How to fix Noise + add Master Volume Fender Bassman 6L6 tube guitar amp 

Okay, guys, just got the amp back. Insanely awesome! Can’t tell you how much better it’s improved. Sounds absolutely amazing! Terry’s work is A+++++ . Seriously, I’ve dealt with a lot of techs in nearly three decades of playing, and he’s head and shoulders above the rest. Great guy that does great work, can’t ask for anything better.

I don't even know why I watch this channel. I don't even work on electronics, but I watch this shit everyday.

I like your perspective on cap changing. Normally I hear that ceramic caps are invincible. Nothing is invincible. Very nice workmanship, as always, too.

Excellent job, Terry, as usual. This has inspired me to finally take a look at the “yard sale find” black face Bassman that’s been in my basement for years. I always enjoy your videos, and always learn something. Thanks for sharing.

Very clean amp. Also nice troubleshooting and modification. Excellent work as always Terry.

If anyone is curious, that’s my amp, and I sold those two Ajax coupling caps for $50. People will buy anything vintage.

I learned a lot from this video. Great emphasis on the wiring to the master volume. I agree it is a brilliant modification to this circuit. Thank you, D-Lab.

Excellent video. You know how much we love Fender Amps. Thanks Terry.

Terry, great video, systematic and thorough trobleshooting

I find it hard to add more than what has already been said in the comments. I had the same Bassman back in 1969. It was 5 years old. It had the 12 inch JBLs in it. I was a fool to have sold it. 1st wife did not understand the worth of the amp. I am going to build a single channel version with 3 band EQ. of this amp. Try to make it as clean a sound as this one. Great video Terry. Brought back some wonderful memories. Thanxz

That's one damn clean amplifier! Great video, Terry!

Boy that brings back memories. At the music shop (a Fender dealership) I worked at I saw a lot of these in rough shape like all the solder connections shaken to death. 100% resolder job. But when looking for upstream microphonic elements you have to have the volume controls UP not off.

I loved seeing that amp. but, more so.. I enjoyed learning a few new things. Thanks Terry.

You da' MAN, Terry! Now the sound matches the incredible looks of this excellent Bassman.

Hey D-Lab thanks for another video!

6:57 I just watched a "home movie" of the fender factory from 1957, the narrator spoke of how out of sorts fenders parts inventory was, so the differanct colors would verify this possibly? a must watch video on youtube

Great video Terry as always, and I learned a lot. Such a lovely clean amp, I really wanted to see the filter caps under the dog house cover too !

Thank you very much Mr. Terry for this beautiful class, these amplifiers are excellent and deserve this love. 73 by PY2SNN Sebastian

Excellent work right through.

Thank you much for the videos I have a fender bassman and a twin reverb I worked on the bassman but not the twin Now I can go back and do them both the right way Thanks again From Canada

Terry I just fnished my first MV on a Bassman AA864 That I scratch built. Man I love it! This thing ROCKS! Thanks for the awesome instructions!

Thanks, Terry! Looking forward to rocking this out!

I’ve watched probably 500 of his videos, but when it’s your amp, man, that’s really cool.

Cool video, appreciate the detailed instructions and clear explanations of what is being done. You have a new subscriber! Thanks!

Another great video, thanks! Nice to see a vintage Bassman that hasn't been hacked to death. I've restored a few vintage Fenders that were in a sorry state compared to this one. In addition to what you did, I always swap out the 2W screen resistors on the power tubes. They tend to get baked to death as the heat rises from the sockets and are often way off tolerance. Cheers.

Wow. I wish I'd had this knowledge when I rebuilt my old Wurlitzer juke box amplifier. It worked well for my bass guitar and I understood grid bias, but I could have done so much more. Thank you.

This Amp saw the inside of a home and a Studio..it never saw a Club or any type of hall ..its been only home and studio used..another great video Terry always learn something from you

Nice one Terry!

Great looking amp

Good one Terry! I think I'm ready for a soldering station upgrade, too. Merry Christmas to you and your family!

