Oahu Publishing Company lap steel with in-case amp 1941

[xtian]

This is special. Here is the only web page I could find that shows this lap steel with in-case tube amp:

http://www.magnatoneamps.com/dickerson.html

This page suggests we're looking at a 1941 Oahu.

It's in remarkably good shape. I'll post gut shots in a minute.

[xtian]

Gut shots.

What's that big yellow box? Appears to be a pair of e-caps, but I can't read the label.

Tubes are, from top left, clockwise: 6V6, 5Y3, 6V6, 6N7.

How should I approach this with the client? It will take me about an hour and half to install a new power cord (2-prong, because chassis is neutral) and replace the e-caps. But no guarantee at all. Might take a whole day or more to make a schematic and replace all the components.

Find out what resale value is before touching it?

[Phil_S]

No other takers on this one? I'll put in my 2 cents.

Woweeeee! It is quite the piece, old and actually fairly clean looking.

Establishing value will be a challenge simply because with (assumed) so few in circulation, there isn't a "ready market." I think we know the value is high, but probably not over the top. I'd be inclined to let this go. How important is this information to you?

As for the work, unless the customer is a difficult person, a little bit of frank and honest discussion should carry you a long way. I think it's important to be really clear with him about the challenges of working on such an old piece and that it is so difficult to know what problems will emerge after the cap job. I know you know, but the customer might not understand that the cap job has to be done in order to do any other diagnostics and you'll do yourself a favor by helping him understand this. Also, that additional charges will apply for fixing whatever is discovered after. The customer may also need some comfort here that you won't be running the labor clock for 10 or 20 hours, so do something to help him get comfortable with the unknown so his imagination doesn't run wild.

While I don't know all that much, it seems to me there are not many parts left after you do those 5 or 6 e-caps. Resistors and signal caps could be just fine -- maybe a little out of spec, maybe a leaky cap here or there.

I suspect the big "risk" is that the iron is blown, or pots aren't serviceable (noisy, sticky, etc.) and need to be replaced. I mention pots because a replacement will need to have the correct shaft to work with the knob and that could prove to be a challenge on something this old. Actually, I don't see any pots, but I figure there has to be at least one!

Having said this, I think my inclination would be to test the transformers first and if bad, call a halt to the work and discuss with the customer. The simple turns ratio test and the neon bulb test can be done fairly quickly. I think you know, doing the cap job first and then discovering a bad transformer is not going to sit well with the customer.

You have a rare opportunity here. Try to enjoy the thought of restoring something this antique. Do your best. Good luck with it.

[xtian]

Thanks, Phil. And no, there is not a single variable resistor (so called "potentiometer"--modern, newfangled gizmo) in this thing.

[Firestorm]

I worked on a similar one years ago. It's not just the amp you have to consider; half of the "coolness" is the guitar so you need to have some luthier chops, too. All of these things have disintegrating tuner knobs (looks like this one's are gone) and you'll need to evaluate the guitar electronics. If enough is wrong, restoration will quickly exceed the value.

[billyz]

I see 2 e caps and 2 film caps . Not sure what the orange box is. It appears to be across the choke. I would call it $65 plus parts. The 2 e caps at the least. High probability the coupling caps are very leaky, but have to be tested. The test might well be ok. Maybe a noisy resistor maybe not. Not sure what the 2 red tubular things are maybe an older type coupling cap. Would need to study the circuit for a couple of minutes.

[xtian]

Firestorm, the guitar itself works. Though I didn't attempt to tune it for obvious reasons...

How did they apply that celluloid so evenly?!? It's awesome.

[billyz]

I think the red tubulars are power resistors. Not much too this, if transformers are good, most likely, should be pretty easy.

[billyz]

Firestorm, the guitar itself works. Though I didn't attempt to tune it for obvious reasons...

How did they apply that celluloid so evenly?!? It's awesome.

They held the material over a heated vat of solvent to soften and form it to the cabinet etc. a very toxic and dangerous process.

[armillary]

Cool guitar, amp and website. I agree it's probably an Oahu model, but the De Luxe Professional Model 8 on the same page seems to have the same tube lineup. Maybe those are more common. I couldn't find a schematic though.

Some incarnation of Magnatone exists at this website, with pictures of early models. They have a support email address. Maybe they have old records or an archive or something and a schematic is there. Maybe worth an email.

http://www.magnatoneusa.com/support/

[Phil_S]

Thanks, Phil. And no, there is not a single variable resistor (so called "potentiometer"--modern, newfangled gizmo) in this thing.

So the volume control depends only on the guitar. Ingenious, dontcha think?

[printer2]

The yellow box is a electrolytic cap. The amp is simple enough, two output tubes and two triodes, not a lot of options for a schematic. From the OT I am guessing P-P although parallel 6V6's in a SE amp has been done more than once. If it is P-P then maybe a self-split arrangement, no need for a PI stage. I recall seeing an amp-in-case amplifier done that way, can't remember which now.

[xtian]

Yes, appears to be push-pull.

Hey, Phil, it doesn't even have an on/off switch!

Here's a closeup of the yellow box. Dry electrolytics!

Owner said go for it, so we're going for it!

[Phil_S]

That box is in near pristine condition. Sell it as a collectors item on eBay. Oh, I guess you are ethically bound to return it to the owner. Ask if you can keep it.

[xtian]

Question.

I'm trying to trace the HT rail. Starting at rectifier, goes first to choke, out of choke to voice coil on speaker, out from coil to screens.

Is this valid?