Really OLD amps of all sorts

Here is a 1930's Wurlitzer Jukebox amp, one of my early 

vintage restoration jobs 

This is more like the kind of gear I work on, a very old tube amp that might work after
spending hours of hopeful work shaping all the vintage parts back into some possible
working shape, and hopefully all will stay together and keep running, at least for a while

Here you can see the wild, running all over the place wiring job, and now all the wire colors have
faded so they are all brown!


This amp really surprised me when I brought it up on the Variac, quiet, great smooth
tone, and very well behaved amp. The speaker sounded great also, with solid bass and
very good highs.


This amp like other all triode amps of this era, uses triodes with no cathodes. Then very clever wiring of the filaments seperates the tubes so each has it's own "cathode" grounding and biasing.


This amp uses two #30 triodes as preamp stages, a $45 driver, and two #45 output tubes, very much a "SE" amp.


This amp also devolops negative bias for the two #45 triodes in the power stage by
placing the feild coil of the speaker in series with the center tap of the high-voltage coil.


So this amp has all the same circuit functions of a modern SE amp, three triode tube
driver stage and driver transformer, and push-pull triode output stage with fixed bias, way before diodes of any kind. One circuit has a #45 backwards as a bias rectifier, very clever for 1933!

The amp comes up very fast also as they selected #30 tubes for the preamp, and the
#45 driver and the 5Z3 rectifier tube come up fast also.


Jukebox amps have to come up fast as the time between the customer putting in the quarters and the record playing can be very short, and the amp has to be ready before the needle hits!