Univox U1011: couple questions

[g1]

According to your photo and the schematic, yes you can just clip it out.

[Jonny toetags]

According to your photo and the schematic, yes you can just clip it out.

Thanks g-one. Yeah, it's definitively a 1226.
I started working on it yesterday: grounded plug, new filter caps, changed 1 preamp socket.

[Jonny toetags]

One thing i noticed on this amp is the high plate voltage. I was reading 700vDC on Pin3 of the powertubes.
I read online that some people measured up to 730v. The 6L6's bias reading was about 23mA. I raised it a bit but I'm thinking the lower bias would be easier on the new Tung Sols

[g1]

Yes, the lower bias would be better for tube life. Suggest you always bias as cold as you can get away with without having too much negative effect on the tone.

[J M Fahey]

Yes, Univox used crazy high +V voltages.
Scary.

Not sure (that's an understatement) modern tubes can take it.

FWIW, not many old tubes would either.

[Jazz P Bass]

To the best of my knowledge, it's the fact that the screens are held at 300 some volts that they got away with such insanely high plate voltages.
And I agree, keep the bias as low as you can.

[Jonny toetags]

Yes, Univox used crazy high +V voltages.
Scary.

Not sure (that's an understatement) modern tubes can take it.

FWIW, not many old tubes would either.

I put in some Tung Sol 6L6GC's. I'm going to bring the bias back down tonight (it was at about 21/23mA and I put it up to 30mA)

[kilroy]

Sorry for sounding like an idiot but why do you cut off the grounding cap?

[Enzo]

When you install a three-wire (grounding) power cord, the cap not only becomes irrelevant, it also has potential to cause problems if it fails.


In the days of two-wire power cords, the cap served to reference the chassis and thus circuit ground to the AC power line ground. In 120v systems, one side of the two wire feed is connected to earth ground at the service panel. So one of the two holes in the outlet will be essentially ground.

Many amps like Fenders had a ground switch to select which side of the power cord the cap linked to chassis. When you powered up the amp, if you got shocks off the chassis, you flipped the switch. It also hummed less that way. Your amp lacks that switch, so if the amp hummed or shocked you, you would unplug it and turn the plug over and plug it back in. That used to be the first thing we did after setting up the stage, getting all the ground switches and plug set up so no one got electrocuted. Believe me it mattered. One night we got one wrong, and my guitar player lifted his guitar up, and the high E string touched the microphone and BZZZT, it melted that E string in half. Good thing he didn't play and touch his lips to that mic.

Nowdays, we ground the chassis with a three-wire plug and cord. That is much better and safer. We no longer need that cap to reference the chassis to ground, the direct wired connection is there to do it.

[Silvertone Jockey]

To the best of my knowledge, it's the fact that the screens are held at 300 some volts that they got away with such insanely high plate voltages.
And I agree, keep the bias as low as you can.

In the RF realm high plate volts, low to medium screen voltage is done regularly when using audio tubes for RF designs, and yes that is why the tubes are able to handle the voltage that seems high to you guys, but is quite commonly seen on designs using 6L6's or 8417's for RF amplification (not that there are many circuits that use those tubes) The ones that do are obsolete, as in legislated out of business, but that doesn't stop the average CB'er from having them repaired should they come across the opportunity to obtain one or already own one needing servicing

[kilroy]

Mine has what appears to be the original grounded three wire cord (grey) and still has that cap......??? I need to find someone in the Toronto area that can take a look at this one I just bought it is not working right and doesn't have the volume a 60 watt amp should have. One of the output tubes has a blueish glow to it. I read this is likely ok I'm not sure what's going on. Trem doesn't seen to work either. All tubes light up. Maybe a little brighter than tubes in previous amp. Also it has 6L6WGC instead of just the 6L6GC. I haven't even checked to see if the preamp tubes are the right yet. I also read on an earlier post that. The grey can caps should be changed?????