IEC mod opinions please - Bogen DB30

[whittington]

We have two beautiful Bogen amps that my boy and I are making into monoblocks. They are in very excelent shape cleaning up very nicely for sixty year old units. (Pics to. Come) As we plan, we are contemplating the viability and "moral" considerations of adding an IEC plug in. Our considerations are in this order:

1) SAFETY - Please enlighten us, as we are newbies, the feasibility and reasoning first of putting a grounded plugged cord in as a replacement to begin with. Of course, the current AC cord is cracked and cut off as a prevention to others who might otherwise attempt to plug it in in my absense. Seems I have read somewhere though that that is both a good idea and a bad idea (adding a three way grounded plug) based on the particular unit one might be working with.

2) PRACTICALITY - If we were to add a grounded cord, and all originality is abandoned, my thoughts were why not add an IEC Jack so different AC cords could be rotated if one chose to. Help here, because as I see it, I will have to cut into this beautiful hammered green chassis to mount it. (unless I am missing something). Imagining dropping the value of the unit, I am having a hard time with that. Remember, these are not MacIntosh units. The Bogens I am working with can be had for less than $500.00 all day long although these are beautiful matched minty survivors. Am I wrong to consider doing this? (I haven't considered replacing RCA plugs or speaker attachments, yet). These units have a waxed finish and polished cans. Torn.

3) METHOD - Lets say for the moment, I get past cutting the chassis (visions of those fools who cut big holes in their dash so they could have a modern radio in their Chevelle), any tips on how to do this the cleanest way?

 

[UncleBingo]

Personally not a big believer in the boutique AC cable unless the wiring leading up to it is on a dedicated circuit and clean power to begin with.

If the chassis is steel, you're in for a treat unless you have a nibbler to make the cutouts. Personally I'd put the time into the rebuild. wire it 3 prong using a standard pigtail through the existing grommet (if possible or slightly enlarging the hole if need be) and roll with it.

Downside is ground-loops are real, and voltage variations on chassis traveling between components can be a pain.

 

[trainbuftony]

No shame in upgrading. One point in the safety area that you didn't cover is that there will be no AC cord to trip over when you are moving them around. I have successfully used a dremel rotary tool to enlarge the holes, then blasting out all the shavings with compressed air.

 

[cademan]

In my humble opinion, the engineers didn't think it needed a grounded cord so neither do I. Sometimes (I stress sometimes) you get hum or other sounds that were not there before the modification.

Since the amps have power transformers, they are pretty much isolated from the mains anyway.

Don't let me discourage you. Go ahead and use an IEC if you want. It may work fine and a lot of times they do depending on the circumstance but I'm all for originality.

 

[triode17]

On old amps. I rebuild, I always add a 3 conductor cable. First of all, the amp, has high voltage inside, which is referenced back to chassis.
If a high voltage lead lets go and touches the chassis, the fuse blows, instead of you. Second, it eliminates having to use safety caps from line to gnd, neut. to gnd and across the line. All conducted noises will be shunted to Earth. Third, if Greenlee will get off its ass and design an IEC punch, it would be very easy to do. I prefer using the existing hole for the line cord and adding a new strain relief. If you Earth all your equipment to one central outlet, you shouldn't get any hum, I don't.

 

[Palustris]

You are definitely on the correct track if you are intending to replace the two wire power cord with a grounded cable. When the Bogen was released into commerce, the three conductor power outlet was rare in the home environment, so the design engineers provided what most households could accommodate. Safety practices have improved substantially in the last 50 years and so it is standard practice to retrofit electronic devices with the three conductor cord when restoring; it won't affect the value since it is easily reversible if you just replace the grommet and cable.

As some have come to realize, it can be challenging to update some equipment that uses the chassis as ground instead of a ground bus. So part of the rebuild plan is to reconfigure the ground bus to ensure that there are no ground loops. I don't see this as a big job since I find that the best way to restore a unit is to strip all the old passive components such as caps and resistors from the chassis before giving it a good cleaning. Then rebuild from the "ground" up with a wiring plan that ensures there will be no ground loops and eliminates every ground connection to the chassis except for one.

If this were my unit, I would simply replace the grommet where the power cord enters the chassis and install a new power cord. Home Depot sells a grommet collection that should have a close size. HD also sells good quality 16 gauge cables unterminated at one end and with a grounded plug at the other end. That's what I use for my projects.

 

[peterh]

An IEC power inlet is a good option. Future powercord replacements is easy!.
If the ground connection causes problem one can always disconnect inside the amp.

 

[Tom Bavis]

It's possible use two diodes, reversed in parallel to "break" the ground connection for low voltage (< 0.5V) yet provide a safety ground. Best way is to use a high-current bridge, connect IEC center pin to both AC terminals, plus and minus to ground. But I've had no ground loop problems with 3-wire cords.

 

[gadget73]

The only reason I hesitate to do this is because I don't have a clean and easy way of making the hole. If I had the proper rectangle chassis punch, everything I own would have one.

The ground argument can be had all day long. I have things with non-polarized cords, I have stuff I have converted to polarized, and I have stuff that I have added grounds to. None of the amps i added a ground to hummed, or at least not because of the ground connection. Fit a 3 wire cord and land the ground to a terminal strip. Add a jumper from there to chassis. If it makes horrible noises, remove the jumper and leave it out if that makes the hum go away.

 

[mcgjohn]

I would agree with UncleBingo; stick with the stock cord, or maybe upgrade and add a polarized 2 prong plug. Stay away from the 3 prong, or you may create a whole series of head aches trying to chase ground loop problems.

Don't forget, in your breaker panel, the common lead and the ground lead end up at the same place inside the panel if you home has wiring from the last 20-30 years. If its older than that and still has 2 prong outlets in use, then would not even attempt to go with a 3 prong plug.

I have experimented around with boutique power cables and can some times hear a difference on sand gear, but have never heard much of a difference on tube gear.

beset

 

[gadget73]

Just because its got 3 prong outlets doesn't mean it should, or that they are wired properly. There are inexpensive testers you can plug in to any outlet to find out whether they are correct. I've seen plenty of backwards outlets, and once in a while you'll find a 3 prong outlet in an old home that does not actually have any grounds. Not legal to do that, but it doesn't stop Joe Homeowner from running to the hardware store and grabbing some sockets to install.