power tube biasing

marvda1

i had one tube amp manufacturer say bias the tubes with no signal going thru the amp and another say use low volumn music playing. which is the correct way?

inspiredsports

You answered your own question. You mentioned 2 different manufacturers.

Bias according to what the manufacturer of the specific component you are biasing prescribes.

Most say preamp on, volume zero, no signal.

zingo

I've done it both ways with a number of amps. The most important thing is to burn in your tubes so they hold the bias well.

george daniel

I've just always biased at idle

decal

marvda1 wrote: »

i had one tube amp manufacturer say bias the tubes with no signal going thru the amp and another say use low volumn music playing. which is the correct way?

The "best" way is the way the manufacturer of your amp recommends. They built it, they should know. Good luck.

doctor r

No signal. To set an idle (which is what you are doing when you set the bias) a moving baseline, i.e. the signal, could make it much more difficult to have all the tubes set the same, IMHO. Obviously some manufactures have found their equipment does well at this stage with a signal if they recommend it.

heiney9

I have always done it at idle as well. You may know this already but it hasn't been mentioned and is standard procedure, but a load must be hooked up.

H9

inspiredsports

heiney9 wrote: »

I have always done it at idle as well. You may know this already but it hasn't been mentioned and is standard procedure, but a load must be hooked up.

H9

Good point, but I did "imply" that in line 3 of post #2

heiney9

inspiredsports wrote: »

Good point, but I did "imply" that in line 3 of post #2

Hmmm...guess I missed the implication of having speakers hooked up. Still don't see it, but atleast we covered all the bases for him and future tubeophiles that stumble on this thread.

H9

george daniel

Pre=on
Amp=on/warmed up
Speaks=connected
Bias procedure starts

marvda1

this is an integrated.
this is what the manufacturer says: " set the volume at lower level (less than one quarter). i guess you could take this as no signal present or with a signal.

heiney9

I don't think any of us here are inclined to advise you to override the manufacturers suggestion. If that's what they say, then I'd follow that advise or call the manufacturer for clarification.

H9

BlueFox

marvda1 wrote: »

this is an integrated.
this is what the manufacturer says: " set the volume at lower level (less than one quarter). i guess you could take this as no signal present or with a signal.

To me, that does not imply a musical signal. It seems they want some gain in the circuit while performing the bias, versus having the volume potentiometer turned all the way down, and blocking the background noise which is inherent in any electrical circuit. As others said, drop the manufacturer a note for clarification.

F1nut

marvda1 wrote: »

i had one tube amp manufacturer say bias the tubes with no signal going thru the amp and another say use low volumn music playing. which is the correct way?

I've never heard of any manufacturer that recommends having a source playing while biasing the power tubes. Which one did?

this is an integrated.
this is what the manufacturer says: " set the volume at lower level (less than one quarter). i guess you could take this as no signal present or with a signal.

No, that means exactly what it says and it doesn't say a thing about a source playing.

Tour2ma

Actually have to agree with Jesse on this one... hate it when that happens. Of course it could just be my head spinning from trying to equate any or all of "Most say preamp on, volume zero, no signal" with "a load must be hooked up."

I agree with doctor r, introducing a variable input signal into a hopefully, steady-state, biasing process makes no sense to me. A low level, input signal is a part of the (or at least my) variac process when reforming caps, but not my biasing process.

Granted it turns out we are talking about an integrated here, but in the separates' case I was not aware that a Pre had to be hooked up to bias a power amp. If no signal is desirable, why would a Pre be needed?

On a positive note, gd's "warmed up" requirement was a valuable addition to the discussion, although his item 4 needs to be item 1...

A clean, step-by-step tube system set up thread would be a valuable addition to the forum. Maybe even "sticky" worthy. However, this one ain't it. There has to be one at AK or some other site worth a linky.

heiney9

Actually if you really want to get technical the bias should be set right when you power up and then checked and set again after the tubes are warm. If for some reason the bias is way off, in just the time you power it up and let it idle for the tubes to get warm, you could damage a tube if the bias is way off. This in fact did happen to me when I first recieved one of my tube integrated's. Took out a very nice 1957 RCA gray glass, black plate 6V6. I put the tubes in and waited for warm up to set the bias never checking it initially. By the time the tubes were warm and I started to set the bias, it was too late, the tube was toast, I was not a happy camper. I always set my bias at first power up and then I check it after warm up and adjust accordingly. Actually I'm fairly anal so I tend to check and re-check several times starting at first power up all the way through full warm up.

