^ Excellent, I also remember to ignore the bias lights when you have a signal going through the amp. These lights are used during no signal indications?
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The Fender Super Bassman 300 thread
- Thread starter Tim1
- Start date
I thought the bias indicators on the SB300 are digitally controlled. I.E. I would not expect them flicker while playing like analog indicators. Is this incorrect?
I don't have that answer, I don't know how it would discern instrument input from a noisy input like poorly shielded bass? You would think that would entail a "test switch" instead of an always live indicator.
From the OM
Blinking green means the circuit is adjusting. It's supposed to show solid green when done. If it doesn't stop blinking = worn tube
Solid orange means a tube is worn.
Solid red means bad tube...the associated pair is turned off
BTW out of curiosity I looked up the owner's manual and since you don't seem to have it here is the link Link Removed
Thanks, B, but I don't think anyone else can see your J: drive. Can you post the more universal URL?
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I really should have paid closer attention. No link, you had to download from Fender. so lets try an attachment.
cheers - thanks - have reviewed the owners manual and agree with @Wasnex that this is some sort of faulty autobias situation. Tubes are good, I know this, so I've got to find a tech that can look at this thing out of warranty. Not an easy thing to do as I'm learning. Traditional tube amp repair guys are hard to come by in my area nevermind tube amp repair guys that understand this amp with an autobias computer.
Really a shame - I was hoping my v.2 auto bias computer wouldn't pull this kind of stuff.
Upon searching the internet for other input about this circuit I found this thread regarding the 100T autobias. See the post from chriscolt / "twobie" where it's suspected / resolved to the way Fender zip ties this stuff together. MOUSER is the brand cited for replacement parts - not sure how much of this is shared with the SB300
See link here:
Fender Auto bias circuit - Music Electronics Forum
Post of interest fromchriscolt / "twobie":
Fender Auto Bias - Bassman 100T - Issues RESOLVED
Hello all - I realize this is an old thread but I have found a solution to the autobias issues related to the Fender Series of Amplifiers with this feature. The amp model that came to my shop was a Fender 100T Bassman - an excellent sounding amp and well designed WHEN IT WORKED. My customer bought this amp second hand - so out of warranty (no original receipt & past warranty expiration anyway). I mention this because my experience dealing with Fender Tech support was not at all good - I am not an authorized service center so I didn't expect the best support but the support I did receive was awful. In essence, exploring my options - I was told I could buy the bias board assembly if need be and to my surprise it was listed on the Fender website parts list @ what I thought was a reasonable price of around $60. But when I tried to put it in my checkout basket message popped up that it was no longer available - after several calls and emails back and forth I was told that they removed it from on-line parts and ONLY authorized service centers could purchase it - when I asked for some help determining if it was in fact the cause of the problem (had my voltages and component readings all ready) they wouldn't help me - and when I asked what they did with others who had this problem which is common - they told me that if the amp was in warranty they would just replace it if not customer was out of luck. More to come....
Anyway - the problem was similar to what is described here - one of 4 6L6s would bias up then eventually most times within 5 minutes - one of that pair would turn LED orange, then entire pair would fail. Swapping know good tubes would not fix problem moving suspect "bad" tubes to other sockets did not have problem follow tube - it stay with socket - I spent hours monitoring voltages and checking every component (except ICs on bias board) in the bias circuit - most of the resistors that are feeding the bias control circuit are high quality precision resistors and were for the most-part well within tolerances for that component.
