Altec 342B Tube Amplifier - What is it good for?

[tigerzilly]

Oh, I just looked closer. Those lovely mic impedance transformers - the green things. You don't want those, send them to me. I'll, uh, recycle them properly. No really, sell those. What number/type are they?

They're Type 4722. Same as the eBay listing.

[Enzo]

Well tiger, 4722 is the type I linked selling for $600 a pair. You got $1200 of transformers sitting there.

[The Dude]

Good score! You can build a guitar amp and make money on parts you don't need!

[nevetslab]

This is an dear old friend....the 342B. I had one back in the late 60's that our band's manager got from somebody. It only had two input xfmrs, but they were the 4665's rather than the 4722's, which these days are even more valuable. Very smooth sounding mixer, and for sure worthy of restoring to it's full glory. And yes, replace the Selenium Rectifier! I have one of the 3.5' thick Altec Binders, and have both the Green Data sheet as well as the Service Bulletin which I'll scan and post in the next few days. Probably have the data sheet on the xfmrs.

Years later, I think I sold that at a swap meet for probably $25. Kept the premium xfmrs, of course, which made excellent DI xfmrs!

[tigerzilly]

This is an dear old friend....the 342B. I had one back in the late 60's that our band's manager got from somebody. It only had two input xfmrs, but they were the 4665's rather than the 4722's, which these days are even more valuable. Very smooth sounding mixer, and for sure worthy of restoring to it's full glory.

I'm a sucker for nostalgia. I'm really bad at parting out old gear that could be fully functional. I'll restore it to original spec then see how it sounds with a guitar plugged in. Then take it from there.

[Enzo]

COnsider: Guitars have unbalanced outputs. The inputs on this amp appear to be XLR for low-Z inputs, and that is what the transformers are for. You don't need them, you can ditch the transformers and put 1/4" jacks back there. When one did not need low-Z inputs they made jumper plugs to put in place of the transformer cans.

[tigerzilly]

What about a DI box in? Is it worth a try to hear the sound?

[Enzo]

Sure, you could do that. Or tack solder a jack into the circuit just during tests. ANy way you can think of to get a guitar signal into it.

[tigerzilly]

Looks like I will be selling off 4722s. I replaced the busted power cord with a three prong. Checked the fuse and noticed it was blown. So I put in a new fuse. Started to power up, no tubes, and didn't see the pilot light going on. Checked the bulb and it was blown. I put in a new bulb. Brought up power and nothing. Found the power switch not working. Jumped the switch and tripped the fuse in my power supply. Plugged into a light bulb limiter. Jumped the switch and get a bright light. Checked voltages of the PT and I get nothing. That explains the nastiness on the wires coming out of the PT and the burn spot on the chassis cover. Blown PT.

[The Dude]

Did you unhook the PT secondary and test to verify that it's not just a shorted load?

[tigerzilly]

Did you unhook the PT secondary and test to verify that it's not just a shorted load?

That's exactly what I did after you suggested it. Still lighting up the bulb limiter.

[nevetslab]

Altec 342B Data Sheet, Operators-Service Doc & Input Xfmrs Doc attached

While I did scan the Altec 342B Data Sheet, 342B Operators-Service Document & the brief Altec 4772 & 4665 Input Xfmr Information sheet, I see from the results, I'll have to go back to that copier and see what I have to do to increase the resolution, as what I'm attaching here isn't great. But, it's a start.

[The Dude]

Actually, if you click the pic, then click again so it opens in a new window. Then click once more so it's full size, the resolution is fine.

A lot of that is in the pdf I linked in post #2 anyway.

[nevetslab]

That's exactly what I did after you suggested it. Still lighting up the bulb limiter.

Now that there's a schematic to refer to (assuming you didn't have one yet), notice that the Power Xfmr secondary has twelve wires to disconnect, to be certain there's not a load still present. I see it DOES call out the color code of the secondary wires. Of course, you're dealing with point-to-point wiring in the chassis, so completely disconnecting the secondaries so you're sure it's fully unloaded is a bunch of work.

[nevetslab]

Looks like I will be selling off 4722s.

You might want to hold off selling off those 4722 input xfmrs until you're totally sure you have a failed power xfmr. There are 12 wires on the secondary side of the power xfmr, so make sure ALL of them have been disconnected and isolated. You could be right, which would be a real shame. You're not apt to come upon a direct replacement power xfmr, though one could find something to adapt to get it working. I wouldn't sell off those input xfmrs until I had the mixer back up and running, and got an opportunity to hear it with them plugged in and a decent mic or two connected. This IS a classic piece of tube gear, after all.