Help with Seeburg MRA4-L6

[Steveisme]

Hi,
I'm rebuilding a M100C - my first juke and having a blast. The juke was refitted with an MRA4-L6 amplifier which had been partially recapped. I did a complete recap on it and noticed a couple of other mods. First, the 10K R7 resister had been replaced with a 39K, which I believe is because the machine has been retrofit with a stereo Redhead cartridge with the stereo outputs wired in parallel together feeding the mono amp input. I thought it was supposed to be 47K, but perhaps not enough to matter? Also the AVC had been disabled by removing the C-22 cap, which I understand from other postings. The one that I can't find any reference to on line is that R13 was shorted out intentionally. When I disconnected this it made a large difference in overall volume. Apparently, shorting out R13 really increases the volume. I'm not sure if this is doing any harm (or has done any already)?

The other issue I have is a real lack of bass. Regardless of the volume setting or the R13 short, the bass adjustment doesn't seem to have any effect. The treble control does make a clear difference at each level. I have one extra set of tubes and did try swapping them out, but can't really hear any differences. I don't have a signal generator or a scope.

- Any ideas on R13 - is shorting this out hurting anything?
- Any ideas on the bass?

Thanks!
-Steve

 

[coinopwizard]

Seeburg fun

Steve,

on R13 your volume pot resistor, jumping it is normal for more output etc, I have seen some people even put another small pot in place of it for tweaks to volume output in the field, I have never seen that hurt the amp, as for your bass being low, if you have the original speakers, they may be dry and not moving much anymore, you could also try contact cleaner on the bass switch of the amp, or the switch may be faulty.