Fairchild 260 rebuild questions

[WBS]

1. I'm adding 3 prong grounded power cords to my Fairchild 260s. I recall reading somewhere that simply grounding to the chassis can cause a 60Hz hum in old amps. So I'm wondering how to do it in a way that will avoid this problem.

2. I'm replacing the selenium rectifier with a 1N4007 or a UF4007 diode and wonder, is it a simple swap 1 for 1? The diode is tiny compared to the rectifier!

3. I've read a lot about star grounds and busbar grounding wire. The stock amps have grounding points attached to the transformers. Would I benefit from upgrading to a single bus bar?

Any suggestions and or schematics to accomplish the above will be greatly appreciated!

[aletheian]

There is a selenium rectifier in your 260?? I thought they all ran tube rectos. Do you mean the bias supply diode?

[WBS]

Originally posted by aletheian
There is a selenium rectifier in your 260?? I thought they all ran tube rectos. Do you mean the bias supply diode?

They each have 2 5V4 rectifiers. They also have a selenium rectifier as well.

[WBS]

Originally posted by aletheian
There is a selenium rectifier in your 260?? I thought they all ran tube rectos. Do you mean the bias supply diode?

It is attached to a couple of 20uF caps which are connected to the bias control pot.

[aletheian]

Originally posted by WBS


It is attached to a couple of 20uF caps which are connected to the bias control pot.

Yes, that is what i thought. You can just drop any rectifier diode in there, no problem. As far as the 3-prong AC modification... the additional green lead is just a chassis safety ground and should not effect the performance in any way and may just save your life, so I say just do it, and just solder a ring terminal to the lead and screw it into the chassis near where the AC enters.

I would personally leave the layout and grounding alone, and just replace the inevitably dried-up capacitors and old resistors, which have probably drifted with age and heat.

[SY]

Vincent, I'll be up at the office tomorrow, if you want to stop by and get some drawings. I'm tied up between 10 and 1, but free after that.

[WBS]

Thanks for your replies.

SY, I'm scheduled to work in the City tomorrow. If it cancels (which I'm hoping) I'll give you a call. Otherwise I'll try to reach you after the holidays to see if you are around.

V.

[kevinkr]

SY will steer you in the right direction regarding safety grounding, but ground loops are a concern. I have added 3 wire cords to most of my vintage gear and have had to deal with ground loop issues in all cases.

Incidentally the Fairchild 260 is considered an extremely rare and desirable piece, so tread very gently if you want to retain its collector value. (Do nothing that cannot be easily reversed. Keep the old parts too.)

[SY]

Too late, he got those amps from me and they'd already been fairly thoroughly disassembled. One of them even had another circuit put in it at one time. This is an iron-and-chassis deal.

[WBS]

Yeah, but the idea of rebuilding them to factory specs with today's precision parts makes me drool! Plus, even though they're a little banged up, I plan to repaint the trannies so they'll still look really cool!

Funny though. While I'm looking forward to their sound and appearance, the wife recently asked, "Where do you plan to put those?"
"On a shelf, right below the TV", was my reply. She was pretty quiet while she noodled that one.

I may need to upgrade the "entertainment center" to garner a higher WAF.