Excellent video

Really great video

Great job Terry! You are a master with the scope! I hear those big ceramics add “character”, it appears that you don’t believe! They work great in pedals though.

thx terry :) have a great day!

The first place to check for noise in an amp of this age, is the Filter Caps. Under the Dog House. On the bottom of the chasis. That's where you'll find the source of 60 cycle hum.

Terry, there's a little 1/8" plug jumper that comes with the Hakko station. Jump the power supply to the stick holder; it has a microswitch that puts the stick to sleep which makes the tip last *years* longer than it does without it. And the stick comes back up to temp as soon as you lift it from the holder.

Good job!

SEE *Trainwreck Pages - Rob Robinette's* and scroll to TYPE 1 MASTER VOLUME. This will be the one D-Lab is doing. EVERY BRITISH 50-200 WATT HARD ROCK/METAL AMP (Marshall, Hiwatt, Sound City, Orange, Laney) [not sure about CLASS-A VOX amps], as well as U.S. amps- Ampeg, Mesa Boogie, Kustom, Peavey,Soldano, Trainwreck(US?), etc....all of these amps sound great with this Master volume.

Good call changing those ceramic disk caps. They have no place in audio circuits! . I've found them to be generally microphonic. Another great vid, thanks.

Terry Great video. One question-should you terminate the AC lines for the deleted two pronged plug before powering it up ? Thanks !

I'm planning on installing a master volume control on my Silverface Bassman. I can't find the model number anywhere but the closest schematic is AA371. My amp has 100K grid leak resistors so the 250K pot sold by Triad should not be used - I didn't find this out till after I bought the kit. This isn't mentioned the Triad instructions. See the rob robinette website for the "Frondelli" master volume circuit where this is discussed. I had to order another 100K pot so I can make the modification.

Great video! Can you apply this master volume mod to an Ampeg SVT VR as well? So you can dial in a "dirtier" tone with preamp volume knob but control the overall output volume with a master volume without sacrificing any of the tone?

Great info Thanks

I suggest using an insulated sleeve when mounting the master volume pot. This might prevent shorting the tube bias to ground if the pots fail.

I need to replace my scope. What would you recommend for repairing amplifiers such as what you work on? Thanks.

I have a blackstar with a master volume which allows you to run your tubes wide open and still have playable volume levels.

Terry really enjoy your videos. Just wish you could do one on a Guild Thunderbird. I am having trouble with mine. Thanks

Ceramic capacitors are always prone to produce some kind of noise. I replaced all of them inside my amp with polypropylene ones. I believe they sound even better than Orange Drops.

It would have been good to have heard the amp after the modifications to see the difference.

I need to see it on a schematic to understand what it's doing.. are we just shunting some signal from output tube grids to ground with the pot?

fantastic video, thumbs up from me!

What is your going rate to work on an amp. I just got a 68 Bassman. It has a little hissing noise and it seems like when your playing the guitar it goes a little lower sometimes. Usually when you first turn it on. Let me know thank you sir. Love the videos so interesting.

I like that dummy load you have made, looks like you attached it to a jack, what's the spec?

Even brand new ceramic caps are suseptible to physical manipulation and produce voltage by themself if manipulated. If im not mistaken. Were those actually bad?

I agree Terry those grid coupling caps are known to go bad even in old radios it's just not worth the risk

Can you recommend a decent, new oscilloscope, easily available via amazon or similar? I used to work on tube amps a long time ago, but starting to get back into it, and just found that my old scope is toast. I was looking at the Hantek DSO2C10, but not sure if that's overkill or? I have a lot to re-learn, but your videos are helping a ton (and inspiring). Thank you!

You do great work, however, it's very anti-climatic for us guitar players, not hearing a guitar through the amp. Can you get a cheap guitar and have it tuned to a chord and hang it on the wall for plugging into the amp so that we could hear a guitar through the amp? You could strum the strings and it would be a test signal.

