Burning varnish smell!!!!! Oh No :-( PT suddenly got hot

[rogb]

Hi rogb, before you refire it, insert a light bulb current limiter with the tubes out of the circuit. If you don't have one, look here:

http://www.recycledsound.net/10_Build_a ... imiter.pdf

or

http://www.antiqueradio.org/dimbulb.htm

It is a must have item for us amp builders, should cost you about US$10.00 (I'll let you do the converting to BP).

Instructions on its use is on the second link.

Best wishes,

Thanks and a very good point!
I do have one and always have used it.

Good to be reminded though, it's easy to forget when you get
excited about being back in the game again

[alvarezh]

All the best.

[rogb]

Well the new PT is in and working great! It is barely warm to the touch, actually cool. I am running a 160mA HV fuse and 160mA mains fuse, slo blo, both are holding up fine.

Diodes are Vishay 1N4007, 470K grid resistor in.

Fired up with bulb limiter which I tested on my 50W first, no problems with tubes out, checked some voltages, added the tubes checked voltages again, they were perfect.

I tried my Miniwatt EL84 in a friend's amp and it was fine so I fitted it, it really does sound better than the old Harma I used to start. Feedsback nicely and has a good warm tone.

I think I will send this PT back to Hammond to check as I cannot find any circuit reason ie shorted tube, cap - for the failure. See what they say. Unless the open diode managed to take out the PT... I don't know if that was the result or the cause.

Yet more lessons learned on this 5 watter, one of which is keep the fuses nice and low

[alvarezh]

Congrats rogb, thanks for the feedback.

So, a bad tranny eh?

I usually check my new ones for open or shorted circuits as soon as I receive them. But, from now on I will connect the primaries on the amp and then check the voltages on all the secondaries before I connect them to the circuit, then follow up on the limiter test as usual.

Thanks for the lesson.

Cheers !

[rogb]

Thanks to all that helped,

all the best
Rog

[mat]

Thanks to all that helped,

all the best
Rog

Hi Roger,

Great thing You got the amp up and running again

On my first build (a kit with hammond trafos) few years ago I also got smoke out of the OT. The guy who sold me the kit checked the amp and did not find wiring or other errors in it. New OT and the amp worked just fine for years before I sold it. So it does happend sometimes

[rogb]

Thanks to all that helped,

all the best
Rog

Hi Roger,

Great thing You got the amp up and running again

On my first build (a kit with hammond trafos) few years ago I also got smoke out of the OT. The guy who sold me the kit checked the amp and did not find wiring or other errors in it. New OT and the amp worked just fine for years before I sold it. So it does happend sometimes

Hi Mat, hope all is well with you

You know, I really think the new PT sounds better, runs cooler, like cold nearly, or does the 470K grid resistor bepone recommended affect the tone?

Anyway, I'm happy now, it's lightly fused (if you can say that) so it should be protected in future, but I am going to ask Hammond to check it and if it is faulty, to send me a replacement, so I will have a spare.

[rogb]

1A mains fuse blowing in UK after a little while means the current was above 1.5A which equates to ca 350VA power consumption. Something is very wrong with the circuit OR PT itself could have had an isolation breakdown that progressed to a massive short circuit.
Now the £10.000 question to the OP: is there a CE mark on the PT?
Have fun at the Notting Hill Festival!

Just spoke to Hammond UK, who are only an import warehouse and have no technical dept , I asked about the CE mark (or lack of it) and they are going to find out and let me know...

As far as I am aware, transformers sold in the EU need a CE mark to show conformity with the Low Voltage Directive. So, a very good point made there, VV. CE compliance also ensures thermal overload protection and other tests on this type of equipment.
They also refused to take the transformer back for testing, forcing me to go back to Phil at Bluebell. I will post it back to him and he will send it to Canada for testing, but said "they won't replace it as it has been used".

We'll see what happens here, but I will contact Canada directly if they prove to be difficult.

Great! Looks like the end of the road for me and Hammond Can't stand companies that don't stand behind their products.

