Herbert bias question, need HELP

  • Thread starter Thread starter shadow070
  • Start date Start date
S

shadow070

Active member
I had a weird sound comming out off my speakers (like wind whent through my cab, could hear this easy on the clean channel). I swapped all preamp tubes and still had the problem. I have currently the 6550 power tubes in the amp and just started swapping pairs to find the bad one.

I have now 4X6550 and 2XE34L

I started biasing the 2 e34l and could not turn the bias trimmer to the right anymore. The MM showed 00 as voltage so i started turning slowly clockwise but it stoped turning at 60ma (like its stuck).

What to do now guys? :confused:



P.s. this morning my volume dropped a view times and after switching to standbuy it went up again, so it was time, only prob was that all tubes looked normal so its difficult to find the bad one.
 
OK,

I just managed to bias pair A and C (both 6550 tubes) to 90MA and pair B (E34L) biased to 60. It stopt turning at 60.

Should i turn all trimmers counter clockwise before biasing?

Kind regards,

Robert
 
Try switching your EL34s to Pair A ( the inner pair). Everytime i had mixed tubes i would run the "odd" pair in the center & i never had an issue.

Pair A- EL34 (3&4 inner pair)
Pair B- 6550 (2&5)
Pair C- 6550 (1&6)

and an EL34 pair can be biased to 60mA if need be.

give that a try. :thumbsup:
 
Pauly thanks for the reply.

I just finished testing the combo of tubes. Tho its biased a little cold, i prefer a all 6550 poweramp.

Damn, its gonna cost a view bucks again :lol: :LOL:

I miss the thump i got from the all 6550 tubes, they also had a surtan debt in the tone. The El34 has a little more note definition when playing leads.

Aint that a shame, i just got andy timmons cry for you backing track and wanted to freestyle a bit, with the tone i had :doh:

Ill try the el34 out in sockets 3&4 and see what happens.



I also wanted to know if the trimmer has a max to it or that you can keep turning clock and counter clockwise?
 
Im not sure about the Bias Trimmer having a max.I would imagine it would...but i doubt @ 60..since the others went to 90 with no issues! But i know mine is super sensitive. If i would breath too heavy it would move. So i cant help u there.
 
Thanks for the info pauly, ill have to wait for peters answer then on this one.

I read that you have the new cab. Im using a Engl pro V30 cab at the moment, hope to get a new D-cab asap. I still wonder how much off a difference it is compared t0o the Engl, i gues ill have to wait till one off the shops here stocks them.

Enjoy your Herbert to the fullest :rock:
 
ill have to change the inner pair, not just because you mentioned it, but i just had a volume drop so the bad tube can only be in the inner pair :doh: here we go again :lol: :LOL:

Can a preamp tube cause a volume drop? they are still new but you never know.

Mixing the 6550 with el34 isn't that bad, i just had to get used to it a little bit, i got much more midrange and a better tube kinda feel(this at low volume, im at home now), difficult to explain, the cleans were very nice, it didnt have that in your face thump, makes it better for my clean channel. Without the lowend that the other pair off 6550 had, the tone was much clearer, perfect for fast lead playing.
Wish i had 3 Herbert's. 1: all 6550 tubes, 2: all el34 tubes and 3: mix and match. This takes away the hassel, but also food for the near future :thumbsup: Pauly when you get tired off your amp and feel like giving it away, please think about me and my future need of food :lol: :LOL:
 
i think its time for some new tubes. take the guesswork out of it & get you playing again. I know..its frustrating.But may be ur best option

And the only way i will part with my Herbert is when they have to bury me. And i may make arrangements for it to come with me

Hope u get ur tube issues straightened out...and your new Diezel cab on order :thumbsup:
 
Thanks, ill change the inner pair tonight and def. start playing again, cant wait.
 
If it kills the new tube in the same position, check the bias resistor. Usually the offending tube will be glowing cherry red though if the bias resistor is dying. ;)
 
deathtoll":5hz27ng5 said:
If it kills the new tube in the same position, check the bias resistor. Usually the offending tube will be glowing cherry red though if the bias resistor is dying. ;)
Click to expand...

Ok ill take this in mind when changing them later on the day. Its just that it looks like all tubes are running normal.
 
I just finished, it took me to damn long.

Pair a: 6550 tubes biased at plm. 95 ma
Pair b: e34l tubes biased at plm. 68 ma
Pair C: e34L tubes biased at plm. 69 ma

Wow this has a nice tone, better then with only one pair e34l in it. Even more mid range, creamy and mid bite, i like this :rock:

Cant wait till band practice
 
You must log in or register to reply here.
Back
Top