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Hi Stuart, great comprehensive video! I was wondering is there any update on the contact cleaner test on the pots you were doing over 1 year?

Heathkit made kit amp of the Quad II valve power amp

I have seen other BJr bias vids but yours explains measuring the bias using the transformer resistance method quite well. In lieu of a 1ohm cathode resistor or a cathode biased amp, I always use this method. Thank you

would you like to take a look at a tube amp for me i think its a 78 fender studio bass 200 watt tube amp? its got a bad quivering popping hissing noises when u turn it up and does not play as loud as it did some one plugged a small amp in to the input to play distortion which was pretty good for about 5 minutes then the sound started going crazy then there was no sound now its crazy loud quivering popping hissing noises befor this this amp would rock the house now you cant turn it up with out hearing all that.

Is there a way to lessen the treble on this combo amp? Even if i put the treble in zero. Still too sharp

well im in my hd130rev. 2275 coming into a reverb issue having some distortion and effecting the trem system. take the reverb out of the loop and trem works perfect, verb in loop and normal playing on guitar the trem doesnt like it, easy on strings and trem likes that. swapped the ic cans around and tried nos so i know its not in them, looking for a better more eligible schem , and help be great

Had a Blues Jr with the same crackling issue on the bench. Using your advice and blowing on the junction between the ribbon cable and tube PCB also temporarily got rid of the crackling noise.....but..... The owner had changed the input jack and his solder joints on the PCB were not shiny. When I reflowed them they made a crackling sound. I asked the owner what solder he had used for the repair and it turns out he had used PLUMBING SILVER SOLDER! Removing the plumbing solder and then using normal electrical solder SOLVED THE PROBLEM. Who would have guessed???!!!!

Not ideal but it is possible with a delicate hand and a lot of patience to replace surface mount components. Obviously not remotely ideal but in a pinch... Anyway, the state of that board around those FETs - would love to know the story behind what happened there!

Great video! Thank you.

On the tag board the high value resistors (1 Meg Ohm) drift way out of spec and should be replaced.

I have the Execelsior, also from the pawn shop series. I just dug it out, very little hum, but still some and similar to what you have there. I did have a similar hum issue with my fender champ reissue of which one of several fixs was to rotate the output transformer 90 degrees and remount....modern fender amps sure do love to have transformers that are magnetically coupled.... i.e. almost bloody well touching! In the champ i also added additional power filtering capacitance as well as rectification on the heater wires, and the lead dressing is usually horrible on these cheapo amps as well. It very quickly gets to the point where it would be easier to buy a blank chassis and build the sodding things on tagstrip :(

I just stumbled upon this video after finding out that the Valvestate S80 (8240 model) that I have has a similar problem. Basically, when I move the pots, the sound is very intermitent but it also cuts out the right speaker when the Master volume is low. When it's high enough, the right speaker makes the crackling sound and seems to come back to life. I sincerely hope that it could simply be the pots that are problematic. From what you mentioned in the video, you use WD40 on the pots? Wouldn't that oil up the entire board? And thank you for your video, it reassures me that there are some chances that it won't cost me an arm and a leg to repair it!

Cool video !! Your customer should just pay you to upgrade the amp to 100% hand wired.

Great job and thanks. I have a Marshall AVT 275 amplifier that is fully functional with all of the lights working and everything else but no sound of the speakers. So I have to do a bit of diagnostics even though I’m not a repair technician. I am an electrical engineer and have a bit of experiencewith amplifier electronics. I can probably find the obvious stuff but not be able to check the signals as I don’t have a scope I just have a voltmeter.

Wonderful video, i truly appreciate the full on tinkering. The process is very important!

Wow. What a breath of fresh air. I've been an Electrical Engineer for over 45 years, and I've actively avoided online tech-related content (even since the old BBS days) specifically for the reasons you alluded to. It's mostly populated by anonymous, clueless hobbyists with fragile egos who feel no responsibility to provide fact-based information. Feelings and baseless opinions are fine. However, in the engineering world, Step 1 with any product you're considering using is to contact the manufacturer to make sure it meets your specifications. And when you mentioned that you'd actually contacted the manufacturer my jaw dropped. Wonderful. And the long document in the video notes detailing the manufacturer's response was perfect. And to actually perform your own tests is often Step 2 in the real world, but most online experts can't even comprehend doing something so logical. Sadly, technology is becoming nothing more than "I saw a video (or asked AI), and now I'm an expert".

