try swapping the tubes around meaning
just switch sockets they are in and sometimes depending
on screen current they may match up better but as Steve said
They usually drift apart over time...

 

[Woodsie]

Good to know. Thanks guys. I'm looking forward to experimenting with different tubes in this. I think KT88s are next.

 

[steve_k]

Good to know. Thanks guys. I'm looking forward to experimenting with different tubes in this. I think KT88s are next.

34's and 88's aren't interchangeable. -10V difference in bias supply will require a bias resistor change to get into range. You can try 77's though, depending on the range of the bias pot.

 

[baron55]

Keep in mind, when tubes are matched, they don't always track the same with different plate voltages.

 

[Woodsie]

Good to know. Thanks guys. I'm looking forward to experimenting with different tubes in this. I think KT88s are next.

34's and 88's aren't interchangeable. -10V difference in bias supply will require a bias resistor change to get into range. You can try 77's though, depending on the range of the bias pot.

RV50 MKII has a switch on the back. I can run 34's, 6550, KT88, 6L6.

 

[steve_k]

Good to know. Thanks guys. I'm looking forward to experimenting with different tubes in this. I think KT88s are next.

34's and 88's aren't interchangeable. -10V difference in bias supply will require a bias resistor change to get into range. You can try 77's though, depending on the range of the bias pot.

RV50 MKII has a switch on the back. I can run 34's, 6550, KT88, 6L6.

Cool option. Didn't know the Orange amps had that feature.......go for it. But, expect it to get stiff and glassy with those 88's

 

[Woodsie]

The new Rockerverbs have it. Stiff and glassy might be good. Although, with EL34s, it's awesome.

 

[jlbaxe]

How is the RV compared to the AD30 you had?

 

[LP Freak]

What about the push pull factor? If I have a 100 watt Marshall head and my tubes have Ma's of 28,34,37,24 Then I should pair up the 2 outer (34 & 37) and the inner (24 & 28). But should I:

1) Put the higher Ma pair in the outer sockets or inner &
2) Should I place the higher Ma tube from each pair first or second (24 & 34 first for each pair or 28 & 37 first)

I gave some wrong info here. I meant to say add V4 and V5 and compare to V6 and V7.

You take the highest testing for current draw and the lowest testing and thats a pair. So 37 and 24 would go in V4 and V5 and 34 and 28 would go in V6 and V7. By doing this, your tubes are within 1mA. It dosen't matter which order you put the tubes as long as you keep the correct pairs together.

 

[Woodsie]

How is the RV compared to the AD30 you had?

It's great. The AD was a great amp but it just didn't have enough gain. I had to push it with pedals and that just made it noisy and caused a lot of feed back. The RV has the exact tone I was looking for. Great clean channel, reverb and fx loop and tons of gain if I need it.

 

[jlbaxe]

How is the RV compared to the AD30 you had?

It's great. The AD was a great amp but it just didn't have enough gain. I had to push it with pedals and that just made it noisy and caused a lot of feed back. The RV has the exact tone I was looking for. Great clean channel, reverb and fx loop and tons of gain if I need it.

I was checking out the TH30 last night seems well rounded

 

[Woodsie]

How is the RV compared to the AD30 you had?

It's great. The AD was a great amp but it just didn't have enough gain. I had to push it with pedals and that just made it noisy and caused a lot of feed back. The RV has the exact tone I was looking for. Great clean channel, reverb and fx loop and tons of gain if I need it.

I was checking out the TH30 last night seems well rounded

I haven't had the pleasure of playing one of those. I haven't met an Orange I don't like though.

 

[bananaladonpcp]

Man... I've had that issue (only worse) with tubedepot 3 times... No more dealings with them. I suggest you find another supplier. I hear Laura aka Valve Queen is fantastic to deal with from pretty much everyone on this forum lol.

-Alex

 

[Woodsie]

I'll have to check her out.

 

[LP Freak]

You take the highest testing for current draw and the lowest testing and thats a pair. So 37 and 24 would go in V4 and V5 and 34 and 28 would go in V6 and V7. By doing this, your tubes are within 1mA. It dosen't matter which order you put the tubes as long as you keep the correct pairs together.




But do the 2 outer sockets (V4 & V7) or 2 inner (V5 & V6) have to be matched in a Marshall due to the pairing of the power tubes? So should the tubes be set up as 37,24,28,34. This way V4 & V5 are within 1 MA of V6 & V7 and the 2 outer and inner sockets are matched too?

Thanks.

You can do it either way because V4 and V5 work as a pair as well as V6 and V7.

 

[LP Freak]

Your a gentlemam LP Freak and thank you for all your help.

I wouldn't go that far now.