Need opinion on warranty

[Gaz]

I sold someone an amp I'd built for myself, and after I couple months the PT died quite catastrophically. Smoke! It turns out two tubes failed, and took out the PT. The one mains fuse wasn't quick enough

There was no warranty agreement with this person, but I want to be nice and replace the PT, and I should've probably added an HT fuse anyway... But should I pay for a new tube set? They were used, and even new tubes are generally warrantied for 3-6 months.

What do yo guy think? What would you do?

[Structo]

How close of a friend is it?

Do you think there was any fault in the way the amp was built?
I assume it was the power tubes that shorted and blew out the PT?
Type?

What size fuse did you have in it?

Makes me want to install a HT fuse in my Dumble.

[Gaz]

Yeah, it's hard because the person is not a friend or complete stranger.

I played the amp for months, and all was okay, I decided to sell it to pay for another build (of course). It did have JJ KT77s in it, which have given me nothing but nightmares in the past as EL34 replacements (the screen grid fails very easily, and I'm sure that's what happened with these).

It was 100W and had a 4 amp fuse. It did blow, but only after the PT did :/

FWIW, I've been adding HT fuses in my amps anyways after reading Merlin's power supply book in the PT secondaries.

[Colossal]

That sucks Gaz, sorry to hear it. FWIW, I add TWO B+ fuses, one on each secondary, in addition to the Mains fuse. A couple of extra fuse holders are cheap insurance.

[passfan]

I stand behind everything I build. I know you didn't have a warranty agreement, but you did let it go with a known terminal fault ( the power tubes). In for a penny in for a pound. I sell mine with used vintage preamp tubes in them. If one goes bad I replace it. Power tubes are always new with the request they be changed every year. Now that's at my top price. If I let one go for cost things are a lot different.

[Phil_S]

I think it would be appropriate to replace the PT. The new owner should pay for the tubes. I think the 4A fuse proved to be too large, and that's your reason for replacing the PT, but you don't need to discuss this aspect of it. The new owner knew it was not a manufactured build and should have factored in that element of risk. He should cover the tubes.

See if you can rethink the fuse value and reduce it. Put a 500mA fast blo fuse on the HT CT while you are at it.

[Gaz]

Thanks for the opinions. I sold the amp for $200.00 over cost to be fair to the person and myself. I mean, I didn't know the power tubes would fail, and when they've failed before it's been a little more graceful, taking out the fuse and a screen resistor at worse (yes, even a 5W block!).

Colossal, I've just been using a single 1A slo-blo fuse in one leg of the PT secondary because I'm using a bridge rectifier.

BTW, the amp is across the country, so I'm paying for the tech as well.

[VacuumVoodoo]

Be happy that no harm came to person or property, pay up and learn the lesson.

[Gaz]

That's what I'm thinking - it's not worth the $40.

Perhaps I should start a new thread, but I have a general question about fusing the PTs secondaries: Do i size the fuses the same way I would in the B+ line? I assumed so, and am using a 1 amp slo-blo in one leg coming into a bridge recto like I mentioned before. This arrangement is suggested on Merlin's site.

http://www.freewebs.com/valvewizard/fuses.html

[guitarmike2107]

Be happy that no harm came to person or property, pay up and learn the lesson.

100% correct. For those who sell amps you should ensure that the safety features are up to date with current design standards.. however tubes still blow and PT still die.

Ideally you should also build in some warranty costs into your selling price. i.e. minimum cross country shipping cost etc

[Structo]

Anybody know how you would calculate an HT fuse size?

[Milkmansound]

I only sell my amps with brand new Ruby tubes, because they come with a 6 month warranty. Its easy enough for someone to find their own NOS tubes - and there is no profit margin on them anyway.

Because of this, I feel much more comfortable offering a warranty.

Also, Mercury magnetics will dissect a bad transformer and find out what the cause of its demise was - if its their bad, they will replace it. More warranty comfort.

My only weakness is the old AB resistors - those could definitely lead to some warranty issues, but have proven to be very reliable thus far.

[guitarmike2107]

Anybody know how you would calculate an HT fuse size?

It is my understanding that on commercial amps they would be tested in specific fail modes to ensure the fuses work correctly.

For most people, looking at existing commercial amps that you know have been tested is the quickest way to get a baseline. i.e. Marshalls and Fenders etc

I can't advise on a method for calculating them

You also need to make sure you use flameproof resistors in your filter section, as a short after most of these will cause the power dissipated to far exceed the resistors wattage rating and the HT fuse will not protect it.
i.e. a 10k Resistor with 350v across in a fault situation will have 0.035A going through it, not enough to blow a typical HT fuse, but the resistor will be dissipating 12W!!! FLAMES

[brentm]

Well, since you're asking for opinions.

Did you negotiate any warranty up front? In cases like this, it's always important to get that stated early. "As-is" is generally safe and assumed if none is given and the item isn't a brand new mass-production item.

A handcrafted masterpiece such as this, I wouldn't think a warranty would be assumed.

Then there's the "red face test". You stated you had problems with the JJ tubes in the past. Selling the amp, it might have been prudent to put in more rugged/long lasting/known good tubes. But, you still haven't mentioned that you have positively identified that as the issue.

With all that said, I'd say it'd be fair to split the cost of the repair with the new owner. Or pay for parts and not labor (given that he could ship the amp to you and you could repair it for cost of parts). But to completely pass the red face test, pony up for the whole thing.

All in all, anything you do is goodness. These things have a way of coming back around; the internet made the world even smaller. And in the end, it's the customer's perception of what happened and how it was handled. His perception should be your reality.

[Structo]

Amps can be a tricky thing.
As we know, with tube amps many things can go wrong due to the high voltage and heat produced.
Things fail, sometimes catastrophically.


When I have sold tube amps in the past, it was with the understanding that they were being bought "as is".

However, I haven't sold any that I have personally built, yet.

It's nice of you to take some responsibility but on the other hand, you don't have any idea what the user subjected the amp to or how hard he may have abused it.