jwdubois
New member
I got some new preamp tubes in yesterday to try in my Rebel 20. After wading through various reviews describing tubes using wine tasting terms such as "silky", "full bodied", etc, I ended up buying a set of Tung Sol 12AX7's (including one with matched triodes for the phase inverter), and a pair of Jan Philips 5751's.
My ultimate goal is to achieve smoothness. Since I'm not a metal player, the 5751's were pointed out to me as a way to smooth things out, at the cost of some gain.
Question, is this an “official” document? It’s what I was going by ….
https://www.thegearpage.net/board/showth ... p?t=481854
First up, I replaced the stock GT 12AX7's in the Rebel with the Tung Sol set. I noticed an immediate difference. The Rebel seemed to have more available gain and seemed smoother at the same time. The low gain settings were much better, very punchy and Fender like.
Then I replaced V1 and V2 with the 5751's (I didn't buy a 5751 PI tube). While there was less available high gain, what there was very smooth and Marshall-y. The bass seemed a little tighter as well, I could go to the low E on my Strat on the front pickup without as much mud.
Results: I liked the Tung Sols better for low gain and the 5751's for high gain. This may seem backwards, but that was my first impression. We'll see how that stands up when I try it all again with fresh ears.
Newby questions:
While I was at it, I checked the power tube bias. According to my DVM, the EL84s were slightly hot and the 6V6s were spot on. I assume the tube bias current is:
(mv reading/ 1 ohm) / 2
so that the 45mv reading is actually 22.5mA per tube (not counting screen current?)?
There is a lot of information on the various benefits and drawbacks of different bias levels. As far as I can tell, most of the benefits of a “hot” bias have to do with improving the sound of the amp at high power levels, in particular, to prevent crossover distortion. Question: is there any benefit of a “hot” bias when you are primarily running clean? As in, I'm not really playing loud enough to get into the power tubes much.
JWW
My ultimate goal is to achieve smoothness. Since I'm not a metal player, the 5751's were pointed out to me as a way to smooth things out, at the cost of some gain.
Question, is this an “official” document? It’s what I was going by ….
https://www.thegearpage.net/board/showth ... p?t=481854
First up, I replaced the stock GT 12AX7's in the Rebel with the Tung Sol set. I noticed an immediate difference. The Rebel seemed to have more available gain and seemed smoother at the same time. The low gain settings were much better, very punchy and Fender like.
Then I replaced V1 and V2 with the 5751's (I didn't buy a 5751 PI tube). While there was less available high gain, what there was very smooth and Marshall-y. The bass seemed a little tighter as well, I could go to the low E on my Strat on the front pickup without as much mud.
Results: I liked the Tung Sols better for low gain and the 5751's for high gain. This may seem backwards, but that was my first impression. We'll see how that stands up when I try it all again with fresh ears.
Newby questions:
While I was at it, I checked the power tube bias. According to my DVM, the EL84s were slightly hot and the 6V6s were spot on. I assume the tube bias current is:
(mv reading/ 1 ohm) / 2
so that the 45mv reading is actually 22.5mA per tube (not counting screen current?)?
There is a lot of information on the various benefits and drawbacks of different bias levels. As far as I can tell, most of the benefits of a “hot” bias have to do with improving the sound of the amp at high power levels, in particular, to prevent crossover distortion. Question: is there any benefit of a “hot” bias when you are primarily running clean? As in, I'm not really playing loud enough to get into the power tubes much.
JWW
The Led is still shining and i can hear the usual noise when i turn the Watt-knob (also if i crank the gain,Bzzzz) but nothing else 
Is it characteristical of a dead pre-amp tube?I guess it's the new JJ 12AX7 but it's a real new one ,never used before... 
It was very late,so, i decided to wait until tomorrow... 
and ask here before anything 
!If you found a nice sound with the TS's,don't mess with it 
!It's not easy to find the right tube combo...I own a M&B Nomad55 and i once had to replace a GT12AX7M (Mullard re-issue).I couldn't find it and went for a full set (5) of TS12AX7's instead.The result was not good to my ears,though, and i still have these 5 brand new TS's!That's why i hope i'll like them,as much as you do, in the Rebel !Based on your description,i think i will...And,of course,i'm also waiting eagerly to try the Rebel30 and,even more,the Renegade 
!