How to fix Fender smoking Bassman guitar amp process for tracking down and repairing negative bias
Вставка
- Опубліковано 7 жов 2024
- Hello my friends, another Fender Bassman hits the bench at D-Lab! This one is from the original owner. Had been stored for many years. When he decided to power it up, what happened? Yep smoke! So, the amp was hand delivered for evaluation. I searched the chassis for charred components, none found. Mystery? Well after some probing around, I determined that the negative bias adjustment pot was defective, causing loss of bias and baked tubes! It's not often that these pots fail, so I was a bit surprised. Hope this information is of value to you. By the way, my channel just went over 50K subs! Thank you all for your support over the years. TD
That's the cleanest 50+year old Fender Bassman I've ever seen.
As always, a great video, you can never go wrong by switching the bias over to AB763 and correcting the NFB on these. Keep up the amazing videos!
Nice job sir. Sure was lucky it only killed those old tubes and didn't go into self-destruct mode. This is a component I've never seen fail before but it's not something I'll ever overlook again.
Thanks for all the pointers Terry
Cheers my friend
Cool old amp. Outstanding service.
Love these amp repairs, thanks
No wasted troubleshooting time. The master!
So clean and good looking amp, happy that it got some love from your skilled hands.
As they say on the cartoon, "Archer", "Phrasing".
Mission Not Impossible! Well done Sir!
Well done Terry. That was a great lesson !!!! Weird problem that makes me wonder.. did the pot kill the tube, or did the tube kill the pot.... we'll never know.. but your detective work narrowed right in there !!!! Excellent
I'm just a guitar player ... but with the age of that tube ...
Good job, Terry.
Just making sure folks are sending enough love your way for all you send to them ...
Great videos Terry!
luv the t-shirt
great content as well keep it up Terry 73's
Love you amp repairs Terry..Great fix and step by step information.. Thanks for sharing your expert knowledge.. Learning all the time..Ed..UK..😁
As always great demo of repair work by D lab.
Please make a step by step video of how to add the bias pot to this circuit, replacing the bias balance system. I have this same amp and would like to do it (I’ve serviced it with new filter caps and grid caps) but would like to see a video on how to add the better bias adjust pot.
Gotta say it: He was trying to play, "Smoke Gets In Your Eyes"! Right? :-) New shop looks real nice! Happy Middle of the Year, Day! (ALREADY!)
Great Job. Congratulations from Brazil.
A bad power toggle switch can indeed smoke. Had this happen on a Fendor amp repair.
Good job Terry!
Nice shirt. Thanks for the video :)
Nice Allen Bradley plug there.
Terry I bet that variable resistor has what I have ran across on a few radios lately is Tin whiskers !
Very educational! Thankyou.
Great advice, thanks!
Hey Terry !! Great lesson. Quick question. When you convert from a bias balance to a bias set pot - what do you do if/when the bias at the grids are unequal ?? Are there any designs where there are both a bias set and a bias balance pot ??
"Inspectium" :-)
This just happened to me today!
what's the .01 cap off the grid is that for oscillation
Is the Allen Bradly pot you installed still available for purchase
It was a NOS one I had on hand
@@d-labelectronics I thought so, it worked perfectly for the application...worth its weight in gold
They're still available but made by other companies.
www.newark.com/tt-electronics-bi-technologies/p270-sf21br10k/rotary-potentiometer-10kohm-10/dp/46M2514?ost=p270-sf21br10k
I'm confused what was drawing 100mA of current, the plate or cathode on the BAD tube? The GOOD tube was drawing 60mA of current?
Both RCA 6L6's were bad. The one drawing over 100ma was a red flag. Normal current draw on this tester specs around 75ma max for 100% emission. The new Tung-sols are nicely matched.
@@d-labelectronics 75ma is the plate current draw or cathode current draw? Because I'm confused because mostly you set the current draw for 30mA in all your videos for biasing tubes but on the tube tester considered good normal current is at 75mA being draw by the tubes plate and cathode which doesn't make sense.
Hello, The current shown was on the Amplitrex 1000 tube tester, not installed in circuit on the amp. When I install the tubes, you are correct, I adjust the negative bias so that each tube draws approx 30ma
smoking must be a hot amp
Terry, what make of variac are you using?
Tenma
Is smoke bad?
Amen brother. Thanks for the look.
Great advice!