Bedroom Practice Amp

[Cephus]

This is a small bedroom practice amp I gave to a good friend of mine from the UK when we met up at the Dayton Hamvention in Ohio a couple weeks ago.

I have scores of old AA5 radio tubes, and with help from Tino Zottola's books, I built what I believe to be a very nice practice amp. It uses 2 12AT6 tubes in the preamp, a 50C5 power amp, and 35W4 rectifier. Unlike the widow maker amps of old, this one uses an isolation transformer. The primary can be wired for 120 or 240. Rated for 3 watts undistorted, then overdrives very nicely.

The first version of the amp was built on a bread tin to allow for any quick changes, then the final version on a powdercoated Hammond chassis.

In regards to low power practice amps - is there an aversion to the old receiver tubes like the 50C5 or 50L6, or is it just that nobody builds anything with them anymore? They really can make a nice amp!

[/list]

[stoo]

no o/p tranny?
Stew

[Cephus]

no o/p tranny?
Stew

Yes, on the finished chassis it is behind the 12AT6 tubes, in the prototype, it is on the underside.

[M Fowler]

Very kool I have three of tony's books and have eye balled this All American Four many times.

So you found a suitable PT for that amp huh?

Mark

[Cephus]

Very kool I have three of tony's books and have eye balled this All American Four many times.

So you found a suitable PT for that amp huh?

Mark

The PT is a Triad N-68X available for $11.20 from Mouser. It's a 120/240 / 120 50VA 50/60 cycle isolation transformer. The entire amp, including the series heater string is on the secondary side ensuring complete safety. Since the PT can also be wired for 240 at the primary, it made a nice gift for my UK friend. The OT is a surplus 2500 ohm 3 watt transformer from AES.

Just a hint - if you have Tino's books and want to build an MA1 which uses a 12AX7 in the preamp and a 50L6 as the power stage: Use the same Triad transformer. Wire the primary for 240, which will then give you the necessary 60V at the secondary when powered by 120v mains. The solid-state doubler provides the proper plate voltage. The MA1 is an equally nice amplifier. I just did a 'Big Muff' tone mod to mine. Far superior to the treble cut control which it previously had.

Cephus


Cephus

[Kregg]

So, the affair started off in the kitchen and ended in the bedroom?

[drhulsey]

So, the affair started off in the kitchen and ended in the bedroom?

And a beautiful 3W child was born

[Cephus]

So, the affair started off in the kitchen and ended in the bedroom?

The kitchen table often makes for a good, er, work surface.

As a ham operator (the radio type - no pork) I've often used cookware for a prototype chassis to troubleshoot and get the bugs out prior to building a more permanent version on a chassis.

Cephus

[Sonny ReVerb]

As a ham operator (the radio type - no pork) I've often used cookware for a prototype chassis to troubleshoot and get the bugs out prior to building a more permanent version on a chassis.

I used a cake pan for my 'salvage' amp chassis. I cut one long side off and pop riveted on a piece of 1 1/2" angle aluminum so I could mount a faceplate. Worked pretty well. The most expensive thing in the amp was the faceplate. I'd much rather use an aluminum chassis, though - I hate working steel.

[img:800:505]http://img17.imageshack.us/img17/8985/cakepan03.jpg[/img]

[M Fowler]

Cake pans and all nice

I still look in every store for things to make amp chassis out of so now I am worse then my wife on shopping trips. But I seldom buy is the difference.

Mark

[Structo]

We're a weird lot aren't we.

I do the same thing when I'm at a thrift store or garage sale.

I see something rectangular and shiny and I instantly think chassis.