Juke Box

[supro66]

This guy at work bid on a ROWE juke box and won it
He is an Enginneer

Anyway it is the same as a Guitar amp all tubes
5U4GB, 12AX7, 7868  7 TUBES

Anyway no sound

I keep telling him the MUTE SERVICE switch is on

Two sections
Preamp
Power amp

I am not going to travel 50 miles one way to turn the switch on for him
so I told hime to bring the two boxes down to me

Anybody worked on these things




OK PEOPLE I HAVE TO ADD THIS

He emailed me this back
I gave him a Mic told him to plug it into the inputs on the power amp he should get sound
came back the next day told me no sound

here is his email today

Hey, besides pulling out the mute cord and plugging in the mic box I think I MIGHT even put the fuse back I brought in the other day.


Now what is that about leading a horse to water

STAY TUNED

[labb]

I picked up a Peavey Classic 50 at a pawn shop a couple of years ago for $100 because every time they turned it on it blew the fuse. Took it home, put in a slow blow fuse and it has been playing every since..They were using standard fuses..Only good deal I ever got.

[dynaman1]

I used those outputs for a couple of 6V6 builds. What a PIA it was to figure out their secondaries!

[supro66]

Ok he brought it into work

I guess I have a weekend project now

It looks real old and dirty inside

Caps are dried and cracked

Post pictures Monday


See it is just two amps in one
Left side and right side

[rafe]

Looks like huge iron in there.......good luck

[RicharD]

That thang looks like it's been sitting for a couple of decades.  I wouldn't dare light it up w/o a lamp limiter.  Plan on a cap job.  You might have some dry-rotted wires too. 

[66merc]

This looks like the one I gutted and turned into an ipod player last year.

http://www.el34world.com/Forum/index.php?topic=6030.0

[supro66]

Here it is Sunday morning

No work today I will play with the AMP

I still think it is the MUTE switch

Lets see

 KEEP ONE HAND IN MY POCKET 
REMEMBER YOU HAVE A HEART PACEMAKER NOW

Discharge caps   

[sluckey]

I still think it is the MUTE switch

It'll take about a minute to find out for sure.
1. Locate that big ole 20K/10W resistor in the power supply. It should measure zero ohms because it is shorted by the mute relay MR-1 contacts. (This won't totally kill the sound)
2. Measure grid to ground resistance for V2 pin 2. It should be 1MΩ since mute relay contacts are open. (This will totally kill the sound if the contacts are closed)
3. Repeat step 2 for V5 pin 2.

Measure voltages for all tube pins (including the rectifier). That should point you toward the problem.

[PRR]

> it is the same as a Guitar amp all tubes 5U4GB, 12AX7, 7868

All Audio Amps tend to use these same tubes: reckyfier, hot twin triodes, and 6L6/6V6 guts in whatever package was "new and improved" that year.

This is not a guitar amp. It is a hi-fi genre power amp. It expects a 1V signal, and most sources will need some pre-amplifier. I would not expect an audible signal from a mike, and hardly-audible from a hot solid-core guitar.

The preamp "might" bring mike/gitar up to 1V line-level.

It is very conventional except for that crazy output switching. How can you even know if you are on the right connections? That alone would explain "no sound".

Adding in the too-many connections on the preamp, this will be a hair-ripper, FAR too complicated for a highly-trained Engineer.

Jack an iPod or CD-player to the power amp Input jax, leave that preamp for another day.

[supro66]

> it is the same as a Guitar amp all tubes 5U4GB, 12AX7, 7868

.

This is not a guitar amp. It is a hi-fi genre power amp. It expects a 1V signal, and most sources will need some pre-amplifier. I would not expect an audible signal from a mike, and hardly-audible from a hot solid-core guitar.

The preamp "might" bring mike/gitar up to 1V line-level.

It is very conventional except for that crazy output switching. How can you even know if you are on the right connections? That alone would explain "no sound".


Jack an iPod or CD-player to the power amp Input jax, leave that preamp for another day.

You are right the MIKE did not work
I was going to give him my Guitar tuner with sound
I bet that would have worked

I did use my CD player

Anyway I used WD-40 to all of the tube sockets replaced all of the tubes
Sprayed all of the switches
It worked

First CD player thru the stereo amp earphone chord into the juke box power amp
I got music

Then just the CD player no amplification thru the Preamp stage
I got music

I look at the mute switch 3 open and one shut

There is a 12AX7 tube HOLLAND it glows real red at first then goes down the other 12AX7 tube does not do that


MUTE SWITCH

POWER AMP

PRE AMP


I am going to hook up a turn table later to day
when I dig it out

The data sheet says 28 watts for the 7868 tube
two tubes equal 54 watts ?????????

[RicharD]

>There is a 12AX7 tube HOLLAND it glows real red at first then goes down

That's typical for some Amperex tubes.  Don't worry about it.

[PRR]

> The data sheet says 28 watts for the 7868 tube

Yeah, for 450V cathode-bias.

Here we find 360V fix-bias. We really want to know the load impedance, but assume that smart designers simply use the tube-maker's recommended conditions.



30 Watts.

> two tubes equal 54 watts ?????????

"Push-pull" suggestion is always cited for two tubes. Each pair will give about 30 Watts. The whole chassis can deliver 60 Watts.

[supro66]

Thank you guys I can always find answers here

"Push-pull" suggestion is always cited for two tubes. Each pair will give about 30 Watts. The whole chassis can deliver 60 Watts"

Looks like the manufacture lies


Now where should I sell my BOEING stock at  

[sluckey]

Looks like the manufacture lies

No. That 330W figure is the AC input power rating. IOW, that amp consumes 330W from the wall outlet.

[phsyconoodler]

There are losses in any tube amp and you cannot bias to get 28 watts per tube or they'll burn up.They set up those amps so you get clean output and low distortion,so expect about 30 watts with two power tubes.This is totally normal.
  Two 6L6 power tubes have 30 watts disipation.Two of them in a push-pull amp like a super Reverb deliver about 45 watts.
  Cathode biased about 30-35 watts. 30 watts is right where you should be.