Princeton clone build: blowing fuses

[Firestorm]

What transformer is that? I see a black/yellow wire; could that maybe a CT for the 5VAC winding? Causes all sorts of trouble when they include that.

[timrobertson100]

Hey Firestorm,
It's a http://www.tubeampdoctor.com/en/shop_Ma ... models_103

The 2 unused are red/black and black/yellow and they're both on the primary.

[timrobertson100]

Hey Firestorm,
It's a http://www.tubeampdoctor.com/en/shop_Ma ... models_103

The 2 unused are red/black and black/yellow and they're both on the primary.

[ToneMerc]

Now it's back to intermittently blowing fuses with no rectifier in. Maybe that's enough for 1 day.

One way to shotgun troubleshoot would be to disconnect the secondary connections until the fuse stops blowing.

When you get this sorted out, you can connect the orange wire back to chassis ground, it's connected to the PT shield band.

TM

[Firestorm]

Okay. I just saw that in another thread involving a Hammond tranny that provided a center tap for the 5V winding. Wanted to be sure you didn't have a potential HT short that way.

[timrobertson100]

Ok... So with all secondaries disconnected, the fast blow fuse just blew on power up immediately (with a nice little flash just like the others).

PT is hosed right?

In doing this, I saw a small hairline strip of solder across the lamp -> ground. Would that have been enough to bring this all down?

Thanks guys.

[ToneMerc]

Ok... So with all secondaries disconnected, the fast blow fuse just blew on power up immediately (with a nice little flash just like the others).

PT is hosed right?


.

If every secondary connection is unterminated and flying, with the primary wired correctly and it's still blowing mains fuses, yes I would say it's hosed.

TM

[Firestorm]

The question is why? You don't want to kill another one.

[timrobertson100]

Indeed... This is intermittent. I feel kind of ridiculous having blown 13 fuses today. But I tried again - a slow blow this time, all secondaries either free flying, or connected to the octal for the rectifier (no tube in, so they are open). Powered up fine - I switched on, off several times - no problem. Checked the secondary voltages and 5VAC, 6VAC and 740VAC again as expected.

Maybe with no standby switch, there is just a bit of start up surge methinks and maybe the quick blow fuses were the issue. Maybe it was that tiny hairline solder from 6.3 -> ground which I had removed. So I continued:

I did nothing but connect the 6.3 to the bulb (which has the 2x100R arrangement and I checked both terminals were 50R to ground before soldering). Connected again - fuse blew immediately. WTF.

Appreciate you guys reading this.

[ToneMerc]

Indeed... This is intermittent. I feel kind of ridiculous having blown 13 fuses today. But I tried again - a slow blow this time, all secondaries either free flying, or connected to the octal for the rectifier (no tube in, so they are open). Powered up fine - I switched on, off several times - no problem. Checked the secondary voltages and 5VAC, 6VAC and 740VAC again as expected.

Maybe with no standby switch, there is just a bit of start up surge methinks and maybe the quick blow fuses were the issue. Maybe it was that tiny hairline solder from 6.3 -> ground which I had removed. So I continued:

I did nothing but connect the 6.3 to the bulb (which has the 2x100R arrangement and I checked both terminals were 50R to ground before soldering). Connected again - fuse blew immediately. WTF.

Appreciate you guys reading this.

What value fuse are you using?

TM

[timrobertson100]

The normal ones are 0.5A 250V (T500mA250V) - same as came in the kit
The fast blows are 0.25A (F250m250V) - I bought today, to just test the heaters.


[I'm in Denmark, so 230 from the wall]

[timrobertson100]

The normal ones are 0.5A 250V (T500mA250V) - same as came in the kit
The fast blows are 0.25A (F250m250V) - I bought today, to just test the heaters.


[I'm in Denmark, so 230 from the wall]

[ToneMerc]

The normal ones are 0.5A 250V (T500mA250V) - same as came in the kit
The fast blows are 0.25A (F250m250V) - I bought today, to just test the heaters.


[I'm in Denmark, so 230 from the wall]

IMHO, those fuses ( 500 and 250 mA)are too small for in rush current and I would use slow blow type only. I'm not surprised that you have killing .250 fuses. If you wired this according to that first diagram, you should be golden. For 230V I would try at least a 1A slow blow.

TM

[tubeswell]

PT might not be hosed - try starting it with a 1A T fuse

Yes a small strip of solder across the lamp can cause it to short.

So the Orange wire is for a faraday shield? Thanks for clearing that up. Hook it up to the ground then.

[timrobertson100]

Thanks tubeswell.

Nothing is open here on Sundays, but I'll get some next week. It's really baffling me this. Can't explain how sometimes it started and gave a light, other times just blew the fuse immediately. I learnt a fair bit though which is good.