I love your videos. Wish I could have you fix my fender twin

Just came across your channel and wondered by chance if you could comment on adding a bright switch to an Orange Brent Hinds Terror head. It’s two foot switchable channels; an amazing dirty channel that’s just right and a “natural” channel that is pretty dark for anything other than Teles or Strats. Some of suggested adding a bright input jack but that would brighten both channels... thoughts? Thanks

@D-lab Electronics, can you do a detail video on your setup with the dummy load and the output to your Scope?

Ceramic discs are always microphoinc; it's the nature of the beast. Piezo effect, and the big disc acts as a large diaphragm. It doesn't mean it's a source of the noise we were hearing. Still great to replace with something better, but it's NOT the problem.

My favorite scope!

If you have to replace resistors in these amps would the metalize resistors work better I like that you use orange drops caps,pricey but nice.you really do great work

man! thank You !

I don't work on apps I play with the two and I use all old Fender Bassman amps as well as Marshall amps from my Bass especially my frettless, I am totally about tone and I'm finding it more now with low volume by the way the Marshalls is in 1970 major you would love to work on that one its stock I loved your video

hello mr I hope you were well I wanted to ask you something that happened to me with bassman 59 I did the master volume and it looks good but now I feel some background noise I noticed that you used a master volume and I could notice that you put a filter in the bia potentiometer Could you tell me if that could remove the background noise that I comment on the master volume?

How's about a dpdt relayed to bypass the msster and simultaneously switch an extra gain stage in/out.

Nice video, Terry! Whatever noise existed after you did the cap replacements you showed---I will GUARANDAMNTEE you that if you replace the 100K plate resistors (4 places in a Bassman--the ones that come together in the "V" shape---with 2 watt metal films---that noise will be 80% reduced. It's pretty much the same as having to replace the electrolytics under the doghouse on 40+ year old Fenders. Gotta get done, except I don't even think about the metal film plate resistors. There's nothing you can do to a Fender amp as cheap as the MF plate R's that will have anything near the effect. The hissing, popping rodent noises...those are the plate resistors. I promise. Any blackface or silverface Fender. 6 places on reverb amps. I have NEVER replaced those resistors without producing a WOW immediate and dramatic noise reduction. $3. Try it, my friend.

Gud job mister. In the end of the video , add one cap. in the Bias pot. Its for stabilicing the negative tension? Thanks for your great chanel.

Nice video, like always. Couls you do a video of how to Black face a Bassman 100 silver face ? It would be awesome

my bassman one power tube out of 4 gets hotter then others. all voltages are correct. only missmatch is after PI 318V and 306V. OT is also warm on idle. Sockets look fine. What could it be or it's normal? Thanx

Do you know of a good replacement .001uf 1kv ceramic cap? I can’t find a orange drop with 1kv.

Hey Terry. What's the blue cap at the bias pot in the final picture?

Great video! Where are you located??? I want to drop off my early 70's Bassman 50.

Great Video! I love the thorough ones. It does make me sad tho because I owned a 67 that was just as clean... in fact I think I traded it to a guy in Indiana... Crap... lol...

Hi from Dublin -- love your vids -- 2 things I find -- sometimes those carbon screen and grid resistors get baked and cracked and make noise -- also may I respectfully suggest to solder the grounds directly to the chassis -- I has seen bias failures etc die to bad continuity on those lugs bolted on the transformers -- peace

Would a pre-phase inverter master volume circuit had been easier to install?

Would that cap issue show up with a speaker plugged in without the scope?

Have you ever checked out the ken Fisher master volume control. It's much simpler and works just as well !!!!!!

Cleaner? No thx Terry I want the sound of every control dimed -red hot crunch and dirt - but at a much lower overall volume. The the way I'd run that master volume for recording would be all channel controls on 10 - but the master at 1-2. The high gain noise...that's why they make noise gates LOL. GREAT work as always Terry you are an artist sir !