Resetting the bias-board cleared the problem - the first time it cleared after I re-tubed the amp - I thought that the board was just glitched and that this corrected the issue - I let the amp burn in (outside the case) for 3 days straight - last 36 hours with 1K tone running through the amp / speaker cab just to be sure - then powered up & down several times - ran another 24 hours and called customer to pick up amp. After putting amp back in cabinet and having customer test amp while he was there picking it up - it failed - very embarrassing indeed!!! - What changed putting it back in cabinet????? First thing I thought was heat - and why wasn't this cooling fan ever turning on was this the problem. - After reading temps with infrared HQ temp gun - no... Fan I later reasoned out was not for general cooling of the amp - it was for the big power resistors which are only used when amp is in silent mode (headphone or pugging head into mixing board) - that's when these large power resistors are used to simulate speaker load - the sensor did work at the rated temperature (tested that with heat gun and temp reader - & it operated as designed) - although as an added bonus I installed an LED lit 2 way mini toggle so that customer can bypass thermostat and power fan on anytime - in the off position is reverted back to factory spec using thermostat (dual color LED - Red =on, blue = factory/off).
So what was problem - well there are these ribbon cables connected to the bias daughterboard and main motherboard providing the PCBs operating voltages as well as the voltages from the cathodes of each output tube and to the output tube connection where the negative bias voltage would be applied to bias the tube (based on the cathode current of that tube in idle). I noticed that the cabinet gently pushed that cable down - so I started moving the cable around while monitoring the tube bias LEDs - (BTW Fender used cable ties on these ribbon cables crunching them and causing tension on the connectors - these are computer grade cables that are not designed for that kind of abuse) - low and behold if the cable was moved or squeezed the amp would lose bias or bias voltage causing one or more of the bias LEDs to go crazy. So I called Fender for a part number so I could replace the cable - again they said they couldn't or didn't know or it came as part of a kit with the board - no help at all - after some trial and error and educating my self on the different type of ribbon cables (pitch, pin count and the various different connector head sizes and types) I found only one supplier that had the exact replacement for this cable - MOUSER (note that the cable connector on one end is standard but on the other end is a low profile head - two low profile heads will work). I am certain that considering the number of failures with this bias circuit that it was either a bad batch of ribbon cables or it was the poor installation method used (cable ties that literally pulled one or more wires off the head especially those wires on either end by taking a flat cable and making it round with a too tight cable tie. I verified the fix 100% and after 3 months - customer uses his Bassman 100T almost everyday with no return of the bias fail problem. Mouser Part # 200-TCSD10D05.0001N Mfg. Part # - Type IDC Ribbon Cable - TCSD-10-D-05.00-01-N.
NOW KEEP IN MIND - this was determined after traditional amp tech troubleshooting - eliminating possible other causes - like loose or dirty output tube socket pins, loose or broken output tube solder connections to board, all resistors / caps from all pins on output tubes checked for continuity, values, bad or broken solder joints, all other cables ribbon and other types criss-crossing the board - sockets, pins and loose connections. After all that using the "chop-stick" test - SAFETY FIRST - with amp out of chassis and speaker load connected - power on and using a non-conductive probe (e.g. wood chopstick) monitor voltages listen to speaker output - touch wires, connectors apply gentle pressure, touch key components in output tube circuit feeding bias board to see if anything is loose or intermittent -
If the ribbon cable is proven to be suspect turn off power and discharge filter caps - carefully remove glue used to hold cable head on motherboard may need to use an exacto knife or similar - CAREFUL not to cut or damage circuit board or other components / wires - IU found problem to be in ribbon cable head connected to motherboard - the one connected to the bias board was OK. No need to remove either the bias board or the motherboard to replace cable - clean area around connector where u needed to remove glue install new cable gently don't bend pins - and then test amp before gluing down ribbon cable. I use E-6000 for gluing components to PCBs (e.g. capacitors etc..) and also for loose fitting cables like these ribbon cables - they do not have any kind of locking mechanism and must be secured using glue. You can use silicone (softer, longer cure, not as strong) or this self leveling E-6000 - very strong use just a small amount - ensure cable head is fully seated all around and perfectly flat to the board not cockeyed - this stuff dries quickly and the odor is strong but completely gone after it cures for about 24 hours. I don't recall if both ends were glued or just the connector on the motherboard (which required that mini head to fit) Just base this decision on how old cable is glued.
