Hello to all. What did I smoke?

[rp]

Hello - I did a recap and new PT (I needed 220V taps) and some other updates on a 5F6A I built 15 years ago. Powered up fine, voltages nice, no bad noises, but in the processes of tweaking I forgot the cap-draining jumper I put btwn the V1 plate resistors and ground and I powered up. I also had the meter on the OT CT and a power tube plate for the OT shunt to measure current draw. So after a few minutes something smoked on the PT side of the amp. Looked like the first filter cap but once I unplugged the swirly grey puff was gone and now I'm unsure. Everything looks and smells ok. It sure looked like it was from the first cap. I'm using 32/32 & 16/16 w/ 10Ks. The power resistors look fine, wires look fine. So did I trash the first cap? Did I trash the 16/16 too? Gotta love these low cost hobbies. Hopefully smoke wasn't from PT or choke wires which are just below the caps.

I should be around on the forum asking questions some more, after 15 years of ignoring my soldering iron I got time to kill and am building amps again.

http://picasaweb.google.com/ardpan/Amps ... directlink

[tubeswell]

I forgot the cap-draining jumper I put btwn the V1 plate resistors and ground and I powered up. ... So after a few minutes something smoked on the PT side of the amp. Looked like the first filter cap but once I unplugged the swirly grey puff was gone and now I'm unsure. Everything looks and smells ok.

One way of smoking the PT for sure is to short the HT winding to ground. I'd be wary of using that PT. Have you measured the VAC on its secondaries since?

[Jana]

I doubt that you smoked the caps. You were probably lucky in that you had the jumper on the V1 node. With it there then all the current you were shorting to ground had to go through the resistors in the B+ nodes. With 2 - 10K (?) that would give you 20K resistance to dump all the current. At 400 volts that is 20 ma. So, not enough current to hurt the PT or the choke either. But, that is 4 watts through each of the 10K resistors. The smoke was probably from them. I would replace them, do some voltage measurements afterwards and hope for the best.

[Phil_S]

BTDT. You smoked the resistor between the jumper clips. Probably nothing bad. Depending which node you put the bleeder on, you might have some premature tube wear. If on the plates, probably OK. Screens damage easily.

[Structo]

Hope you didn't let all the magic smoke out!
That sucks!

I can recommend using a light bulb current limiter when firing up a new amp or one that has heavy power supply work done.
It can save expensive parts.
I know you made a mistake by leaving the jumper.
I would paint that think a fluorescent orange or something so it stands out.

Good luck!

[rp]

Hope you didn't let all the magic smoke out!
That sucks!

I can recommend using a light bulb current limiter when firing up a new amp or one that has heavy power supply work done.
It can save expensive parts.
I know you made a mistake by leaving the jumper.
I would paint that think a fluorescent orange or something so it stands out.

Good luck!

I powered up with a variac, stage by stage, all was good, but I went back in to do the bias. I do use a red or yellow jumper, AND I still forget! Absent mindedness and HV don't mix, but I keep trying.

Actually I was on the terminal side of the 100k plates on v1 not on the tube pin side so i didn't get the benefit of the 100k resistance. Just the two 10Ks 2W.

The PT is a custom 250ma Heyboer - all the VACs still look good, same as before - I haven't thrown the standby yet, not in the mood.

So you all think I can leave the caps in and just replace the 10ks? Odd is that they sure look fine not toasted at all, not even yellowed. Never seen that before which is why I was puzzled as to what smoked.

[rp]

Hey, since I've been known to do stupid things twice, is it possible to make a jumper with a fuse in it?

[Bob-I]

Hey, since I've been known to do stupid things twice, is it possible to make a jumper with a fuse in it?

I put a 100K / 1 watt resistor in the jumper. It serves 2 purposes, drains slowly and prevents sparks, and if you accidently forget to remove it, the resistor smokes, not the PT.

[tubeswell]

I just have ~220k worth of permanent bleeder resistors across the reservoir cap in all my amps nowadays, so I don't have bother with jumper clips etc. (Mind you, I still check that the caps are drained before working on my amps.)