Comments on: What About Tubes?

By: bill

bill — Mon, 09 Aug 2010 13:52:20 +0000

You don’t have adjustable bias until after you do the mods.

By: Doyle

Doyle — Wed, 04 Aug 2010 20:14:54 +0000

Hi Bill,

While I’m waiting for my turn on your mod list for my texas red blues Jr to get your magic touch I though I would replace my tubes.

I know to buy a matched set of power tubes but how do I set the bias?

Thanks!
DW

By: bill

bill — Tue, 27 Jul 2010 12:57:27 +0000

If you’ve done the mods, you should rebias when you install new output tubes. If you haven’t, you can’t rebias.

A balanced PI tube won’t do anything–none of the other components in the PI circuit are balanced or matched. The 12DW7 has radically different amounts of gain in the two halves.

By: bonsai

bonsai — Sun, 25 Jul 2010 15:49:58 +0000

hi bill,

will i have to rebias my bj (stock tubes, stock no-bias-trim), when i swap the power tubes for jj el84?

for the harp section ur telling, that a disbalanced v3 will get the power tubes break up earlier. so i assume, that if i drop in a balanced one, it will brake up a bit later?

thx in advance
bonsai

By: bill

bill — Wed, 14 Jul 2010 23:48:17 +0000

I don’t use 12AT7s in V1, so I really can’t say. They’re not very good as preamp tubes, in my opinion.

By: Rick

Rick — Wed, 14 Jul 2010 14:58:53 +0000

Hi Bill,

Thanks for sharing your research! It brings a to mind a question about tube subtituting. If the clean volume limit for a 12AX7 is “4″ and “7″ for a 12AY7, did you record what the clean volume limit for a 12AT7? I have a few 12AT7′s, that I may put in V1 service.

Rick

By: bill

bill — Fri, 14 May 2010 21:56:29 +0000

The 7189 has a higher voltage rating than the EL84, but since the power supply determines the voltage, it won’t put out any more power than an EL84. Like different brands of EL84s, the 7189 may sound a little different.

By: Golney

Golney — Fri, 14 May 2010 17:12:41 +0000

Hi bill

just wondering how a 7189 might get on in the power section? i hear they are substitutable for an el84.

thanks

By: wm

wm — Tue, 11 May 2010 23:12:50 +0000

ok so I changed the Swamp Thang out for one of these new Jensen Neos and- problem solved. I can turn it up all the way and I don’t get that rattling. The amp isn’t as loud now, but… I’m guessing maybe having such a huge speaker in such close proximity to the tubes, producing that much bass, would be too much for such a small combo?

By: Wes

Wes — Sun, 09 May 2010 05:56:28 +0000

Nice post Bill!

I just wanted to make a comment about Victor’s hum. I’ve found that if I play my ’87 Strat through my Blues Junior anywhere near my PC I pick up a serious (60hz) hum. I noticed he said that the hum is gone when he has no cables plugged int. If you’re running your guitar through any pedals it can make the hum sound rather odd. I reckon this is could be the reason….especially since he says it’s not always there! A blown tube is always “on”