Besides the fan bypass on toggle DPDT w/3mm dual color LED mod, and securing cables in a non-damaging way - the only other mod I Strongly recommend for this amp is changing the lobster claw tube retainers for the 4 output tubes with the spring type Marshall style tube retainers because they hold those upside down heavy tubes better and keep them from shifting especially if you are a working musician moving the amp around = shifting can cause bad pin connections and arcing - which can quickly ruin your tubes - and BTW output tube selection can make a big difference in tone - I personally like the Tung Sol Brand 6L6-STR & KT66 for this amp although I also discovered and tried The Tube Store's Premium line 6L6GC - a bit pricier but I was floored by the tone - much like the now defunct Winged "C" 6L6GCs - see link Preferred Series 6L6GC Vacuum Power Tubes - thetubestore.com . Tung Sol is my favorite for both the 6L6 & KT66. The Kt66 does require a different Spring Retainer than does the 6L6/EL34 - the spring length is the same but the end "cup" that secures the rounded end of the tube is wider on the retainers for the KT66 because the tube is much fatter than either the 6L6 or EL34.
So I repair any new or Vintage tube amplifier any pedals especially the vintage ones - I stock many vintage / period correct parts for both amps and pedals and save my NOS tubes for vintage amps as I see no reason to install vintage tubes on any new production amps - 20 years ago maybe - but today there are so many great choice in new stock - if you have a favorite I can get them but I stock Tung Sol and JJ and now a couple of sets of these Premium 6L6s (which look and sound like Blackplate RCAs - haven't noticed any reproductions that actually look like an RCA tube. - I can be reached via text @ 908 400 2760 - I am located in New Jersey. - Here is a pic of the LED/Fan mod.
Chris
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Hey everyone. I’m having issues with my Super Bassman. When I run my pedalboard into the effects loop for some reason all my effects work fine except my overdrive and fuzz. When I engage either pedal , the master volume of the amp only will only go ip to about 3. Even if I crank it up. It doesn’t really change the volume. If I run it straight through the front of the amp, I don’t have the issue. Also, I noticed after this problem that my bias lights were red, green, red green red green.
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Hey everyone. I’m having issues with my Super Bassman. When I run my pedalboard into the effects loop for some reason all my effects work fine except my overdrive and fuzz. When I engage either pedal , the master volume of the amp only will only go ip to about 3. Even if I crank it up. It doesn’t really change the volume. If I run it straight through the front of the amp, I don’t have the issue. Also, I noticed after this problem that my bias lights were red, green, red green red green.
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The signal level is most likely line level, which is too hot for pedals. Run the pedals in front of the amp.
Solid red means a tube is bad. However, my read of the manual is you should get Orange and Red. Red indicates which tube is bad and Orange indicates the other tube in the pair has been shut off to protect the amp
The reason it works this way is it's important to balance the current in the push and pull side of the output transformer. To achieve this, the tubes are shut of in pairs, rather than just turning off the bad tube.
Since you are getting Red, Green, Red, Green, Red, Green, I suspect your bias circuit is not functioning correctly. If this indication is correct, all of the tubes on one side of the transformer are turned off and all of the tubes on the other side of the transformer are biased to spec. If this were true, the current imbalance would cause the amp to have a pretty loud hum.
You could try resetting the bias to cool, but I think it's probably time to find a good Fender Authorized Tech.
Re the bias lights, remember the amp needs total silence at turn-on until it finishes the initial bias. Could be noise from the pedals in the loop upsetting it maybe? Does it maybe bias up correctly with nothing in the loop and the mute pull-switch engaged?
Also looks like you the bias selected for Hot? As Wasnex suggested, definitely worth trying it at Cool or even just holding down bith arrow buttons for a reset to Normal. And noticed in the photo it looks like you have 4 ohms selected? Does that match your speaker load?
