Jukebox Amplifier

[philipw6706]

Hi
Any one out there help,iv'e got a 1948 wurlitzer 1100 jukebox and had the amp and pre amp rebuilt about 14 months ago.Recently the volume has dropped by more than half,still sounds ok just wont go above about half its volume(i have replaced valves and stylus)could one of the caps have blown?.
Any input would be most appreciated.
THANKS

 

[Mooly]

Welcome to diyAudio

This section is really for intros and so I'm going to move your question over to the 'Instruments and Amps' section where it will get more exposure.

 

[Mooly]

Done

 

[Enzo]

These amps are really simple circuits. First place I'd look would be to check the speaker itself and the speaker connections. Also look at the volume control, the one accessible from the outside on back. I do not recall if they had automatic level control this far back, but if so, turn it off.

 

[Printer2]

I would think Tubes / Valves would be a better fit as this is a record player rather than a musical instrument.

 

[Enzo]

Oh, it is fine here, why bounce it all over the place?

 

[Printer2]

Yeah but we are more likely to suggest gutting it and making a guitar amp.



Well I looked around for a schematic, no luck.

 

[Enzo]

Well, that's true. KInda doesn't matter what it is, we want to do that: clock radio, blender... make it a guitar amp.

I used to buy old lab gear from the MSU surplus outlet and make it into various guitar amp things.

 

[Malcolm Irving]

Hi
Any one out there help,iv'e got a 1948 wurlitzer 1100 jukebox and had the amp and pre amp rebuilt about 14 months ago.Recently the volume has dropped by more than half,still sounds ok just wont go above about half its volume(i have replaced valves and stylus)could one of the caps have blown?.
Any input would be most appreciated.
THANKS

I worked on a late 1930s Wurlitzer jukebox amp some time ago. That one had almost all the possible problems imaginable. (Components that old are all very suspect.)

Probably a lot of things can cause a loss in volume, but in the one that I dealt with, that symptom was associated with an anode resistor that had drifted way up in value, and also with a deteriorated volume potentiometer. Also one tube of a push-pull pair was completely dead.

Bad power supply smoothing caps caused hum and leaking coupling caps were causing serious distortion (by messing up the bias of the following tube).

I guess a bad cathode bypass cap would also cause a loss in volume.

 

[Malcolm Irving]

...
I used to buy old lab gear from the MSU surplus outlet and make it into various guitar amp things.

I converted a valve-voltmeter into a fuzz box. Hopeless - no grind whatsoever and all high frequency fizz. Wish I'd kept it as a voltmeter.

 

[Nigel Goodwin]

Probably a lot of things can cause a loss in volume, but in the one that I dealt with, that symptom was associated with an anode resistor that had drifted way up in value

That is probably the most common fault on valve amps, by FAR.

I've repaired countless ones over the decades, basically the resistors they use aren't really big enough (replace with a 1W if you have space), and the values used are the ones that tend to go high over time.

A few years back a friend asked me for advice about a fairly new Fender guitar amp, he had been offered it ludicrously cheap as it was faulty, and the guy selling it had taken it to four music shops, none of whom could repair it. I advised him to buy it, as if nothing else the transformers were worth lot's more than the asking price, and that it would most likely just be the anode loads faulty. So he bought it, brought it to me, and just as I thought the anode loads were faulty - actually three of them were.