Tube Amp Repair
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- Опубліковано 29 вер 2024
- Safety Tips for Working On Tube Amplifiers
Vacuum tubes require a high voltage to operate, this means you can get electrocuted, or burned. Do not place your hands or non-insulated tools in the amplifier when it is plugged in. When probing a live amp, keep one hand in your pocket - it's the current across the heart by way of the arms that kills you. Electrolytic (and other type) filter capacitors can hold lethal charges - be sure to discharge them before working on an amplifier. Don't install tubes with the power on.
Vintage Amp Repair performs maintenance, restoration and custom modifications on all makes and models of audio tube amplifiers.
Awesome video. Thank you for it. I am salivating for part two with you repairing it and then hooking it up and hearing it. Bummer.
The Fisher SA-300 is a Class AB amp not Class B. Each pair of EL34's in p-p will provide about 35-40w per channel....Cathode resistors in a cathode bias ckt always age poorly in these theatre style amps, because they pass idle current all the time. The cathode resistor that measures 5 ohms is in parallel with the bypass cap which has gone leaky dropping the resistance of the parallel ckt. I would change those bypass caps right off the bat anyway, which someone has already done in that amp as you can see... CHeck the resistors only when those caps are out of the ckt...I think he mis-spoke when he said that resistors don't go up in value, because that is exactly what they do unless they have absorbed moisture somehow, which might cause a drop in resistance....
Cathode biased amps idle HOT, and this one is no different, with a 7.8 volt drop across 50 ohms which is 156mA of idle current or about 78mA per tube. It is somewhat unusual that an amp has both adjustable bias and cathode bias.
NEVER let this type of amp idle without a load, be it a speaker of the correct impedance or a dummy load of said impedance.
There are lots of folks still able to repair and/or restore these amps, and even more who act like they can...!!!
Hi!
Thank you for your video and knowledge sharing. About a year ago I purchased a Luxman MQ-88uC and really like the sound but I have experienced one problem that is distressing me...suddenly there's no sound from the left channel.
In one year of intense use it has now happened four times. I am using a single source connected directly to the Variable input and after turning the volume down and up a few times the sound eventually comes and no more issues for a few months.
Since it works well most of the time and I can't replicate the problem it feels awkward to send it to repair service. On the other hand it is very disappointing that such an expensive amplifier has this kind of issues. I replaced the driving tubes after experiencing the problem the first three times, I had hopes this could solve the problem but it happened again. I have checked the bias current and all seems fine, reading near 480mV in all tubes.
Should I worry about this? Any suggestions would be much appreciated.
Best regards.
you guys are cool but you have to have a 8 ohm load on each speaker output or the tubes will hot plate.
TheWarped45 ,Your tubes won't red plate,With out a load.if you hook up a tube amp without. speakers,You will only have a problem if you crank up the volume,Then you can and will have voltage jump across the windings of the OT's,Which will burn them out.....When a Tube red plates,Check your coupling caps out,because one will be allowing DC through....
You're Right Danny ! ( but loading the opt is good practice )
wow!!!...really dude? No load/speakers connected, poking your fingers in there with probably 400VCD+ in there.....if you were working for me...YOU'RE FIRED!! You are clueless buddy!
Open your eyes Einstein, 2:27 he reached over with his left hand and shut it off before flipping it over.
I think he knows to discharge the big power capacitors by now otherwise he woud be long gone.
not a good idea to turn it on without speakers or some load
@@johnmckeown6573 You can get away with it as long as there isn't an input signal. I always put a load resistor on the output just in case .
I want a t-shirt that reads: "IRON MEANS EVERYTHING"
Compulsor have a custom tshirt made locally and support small business.
I'm working on restoring my tube amps which have been sitting around.Maybe I'm one of the few left who can fix these. I used to do it for a living but I had to get a job to pay the bills.
He is telling this stuff to a cinder block. Ask him in five minutes he would be lost. 100 watts a channel my ass. More like 15 -30 watts a channel. That's why I get paid the big BUCKS. Just fix it & shut dummy up.