Re your master volume only going to 3, I'm pretty certain the master volume is BEFORE the loop, not after. If you are bypassing the preamp and running straight into the fx return (power amp input jack) the master volume shouldn't be doing anything at all. I know this mainly because I once dialled my master down to zero and tried to plug a pedal into the fx loop while the amp was running and got a heck of a loud thump that scared the pants off me.
And you scored a white tolex one, damn cool
Block diagram from the manual shows the Master Volume right before the output to fx loop
Also looks like you the bias selected for Hot? As Wasnex suggested, definitely worth trying it at Cool or even just holding down bith arrow buttons for a reset to Normal. And noticed in the photo it looks like you have 4 ohms selected? Does that match your speaker load?
Re your master volume only going to 3, I'm pretty certain the master volume is BEFORE the loop, not after. If you are bypassing the preamp and running straight into the fx return (power amp input jack) the master volume shouldn't be doing anything at all. I know this mainly because I once dialled my master down to zero and tried to plug a pedal into the fx loop while the amp was running and got a heck of a loud thump that scared the pants off me.
And you scored a white tolex one, damn cool
Block diagram from the manual shows the Master Volume right before the output to fx loop
Attachments
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Re the bias lights, remember the amp needs total silence at turn-on until it finishes the initial bias. Could be noise from the pedals in the loop upsetting it maybe? Does it maybe bias up correctly with nothing in the loop and the mute pull-switch engaged?
Also looks like you the bias selected for Hot? As Wasnex suggested, definitely worth trying it at Cool or even just holding down bith arrow buttons for a reset to Normal. And noticed in the photo it looks like you have 4 ohms selected? Does that match your speaker load?
Re your master volume only going to 3, I'm pretty certain the master volume is BEFORE the loop, not after. If you are bypassing the preamp and running straight into the fx return (power amp input jack) the master volume shouldn't be doing anything at all. I know this mainly because I once dialled my master down to zero and tried to plug a pedal into the fx loop while the amp was running and got a heck of a loud thump that scared the pants off me.
And you scored a white tolex one, damn cool
Block diagram from the manual shows the Master Volume right before the output to fx loop
I did score! White with ox blood grill!Re the bias lights, remember the amp needs total silence at turn-on until it finishes the initial bias. Could be noise from the pedals in the loop upsetting it maybe? Does it maybe bias up correctly with nothing in the loop and the mute pull-switch engaged?
Also looks like you the bias selected for Hot? As Wasnex suggested, definitely worth trying it at Cool or even just holding down bith arrow buttons for a reset to Normal. And noticed in the photo it looks like you have 4 ohms selected? Does that match your speaker load?
Re your master volume only going to 3, I'm pretty certain the master volume is BEFORE the loop, not after. If you are bypassing the preamp and running straight into the fx return (power amp input jack) the master volume shouldn't be doing anything at all. I know this mainly because I once dialled my master down to zero and tried to plug a pedal into the fx loop while the amp was running and got a heck of a loud thump that scared the pants off me.
And you scored a white tolex one, damn cool
Block diagram from the manual shows the Master Volume right before the output to fx loop
I still have the same problem with nothing but the speaker cable pulled in. I’m running into a Eden 410xlt @ 8ohms even though it looks like it’s at 4 ohms
Thanks for you input! I’m going to try running at factory “normal “ settings
It’s weird because it works fine at first. Even though a full gig
Thanks for your advice. Definitely going to try it in normal setting
AKG P2. Not scooped like a kick drum mic. I used one with mine for quite some time.
Not expensive either.
Greetings from the North,
The Sennheiser MD421 is an outstanding bass mic. I've preferred using them in the studio and for live situations when ideal. In fact I not only used them when provided I went out and bought my own and recommend them to discerning bass players everywhere
Rezdog
The Sennheiser MD421 is an outstanding bass mic. I've preferred using them in the studio and for live situations when ideal. In fact I not only used them when provided I went out and bought my own and recommend them to discerning bass players everywhere
Rezdog
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