UA 2-610 Troubleshooting

[rickc]

Crudler, the ebone guy who is selling some 1008s has his blurb wrong too. He says they're balanced throughout, implying that it's a classic all push-pull design like the Langevin 5116 or the old Altec 400-series amplifiers, or even the UREI 1016, but the truth is that it's a cascode front-end feeding a single-ended output stage. The only places that the design is what I'd call balanced is at the input and output transformer windings.

 

[mitsos]

I was thinking the same thing when I saw that ad.  Wouldn't mind trying something balanced, but I don't think the 5116 is? Looked up the Altec 458A... wow, 2 dual triodes, 4 resistors, two caps, and trafos. wonderfully simple.  I think I have some russian dual triodes that need a home..

 

[lassoharp]

Looked up the Altec 458A... wow, 2 dual triodes, 4 resistors, two caps, and trafos. wonderfully simple. 

Yes, and it sounds like the price was paid elsewhere.  Good 'ol PRR.  8)


http://www.groupdiy.com/index.php?topic=6128.msg72581#msg72581

 

[rickc]

no, all of the units named in my post were classic all-push-pull designs.

again: UA/UREI 1016
          Langevin 5116B    only the B version is push-pull, the A version is a miniature tube version of the 116 preamp
          Altec 458, 459

adding: Langevin 117A, which is more a small power amp, +40dBm maximum output
            McCurdy AU300

The Altec 428B, predecessor to the 458, is single ended at the beginning, but push pull output
The Altec 429B is like the 428B, but has more output level

 

[mitsos]

Looked up the Altec 458A... wow, 2 dual triodes, 4 resistors, two caps, and trafos. wonderfully simple. 

Yes, and it sounds like the price was paid elsewhere.  Good 'ol PRR.  8)

Yikes. hmm, after the "simplicity" of the HS56 I'd be willing to take this on.  I would think that in todays world with CNC winders available, this thing shouldn't be AS hard as it was back then.  Then again, it says "the vital requirement for balance in this circuit design is explored later in this paper." which makes me curious enough to grab the paper now. 

no, all of the units named in my post were classic all-push-pull designs.

Sorry I misread you to mean balanced throuhgout, like the ebayer says about the UA amp.

thanks to both of you for bringing up these circuits, lots of stuff to go over... maybe we need a new thread..

 

[rickc]

There is a large load of UA SS preamps and equalizers FS on Ebay right now.

http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=150779063196&ssPageName=ADME:B:SS:US:1123#ht_34320wt_1299

Of course, the price is high, about half of a car. But what makes this auction worth looking at is the load of pictures. There's pictures of the guts of the equalizers (508 and 509) and of the preamps (1108), and the pictures are probably sharp enough to answer circuit questions.

This stuff was part of a console used at Wally Heider Recording in San Francisco. It's too bad you can't strap the correct two pins together and have all the music that flowed thru each module come streaming out again.

 

[bockaudio]

Not that it helps with repair of the new 610, but if you want your DIY units to resemble the originals, you'll have to use a real linear supply like they did. No DC-DC.

 

[EEMO1]

I bought a la-610 mk1 for a pretty good deal second hand. doesn't have a dc-dc power supply... I was hoping there would be a schematic somewhere, but no luck. at least something to measure voltages etc...


edit: pictures here:

http://twin-x.com/groupdiy/thumbnails.php?album=502

 

[Maltese66]

Bringing this back up. I have the same problem as described in the first post here. Anyone figure this out???

 

[Maltese66]

(Hit send too early.) Distortion in Channel 1 of Grey Face 2-610, cuts level and distorts until a loud signal "clears" it out. Then it comes back. Swapped tubes, cleaned pots, visually inspected... at a loss. I hope the last 11 years have shed a new light on a solution. Thanks!

 

[Ike Zimbel]

Those are still the classic symptoms of an intermittent connection. First suspects would be solder joints, but after that you could be looking at defective components like a cracked resistor (unlikely) or a bad switch or connector. My approach is to try and sneak up on these issues. If the fault reliably occurs when the unit hasn't been used for a day or so, leave it off for that period of time. Then, turn it on and input a test signal that is deliberately on the low side of what the DUT normally sees. The fact that you have a two channel device means you can "Y" the o/p from your source and then see what signal will pass. This is a mic-pre, yes? So I would start with a signal around -50 dBu. If the good side will pass that in a way that you can test at various points along the signal path, then test at those same points on the bad channel. That should give you some indication where the signal is not passing.

 

[Maltese66]

Those are still the classic symptoms of an intermittent connection. First suspects would be solder joints, but after that you could be looking at defective components like a cracked resistor (unlikely) or a bad switch or connector. My approach is to try and sneak up on these issues. If the fault reliably occurs when the unit hasn't been used for a day or so, leave it off for that period of time. Then, turn it on and input a test signal that is deliberately on the low side of what the DUT normally sees. The fact that you have a two channel device means you can "Y" the o/p from your source and then see what signal will pass. This is a mic-pre, yes? So I would start with a signal around -50 dBu. If the good side will pass that in a way that you can test at various points along the signal path, then test at those same points on the bad channel. That should give you some indication where the signal is not passing.

Yes a mic PRE. I will do this today, trace/test everything. Thanks.

 

[Maltese66]

Haven't yet gotten to run signal through per above, BUT I did notice a darkish resistor (R10) in the center power board (runs to phantom power switches) when I read with meter it starts at 3k OHMS and bounces between that an 55k (power off, in place in circuit). If I'm not mistaken its BLUE GREY RED RED RED = 68.20k? Or possibly BLUE GREY BROWN BROWN BROWN (due to darkness) = 6.81k? (Or RED RED RED SILVER BLUE?) Just can't tell without schematic. Wrote Universal Audio for the value...

 

[Ike Zimbel]

That resistor is common to both channels and very unlikely to be the issue. If the 1/4" jack interrupts the mic input path, that is the very first place I would look...the switching contacts in that jack. This is a very common issue in other mic-pre's with Instrument input (the list is long).
"Beware the switch you never use!" Me.

 

[Maltese66]

Examining the 3-pin female XLR input. Pin sockets are very very loose within the plastic. Is that normal? Running signal tests...