If the output tubes are passing current at idle, it's not Class B, it's Class AB.
Silas Fatchett it's a class A/B , I laughed when he said B.
It's considered as a Class B amplifier , just like a MAC is a class B , there's always some current at idle ..... without some current you get cross over distortion.. most announced as class A amplifiers do also commutate in class B at a certain level....class AB does NOT exist as is or would be ... amplifiers work in class A than commutate in class B ..pure class A is rare , so is pure class B ....you wouldn't want to listen to a pure class B amp.
@@vsmichael1 Keep on laughing , the man is more skilled than most of us.
I have a large collection of tube amplifiers and hand build them and do testing of new circuits
I like these amplifiers but I like them untouched and in factory condition sometimes you have to fix other peoples mistakes if you don’t have the schematic
But I spend more time testing then anything I learn so much from these type of videos
Many people still think you can plug these amplifiers in a USA outlet mine being 123 vac plus or minus 3 volts and my ac heaters where getting over 7 volts vac and not lasting long now I use a variac to bring my voltage to 115 at input I know some people add resistors and thermistors and diodes to drop voltage
What are your honest thoughts on this Matter what would recommend?
You’re poking around in a live amp with charged capacitors...with both hands in there. How many times have you been knocked on your ass?
I hate that mushy sound that digital music has
You don't adjust for a weak tube replace it really. Cant believe you would even say that. EL34 or not $100 dollars each Please look at eBay
A really nice amp that would have worked well with my EV Patrician 800 speakers.
This amp puts out about 40 watts a channel with EL 34s not 100 watts, not even with KT 88 in it. Its a Fisher 300 I have one
That's what I though, also new EL34's are readily available, not too expensive too.
You are right.
I been fixing Audio Research equipment for many years and I know a little bit of this.
Cheers.
I was thinking 40 watts a channel also.
i do i am 40 years old i was tough by a good vale tech
2nd thing with tube amps you never run tube amps with out speakers
yup best to have a load on ampy i build heads of valve amps
Right. If I was the owner, I would say to this guy...."you bought it".
Also, don't stick your fingers in there with the amp on. JEEZ!!
Yeah... I was thinking the same things. This guy knows some things and loves to hear himself talk, but I CRINGED when the amp was on without a load, and when he was poking his fingers around in there... UGH!
You can run it at idle without speakers, no input signal, and no output. I know that this guy may seem a little weird to some of you but it was men like that who propelled this nation to be a world power.
I have a fisher 100 one side works the other no sound,
Can you fix mine ?
I am in the usa.
+clemmtec Paul has a service center, and can repair it send contact information to tvecourse@gmail.com
Problem with my preamp Ming da, sometimes the sound is cut in one of the speakers when I touch the knob to select the input, it is also cut when I move a little the input cables that come from the dac, what can be the cause?,thanks
Corrosion or bad cables.
You are quite right. Leaky coupling capacitors can be found in any old tube radio or amplifier. Sometimes, particularly in consumer radios or record players, a leaky cap will cause low or muddy sounding sound. It will increase the current thru the tube and over time contribute to tube failure. In high end amplifiers running class B you have coupling caps and a supplied negative voltage for bias. The leaky caps' positive voltage will cancel out the negative bias. This causes a good tube to glow red. Not good for the tube or the output transformer. Class B amps are biased so that the tubes pull little current when idling (no sound) They only conduct fully when driven with a signal. This makes the tubes run cooler and lost longer. Some people like to bias their tubes little hot to get a smoother sound. The eats up tubes. Bias should always be set to the manufacturers spec. Using a meter to measure the current flowing from the cathode to ground is the best way to set bias. It will also help you get the tubes to balance i.e. the tubes are pulling the same current.
What you're describing is not Class B, it's Class AB.