Amazing tenacity. Thanks Stewart.

I found that if you shoot it down the front side of shaft it will get in there and do the same without having to take your amp apart i did it with my 5150 amp !

AGAIN !!!!!!!!!!!! @johnsuggs7828 6 months ago As stubborn as ever. As a scientist with over 30+ years in many areas. I'm always amazed at how people can just easily dismiss the most basic of scientific facts. F5 is formulated and specifically for Faders. Says so. Not sure why if both do the same thing, why the company would make and push them as two different things. That would get them sued. It's called misrepresentation and it's illegal here in the United States. Sometimes called bait and switch. D5 literally says NOWHERE STUART. Nowhere, that it is to be used on faders and pots. Logic is clear......but not to you

Here's the douche ! @johnsuggs7828 6 months ago @stuartukguitarampguy5830 Evidence? You need evidence that your body processed oxygen Stuart? How about evidence the earth is round and moving? Both things based on basic scientific truths we can extrapolate other truths. It's how things outside the confused world of Stuart moves along logically. The company has a product that specifically states it is for faders. There is a reason for that. The one you're pushing DOESN'T state that.....anywhere. Explain that. Then there's the science genius. Mineral spirits (while you were correct in stating that it doesn't break down carbon), it will losen it. It's why it's used in engine cleaner. The process of destroying over time the carbon track is slow and you may never see it. But it's like the speed at which you comprehend things. It's slow, but it moves.....really slow

Show me a video that shows the carbon is damaged funny there's not one out there so dont worry Stuart these clown's are just that and based on what he said to you and HOW ! he said HE'S JUST LIKE I SAID A CLOWN !

Ya i just saw another video and didn't even see your name cause as i listened i was like hmm this sounds familiar and then i looked and yes Stuart the amp guy ahhh so your talking about ( john the scientist) what a moron ! backed your comments up Stuart there's always clown's like this !

Great work Stuart! Love the pot experiment you came up with! Might try that myself!

i was wondering if i can make my own d5 with mixing mineral spirits with deoxit d100...

love this. had me transfixed.

Howdy. For the future. I would suggest introducing anti-hum to the driver or splitter tube through a cap. and a high ohm resistor. If the hum is 50 / 60 Hz the feed point is either one of the anode voltage trafo connection. If the hum is 100 / 120 Hz the feed should be after the rectifier. One may need to experiment where to introduce the anti-hum to actually fight the hum and not amplify it. Regards.

Hi, just wanted to say that I've had the exact same problem, watched your video, and it saved me a bunch of money. Did the same procedure as you showed in the video and the low end rumble stopped. Thanks so much for your methodical approach and good will to put this online.

Thanks Stuart! Youre tha man!

These amps were only ever intended to be a one-off limited edition production run. So probably accounts for Fender shrugging their shoulders and turning a blind eye to that basic transformer error.

i had one of these in 1992 and regret selling it to this day. they make a awesome boost type pedal as well.....besides killer slap back. what a shame the client did not get you to restore this bueaty..

once again a great video of excellent amp work...ive lost all faith in any modern fender amps tbh..ill stick with my old pro reverb 1970..old amps are built like old holden cars. solid easy to work on etc.happy xmas Stuart and thanx for the videos it was entertaining and I've learnt a lot..i did share your work with Brad guitaroligist or shared a link..his another great tech.you two have a similar approach . which is to get it working , quality and save the clients money. ive also learnt a lot from pisonic amp repair dude.his work is very nice. Anyways where would the world be without good amp techs cheers mate

