General

[Tea-Bag]

no the size doesn't matter, correct voltage or higher is more important. Some are different sizes I am sure because of construction, and likely to make a fit. The higher temperature rated caps (105c) are larger than the same in 85c.

[bull041161]

Thanks alot TEA-BAG i will order some smaller higer voltage ones then

[bcherry]

I've started posting your projects as well as the ones we've done in in-house on our Module Showcase page.
If there is anyone that would like to have their projects featured (with permission), please drop me a line with some pictures and comments.
Getting your comments and implementations will help us with future revisons to the modules as well, so are much appreciated.
regards
Brian

[jdunham]

Can anyone point me to what might have gone wrong here please?

One of my LD91+ amps was shorted via its speaker cable for a while (who let that bl***y puppy into MY listening room?!!). So I discovered it some time later and its now not working.

So to those with more electronics skills that I have, what is the most obvious thing that could have been taken out by doing this? The secondary Output TX still reads the same value as the other one at just over 1 ohm from the 16 ohm tap. But what else will have blown?

Many thanks,

Jonathan

[ThorstenL]

Hi,

Originally Posted by jdunham

One of my LD91+ amps was shorted via its speaker cable for a while (who let that bl***y puppy into MY listening room?!!). So I discovered it some time later and its now not working.

"Not working" covers a wide range of problems. Could you kindly narrow it down?

Does the Amplifier power up at all (if not check fuse)?

Do the tubes heaters all light up?

Do the tubes emit normal amounts of heat?

Ciao T

[jdunham]

Hi Thorsten, thanks for replying. And long time no speak, I hope you are well. I'm still enjoying my front horn / dipole bass system that you helped inspire me to build a number of years ago!

I realise I should have given more detail on the LD91 than I did, so my bad.

The amp does power up ok, but only makes a hum through the bass system, with a normal signal, so I'm guessing this is a mains frequency.

Heaters are fine, I swapped all valves from the other amp one by one, then back again to check they were still ok.

I'm going to get them both apart today to check the HT windings etc, and see what I can establish.

Brian will know that I've had these amps apart a few times now. As over-voltage at my house managed to fry the HT windings twice now!

Kind regards,

Jonathan

[ThorstenL]

Hi J,

Originally Posted by jdunham

Hi Thorsten, thanks for replying. And long time no speak, I hope you are well.

Pretty well, thank you. Getting a lot of sleepless nights thanks to a nearly three month old young lady called Roxana...

Originally Posted by jdunham

The amp does power up ok, but only makes a hum through the bass system, with a normal signal, so I'm guessing this is a mains frequency.

Heaters are fine, I swapped all valves from the other amp one by one, then back again to check they were still ok.

When you swapped the Valves over, the same fault stayed with the Valves, yes?

Originally Posted by jdunham

I'm going to get them both apart today to check the HT windings etc, and see what I can establish.

I guess that will have to be the next step.

Originally Posted by jdunham

Brian will know that I've had these amps apart a few times now. As over-voltage at my house managed to fry the HT windings twice now!

Some UK Mains are notoriously bad. One place where I worked in London we had problems that batteries in our UPS's for the server room ended up completely shot and in need of replacement several times in under 1/2 Year. With around a dozen servers and individual UPS on each that got expensive quick. And we had many PC's and monitors in the offices blow up their power supplies (usually one or two a month, some times more), lightbulbs and fluorescent strip lighting were constantly out.

We eventually put a paper strip recorder on the Mains and found regular and persistent variations between 215V (lowest) and 264V (highest), all of which of course was outside the standards for power delivery (and which incidentally got the UPS's kick in to protect the severs, thus massively cycling the batteries).

The best response we got from the power company was a shrug and "sue us"...

That place eventually invested around 20 or 30K IIRC into a massive multiphase 50KVA on line UPS System and put every PC, server and Lightbulb on it. After that the PC's stopped blowing up, lightbulbs and fluorescent lights lasted forever and our maintanance cost on most electrical things dropped to near zero.

Maybe time to put your whole system onto a suitable UPS? With some added filtering and maybe a mains balancing transformer with electrostatic shield even common inexpensive UPS systems perform quite well for audio systems.

At least it can cut the costs of tube (and transformer) replacements and IME does improve sound consistency and quality quite a bit.

Ciao T

[jdunham]

Hi T, thanks again,

Getting a lot of sleepless nights thanks to a nearly three month old young lady called Roxana...

Congratulations! And yes understand that condition very well (x3!).

When you swapped the Valves over, the same fault stayed with the Valves, yes?

Yes, the amp is still not working with the other valves in it.

I guess that will have to be the next step.

Yes. I will post an update, hope to get to that today. I miss my nice sounds!

And thanks for the insight and suggestions regarding the UK mains. I have recorded up to 265V here on a number of occassions. And actually it seems to be a Friday night / Saturday morning thing. I accidentally left the amps on overnight and then came back to fried amp in the morning! And then measured 265V until around 11am that day! And yes my mains supplier didn't want to know either.

I'll look into the UPS things. I was thinking of going for a balanced transformer with a step down to lower the voltage. I have lowered my HT voltages a bit anyway to cope with the problem. The LD91's definitely sound better that way.

Kind regards,

Jonathan

[jdunham]

Really weird!

I got both amps on the bench and tested the DCR on the TX's and the voltages, with and without valves in with them switched on.

The first time I tested the faulty amp, I got no HT voltage on the rectifier (but around 825V on the good one). So after I fully tested the other amp, and went back to the faulty one, I prodded a few solder joints and redressed the wires coming out of the TX, and then hey presto it worked! I now get all the correct voltages (790v AC on the HT). I connected it up to my iPod and an older speaker and it does seem fine!

Its a bit worrying though. I don't beleive that what I did should have fixed it.

Any thoughts?

Regards,

Jonathan

[ThorstenL]

Hi,

Originally Posted by jdunham

The first time I tested the faulty amp, I got no HT voltage on the rectifier (but around 825V on the good one). So after I fully tested the other amp, and went back to the faulty one, I prodded a few solder joints and redressed the wires coming out of the TX, and then hey presto it worked! I now get all the correct voltages (790v AC on the HT). I connected it up to my iPod and an older speaker and it does seem fine!

Its a bit worrying though. I don't beleive that what I did should have fixed it.

It suggests something has an "intermittent contact". Hard to say where exactly, you will have to poke around, CAREFULLY, using an all plastic biro or the like.

Ciao T