Grey Bell Stancor A-3801 clone by Mercury Magnetics

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geetarpicker
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by geetarpicker »

You mentioned that MM took apart your original 3801 to clone it, then rebuilt it. That said, do you have an original grey 3801 that was never pulled apart or "rebuilt" for a true comparison to the new MM 3801 clone?
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by RJ Guitars »

Geetarpicker, I have a pair of Triad S60-A output trannies that I believe are identical and original. Apparently they all came from the same factory somewhere in the midwest if I remember it right. I am suspect that the rewind on my original could make it perform differently, although not necessarily in a bad way. I also have a black A-3801 that is in an old Bogen PA amp that was modified into a guitar amp and sounds really awesome - very clean and loud. If I need to, I'll pull it and test it in this platform as well.

This whole testing process has me really scratching my head. I am working over the Pacific part number 11415 tranny now and it's much more like the MM and first Heyboer I tested, but still has it's own character. I'm certain I'll have to establish some standard test points and make recordings to keep this evaluation credible. I can move the amp settings around and get great sounds and often even get similar tones from each of them, but at a standard baseline setting each gives me a unique result with each of them.
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by Jackie Treehorn »

RJ Guitars wrote:
M Fowler wrote:rj do you really believe the Rocket used 500vct PT and 5k OT?

You know I have no knowledge either way just wondering. :)
Mark, for me the reality of studying Trainwrecks is that it can be a deceivers game and occasionally I find I have misinterpreted the facts and on other occasions I find I'm in pursuit of a red herring. Making mistakes is critical to learning and I've found that even when we chase red herrings we learn something. Either way bits of the truth eventually make their way to the surface.

The thread on Rocket power transformers that is going now ( http://ampgarage.com/forum/viewtopic.php?p=302766 ) has identified that more than one PT was used in the Rocket and to the best end I can sort through all the info, it looks like the AC voltage was somewhere between 500 and 520 volts, depending on which Rocket your talking about. One interesting observation I've made is that the same resistor dropping string was used (18.2K - 9.1K - 9.1K) on all the Wrecks I've had a look at. That is a pretty limited data set...

We probably need to run a thread on just Rocket output transformers... One consistent item identified in Rocket OT's has been that the Rocket used a Dynaco 470 or modified versions of the Dynaco 470. The 5K primary impedance has not been confirmed anywhere that I have found yet. Here is a note I posted on another thread earlier today:
"I have talked about building the ultimate AC-30 with Chris Merrin before and he gave me some transformer thoughts to mull over. Firstly, he doesn't want to lean on or market his connection with Trainwreck in any way. He was really clear that he didn't want to make any money from Ken Fischers work... then we got down to talking about transformers and AC-30's. He defined a sweet spot in the AC-30 tone with a B+ of 305 to 310 volts when combined with an impedance of 3.7k to 3.9K on the output transformer. There was a very clear connection in finding the sweet spot based on this relationship of values. I am not saavy enough to sort this out in my head but suppose it could be done mathematically to verify and understand why this would be true. Up to this point I was thinking that the amp might benefit more from a slightly higher OT impedance... but based that mostly on KF's preference of a higher impedance OT for his high gain amps."


So I believe 500V is on the low side but still appropriate for the Rocket PT and 5K is a just a good conservative starting place but is not based on any actual measurements.
Ken did have a Pacific transformer made up with the 5 volt tap. I had to search an old post of mine to get the numbers...

"I've posted about this before, but 5 or 6 years ago I bought a Trainwreck power transformer off of Ebay. Apparently, Ken gave it to the person I bought it from to repair one of his amplifiers. It's slightly smaller than the Heyboer 260v/300v transformer and I've suspected that if it was ever used in a wreck, it was probably the rocket. So, I stuck it in my rocket build.

It's got 300v, 275v, and 250v taps, and the center tap, (technically 600v, 550v, and 500v, I suppose) at 250ma. 6.3 volts at 5 amps and a 5 volt winding of unknown capacity. It also has a wire to the copper ground shield which I thought was unusual.

It has two numbers stamped on it. 00249 is visible on the copper shield and underneath the Trainwreck sticker, is 10421, which seems like it might be a Pacific part number since the output transformer model is 11415. "

When I stuck it in my rocket with the 250 volt tap, it came right out at 300 volts.
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by RJ Guitars »

I have a photo here somewhere of an amp with Heyboer transformers with part#s 11415 & 11410... I'll see if I can find it. I thought that was very odd myself. You can typically tell the Heyboer from the Pacific by the end bells. Heavy end bells with strong feet are pacific, thin are typically Heyboer and everybody else except MM...

