AR3a transplant

[Carlspeak]

I recently transferred the drivers and crossovers from a pair of 3a cabinets that were in poor shape to a pair of very nicely restored AR3 cabinets. The 'transplant' included the addition of new caps and modern, gold plated binding posts that fit nicely flush with the back of the cabinets.

Note in the crossover picture, the 150 uF cap is not shown because it was attached between the pos and neg terminals on the woofers. Also note the 1/2 ohm cast resistor in place of the original thin wire following the 50 uF NPE Erse cap. The original 3a inductors were salvaged and placed as best I could with room available. The large #9 coil wouldn't fit well in it's normal spot above the mid pot. The proximity of the 3 coils did not affect the finished performance. The pots shown are 16 ohm factory replacement pots that came in the 3a cabinets.

[fran604g]

Carl, how do the AR3 cabinets differ from the 3a?

[xmas111]

Carl,

Nice job!

When I was rebuilding my 3a's earlier this year I was going to replace the knurled nuts with banana jacks......and almost had my head handed to me for even thinking about it!

I do like the banana jacks even though it not the original look. If I ever have to take mine apart again I think I'll go the route. I really dislike the knurled nuts..

John

[Carlspeak]

Carl, how do the AR3 cabinets differ from the 3a?

As far as I know, very little; except for the grille mounting. The AR3 grilles are longer (top to bottom) than the AR3a's. They fit into machined slots at the top and bottom of the cabinet. This requires one to physically bend the grille frame a bit to get it into an AR3 cabinet. Other than that, the tweeter and mid fit perfectly. The woofer's I installed were quite late vintage (factory drop ins) and getting all of the 8 screws to line up with the T-nuts was as challenge.

[Carlspeak]

Carl,

Nice job!

When I was rebuilding my 3a's earlier this year I was going to replace the knurled nuts with banana jacks......and almost had my head handed to me for even thinking about it!

I do like the banana jacks even though it not the original look. If I ever have to take mine apart again I think I'll go the route. I really dislike the knurled nuts..

John

Authenticity is always a personal decision regarding restorations of 3a's. In this case, the customer, like you, didn't like the original knurled nuts and asked for something better.

[RoyC]

Nice, Carl...

This may be a more common project as time goes on. I converted an AR-3 to a 3a last year for Larry Lagace/Vintage AR, and recently provided assistance with the restoration of 3 pairs of AR-3's. We are seeing more and more seriously degraded AR-3 mids and tweeters. The suspensions of both drivers are deteriorating and stiffening, and there is some concern that the most common (2nd generation) AR-3 mid is experiencing loss of magnetic strength. The result is a somewhat muddy,.boxy sound. The AR-3a type midrange has very different, more reliable, constructiion, and has held up well. It can be used with the last AR-3 crossover (there were three slightly different AR-3 crossovers), or with a conversion to the AR-3a crossover.

As stated above, the only difference in cabinet construction is the grille mounting arrangement. An AR-3a grille can be made to fit the AR-3 cabinet, but the AR-3 grille frame will not fit the 3a.

This may be obvious, but I'm surprised at how many people don't know this ....For those struggling to wrap speaker wire around AR input terminal screws, the solution is #8 ring terminals (or #8 spade connectors), both available at any hardware store. They can be crimped or soldered to speaker wire, and provide an easy conenction.

Roy

[ra.ra]

Another nice job with the transplant and restoration, Carl.

I suppose I can understand why some have a preference for banana jacks, but similar to Roy's final comment, I simply fit up some speaker wires to better accommodate the original knurled nut terminals. I always felt that twisted stranded wire connected to these threaded screws was never secure enough, but with a soldered and fitted wire terminal, the knurled nut screws down very tightly, and the wire will not pull off due to the circular ring shape.

I cannot remember the size designation, but for this pair, the ring terminals fit perfectly over the speaker screw stud, and the spade connectors were one size smaller to fit some small and tight screws on a vintage Scott amplifier. The wire itself is rather heavy duty lamp or appliance cord, maybe 14 ga. or so, which I found at a yard sale still wrapped on a funky metal spool. Based on the spool graphics, I suspect this wire is quite old, but the black insulation wrap is soft and extremely pliant, and there is a hefty core of copper inside. Add a small piece of shrink wrap for identification and protection and they're ready for music.

[gary_wong5]

Carl, you install 15 ohm L-Pad?

[Carlspeak]

Carl, you install 15 ohm L-Pad?

The 15 ohm L pads came with the bad cabinet 3a's. I did not buy new ones.

[RoyC]

The 15 ohm L pads came with the bad cabinet 3a's. I did not buy new ones.

They appear to be the replacement control sold by AB Tech in the mid 90's. They were excellent repalcements for the original pots. Today, ABT sells ordinary 8 ohm L-pads.

Roy

[HarryM]

Which Lpad should the 3a have.I thought the guide said 16 ohm.

[RoyC]

The 15 ohm L pads came with the bad cabinet 3a's. I did not buy new ones.

Harry,

You are confusing L-pads and Potentiometers.

The 3a was originally equipped with 16 ohm potentiometers, not 16 ohm L-pads. There are electrical differences between pots and L-pads. L-pad level controls are not appropriate for the 3a if authenticity is a goal. The replacements seen in Carl's photo are probably 16 potentiometers sold by AB Tech 15-20 years ago. They looked like modern "L-pads" but they were actually pots, and were perfect replacements for the original pots.

AB Tech, Vintage AR, etc, are all quietly selling 8 ohm l-pads as replacements these days, which are also electrically different than the original pots. They remove the "8 ohm" stamp from the back of the housing to minimize questions. An 8 ohm L-pad lowers the crosssover frequency and produces more output, especially at the maximum setting. Most people don't know the difference.

Roy

[Carlspeak]

Ohmite 15 ohm rheostats (P/N RHS15R) are available, but at a price significantly higher than L-pads. The ohmite units will function identical to the original AP rheostats. However, they do need to be covered somewhat because their wiping element is exposed and you don't what to get non-conducting fibers like FG or PET in the wiping works. However, they are very well built and should last a lifetime.

Just another option to consider if you have the $ to spend.

[HarryM]

Thanks Roy and Carl,that clears things up for me.

[michiganpat]

This may be obvious, but I'm surprised at how many people don't know this ....For those struggling to wrap speaker wire around AR input terminal screws, the solution is #8 ring terminals (or #8 spade connectors), both available at any hardware store. They can be crimped or soldered to speaker wire, and provide an easy conenction.

Roy

and for those who HAVE to have bannana connections, IMHO the easiest, non destructive way to do it is to make some short (4-6") jumper wires with #8 ring terminals on one side, and banana plugs on the other.....