Keep sticking your fingers in there on a live amp and we will never hear from you again...I was cringing watching this guy lol
Old school ....and STILL ALIVE _
I need your HELP - I have a vintage Crate Palomino V16 guitar tube amp.
I haven’t played it in a while and it worked and sounded great before putting it away.
I just played it today and it has a HUM that wasn’t there before.
I heard that in tube amps IF it’s a low-level pitch 60 cycle hum it’s probably a bad tube,
BUT IF it’s a high-level pitch 120 cycle hum it’s probably a capacitor that needs replacing.
I took out my guitar tuner and it shows the hum to be about an “A#”, and on another
Audio scale it says it’s a 120 Hz pitch MINUS 49 cents ??? What the what ??
The Hum does Not respond to the volume control - does that info help also ??
I do own a multi-volt Meter - How do I locate and test the capacitor if it’s bad or not?
Awaiting your reply, and Thanks In Advance - I REALLY NEED HELP WITH THIS.
I got an old Magnavox 9304-20 from the 50's that I need converted to a guitar amplifier... Not sure where to start yet.
According to the Fisher 1962 advertising the list price was 199.00.
Excellent video, bit it begs the question why wouldn't you just switch the tubes on that one channel to see if a loose socket is making the tube under perform?
Looks like an AO-28 preamp out of a Hammond
where is the repair please ?
Very Enjoyable Video..Thanks Guys!!!!!
congratulações ótimo vídeo gosto de amplificador valvulado para guitarra
obrigado por publicar documento importante sobre trabalho South of Brazil
If you had repair it while you were educating that fellow and let us hear it that would be great,
The end of the world will come in 499 years sir! point
I’m a guitar player. Could you use something like this to create a better guitar amplifier?
I’m a guitar player who builds his own guitar amplifiers. Could I change one of these beasts into a guitar amp.? Would it make much of a difference in the quality of sound compared to a regular guitar amp?
He must be dreaming or on Acid thinking this amp is a 100 watts PER channel!
Wrong ......PP EL34 can deliver 100 watt.....
Please make some guitar amp repair videos too.
Hmmm, probably the last guy I'd let repair my tube gear...
Dream on. for a $1k-$3k budget you can get Rogue magnum II
chinese junk
what is the name of Paul's shop? He doesn't seem like the type of guy that cares much about a Web page and relies mostly on word of mouth. His knowledge and and skill are a lost craft. (by all means if he is online send me his info please!) cheers fellas!
sending this to Paul
I been fixing tubes amplifiers for many years, I am 40 years in electronics.
Sorry you are wrong, This tubes are EL 34 and is imposible to obtain 100 watts with two of this.
Cheers.
When probing a live amp, put one finger on ground and the other middle finger on the positive of the filter capacitor to check if it is working properly. That way you don't need to purchase unnecessary tools and in turn save money money in the long run! Regards point
very funny.
like, after you're dead ?
'Valve'
saan po ang belehan
Carlsons Lab
good day ! Greetings from the Philippines ..
I have a question. can i replace any tube (of course, a power tube to a power tube ,etc) even my amp is not a fender or vox, or any other known tube amps out there ?
thank you !
Your workingdesk looks like mine... :D
In case of transformer failure of almost any kind, just wind off the windings, examine how there are wound and then rewind it the exact same way. Time and money consuming for sure but you definately get an exact copy of the failed transformer. So, there is not that much magic about OPT´s. The vintage ones in particular, were most often quite simple transformers(Even The Fisher ones). Just saying, because Paul or Al, I don´t know who is Al an who is Paul, acted like if a OPT would fail there is no chance to get a new one...
how many have you ACTUALLY wound ?
Zero I bet.
OPTs are impedance matching devices - period. Contrary to your opinion OPTs have no
wonderful audible qualities. I will concede that some OPTs are wound better than others.
OPTs with 'lots of iron' have a wider frequency response.
don't forget primary inductance, and leakage inductance and inter winding capacitance and how to increase, reduce and reduce respectively.
other than that they are quite simple.