ODS Clone Bias Question

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kevster
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ODS Clone Bias Question

Post by kevster »

All,

I just pulled my Ceriatone OTS50 #102 (Modern Eagle Mod) out of the cab for the first time in five years to service and update a couple of things.

I checked some voltages and the bias, and I got an odd reading. My checks of Pins 4 and 5 on the two "matched" Winged C 6L6GCs were 498V and -44.6V/-44.7V respectively. Those are high, but the output of the OT is (was) hotter than the typical 450V anyway. Then I checked the bias, which was 25.8 and 34.3 for V4 and V5 respectively. I cranked on the pot just a bit, and they went up to 35.9 and 44.6. It didn't take much, BUT...

So, why are they off so much? Any ideas?

Thanks!

Kevster
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martin manning
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Re: ODS Clone Bias Question

Post by martin manning »

5 years? How many hours of use? It would not be surprising that the pair drifted apart with time. In any case, it sounds like you need a new set.
kevster
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Re: ODS Clone Bias Question

Post by kevster »

Hours? It was "on" at least 3,500. Maybe as many as 6,000. It is actually about 5.5 years since I last had it on the bench...

Almost three straight years of that was every weekend (50+ per year), plus some time during each week. So, 16+ hours weekly each of those years. Since then, I'd say probably 50% of that (easy). Some weeks/months 2+/- hours. Some: 30+/-...

Wouldn't be surprised that they might be getting a bit tired. But still, that still seems like a large difference to me...

Thanks
kevster
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Re: ODS Clone Bias Question

Post by kevster »

Two new, matched Mullards 6L6GCs are now in.... I have V4 at 37.7 and V5 at 39.2. Is a 1.5 difference with new tubes fairly normal?

Some tube rolling helped the tone a little before the new tubes arrived. The Sovtek 12AX7LPSs from V1 and V2 are now in the PI and the CLator. The JJ 12AX7 Gold Pin from the PI and Sovtek 12AX7WA from the C-Lator are retired, and I have new Mullard 12AX7s in V1 and V2.

New tubes/positions: A LOT more headroom, and they've only been in for 10 minutes! "Drive" on the Clator could never go above 9:30 without break-up, and now it sounds fine at nearly 2:00. The amp is definitely more open, and ever so slightly brighter. The tone may be slightly more "glassy," which is fine with me! At least there is no brittleness or ice-pick highs!!! The bloom may be SLIGHTLY better at the moment, but not too much of a change. Of course, I still have to set the PI... I expect everything will evolve as the tubes burn in. I need to have the amp buttoned up by Wednesday evening, so I need to put in some hours playing through it. Tragic, I know... ;-)

Any comments, observations, or advice about the burn-in process?

Thanks!
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martin manning
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Re: ODS Clone Bias Question

Post by martin manning »

I've had mixed experience with so-called matched tubes. If they are within a couple of mA that's reasonable (5%). Never bought burned-in matched though. I'd put a few hours on them and recheck the bias.
kevster
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Re: ODS Clone Bias Question

Post by kevster »

Thanks for the feedback.

Yeah, the first PI adjustment was noteworthy too, as you might expect. Using Gil's method, I bounced back and forth over parity three times. I'm within 1-2V. This too will likely change a bit as the tubes burn-in anyway. It's still outside the cab for a reason...
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drew
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Re: ODS Clone Bias Question

Post by drew »

kevster wrote: Wed Jul 26, 2017 2:27 am Hours? It was "on" at least 3,500. Maybe as many as 6,000. It is actually about 5.5 years since I last had it on the bench...

Almost three straight years of that was every weekend (50+ per year), plus some time during each week.
Pretty impressive reliability there. Is this one you built, or did Ceriatone assemble it? Was it being moved around all the time, or sitting in one place? Road case or no?
kevster
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Re: ODS Clone Bias Question

Post by kevster »

drew wrote: Sat Jul 29, 2017 6:05 pm
kevster wrote: Wed Jul 26, 2017 2:27 am Hours? It was "on" at least 3,500. Maybe as many as 6,000. It is actually about 5.5 years since I last had it on the bench...

Almost three straight years of that was every weekend (50+ per year), plus some time during each week.
Pretty impressive reliability there. Is this one you built, or did Ceriatone assemble it? Was it being moved around all the time, or sitting in one place? Road case or no?
An honest answer to each question could appropriately be, "yes." I got an assembled Ceriatone Kit, and installed my tubes and transformers. I built everything else, to include a matching Thiele cab. I bought the C-Lator assembled.

Regarding the routine: About one year of that was static at one venue, and the rest required humping the rig in and out. I have my rig on a flat furniture dolly, so it is a breeze except for in and out of the vehicle. I had to reassemble the cabling for the rig several times during that timeframe, but the amp chassis and C-Lator never left the cab after the first couple months when I replaced a damaged Standby/Operate switch on the C-Lator. No road case, but I'm a pretty careful guy...

I built my cab with two rack spaces in the bottom. I had a TC Electronic G-Major II in it with the C-Lator, but I replaced that with a power conditioner, as well as an X-blender, reverb pedal, and Boss DD-500 between the tubes/trannies and the top of the power conditioner. By doing it that way, the amp is self-contained, or it can be midi-controlled with a rack and ground control pro for higher production gigs.

Here's a picture of the rig right after I moved to where I am now (with the power conditioner in it): Image

And from a few years ago: Image

And, yes, that is a 1958 Hammond Leslie speaker and RT-3 next to the amp in the stage photo...

And the oversized Thiele includes storage for the cabling, and it is extra-deep as I have a "built-in" Sennheiser e906 in the cab. Easy/fast set up!

Of course, it appears that the forum may have rotated the attachments when they uploaded or posted... Sorry.
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pompeiisneaks
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Re: ODS Clone Bias Question

Post by pompeiisneaks »

kevster wrote: Sat Jul 29, 2017 8:08 pm

Of course, it appears that the forum may have rotated the attachments when they uploaded or posted... Sorry.
That's just some weird bug with the mini format in the forum itself, if you click the link it shows up normally...

Weird I know.

~Phil
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kevster
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Re: ODS Clone Bias Question

Post by kevster »

martin manning wrote: Fri Jul 28, 2017 10:03 pm I've had mixed experience with so-called matched tubes. If they are within a couple of mA that's reasonable (5%). Never bought burned-in matched though. I'd put a few hours on them and recheck the bias.
So, in checking the bias this evening before I put it back in the cab, I have 37.1 and 37.3 respectively. It's just under 62%. The values tightened up after putting some hours on the new tubes. I can live with that!!!!

Thanks for sharing your experience.
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martin manning
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Re: ODS Clone Bias Question

Post by martin manning »

Great! Good for another five years ;^)
kevster
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Re: ODS Clone Bias Question

Post by kevster »

Yeah, I doubt that these tubes will last all that long. I'll replace the tubes a whole lot sooner going forward. The meter will tell the difference.

The amp sounds great after another 20+ hours of tube burn-in. The amp has got more bloom now than EVER. I'm getting some very musical bloom at conversation level. Over the weekend, I had the speaker cab in the wings stage-left and pointed diagonally toward the back wall of the stage (giving me indirect projection/monitor for when the sound man screws up and doesn't unmute the band in time...), so about 25' from me and my guitar. I never heard any noteworthy bloom during that, but it was obvious how much the extra hours on the tubes had sweetened them up when I reconnected the rig at home and tested it at typical TV volumes. I wonder if another 20+ hours of time on these tubes in the next few weeks will make any additional difference? I thought that they'd be ready for the weekend as I'd probably had 30+ hours on them by Saturday, but SURPRISE!
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