Kent DR-77 cardboard amp

[PRR]

Yard-sale find.

Kent DR-77 cardboard amp (actually the kind of "masonite" that has wire-screen pattern).

Hot-chassis. Barely 1 Watt out. In no rush to plug it in.

Only odd thing is PCB construction.

'Pears to be in good shape. Probably hardly-used, and the spiders kept the mice out.

[DummyLoad]

In no rush to plug it in.

are you going to?


i think that amp takes the prize for lets see how little $$ we can build an amp for.

may very well be last specimen of that model.

cool find.

--DL 

[eleventeen]

"i think that amp takes the prize for lets see how little $$ we can build an amp for"

Boy, no kidding. 2 screws on the speaker...cool.

And yet, with a masonite back on it and plastic knobs on the front, it's perfectly safe, safe as 5 quadrillion A-A 5 radios that were made...maybe safer, lacking a metal chassis.

[tubeswell]

And yet, with a masonite back on it and plastic knobs on the front, it's perfectly safe, safe as 5 quadrillion A-A 5 radios that were made...maybe safer, lacking a metal chassis.

Unless the cardboard gets damp

[PRR]

> safe as 5 quadrillion A-A 5 radios that were made

Until you plug-in the guitar in your hands.

[Ritchie200]

It certainly wins the prize for total letdown on the speaker size!   Too cool, just because!

Gosh, I had a bunch of those little oddball amps back in the '60s, kind-of wish I still did!

Jim

[Rev D]

 Yeah me too, my first amp you got distortion from the plastic handle vibrating on the top of the amp... Probably the whole package guitar with amp for 50.00... (or less), used to see that stuff down at the thrifty's drug when Dad would test the tubes on our old set.. I have a old bass my Brother gave me, its a Kent in a chip board (really really cheap) case, looks like a 2 pickup ES335, long scale, even with a shim in the neck pocket the strings are off the neck like a double bass... 

Regards,

Don

[HotBluePlates]

Kent DR-77 cardboard amp ... Hot-chassis. ...

You mean "no-chassis." At least, not a metal one...

[stratele52]

PRR your Kent amp don't have any power transformer that isolate you from the wall 120 AC, very dangerous to use it.
This is a low budget amp of the '60.

You can use it in the house  not in basement with cement floor and don't touch to anybody or metal parts, microphone, other guitar = electrocution.

Enjoy

[sluckey]

 

[DummyLoad]

err... 

[sluckey]

Just happy I guess. I can almost see PRR shredding wearing his rubber gloves. Who is this PRR anyway?

[PRR]

> Kent amp don't have any power transformer that isolate you from the wall 120 AC, very dangerous to use it.

Well aware of that. I actually lived through the 1950s, often with the back off the 5-toobe radio.

> You mean "no-chassis." At least, not a metal one...

It IS electrically-HOT chassis. Not clear in the shadows: there is a metal plate supporting volume pot and the ends of the PCB. I have not gone in to see if the metal plate (and pot-shaft) are tied to circuit common.... since it is on cheap PCB I must assume there's some leakage through damp board.

Also as stratele52 points out, one side of the wall-outlet is tied to guitar-cord plug through 100K||0.05u. At 60Hz this is about 35K impedance. Assuming wrong-way wall-plug, and zero "me"-resistance, 3.3mA of AC current will flow to the garage floor. Easily 2mA when I am hot and sweaty. That's not for-sure fatal; OTOH I've taken my lifetime quota of shocks and won't tempt my fate for a cheap amp.

I may stand on a mat and poke a meter at it for fun, but it gets isolation before I touch it or anything wired to it "live".

[loogie]

I love those cardboard amps.  Nice find.  I love the kind that when dialed in for clean compete with the volume of the string pluck.  Nice stereo effect. 

[jojokeo]

I love these threads, always get a little chuckle in some way but this one got me going pretty well on a few of the comments. I still have one of these low watt mouse trap beauties that I pulled outta the rafters a while back and is what actually got me going w/ tubes again after having so much fun messing it.

PRR, this schem appears to be easier to read...(like you even need it)

[JT]

I was hoping someone might post something like this.  I asked a question a while back about a DR-19 amp that I was working on, funny thing is it had the schematic for your amp in the cabinet.  It was thanks to Hoffman's schematic page that I was able to figure out what it was.  It was listed under Kent unknown schematic.  I play in a blues band and wanted to fix up the dr-19 for the harmonica player to try, but I need to make it quiet from hum.  I have found out that the 50c5 tube is identical to a 12c5 except for the filament voltages.  I have since acquired a 12 v 1.2 amp transformer I'm hoping to use for the filaments.  I have a yard sale power transformer with what I believe is 200 volt b+.  I'm hoping to make a nice quiet safe tube amp.  Weird about the circuit board, mine is point to point.  I never finished fixing it up due to finances, but am getting ready to now.  I figure I'll go with solid state full wave rectifiers for both heaters and b+.  Who knows it might be a great amp for harp.

[PRR]

> wanted to fix up the dr-19

Well, but by the time you "fix" it, you almost might as well have started from scratch.

The 50C5 family is rated 135V max plate voltage. While I suspect they don't explode at 136V, 200V leaves all safety-margin far behind. Also the real limit in class A is plate dissipation. Raise voltage, you must lower current to avoid melting. With the very different voltage/current ratio, you need to change the load impedance or you will get _less_ power.

Yes, you might also want to change that teeny-tiny OT. Then you could also select a different impedance.

But if you propose a new HV PT, then you could think 200V _if_ you move to 50L6/6Y6. These can nearly reach 5 Watts, instead of the 1.6W out of 50C5 (and probably less with the toy OT).

However 50L6 at 200V needs more drive signal than 50C5 at 110V. And we see Kent already had problems: Campbell's rendering shows 12AU6 loaded in 470K into 1Meg grid; my plan says 1Meg into 3Meg, extreme (and past-spec), probably desperate to squeeze any little bit of gain possible (without of course any added penny). So a 50L6 amp probably could not be driven to the full output by a standard e-gitar. (Harp-mike may be different.)

It's just cheap all over.

If you do get 2W-5W out, that speaker will croak. Good small gitar speakers are scarce and often not cheap. "Not good" (in a good way) speakers are even harder to find and often don't hold their unique tone for long.

50C5 is "probably" MUCH easier to get than 12C5. I've never seen the 12, my life was full of the 50, everybody had a 5-tube radio.

It's still sitting. I'm working on plow-truck and mower/grader. But my feeling is that pouring $50-$150 of parts into a $5 amp to make a filthy copy of the Epi Jr may be good money after bad, and a loss of a historical artifact. I doubt I would do much more than an isolation transformer and whatever caps are truly expired.

[JT]

Yeah, you're probably right.  I was thinking I would lower the voltage of b+ by running it through a resistor, but I could be confused about that.  I'm still pretty new at this.

I think the 12c5 is available for just a few dollars, I guess nobody wants em.

Thanks for the info.

[eleventeen]

$5 amp worth $5. Whod'a thunk it? 

[billcreller]

 Never thought of an old amp as a wall-hanger 'til now.......