AMP W/O A FUSE

[zozoe]

Hi all~ This is an old Knight KM15/Y784 2 EL84 amp w/EZ81 rect., but it had no fuse. Nothing! Advisable to put one in immediately, & how would I determine what amp fuse to use? And it would be an HKP model?
Pics attached,
Thanks folks

20200719_155715.jpg

20200728_213608.jpg

[thetragichero]

fuse, proper 3 prong grounded power cord with heat shrink around the connections instead of just hangin out, strain relief on the power cord instead of a knot....
needs a lot to be safe to plug in

[roberto]

An amp without a fuse is like...
https://www.youtube.com/watch?v=xFlYCZ3_fPg

Being a EL84 PP I would say 1A time delayed on the primary if you are in US, 500mA if you are in EU.
...and ground the chassis, please.

[zozoe]

In the US,,,, so that wire leaving the ON/OFF switch goes to the tranny, remains, & the wire going from that post back into the same tranny gets attached to my white/neutral wire from my new cord, correct?
Thanks for the scoop!
Kenny

[Phil_S]

This amp needs more TLC than just a new power cord and fuse. Take a look. There are at least 3 red wires that have frayed insulation and the coupling caps in this amp look older than me (and I'm on the downhill side of my 60's.) I'll bet most of the coupling caps are leaky. I can't see the caps in the power supply, but those electrolytic caps, if also old, need to be replaced. Anyway, first things first: power cord, strain relief, fuse, and I'd get a new switch. Wire it as follows:

Hot lead (black in the US; goes to the narrow prong on the plug) > fuse > switch > transformer. Neutral (white) goes directly to the transformer. Both connections need a better "workman like" connection to the transformer -- either a proper splice with heatshrink or connection made on a terminal strip. Assuming you use an internally mounted fuse holder to avoid another hole in the chassis panel, make sure it is screwed to the chassis so it won't move and make sure connections are clean and won't accidentally touch the chassis. The green ground wire gets its own ground point near where the wire enters the chassis -- you'll probably need to drill a hole for a bolt and remember to clean the chassis to insure good contact. Because the location where the cord enters the chassis is so close to that tube socket, I suggest some retaining clips are a very good idea to keep the power feed away from the tube socket, against the chassis and not just flying wherever.

[martin manning]

This amp needs more TLC than just a new power cord and fuse. Take a look. There are at least 3 red wires that have frayed insulation and the coupling caps in this amp look older than me (and I'm on the downhill side of my 60's.) I'll bet most of the coupling caps are leaky. I can't see the caps in the power supply, but those electrolytic caps, if also old, need to be replaced. Anyway, first things first: power cord, strain relief, fuse, and I'd get a new switch.

All true, and something that I don't believe has been mentioned yet is that if you just replace the cord and fuse and power up with leaky and deteriorated caps, you may get smoke. Use a current limiter.

[R.G.]

There's one more layer of issues, even if you get a good three-wire cord, proper safety ground, fuse and switch both in the hot/line side of the incoming AC, you might find a common problem with older amps. Their power transformers were designed for "110Vac" that really was 110 volts. Today's power from the wall is about 125 in most places in the USA (if that's where you are). What that means is that all the voltages on the transformer, in and out, are going to run about 10% high, which can cause capacitor problems, tube problems and heater problems, not to mention possibly overheating the power trans.

The bucking transformer - which I drew up for geofex.com and whimsically named the Vintage Voltage Adapter, can be used to wipe some of this excess off. You would, in this case, get a 120vac to 12Vac transformer, then hook the 12Vac up in the polarity that subtracts 12V from the incoming AC line, then apply this to the 110V rated power transformer primary. Things will be much more like the designers thought they would be.

Let me second the other advice you've been given. Clean up and replace wires that are in bad condition, arbitrarily replace any polarized caps with new ones, and be very, very gentle with your first bring ups.

[zozoe]

Much appreciated everyone, but allow me to make it clear, Ive played gtr for 58 yrs, have collected amps just as long, & even though I know my way most recording studios, I know nothing about the modding & total maintenance of old amps. The ONLY thing I EVER do is install a 3 prong, ,, Nothing gets plugged in, turned on, or touched until my tech takes possession of it.
Mama raised a dummy, but not a fool!!
Thanks again, & be well all, & peace~
🕉

"I love the smell of 50's chassis' in the morning!"

[pdf64]

I can see the merits either way around, but the modern standard seems to be switch, fuse, PT.

[Phil_S]

...the modern standard... switch, fuse, PT.

Thank you. I got it wrong. I was so wrapped up in how everything in that chassis looks so wrong that I wasn't paying close enough attention.

[R.G.]

I can see the merits either way around, but the modern standard seems to be switch, fuse, PT.

I'm not sure what the modern standard is, but the safety lab guys will flunk you out of hand if it's not fuse, switch, PT. Well, OK, strain relief (or IEC socket), fuse, switch, PT.

[thetragichero]

i always was told iec socket must have the ground pin facing up too (by the same folks who install wall outlets with the ground up). seems a little out there for me but i do it anyway
also aes/cedist have iec outlets with a built in fuse holder (with room for a spare fuse) for less than the price of a regular iec outlet last time i checked. i dig em

[Phil_S]

I can see the merits either way around, but the modern standard seems to be switch, fuse, PT.

I'm not sure what the modern standard is, but the safety lab guys will flunk you out of hand if it's not fuse, switch, PT. Well, OK, strain relief (or IEC socket), fuse, switch, PT.

Indeed. I found a wiring diagram of an IEC with integrated fuse. The fuse is between the power connection and the switch. I should have trusted my instincts on this one.

[pdf64]

I can see the merits either way around, but the modern standard seems to be switch, fuse, PT.

Oops, sorry, yes I got it mixed up

[Phil_S]

Oops, sorry, yes I got it mixed up

No worries! One thing I've noticed about TAG, it isn't a gotcha kind of place. No one gets a hard time for missing the mark now and then. It's generally a friendly place. Nice folks hang here. I wish we could all go out for a beer now and then, maybe put faces to the names...