Need some assistance biasing my 2008 Herbert.

  • Thread starter Thread starter spguitar
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spguitar

Well-known member
I have KT88s in it and i was told to bias it to 75-85mA per tube set.
Here are the steps i went through:
Turned all volumes to 0
Turned multimeter to 200 DC current
Hooked my leads up to the bias points.
Pulled fuse for 1-6
Flipped power on
Let heat for 45 sec-60 sec
Flipped standby off

Multimeter shows me 26ma. The tubes seem to be getting plenty(almost overly) hot so i'm really scared to try adjusting it.
Any advice?
 
Dear SPguitar,

I don´t know who told You to put KT88 into
the Herbert. I´m sorry but we don´t recommend
this tube.

The right bias current would be 40 to 50 mA each
tube, 80 to 100mA a pair. This will cause a lot of
heat on the amp.

Why don´t use a good sounding EL34 ?

Cheers,
Peter
 
Peter Diezel":25rdlaxw said:
Dear SPguitar,

I don´t know who told You to put KT88 into
the Herbert. I´m sorry but we don´t recommend
this tube.

The right bias current would be 40 to 50 mA each
tube, 80 to 100mA a pair. This will cause a lot of
heat on the amp.

Why don´t use a good sounding EL34 ?

Cheers,
Peter
Click to expand...

Thanx for the reply! KT88s were in the head when i bought it used.
I just wanted to check the bias before i start practicing with my new band then playing shows.
I'm planning on swapping it to a mixture of EL34 and 6L6 soon or maybe straight up EL34s.
 
KT88's are just flat awesome in the Herbert. Been running them for over a year myself. :thumbsup:
 
RJF":almavjyb said:
KT88's are just flat awesome in the Herbert. Been running them for over a year myself. :thumbsup:
Click to expand...

I'm getting an overall super trebly tone with them. Not sure if it's the tubes or the bias being too cold. Really scared to try to adjust it with the tubes already getting hot.
 
I am not using KT88's in Herbert and Herbert gets HOT!! I just think that 6 power tubes on FIRE, dishing out the tone of DIEZEL, puts out a decent amount of heat.

That said, I would listen to Peter, he is the wizard and knows what the amp is designed for...of course, you can do what you want...tone is a VERY subjective thing :)

Have fun, regardless, let those tubes burn!!
 
Peter.. Have you tried the Ruby el34 BG's in the Herbert yet?
 
Yes, it´s a great tube and I will get another
1000 pieces during the next 3 weeks.
 
I recently did a complete rebuild on a 2007 Herbert whose owner did not change the tubes for 4 years. The tubes became so hot during a recording session that the Herbert started smoking out of every jack in the back. In the process the main circuit board melted and was black with soot. The amp was totaled and the circuit boards (and all tubes of course) needed to be replaced. I put in the Diezel approved tube set and the Herbert sounded awesome. The owner was very pleased.

I would be very careful running those hot KT88s in a Herbert. If you bought the Herbert used you don't know how old the tubes really are. When I sell a used amp I sell it with a complete set of new tubes (preamp and power tubes). When I buy a used amp I do a complete tube swap.

Whenever you are ready to retube your amp I've got the Diezel approved (same as Peter gets) preamp and power tubes available to ship from L.A.

Good luck in the meantime and please contact me anytime you have any questions or concerns !

Jens Kruse
 
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