KIT6550 Blowing Fuses

[CLIPPER]

Hi Everyone,
I've got a KIT6550 I've just brough second hand, the problems is it keep blowing the main fuse when switch on (black) 1.6amp, but not everytime with no valves in and all voltage on the transformer are correct!
Before I disconnect all the wires from the transfromer to eleminate the fault I'm wondering it the surge current and try a slightly larger fuse. has anyone else had this problem?

[bob orbell]

Hi CLIPPER and welcome, this was a problem with most 6550 amps, 2.5 amp quick blow is now recommended, also look at the FAQ for other mods. Bob

[pre65]

I often use a thermistor (or inrush current limiter) with toroidal transformers.

https://www.ebay.co.uk/itm/2pcs-NTC-...EAAOSwvApaIwNd

[Richard]

Originally Posted by CLIPPER

Hi Everyone,
I've got a KIT6550 I've just brough second hand, the problems is it keep blowing the main fuse when switch on (black) 1.6amp, but not everytime with no valves in and all voltage on the transformer are correct!
Before I disconnect all the wires from the transfromer to eleminate the fault I'm wondering it the surge current and try a slightly larger fuse. has anyone else had this problem?

Hi Clipper,

As Bob says a small uprating of the fuse would be ok. A 1.6A SLOW blow is standard so check you haven't used a quick blow in error.

If it was working fine before though and the rectifiers are old I'd try a new pair as it could be they are now working out of balance.

See the FAQ also for fitting balancing resistors to help equalize the current through the rect sections,
http://www.world-designs.co.uk/forum...ead.php?t=3859

[John Caswell]

One of the biggest power problems I strike is that nowadays pretty well all power transformers are wound for 115/230 power lines. Now a lot areas in the UK are sitting regularly at 250v and local to me some at 253v. This is within the supply co's ±10% but no help to us.
Although the fuse will be totally satisfactory for 230v it is getting edgy for 250v so an increase rating is necessary, usually up to 2A T (Trage =Anti surge) but in some cases, especially with big toroids, up to 2.5A.
As pre65 says an inrush thermistor (or two) will ease the situation, but ideally a multi-tapped primary is best but this costs more money.
You pays your money............
For those of you that use 2 off 5U4G as the HT rectifier (which are now becoming expensive) is is a relatively simple mod to replace both with 6D22S, which are a TV boost diode. Main advantages are, indirectly heated slow warm up (30 secs or so) so should reduce the fuse blowing syndrome pretty near bombproof, and most importantly cheap. Although they are a 6.3V heater they run beautifully on 5V as I can testify.

John

[bob orbell]

We have small substation on our estate, workers have installed a new transformer over the last two weeks, I measured our voltage after they had finished expecting to find it closer to 230, it was almost 252 before, it is now 247, better than nothing. Bob

[pre65]

Originally Posted by John Caswell

For those of you that use 2 off 5U4G as the HT rectifier (which are now becoming expensive) is is a relatively simple mod to replace both with 6D22S, which are a TV boost diode. Main advantages are, indirectly heated slow warm up (30 secs or so) so should reduce the fuse blowing syndrome pretty near bombproof, and most importantly cheap. Although they are a 6.3V heater they run beautifully on 5V as I can testify.

John

Have to agree with John re TV damper diodes. I use them on most of my amps as part of a hybrid bridge.

If you only have one 5U4g (or similar) then you would need two 6D22s to replace it.

[Greg.]

Welcome Clipper. Please see the first few posts on this thread that will help you further, and for more advise on things to do to improve your amp, study the FAQ section at the bottom of the forums first page.

http://www.world-designs.co.uk/forum...ead.php?t=7650

[bikerhifinut]

A passing thought.
When I rebuilt my EL34 homebrew as a stereo instead of 2monos, I used a hugely overrated toroid that a friend kindly donated, ( He wound it himself its built like a tank). I was advised by this chap that I should fit a MOV (Varistor) across the primary terminals as the voltage spike that could occur on switch off as the magnetic flux collapses, depending on where the AC waveform was in the cycle, could take out the windings. So I fitted a 275V one.
If that's been covered, sorry chaps.

Andy

[colin.hepburn]

Originally Posted by pre65

Have to agree with John re TV damper diodes. I use them on most of my amps as part of a hybrid bridge.

If you only have one 5U4g (or similar) then you would need two 6D22s to replace it.

Hi All
Yes I also use the 6D22s in my JE Labs Single ended KT66 amp on a 6.3volt heater winding work great and I like the slow start up of these I also have another version which I got for my single ended 5751/12B4A headphone

These are labelled as the 6n20n the n in the number are as the Russian character which I can’t find under that number anymore. I think they are likely labelled under a EY.code of some sort if you can help with the code for the 6n20n I think it could be the EY81 or 83 but not sure maybe our very own Dr, John can help here
Thanks
Colin