Service charges

[Rayme]

What would be a reasonable service charge on a tube amp to replace the power cord with a 3-prong, replace a resistor,install 1/4" jack for external speaker, clean and test tubes?

[Mark Black]

Probably depends a bit on where you are.

Around here (Seattle area), with our cost of living and the price of retail shop square footage it's typically $80 minimum, $80 per hour standard bench rates, with about a 50% surcharge for rush. Other markets will probably vary.

That could easily be a 1.5 hour job with initial customer interview, logging in, diagnosis, repair, and final write-up. Could be more if any research was required to obtain the resistor value or find out why it went bad. Simply installing a 3-wire power cord where there wasn't one before can take longer than a guy might think if any thought is given to the work and/or if the grounded cord introduces any hum/buzz issues. Testing tubes can be time-consuming as well.

Are you thinking you are being over-charged? Or maybe you're thinking the tech is not asking enough and you should pitch in a tip...

[tim]

Rayme,
What kind of amp are we talking about here?
Some amps are easier to work on than others...

[Rayme]

Silvertone 1482

[tim]

Installing a three prong plug on that involves replacing the complete cord which usually involves enlarging the hole on the back so a larger strain relief will fit...
Why does a resistor need to be replaced..is it burned out? If so, why did it burn out?

You can't just pop another jack in there for an external speaker without considering whether or not the output tranny can handle the additional load or how the external speaker will be used...will the external speaker be used as well as the speaker that's in the cab? If so, that can complicate things.

Testing tubes usually involves just playing the amp and seeing what kinds of noises come from it...then you have to determine if the noises are coming from the tubes or from old fried circuitry, especially if that amp has never been serviced. One typically doesn't use a "tube tester" to test tubes used in these amps...we use our ears to test tubes.

In my shop, if a customer brought in an old Silvertone that had never been worked on, I wouldn't touch it unless I was able to go through it, change all the filter caps, screen resistors, etc etc to which I would quote around three hours labor plus parts...otherwise, a tech will change just a broken resistor or a noisey tube and several weeks later it'll come back, humming like it doesn't know the words, and exhibiting all kinds of other maladies and then it's my fault that it now sounds like crap...

If the customer balks at the price, I smile and hand it back to him, waive the bench charge and tell him to save his gig money and I'll be glad to do the job when he can afford to have it done right...I don't have time to be doing a half *** job.

[GHRock]

I must disagree with you. Tube testing should only be done with a tube testor. The test you described is just an audio "listening" test. That's a good test but it is not "testing the tubes".

If you are fixing vacuum tube amplifiers without a GOOD tube testor you are "working with one arm tied behind you back"

We recently did just the job the was outlined above. The total bill was about $70 with tax. And the tubes were all tested on a professional tube testor!

We are Fluke Amp And Guitar Repair in the Seattle area.
(FlukeAmpAndGuitarRepair@gmail.com)

[Mandopicker]

Good day all...my apologoes, but I just wanted to make a comment related to my own experience.

A tube tester is a good place to start...but from my experience using a "tube tester" alone is not necessarily the best way to show how a tube reacts or responds under stress. What I mean to say is that tube testers do not usually apply the same level of voltage and current that a properly running tube amp would and is capable of doing.

On more than one occassion have I tested a tube to be "good" with a machine, (in fact purchased some real nice NOS tubes from suppliers) later to find that when installed in a healthy amp they were microphonic...or...or...

Also, some amps "like" some tubes more than others. That's another good reason to keep a supply of "pulls" hanging around for testing in various amps. You just never know until you try.

I really think that cranking an amp up to max volume can be as valuable a diagnostic tool as using a chop stick or the simple voltage check.

Be sure that the owner of the amp will do all kinds of things that don't necessarily make sense when playing the amp.

Like was stated before, you'd hate to do band-aid repairs on an amp that needs a total overhaul. It is a dis-service to all involved.

Again...just my opinion.

[GHRock]

No one said that a tube testor alone is the way to repair. If you are not using an oscilloscope, signal generator, DWMs, and a tube testor you are not working at a technicians level. Visual and audio listening are also tools of the trade.

But don't tell me you can tell a tube problem by listening. At most you can get a idea of possibilities. Until you have measured, traced, and identified a problem and verified it, you should not make hasty guesses.

Some of the above comments about biasing are misleading, even though they are generally correct.

[tim]

I have a military tube tester in my back room that I haven't used in over twenty years of repairing amps. I find that all that does is tell me the gain of the tube, transconductance, emission, etc...I can see that on a scope under actual dynamics (most tube testers don't actually measure tubes under full plate and screen voltages) and I can hear if there are any issues with a tube, such as microphonics, loose elements, static noises, etc that a tube tester will never find with it in circuit.

In all the years I've been repairing tube circuits and amps (40ish) I have yet to have a return due to defective tubes for any other reason than a tube out and out failed (infant mortality) or became noisy or microphonic within the warranty period, none of those of which a tube tester would have found.

When I buy tubes from distributors (that allegedly test these tubes on a tester), I always test them in an amp as soon as I get them for audible noises...The microphonic ones get used in reverb or tremolo circuits if they aren't too bad...static noise ones get shipped back as defective...sometimes I have to send back 10-15% of tubes received because they are just to darned noisy.

[tim]

Some of the above comments about biasing are misleading, even though they are generally correct.

Who said anything about biasing?

[Mandopicker]

GHRock,

I'll not argue with your point in reply to mine, as we do seem to basically agree. Though you did say,"Tube testing should only be done with a tube testor."

I will say that, in many cases, I am able to tell if there is a problem with a tube or related component just by listening. Not always the correct answer, but well enough to save a lot of time (and the customer money) in the diagnostic process and lead me in the right direction. In fact, I'd probably do the "play and listen" test way before using my digital equipment.

My apologies as their was no intent to second guess your methods, just wanting to add perspective.

[Enzo]

GH, welcome to the forum.

But I also have to point out you did say:

Tube testing should only be done with a tube testor.

I have a couple of tube testers, and like tim, I never use them. They don;t tell me anything useful. They don;t tell me if a tube is microphonic, if it is noisy, or just sounds crappy. Doesn;t tell me if the 6V6 I have is going to run away when I stick it in a Fender amp. I find they are pretty good at verifying a bad tube is bad.