Univox U45-B All Tube Combo - Closet Find???

[misterc57]

Thoughts some of you may enjoy seeing this one. Picked it up yesterday. Looks like it has never been used, still has hang tags, footswitch looks never used.

Mullard power tubes, RCA preamp, IEC rectifier, Jensen 12 speaker, 2 prong power cord (will make great speaker cable once removed), schematic folded inside cab...

Have not powered up slow yet. Will be installing a 3 prong AC cord.

Thoughts? To dos?

Thank you

univox-u45b.pdf

[mozz]

Nice find. I don't think that speaker is original but you never know. 6bm8 are a lot cheaper NOS than other power tubes. Only thing is I don't like those Japanese caps, even the ones marked oil seem to test bad.

[g1]

Agree with Mozz, it's likely most of those Panasonic and Atlas caps will be leaky.

[misterc57]

I'm amused that they emphasize no shock hazard, being a step up from low cost non power transformer models.

[trobbins]

Contact cleaner on the valve sockets, and insertion exercise ? Protection diodes on the valve rectifier anodes ?

[mozz]

Agree with Mozz, it's likely most of those Panasonic and Atlas caps will be leaky.

I forget what i was taking apart, a Japanese radio or tape recorder, for parts, probably tube, and wanted some of the old caps and resistors for a SuperFuzz build. I saw those caps, marked "oil capacitor" and figured they must be good. Nope, they were bad with values no where near what was marked.

[The Dude]

That reminds me so much of my first amp. It may have even been one of these. I don't recall for sure. I was cranking it in the basement once and let the smoke out of it. Being a dumb kid and it being about the time transistor amps were becoming the rage, I threw it in the trash bin and bought a newfangled transistor amp. If only I'd known then what I know now.

[Jazz P Bass]

Remove the death cap!

[misterc57]

Quick bench check this morning and put aside as I have some other amps waiting for service.

I found a faint hum, sounds like filter caps, @ 9 VAC leaking off the chassis, non working tremolo (even with a footswitch attached).

Hope to be back to this one in a week or two.

[misterc57]

Well it has been a week or two. Finally back to this one. Got the recap done today. Did not take much for some of those copper foils to lift.

Next step is install a 3 prong and rewire the power supply.

Nice of Univox to leave an opening on the chassis bottom to access the board.

[glebert]

That looks incredibly similar to a Teisco-made Melody amp I used to have, including the circuit board material and copper foil. Mine was less deluxe though, no tremolo, crappy little speaker. Still sounded pretty good though.

[misterc57]

Finished the 3 prong, rewire PS and bias caps. Amp is connected to my bench 12" speaker and can get fairly loud and very crunchy as you dial up the volume.

Tremolo could be a bit slower. Only operates with footswitch.

The tone control could use more dynamics. Kind of flat on the low side. Bright side is acceptable but could be brighter. Wondering if anyone has suggestions for the tone control?

Thank you.

[Helmholtz]

The input sockets wiring results in a low input impedance of only 70k.
This loads down the PU signal and kills treble.
For a quick test disconnect the 2 lower inputs after R1.

[misterc57]

The input sockets wiring results in a low input impedance of only 70k.
This loads down the PU signal and kills treble.
For a quick test disconnect the 2 lower inputs after R1.

I lifted R2 and R3 on the C1 side. Sounds better and brighter. I will leave it that way. Thank you

Be nice to slow down the Tremolo. I am comparing the speed circuit to the Vibrato Champ. Seems about the same except for the the value of the pot and the 1.5M resistors to ground. Any thoughts on this? Thank you.

[stokes]

There are 3 caps connecting the plate and grid on the trem tube. A .02, .01 and .01. Change one of the .01's to a .02 to slow the trem.