Univox 1236 Bass Amp, any information

[JMMP]

Would appreciate any info on this. Strange animal, 2-6l6'ss, 2-12au7's, 1-12ax7, Ink stamp says 100 watts, 650 volts on the pwr tube plates. Is this plate voltage normal for this amp? Thanks in advance.

[Jazz P Bass]

Yes, Univox used a B+ that high.
With todays mains voltages being higher than when the amp was manufactured, you will see the B+ higher still (approaching 700Vdc)

The trick is that the screen voltage is set much lower (330Vdc by the schematic).

Here is the schematic: Univox U-1236 Schematic.zip

[JMMP]

Yes, Univox used a B+ that high.
With todays mains voltages being higher than when the amp was manufactured, you will see the B+ higher still (approaching 700Vdc)

The trick is that the screen voltage is set much lower (330Vdc by the schematic).

Here is the schematic: [ATTACH]45360[/ATTACH]

Thanks for that JPBass, just did a retube and bias, amp is stated as producing 100w, sounds more like 20-25 watts. Not done the calculation yet, all voltages are what the schematic specifies, sounds nice just not a whole lot of output. Wonder if there is something going on with OT.

[Justin Thomas]

sounds more like 20-25 watts. Not done the calculation yet, all voltages are what the schematic specifies, sounds nice just not a whole lot of output.

What are you using for speakers? A less-efficient-by-3dB speaker can make a 100W amp sound like 50, and there's no reason a speaker can't be broken or inefficient and still sound good...

Justin

[JMMP]

What are you using for speakers? A less-efficient-by-3dB speaker can make a 100W amp sound like 50, and there's no reason a speaker can't be broken or inefficient and still sound good...

Justin

Using a well used WGS Veteran in a semi open cab that I keep in the shop to test stuff. Upon further inspection I found a couple cathode resistors in the pre that had drifted, replaced and it helped considerably. Might add a bypass cap or 2 and see what happens Thanks!

[J M Fahey]

Load it with the proper load, 8 ohms or whatever it requires, feed it 100mV 1kHz , set all tone controls to 5, slowly rise volume until it clips and measure output voltage, then do the Math.
100W is optimistic, even with such high voltage, but I wouldn´t be surprised at 70W or even slightly more ... which is LOUD through a competent speaker.

EDIT: If working properly, you have enough power under the hood to kill that Veteran if overdriven with a guitar.

Of course, it´s not a high gain amp at all, think the clean channel on any Blackface Fender.

[Jazz P Bass]

Yup.

Measure the output.

[JMMP]

Yup.

Measure the output.

Will do guys, have to find my 8 ohm dummy, have not used it in a bit.

[catalin gramada]

Hi. Don-t think can get 100w from 6l6 pair with such 10k impedance which place more in AB class,think more 60-maybe 70w arround as JMF said. If you want to get 100W from a pair with those voltages change to kt88 5-6K instead. Check also the balance in output stage.
edit: put some resistors into screen grids for stability reason