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Fender Bassman 100T Chapter 3
- Thread starter Chef
- Start date
'scuse me...kinda interrupting, but just got this from our Principal Engineer and thought it might help some folks if I posted it. Hope it does. all the best, rob
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Here is some information on Autobias (AB) to help clear up any confusion.
1. The first time POWER is turned ON, the AB LEDs will scan from left to right, one at a time. This indicates the amp is in WARMUP mode which happens only once after POWER is first set to ON.
a. If you turn the POWER to OFF and then ON again (ie cycle power), WARMUP mode will start again.
b. When in WARMUP mode, the LEDs will scan indefinitely until taken out of STANDBY (switch is set to ON).
2. It is recommended to leave the amp in STANDBY (switch set to OFF) for at least 1minute to allow the tubes to warm up (from cold).
3. When the amplifier is in STANDBY (switch set to OFF), the tubes are off (no high voltage is present) and the bias adjustment process is paused.
4. When the amp is taken out of STANDBY (switch is set to ON) the AB will start the tube bias process and all the LEDs will begin to blink together.
a. This can take several seconds to start the process after the switch is changed, and if in WARMUP mode the LEDs will continue to scan left to right. Note: WARMUP mode will prevent the bias adjustment process from occurring if less than 1minute has elapsed from the time POWER switch was set to ON.
b. Each LED will continue to blink until the tube as reached the correct bias and will stop blinking and be solid GREEN (=OK). Bias adjustment is complete when all tubes are solid GREEN.
c. Each tube is biased independently so some may take longer than others. Matched tubes are the most likely to take the same amount of time.
d. It is typical for the entire bias process to take 20-30sec, but sometimes longer up to 1min. This is normal. Generally the bias adjustment time is shorter the longer the amp has been on.
e. It is not uncommon for a tube(s) to make another adjustment again (blink for a few seconds) shortly after being solid the first time. This is normal as the actual warm up time can vary slightly from tube to tube.
5. When the amp is placed in STANDBY (switch is set to OFF) the high voltage is disconnected. It can take several seconds for the tubes to turn off and then AB pauses processing.
a. On the 100T, when in STANDBY the LEDs will be solid and not blink (except during initial WARMUP mode). The LED color will display the last known status before the switch was changed (GREEN = OK, RED = bad, etc)
6. It is recommended to wait ~1min or to observe the LEDs start blinking and then stop before playing the amp every time the amp is taken from STANDBY (switch is set to ON) or switching POWER from 100W > 25W or 25W > 100W.
There is no bias adjustment period between 25W and Silent.
**********************
***********************
Here is some information on Autobias (AB) to help clear up any confusion.
1. The first time POWER is turned ON, the AB LEDs will scan from left to right, one at a time. This indicates the amp is in WARMUP mode which happens only once after POWER is first set to ON.
a. If you turn the POWER to OFF and then ON again (ie cycle power), WARMUP mode will start again.
b. When in WARMUP mode, the LEDs will scan indefinitely until taken out of STANDBY (switch is set to ON).
2. It is recommended to leave the amp in STANDBY (switch set to OFF) for at least 1minute to allow the tubes to warm up (from cold).
3. When the amplifier is in STANDBY (switch set to OFF), the tubes are off (no high voltage is present) and the bias adjustment process is paused.
4. When the amp is taken out of STANDBY (switch is set to ON) the AB will start the tube bias process and all the LEDs will begin to blink together.
a. This can take several seconds to start the process after the switch is changed, and if in WARMUP mode the LEDs will continue to scan left to right. Note: WARMUP mode will prevent the bias adjustment process from occurring if less than 1minute has elapsed from the time POWER switch was set to ON.
b. Each LED will continue to blink until the tube as reached the correct bias and will stop blinking and be solid GREEN (=OK). Bias adjustment is complete when all tubes are solid GREEN.
c. Each tube is biased independently so some may take longer than others. Matched tubes are the most likely to take the same amount of time.
d. It is typical for the entire bias process to take 20-30sec, but sometimes longer up to 1min. This is normal. Generally the bias adjustment time is shorter the longer the amp has been on.
e. It is not uncommon for a tube(s) to make another adjustment again (blink for a few seconds) shortly after being solid the first time. This is normal as the actual warm up time can vary slightly from tube to tube.
5. When the amp is placed in STANDBY (switch is set to OFF) the high voltage is disconnected. It can take several seconds for the tubes to turn off and then AB pauses processing.
a. On the 100T, when in STANDBY the LEDs will be solid and not blink (except during initial WARMUP mode). The LED color will display the last known status before the switch was changed (GREEN = OK, RED = bad, etc)
6. It is recommended to wait ~1min or to observe the LEDs start blinking and then stop before playing the amp every time the amp is taken from STANDBY (switch is set to ON) or switching POWER from 100W > 25W or 25W > 100W.
There is no bias adjustment period between 25W and Silent.
Here you go, hope that helps!
"It is not required to be in STANDBY (switch set to OFF) when changing power modes, but it is strongly recommended to wait ~1min or observe the AB LEDs start to blink and then stop (let the bias adjustment finish) after the switch is changed before playing the amp when changing from 100W > 25W and 25W > 100W. There is no bias adjustment when changing between 25W and Silent, so no need to wait.
The 100T DI post position is always post power tubes regardless of any power mode."
