A bit of "Tube Science History"...
Do not try it out; only for historical purposes.
How the story goes...
When I was a kid, about 10-12 years old (early 1960ties), I met a radio technician who could "measure" the voltages in a radio or amplifier without a multimeter.
This guy was about sixty years old or so and began playing with radio sets since his early childhood, so he told me.
Must have been in the 1920...
Wel the method he discribed me looks a bit dangerous nowadays but probably common in those days as it was a luxery to own a meter.
Again, do not try this and maybe this response will even get removed.
But it's only as a historical fact that this info is given. There is no use for it any longer!!!
Method:
He used a capacitor to charge it with the voltage he wanted to know the value of.
Then he discharged it to ground and the length of the spark give him an indication of the voltage measured.
A bit crude but in those days...
He finally died at the age of 92, kept on repairing tube radios until he was realy to old for it and the transistor took over. He was 81 by then. And I know; it was my oldest brother's father in law...
Do not try it out; only for historical purposes.
How the story goes...
When I was a kid, about 10-12 years old (early 1960ties), I met a radio technician who could "measure" the voltages in a radio or amplifier without a multimeter.
This guy was about sixty years old or so and began playing with radio sets since his early childhood, so he told me.
Must have been in the 1920...
Wel the method he discribed me looks a bit dangerous nowadays but probably common in those days as it was a luxery to own a meter.
Again, do not try this and maybe this response will even get removed.
But it's only as a historical fact that this info is given. There is no use for it any longer!!!
Method:
He used a capacitor to charge it with the voltage he wanted to know the value of.
Then he discharged it to ground and the length of the spark give him an indication of the voltage measured.
A bit crude but in those days...
He finally died at the age of 92, kept on repairing tube radios until he was realy to old for it and the transistor took over. He was 81 by then. And I know; it was my oldest brother's father in law...
I'm curious as to why the OP should take apart his amp first and expose himself to many hundreds of volts DC and AC when a probable fix can be tried without even turning a screw? Geofex amp debug page, Jack Darr's book " Elecrtic Guitar Amp Handbook" and others I have read all put tube failure as the #1 failure after operator error. There is even a section in Ken Fischer's Trainwreck Pages when troubleshooting a Fender he goes over the functions of all the tubes first before he mentions anything else. Yes, after tubes, power supply is next, but why not try simple fixes first? Why take the amp apart? You don't even need tools or a meter. Tubes lighting up doesn't mean that that are working properly.
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You are coorcet to a certain degree.
Not all failures are tube related.
But; As I assume, the OP is not a technician.
I also assume he has no stock of all possible tubes.
Therefore it's a lot cheaper to check the inners of the amp and then buy the suspected faulty tube.
A set of tubes costs more then a decent digital multimeter.
And maybe by following some test methods the OP can learn something.
So; again, measure and then replace.
Not all failures are tube related.
But; As I assume, the OP is not a technician.
I also assume he has no stock of all possible tubes.
Therefore it's a lot cheaper to check the inners of the amp and then buy the suspected faulty tube.
A set of tubes costs more then a decent digital multimeter.
And maybe by following some test methods the OP can learn something.
So; again, measure and then replace.
"You are coorcet to a certain degree." should be
"You are corect to a certain degree."
Small keys on my keyboard...
"You are corect to a certain degree."
Small keys on my keyboard...
I guess since I have been playing since high school(40 years) I assumed people have extra tubes on hand, which is a good idea. I have always had extras on hand from experience. You don't want your amp to go down and not be able to finish jamming or finish the gig simply because you don't have spare tubes. I didn't consider the OP might not have them. You really only need one preamp tube (if all are 12ax7) which is many times the case because you sub in only one tube at a time and usually have a spare set of output tubes since they fail more often than preamp tubes.
You are correct about learning something by checking out the power supply and the rest of the circuitry. I was also hoping he would learn that it is easier to first check problems without resorting to taking apart the amp and then if that fails, by all means dig in and see what makes these things tick. I guess it comes down to a difference in opinion. Since he seems not to be a tech, I was hoping he could solve the problem without exposing himself to those high B+ voltages.
That's what is so cool about the forum, we can have a lively discussion without getting all bent out of shape. Much can be learned this way! We can respectfully disagree and move on. 🙂
You are correct about learning something by checking out the power supply and the rest of the circuitry. I was also hoping he would learn that it is easier to first check problems without resorting to taking apart the amp and then if that fails, by all means dig in and see what makes these things tick. I guess it comes down to a difference in opinion. Since he seems not to be a tech, I was hoping he could solve the problem without exposing himself to those high B+ voltages.
That's what is so cool about the forum, we can have a lively discussion without getting all bent out of shape. Much can be learned this way! We can respectfully disagree and move on. 🙂
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I'm always a bit leary about giving advice to a newb about tube amps. I have been building and fixing tube amps for 35 years and in that time I have met a lot of people I would not want to put their hands into a live chassis. If I can pass on a little safety tip, when taking voltage readings just stick your left hand in your pocket and leave it there. If by chance you you zap yourself it wont travel through your heart.
A simple approach is to start with the circuit diagram at the inputs and work through until the signal disappears.
Also check B+ to see if just fuse has gone.
Also check B+ to see if just fuse has gone.
check fuses all good. well will tinker a little bit and keep you all updated,, being that it is old, may do all caps and change out some resistors
Post nr 11; fuses where ok.
Post nr 30; fuses are still ok.
Heve you teken any measurement?
Do you have a multimeter?
Any other kind of test instrument?
Without more info (voltage values etc) there is no help to give...
Follow advice of post nr 28.
Post nr 30; fuses are still ok.
Heve you teken any measurement?
Do you have a multimeter?
Any other kind of test instrument?
Without more info (voltage values etc) there is no help to give...
Follow advice of post nr 28.
I was going to post a bunch of steps to follow
but you guys have it covered.
I will say that I've known Jon Snell for a long time
and he's a great resource for all this British stuff.
Have you bothered to check what he recommended?
OR
Are you just not going to get back with these fine
folks who want to help you?
OR
Just going to start changing caps and resistors...willy nilly?
Oh C'Mon dude don't be silly?
but you guys have it covered.
I will say that I've known Jon Snell for a long time
and he's a great resource for all this British stuff.
Have you bothered to check what he recommended?
OR
Are you just not going to get back with these fine
folks who want to help you?
OR
Just going to start changing caps and resistors...willy nilly?
Oh C'Mon dude don't be silly?
you might have one of the "weird" 2205s/10s different bias resistors, some some kept/used the 220k EL34 feeds/splitters despite with 6550s...I seen one like that....regardless had it screaming/sounding amazing with old Tung-sol 6550s
hope you get it working man, great amps and were underrated imo.
hope you get it working man, great amps and were underrated imo.
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chizm
do you own a multimeter?
are you able to substitute tubes? as in you have spares available?
being forth coming with details will help the board members that have already weighed in to help you get your amp up and running.
do you own a multimeter?
are you able to substitute tubes? as in you have spares available?
being forth coming with details will help the board members that have already weighed in to help you get your amp up and running.
One really easy problem/fix could be: defect in de effect send-return jacks on the back of the amp. This is what took me days to find 🙂 One of these was "switching" so with an jack inserted the signal could only go through the external affect-path. This switch latched, so without any external effects plugged in -> no sound.
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