As a side note, some prefer the AC-3 over the AC-4 due to the "open air" sort of cooling while the AC-4 has a small number of "hot air exhaust slots". ? I have no personal experience with the AC-3 so I am not aware of reliability versus the AC-4.

On Monday, January 27, 2025 at 11:47:12 AM EST, Steve Wedge, W1ES/4 via groups.io <w1es@...> wrote:

I would simply go ahead and re-cap this supply. Paper bodied electrolytic capacitors are prone to dry out.?

If you want to wait, replace just the bias supply’s capacitor, as if you lose your bias supply, your finals, at best, will be stressed beyond their ratings, shortening the life of the tubes.?

The rebuild kit for the AC-3 costs more than the one for the AC-4 because it needs a “cage” over the board to prevent contact with dangerous voltages. It is well worth it, though.?

Steve Wedge, W1ES

Time flies like an arrow. Fruit flies like a banana.

Sent from for iOS

On Mon, Jan 27, 2025 at 10:54, DavidC KD4E via groups.io <qrv@...> wrote:

I accepted a trade offer of a TR-4 for my troublesome TR-3.

Opened things up and have a few questions for those in the know ...

Images here:

The power supply has some sort of filmy deposit on top - I'm thinking

it's residue from tobacco.

1. I'm real shy about putting moisture on the tops of the paper
electrolytics

but would WD-40 or a citrus-based cleaner using a q-tip be safest for the

chassis?

2. Do the caps appear to be original? (The rig works but I'd rather update

things, if the caps are ancient, prior to setting it up on my operating
desk.)

3. Does the serial number reveal anything useful, please?

Thanks,

David KD4E