I’m surprised no one has chimed in about the master volume mod yet. I’ll explain why I added that. I should preface this by saying I’m a purist, when it comes to gear and tones, but there are realities to deal with, and Fender wasn’t perfect. I play with mostly dirt boxes that like to see the amp at the verge of breakup, what the post inverter mod allows me to do is get that at any volume, whether I’m practicing alone, with a band, or at a gig. Power tube saturation is a HUGE part of a killer recorded sound, that’s why guys like Jimmy Page used small amps for recording, so they could run it full bore. For recording, I’d run this amp as loud as I could before the preamp over saturates, but for cleaner sounds, I can definitely use the master volume to record a more pristine tone that doesn’t need that power tube saturation.

My amplifier is a star force USA amp from the 90s sometimes the gain doesn’t turn on

What is that thing sticking out of the back of the amp? Dummy load? Is that home made? How did you make it?

Where did you get the lighted magnifier

ok, Thts a X over amp, not flat lined AB165 at ..........ALL...............The driver n n Bias splitters say it all..Ive had several in like that great sndg amps..ive got 30 years in, store front repair...seen alot of weird stuff too :) WOO, looked CLOSER at DRIVER Thaz a REALLY REALLY rare amp, the POSITIVE FEEDBACK 220Ks form plates of power tubes to plates of driver tube was wild! THAZ where alot of noise comes from as well......Gives a bassier sound 4 sure... Fender fed back CURRENT from the speaker jack BACK to primary side of driver too, That could be a Dumblish manuever as well :)

Excellent video! I have two of these heads and the work on the first one is almost done so it was good to see this video. Did you check the filter caps at some point or know they had been replaced with the other electrolytic’s? Really enjoy your videos, always learn!

Your a pro impressive

would like this mater volume mod done on my carvin nomad amp

hey dlab that amplifier do sound good gkl

I’ve got a vintage 100 watt Carvin I’d like you to fix

Was something getting microphonic at 1:30-1:50ish. Your audio was a little reverby. Or was that a different mic?

What is the name of the song and the artist you used in the intro for this video?

Kendricks amps charged me $1200 and kept my 63 Bandmaster for a year,shotguned all my caps...,all that was wrong was a old ground wire

If I recall, correct me is I'm wrong. 8:10, ceramic disc caps are essentially made like a piezo transducer, and WILL generate power when moved, pinched or tapped on.... thus the noise on that is expected... at a modest level at 16:25, the older style caps had a higher ESR than the newer stuff does/did. I know ESR can climb with age, but in reproducing vintage circuits, it seems some of our new components perform better.

how about a schematic for the master volume.

I had a master volume added to my 65 Showman thinking I might be able to use it at lower volumes with at least a bit of breakup, turned out to be a waste of time, still no breakup even with the master low and the main vol. high...

My rarely used Fender 59 Bassman 4-10' combo amp has very loud Hum and slight popping sound , it sounds exactly like this but way louder , this is like normal tube amp hum. it did have 2 new power tubes and one preamp tube replaced. I took it to this local amp repair guy he hook it up outside you can barely heart it and he goes I don't hear anything wrong here, he ask me if I have dim light switch , bad grounding etc yea I am familiar with that, but I have other tube amps that does not have this excessive loud hum sound maybe after you biased it the humming sound comes on, so he did not want to check the capacitors voltage make sure all working correctly, I already email you about this issue but you are full of clients at this moment. I think i might sell the amp , I can't stand amp with the loud humming sound going on. I bought a brand new Mesa Boogie amp that had the same problem, loud hum took it back to the store and got my money refunded. So I have no idea what's causing the amp to Hum so loud

I was wondering when the filter caps were last changed?

Wait... how does it sound now???

Terry, I have worked on many of these and that one is pristine.If that had the Drip Edge it would really be a relic. I had that crackle problem Many times, and it was the disc cap as well. One had a hairline fracture. After replacing the amp was quiet as can be. I use the same soldering station - its awesome. I also noticed you added an electrolytic cap on the center of the Bias Pot to ground. Was that to eliminate noise or to ensure the negative bias was not affected ? I did notice the master volume slightly changed your negative bias.. very slightly. Nicely done Terry, as usual !!! P.S. I notice you are not using the Hakko Lockout Key on your unit - Be careful.... Dick from the Internet may come and change the temps on you... LOL Seriously, really quality video again.. well done - THANKS RON