[martin manning]

Rog, it's possible that one of your diodes shorted, but testing at low voltage with a DVM is not the same as putting hundreds of volts across it, and you may not be able to tell. I have seen failed diodes that will blow the amp's mains fuse test "good."

[rogb]

Rog, it's possible that one of your diodes shorted, but testing at low voltage with a DVM is not the same as putting hundreds of volts across it, and you may not be able to tell. I have seen failed diodes that will blow the amp's mains fuse test "good."

Thanks Martin, good point, it's possible the diode went down, dunno if it would take out the PT in under a minute. If the PT went with an internal short, it seemed to take out the diode then the mains fuse.

Anyway the UF4007 diode tested bad with the DVM and tested good when I fitted it, that's as good as I can get.

There's a lot of mysteries in this game

[Structo]

I am thinking from Hammond's point of view so don't take this personally.

You have a PT that failed, you are not really sure why it failed.

You call Hammond and say you have a defective PT.
They have no idea what the end user (you) subjected this transformer to or how it was hooked up or anything.

I can see why they wouldn't want to replace it.
BUT, it would speak greatly of a company to replace it with a new one simply for public relations and then you would be shouting praises on the internet rather than talking bad about the company.

The smart thing for Hammond to do would be to replace it. It would hardly affect their bottom line but maybe over the years they have had a lot of people try to get blown transformers replaced and now they have this policy.
I don't know and I'm just guessing at this point.
Doesn't help you or your wallet though.

[rogb]

I am thinking from Hammond's point of view so don't take this personally.

You have a PT that failed, you are not really sure why it failed.

You call Hammond and say you have a defective PT.
They have no idea what the end user (you) subjected this transformer to or how it was hooked up or anything.

I can see why they wouldn't want to replace it.
BUT, it would speak greatly of a company to replace it with a new one simply for public relations and then you would be shouting praises on the internet rather than talking bad about the company.

The smart thing for Hammond to do would be to replace it. It would hardly affect their bottom line but maybe over the years they have had a lot of people try to get blown transformers replaced and now they have this policy.
I don't know and I'm just guessing at this point.
Doesn't help you or your wallet though.

Yeah, I see what you're saying Tom, but it worked perfectly for maybe 40 hours over the last 2 1/2 months then died. If it is defective, and within a reasonable time frame, under six months, then English consumer law says it should be replaced or refunded, simple as that.

If they say they have tested it and there is no defect, then I have to accept that, there is nothing else I can do.

What I object to is being told they likely will not replace it, even if there is a manufacturing defect. They're in Canada, I'm in England. I don't think Hammond give a damn about a few trannys being sold in the UK each year.

[Structo]

Thanks for clarifying the issue with the PT.

Does seem strange that it worked fine for 2 1/2 months then went bad.

If English law says the defective part should be replaced then they should give you a new PT.

I know the PT I bought from Magnetic Components which is over rated for what I use it for runs pretty hot, which tells me that the wire used inside is not over spec'd by any stretch.

Heat is a sign of loss which in this case is due to resistance of the wire.

It is a strange world we live in nonetheless.

I wish you good luck on getting satisfaction from Hammond.

[Bob-I]

If it's an English law that says it should be replaced, then go to the uk dealer, theyre the ones responsible for replacing it, then they should go to Hammond. JMO

As for defects, I find it unlikely that they'll be able to tell anything after it burned. I'll be interested to see what is found about the EL84.

[rogb]

If it's an English law that says it should be replaced, then go to the uk dealer, theyre the ones responsible for replacing it, then they should go to Hammond. JMO

As for defects, I find it unlikely that they'll be able to tell anything after it burned. I'll be interested to see what is found about the EL84.

Hi Bob, I mentioned the Phillips Miniwatt EL84 earlier, I tried it in another amp and it was fine, it has now run 3 playing hours or so with the new PT and again with no problems, voltages in spec as per Mat's voltage schemo, sounds just great, clean or OD. In these mini HRMs the power tube contributes a fair bit to the tone and drive, as Mat had noted before me, so a good one is important.

The dealer is in Scotland, although part of the UK, has many different laws to England. The dealer has said he will send the PT to Canada, but not for some time, so I guess I will have to wait a couple of months.