All the best,
rob
"It is not required to be in STANDBY (switch set to OFF) when changing power modes, but it is strongly recommended to wait ~1min or observe the AB LEDs start to blink and then stop (let the bias adjustment finish) after the switch is changed before playing the amp when changing from 100W > 25W and 25W > 100W. There is no bias adjustment when changing between 25W and Silent, so no need to wait.
The 100T DI post position is always post power tubes regardless of any power mode."
All the best,
rob
Hi Rob
Point B above peaked my interest . "When in standby ....the LED's will scan left to right indefinitely" . My 100T LED's have never scanned indefinitely while in standby. They cycle for 60 seconds and then go solid green. I then take it out of standby (standby on) and then wait another 60 seconds before playing. This is true even after my most recent repair. So does this indicate a continuing issue with my amp if it doesn't scan indefinitely while in standby?
Hi joemer,
good point/question, and I hope not. Getting back with the guys and probably back on here with you in the morn.
Thanks!
All the best,
rob
My 100t behaved the same way as joemer's and I never had any problems. Once the lights stopped blinking they stayed solid whether in or out of standby. My sb300, on the other hand,reverts to blinking lights when it is on standby (as it is meant to do). The autobias circuits are slightly different in the two amps, I wonder whether someone is confusing the two? I refer again to the excellent response from Fender which Tom Bowlus has now posted twice.
Mine's always worked as the tech describes: When first powered on scans green left to right, and continues to until switched out of standby, then blink green for 5 or 6 seconds and goes solid.
Hopefully, joemer checks his email before the forum, but at any rate here is the answer to the question he posed. Also as Tim1 posts---referring to the Tom Bowlus parts of the thread is a good thing too.
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~rob
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The old version of the software used on SuperSonic 100 did as Joemer described LEDs scan for 60sec and then all go solid GREEN while the amp was in STANDBY. That was updated for the 100T (along with other improvements) to scan until STANDBY was set to ON. So any 100T user who reports this behavior does not have the correct software intended for that model.joemer said:
~rob
OK - so my auto-bias is functioning correctly. Now I have a different "problem" - by mistake I plugged my speaker cable into the "External Speaker" jack. Output was very quiet and distorted. When I figured it out and plugged back into the "Main speaker" jack everything was normal. Seems strange since it says these are parallel outputs. It does say this in the manual:
"A speaker must ALWAYS be connected to the MAIN SPEAKER jack when the amplifier is ON (except while in STANDBY or SILENT RECORD) or damage may occur to the unit. Switch the amplifier to STANDBY {N} while changing speaker connections."
I only played for a few seconds with the speaker plugged in only to the Ext jack, so hopefully didn't damage anything.
Is this normal?
"A speaker must ALWAYS be connected to the MAIN SPEAKER jack when the amplifier is ON (except while in STANDBY or SILENT RECORD) or damage may occur to the unit. Switch the amplifier to STANDBY {N} while changing speaker connections."
I only played for a few seconds with the speaker plugged in only to the Ext jack, so hopefully didn't damage anything.
Is this normal?
i dont know about damage, but I believe that normally if you do that and dont also have one plugged into "main speaker" it will blow the fuse. So its weird it didnt.
I freaked out immediately and quit playing until I figured it out. Of course checked the bias lights first 
I'm a tube amp noob.
I'm a tube amp noob.
I simply won't obsess about this sort of thing unless there is a problem and so far I have experienced no problems with either the 100T or SB300. I refuse to check lights all the time or count seconds, I am working on the "if it ain't broke don't fix it" principal. I could so easily limit my playing enjoyment checking on this all the time - these amps are made to be played, and if they ain't working simply take them to a tech and get it fixed. I very occasionally glance at the back but it is certainly not a regular occurrence - if my ears tell me it is fine that is enough for me.
That said, I always take my Markbass with me to every gig as a backup
.
That said, I always take my Markbass with me to every gig as a backup
.
Yeah I take a micro back up amp always too. Yet to have up use it.
I do the same. I sometimes take a glance at the bias lights but mostly I just use my SB300 as I've used every tube amp I've had. Let it warm up - long as poss. Put it in stand by when on breaks. Let it cool b4 moving it about at gigs end.
Superb amp.
I do the same. I sometimes take a glance at the bias lights but mostly I just use my SB300 as I've used every tube amp I've had. Let it warm up - long as poss. Put it in stand by when on breaks. Let it cool b4 moving it about at gigs end.
Superb amp.
I did the same thing to mine over a year ago, and it totally freaked me out. But like a dumb ass I didn't immediately look at the back, I cranked everything up and was trying to force it to work. What an idiot. When I looked at the back and everything was flashing red and I saw the speaker cable in the external speaker jack I literally almost fainted. But I powered down, reconnected, then talked to it sweetly for a few minutes before I powered back up and everything was fine. I can't believe it didn't fry the amp, or melt the output transformer.
see, Freight Train did it right! If you didnt talk to it real sweet afterwards Tbird, youre screwed!!!!
My replacement 100T performed flawlessly at it's first gig last night with that beautiful overdriven tone that I have come to love. The bias lights are now operating correctly on start up as mentioned above. I want to thank both Rob and Jordan at Fender for outstanding support and for standing behind their product. I couldn't ask for anymore than they have done and I will remain a loyal Fender customer. Thanks again guys !!