Disregarding that voltages look good between those serial connected filter caps, I would use/add voltage divider to split voltages between them. With so many filter caps their secondary function of discharge resistors is quite useful. Over time, and especially with heat, internal resistance of electrolytic caps changes. Voltage divider just makes sure voltages are equal. This is a good measure regarding the longevity of the amplifier. I have never seen the PA version of JTM-100. I really like the JTM series of amplifiers. Black flag amplifiers are rare. JTM-100 is even rarer. PA version must be even rarer than that. Very first JTM-100 amplifiers sported two output transformers. Marshall didn't have the needed output transformer that could handle 4x KT66 tubes. The solid state rectifier debuted there as well. In the Marshall amplifiers, that is. Other brand were using them before. JTM-100 asked for new power and output iron. At the same time, first JTM45 50Watt versions, have used same power transformer as JTM45 but because of the voltage rise when using solid state rectifier and saving on 15 Watt's by not using rectifier tube heater they were able to use full potential of the KT66 tubes and get out full 50 Watt power. Transformer still had 5V heater tap and center tapped HT coil. Just used diodes instead of tube rectifier elements. At the same time 100Watt version had only one HT tap and have used grets full wave rectifier made from 4 diodes. Later black flag 50Watt models have had dedicated transformer without 5V heater tap. JTM-100 is a parent of the Suoer amplifier Plexi series. Black flag introduced EL34 tubes. Once that happened path to Super Plexis was wide open.

Many thanks Stuart.

Many thanks Stuart and all the very best for the festive season and New Year.

Excellent. Curious as to whether the voltages on the caps ended up close to those shown on the schematic.

What an eye opener on Fender design . Simply tragic that one of the best known names on the planet chucks out this junk, knowing full well it is flawed and like other more well known reissues from them, designed to fail by using penny ( cent) pinching components.

Looks like the resistor on the octal socket is burnt? And the ot should be rotated 90° as well if I'm not mistaken? I've seem bluesbreakers assembled the same way. Your right , it's unbelievable that they'd produce them that way

it looks like the transformer coils are in line not at 90° as well as being very close to each other all very odd from the beginning standard practice as far away from each other as possible and at 90°

Single ended amps almost always have a small amount of background hum. You could spend a couple hours dressing/re-routing wires and even putting in a bridge to run filament wires DC. But like you mentioned about moving the transformer...not worth reinventing a budget design.

STUART, If you mount either the power transformer or output transformer in opposite orientation so that the magnetic fields are opposite and not in the same direction it helps out the induced 60hz hum. Just Rotate the output transformer 90 degrees which puts the output transformer magnetic field on a different plane to the output transformers magnetic field. I'm not sure what the correct electronic engineering term its called for doing this? but it helps out the induced 60hz hum

I have an mg10 with a noise like that. I will let you know.

Glad you found the issue. Sleep well, my guitar tech.

it looks like the transformer coils are parallel with each other ,the output trans needs rotated 90 degrees,

Better to live with the hum than to shell out good money on a poorly designed amp. And have a very happy and peaceful Christmas Stuart.

Very interesting Stuart... Would it be possible to relocate the output TX near to the speaker ( as a lot of the vintage amp designers favoured) ? Looking at the thing, I'm not sure Fender had much to do with the design on this and other models using "U" chassis.

I’m not convinced this amp is actually repaired. I’m curious what the idle current is. It shouldn’t take that much capacitance to reduce the hum.

Thanks Stu, Very informative video. The ups & downs that can go on in a repair.

Why would a dropping resistor reduce the 60hz Hum? the dropping resistor just steps down drops down the B+ voltage. What does the B+ stand for? B+ meaning what

I have one of these with 6550 power tubes in it. I'm still figuring out where i need to be. 42ma - 50ma? It has 150K resistors on the grid coupling cap section and a 47K bias trimmer pot resistor. 1ohm r on all caths. The Party likes his 6550's. I say put EL34 tubes back in it as it would be more compressed and controllable. 6550 tubes to me are for a Bass amp or using in a mortar to bomb the other side!😂 A very well made amplifier.

Your Videos are invaluable life saving info for all of us amp tech's. You re a God send. Amen and thank you again!