Distortion problem with Express build

[rawnster]

Over the last several days I’ve noticed that the tone is getting more and more overdriven. As it currently sounds with a pair of good SED EL34s, I cannot set the amp higher that 1.5 (about 8:30 oclock) without it breaking up. I checked all the voltages again, and nothing has really changed. I pulled the SED, and replaced them with a pair of JJ EL34s. With the JJ’s, I get quite a bit of the headroom back. That’s good, but it’s got me puzzled. I had plenty of headroom with the SED when I first used them. The bias is set to 42ma. Another thing I noticed is that V4 glows quite a bit brighter that V5. If I turn the amp up to around 9 – 9:30 and turn my guitar all the way up and pound a chord, V4 brightens up and then dims down again to its normal glow. V5 doesn’t do that at all when I pound a chord.

Please forgive my novice/ignorant knowledge here. Just trying to figure out what’s up.

FWIW: On a positive note I put a JJ ECC81 Gold Pin in the V1 slot. Great sound…AND a much lower hiss level. I like it!

Thanks for your help!

[gearhead]

If you could post a voltage chart, that might help.

[rawnster]

If you could post a voltage chart, that might help.

No problem. At work at the moment. I'll post voltages later this afternoon.

Thanks.

[jjman]

ECC81 will also provide less signal amplification than the "normal" 12ax7=ecc83. Result could be distortion later on the dial but around the same volume point in this application. Max setting could be less sustained/distorted than ecc83.

Of course this is not on the original topic.

[rawnster]

ECC81 will also provide less signal amplification than the "normal" 12ax7=ecc83. Result could be distortion later on the dial but around the same volume point in this application. Max setting could be less sustained/distorted than ecc83.

Of course this is not on the original topic.

I see. I was just trying to lower the rush of hot steam that emanates from the amp (i.e., hiss).

[rawnster]

Here is my voltage chart:

b1=409
b2=395
b3=313
b4=294
b5=279

v1:
1=208
2=.6
3=1.8
4=3.3
5=
6=181
7=
8=1.4
9=3.3

v2:
1=262
2=7.0
3=3.0
4=3.3
5=
6=
7=
8=
9=3.3

v3:
1=192
2=25
3=38
4=3.3
5=
6=205
7=24
8=38
9=3.3

v4:
1=
2=3.3
3=408
4=392
5=34
6=397
7=3.3
8=

v5:
1=
2=3.3
3=408
4=393
5=34
6=398
7=3.3
8=

[Allynmey]

Voltages are at a proper ratio. What tranny are you using? The B+ is about 15-20 volts higher than my builds. I use Pacifics though. The ratios are correct though. You might want to try biasing around 38mA and seeing whats what. Remember, the proper tubes are NOS Siemens EL-34's and Tungsram 12ax7's

[rawnster]

Voltages are at a proper ratio. What tranny are you using? The B+ is about 15-20 volts higher than my builds. I use Pacifics though. The ratios are correct though. You might want to try biasing around 38mA and seeing whats what. Remember, the proper tubes are NOS Siemens EL-34's and Tungsram 12ax7's

I'm using the vintage Heyboer tranny from Toneslut. I set the bias at 42mA, based on the 70% rule. I'll drop the bias down to 38mA, as you recommend. Aren't those NOS Siemens a ton of doe?

[Allynmey]

They go for about $99.00 a pair.