H9

thsmith

On my Wright I have to change a selector from opererate to test which cuts out the incoming signal. So it would seem in my case it does not matter if the pre is on or off or playing something or not.

Probably don't help much with OP question just thought I would share.

Here are the instructions from Anthem on the AMP one on biasing.

1. Disconnect the power cord and allow the amplifier to
cool 15 minutes before removing the top cover.
2. After removing the top cover, with the front end of the
chassis facing you and referring to Fig. 6, observe the
location of four test points TP-1, TP-2, TP-3 and TP-4.
These are located left to right along the the top edge of the
main printed circuit board assembly. Also note the position
of the four potentiometer adjustment shafts protruding
from the rear of the PCB mounting bracket. The potentiometers
from left to right are VR1, VR2, VR3 and VR4.
3. Connect the multimeter’s negative test lead to the AMP
1’s left channel output COM or black binding post on the
rear panel.
4. Carefully apply line voltage to the amplifier and observe
that all the tube filaments light. As the amplifier is warming
up touch each test point, TP-1, through TP-4 in succession
with the positive meter test probe, noting the voltage at
each point is less than or equal to 0.4 volts. Adjust the
corresponding potentiometers VR1 through VR4 to maintain
voltage at 0.4 volts at each test point over a twenty
minute period.
5. After 20 minutes if no further movement in the test point
voltage is observed, then disconnect the amplifier from the
power source and replace the top cover.
*Optional periodic checks of the bias may be made every
500 hours or so. Dramatic changes in bias over a 500
hour period generally indicates that the output tubes are
becoming weak and should be replaced.
9
TP-4
TP-3
TP-2
TP-1
VR4*
(for V7) VR3*
(for V6) VR2*
(for V5) VR1*
(for V4)
PCB Mounting
Bracket
Amp Rear
* To increase bias turn knobs counterclockwise.
FIGURE 6
Adjustment of the output tube bias.

Tour2ma

^ More or less consistant with h9's cautionary post...

heiney9 wrote: »

Actually if you really want to get technical the bias should be set right when you power up and then checked and set again after the tubes are warm. Took out a very nice 1957 RCA gray glass, black plate 6V6. By the time the tubes were warm and I started to set the bias, it was too late, the tube was toast...

I love gettin' technical....

What turned out to be the issue with the integrated's bias that took out the RCA?

heiney9

Tour2ma wrote: »

^ More or less consistant with h9's cautionary post...


I love gettin' technical....

What turned out to be the issue with the integrated's bias that took out the RCA?

IIRC, It shipped with JJ 6V6S tubes which are known to handle much more bias than a typical 6V6. When I swapped out the JJ's for a Quad of RCA gray glass, black plates I never rebiased assuming the bias was correct. By the time I went to check/set the bias it was too late. My integrated has seperate bias pots for all 4 tubes. The one that got toasted was supposed to be 200-250mV and the one tube read something like 340mV or some much higher number. I learned the hard way since that was back when I was a toob noob.

H9

zingo

The same is true with my integrated. Since it can handle EL34, 6L6, or KT88, when it put new tubes in, I have to remember to turn the bias all the way down before I turn on the amp. I did not turn it done fall enough once and red plated a quad of 6L6 because the initial bias was too high. This can be true not just with changing the type of power tube, but also different rated power tubes as H9 was saying. Once tubes are well burned in, good tubes should not require much biasing, but my rule when I'm installing new tubes is:
-Ensure the bias is all the way down (or down as far as needed in your experience with the amp)
-Test the bias on start-up to ensure you're not overloading the tube
-Once the tubes are warmed up for 10 minutes, slowing bring the tube up to the correct bias
-Check the bias every 5 minutes until it has stabilized between checks
-Check the bias every 10 minutes until it has stabilized between checks
-Check the bias every 15 minutes until it has stabilized between checks
-Check the bias every 30 minutes until it has stabilized between checks
-Check the bias every 60 minutes until it has stabilized between checks
-Check the bias every day until it has stabilized between checks
-Check the bias every week or every few weeks ongoing to ensure good tube life (I never get to this point because I change tubes too often...)

Tour2ma

Thanks, h9...

zingo wrote: »

... remember to turn the bias all the way down before I turn on the amp.

Seems like a value added step for tube swaps and initial operation of a new/ new-used tube toy.