Univox U-1011 Lead - tube chart?

[DonMoose]

Gentlemen -

I've snagged a Univox U-1011 105W head to use as an ODS donor, but would like to play through it while I amass the parts.

I've apparently gotten the preamp tubes out of order putting them back in - there's a a 6AN8 among the 12A_7 types and I think I got it in the wring slot.

I have a schematic, but there's no V1, V2 info and no tube chart (that I noticed) inside the cab.

assistance?

/ off to see John Mayer tonite.

[Phil_S]

Find the reverb trank and then trace the circuit back to the tube socket with the 470 ohm resistor on pin 3 that's grounded. There is another 470 ohm resistor from pin 2 to ground. You'll see the .01 coupling cap and the 10k 2w resistor to ground. That's where the 6AN8 goes.

I'm not trying to be mean spirited when I say this, but I suggest that you could benefit from spending some time with the schematic tracing the circuit and making a layout diagram. This will sharpen your schematic reading skills. If you think you can build an ODS, you should know how to use a schematic. This is not hard to do, but it does require your time. I've thrown you a fish when you've got the rod and bait in your hands.

[Cygnus X1]

Good tip Phil.
Seems to me making an ODS from a donor would be exponentially more difficult than just starting from scratch.

Best yet-get a kit.

[Phil_S]

Tracing a circuit today is much easier than years ago. Make some digital pictures, enlarge and print them, and label the parts by hand. Presto, you're done!

[Trout]

On my U1511(more or less the 150W 6550 tube version) there is no tube chart either, however the chassis is labeled near each tube. Sometimes it takes a bit of cleaning to see them.
The 6AN8 is indeed the reverb tube in this model as well.

Good Luck

[Bob-I]

Good tip Phil.
Seems to me making an ODS from a donor would be exponentially more difficult than just starting from scratch.

Best yet-get a kit.

I disagree with that, and add that older donor amps tend to sound great because the xformers are well broken in.

Once you gut the amp, building an ODS in the old chassis is no more difficult than building from scratch.

I wanted to convert one of these for a friend but he refused to gut the old amp, claiming vintage value. I ended up just restoring it to orignal and it sounded great.

[Phil_S]

Please explain, "breaking in transformers." Umm.....I mean, there are no moving parts at all. This sounds like a myth. Is there some scientific evidence to support such a view? Inquiring minds want to know.

[Trout]

Please explain, "breaking in transformers." Umm.....I mean, there are no moving parts at all. This sounds like a myth. Is there some scientific evidence to support such a view? Inquiring minds want to know.

Old transformer break in = plates rusted tightly together with screws seized in place. Cloth covered leads beginning to fray, internal insulation on the wire cracking and leaking.

[Bob-I]

Please explain, "breaking in transformers." Umm.....I mean, there are no moving parts at all. This sounds like a myth. Is there some scientific evidence to support such a view? Inquiring minds want to know.

I don't know why, but old iron just sounds better and lots of the pros support that as well. Lord Valve, Dumble, Diaz all used old iron, plus I found that there's a distinct difference in the way old iron sounds.

I started doing donor amps because of price. A few years ago I could get a carcass of an old Peavey VT for $20, I even got one for free complete with 2 blown EVL12L's. Very cool way to experiment with circuits.

[Cygnus X1]

Old transformer break in = plates rusted tightly together with screws seized in place. Cloth covered leads beginning to fray, internal insulation on the wire cracking and leaking.

Sounds good to me!

[sliberty]

I did a conversion of a U-1086 (PA head) to an Express (my UniWreck). I ended up replacing the trannies so that the Express would have proper voltages and an appropriate OT. I still have the Univox iron thought - it's f'ing huge!

Good luck with the conversion - should be a lot of fun.

[Phil_S]

...I found that there's a distinct difference in the way old iron sounds....

I don't think that is because it is "broken in." I think that is because of the quality and quantity of materials used, as well as the actual construction of the transformer (winding pattern, etc). I use recycled iron quite often and have had very good results. I just don't believe there is any "break in" factor. Well, at least we agree on reusing the good stuff.

[Andy Le Blanc]

I can support the "old" and "broke in", for such a simple thing transformer
are very complex to describe at more than freq. simultaneously.
The core materials are "permeable", any change over time in their magnetic
qualities will alter its impedance, it will effect its frequency response at
different voltages and alter any wave form you put to it, linearity goes out the window.

[DonMoose]

Find the reverb trank and then trace the circuit back to the tube socket with the 470 ohm resistor on pin 3 that's grounded. There is another 470 ohm resistor from pin 2 to ground. You'll see the .01 coupling cap and the 10k 2w resistor to ground. That's where the 6AN8 goes.

Since I have to bust the thing back open to do that, and being short on time, it seemed worth asking if anyone had a suitable document handy.

I'm not trying to be mean spirited when I say this, but I suggest that you could benefit from spending some time with the schematic tracing the circuit and making a layout diagram. This will sharpen your schematic reading skills. If you think you can build an ODS, you should know how to use a schematic. This is not hard to do, but it does require your time. I've thrown you a fish when you've got the rod and bait in your hands.

Thanks, Phil, but I draw them for a living - motherboards for PCs and Servers, mostly. The drawing standards where I've worked require not just value and reference designator, but tolerance, power (or voltage and dielectric) and footprint for each one of the literal thousand little bastards.

Not to mention special properties for the high speed signal groups, and these days they're ALL high speed. (it's not the frequency, it's the rise time)

Still, thanks!

[Phil_S]

Hi Don,
Sorry, I mistook you for someone who didn't know how. Those who do know how deserve a free fish when they can get it. It will probably take longer to pull the chassis than to identify the socket once you've got it open. Well, good luck.
Phil