I found the amp with that tranny... it's in my first Rocket build and it's an output tranny??
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by Cantplay »

I asked about the steel, because when i've used Magnequest chokes they have an option for high nickel steel(more money)

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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by RJ Guitars »

as I was pondering this over it occurred to me that I haven't checked much less reset the bias with each transformer swap... *%&#!$ ... :oops:
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by rooster »

Hey, this is a great post, RJ! I for one very much appreciate your efforts/desire to search the depths of the this OT 'thing'.

As to the re-biasing, eh, I don't think - considering the fact that these are all 6600 ohm primary clone OTs - that the bias would be that affected. Did you find much variance? I also wonder if there is any sonic difference with the MM products - the version that includes all the taps vs. one that does not. I guess here I am just wondering if I could actually hear a difference. :lol:
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by RJ Guitars »

Yeah, I am in the middle of a really big experiment at work and haven't been able to get back to this... but mostly I was just embarrassed because I didn't check the bias. I dunno how big a difference it will make yet?
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by Zippy »

RJ Guitars wrote:Yeah, I am in the middle of a really big experiment at work and haven't been able to get back to this... but mostly I was just embarrassed because I didn't check the bias. I dunno how big a difference it will make yet?
Just A/B the last one that you put it there. Measure the bias before and after you adjust it, then listen. If there's little/no difference, don't break a sweat. It's OK to be compulsive (at least that's what I've told myself), just recognize that some of the small stuff really doesn't matter - and isn't audible, tangible, or otherwise significant. You do great work.

I'm swamped today too. Let's meet later in the week and decompress over some coffee.
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by RJ Guitars »

I finally got out from under the work pile for a bit and ran some more tranny tests... resetting the bias does not significantly redefine the character of the individual transformers so that was a huge relief. I have run the last couple trannies at -32 volts and it didn't take any tweaking of the knobs between the last two trannies to keep it there.

I ran the Pacific 11415 original TW spec and it was easily the worst of all I've tested. Initially i struck me as harsh and colorless... basically uneventful. It was in there when I sorted out that I hadn't been changing the bias so I ran it at several bias settings... that only made a small audible difference. It was so radically different sounding than the K&M Analog 25575 that I actually called Pacific and talked directly to an engineer. He verified that they are absolutely identical in materials and fabrication technique. I have a whole box of the Pacific original part# TW trannies and I won't be surprised if every one sounds unique... and hopefully most of them sound better. I left this tranny in the test system for most of the last week and as I have played it it has loosened up and is starting to sound much better, but still nothing close to as good as the first Heyboer HTS-9384 I tried and the Mercury Mag - those are the top two going right now.

After that I tried one of my Edcor EM-0721 OT's and it sounded quite nice. I would characterize it as "focused and jangly" and is a great candidate to clean up amps that tend to get muddy. It does not have the low end fullness of the Mercury Mag but is really a pleasant sounding unit.

I've got a decent comparison chart that I'll get posted up this weekend.
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by rooster »

RJ, Ha! Man, are you kidding me about that Pacific 11415? :lol: The one I bought from you recently is awesome, to my ear anyway. But this reminds me of a conversation I had with Gregg Levy not too long ago. He stressed that Kenny would order his OTs in sets of 10 and then have a friend come in and assess them for magnetic voodoo. The man changed and eventually Gregg became #3 for a brief time. All were described as having the 'touch' to sense something different regarding the magnetism of the OT.

So this is odd, but as I thought about it, if the manufacturer fired these individual pieces up for test - putting a current through them - then its possible the steel would have a slight magnetic charge to it. And make no mistake, using a magnometer of the type used to check for magnetism used in studios with tape machines, a used OT will easily display a magnetic field. But what if they didn't put current to them? Well, then I think they would just arrive as steel and copper - no magnetic charge to them. So is/was every piece given a current test? I dunno. After use in an amp however, an OT will be magnetized. Will it change it's character? I dunno.

OK, another added note from Gregg, is that Ken decided that 1 in 10 of these new arrivals to his shop were what he considered the 'Best', and then there were typically 2 more that were 'pretty good'. Which then left you with 7 duds. :cry:

I'm not making this up. I was also told that Ken did blind tests on the results of these hands-on magnetism voodoo assessments, loading/attaching the various OTs into a prebuilt amp and letting his shop friends/visitors make the call, blind testing them. I was told there was a discernible and notable difference that all there could and would agree on - it was always obvious apparently.

What do all of you think about this? :?: I, personally, am on the fence. I see electricity as very logical. However, I am not so sure about an OT. 8)
Last edited by rooster on Thu Jun 26, 2014 10:40 pm, edited 1 time in total.
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by redshark »

Very interesting Rooster!!

I like this type of stories. Always add some mystic to the trainwreck legend! :)
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by RJ Guitars »

I've heard these kind of stories too... that is why it's hard to figure out how good KF really was technically. I believe physics will explain it all but the challenge is to find somebody who can explain the physics. I do find some merit in transformer breakin artifacts, but this particular unit started out way more stiff and lifeless than any other so far. I'll need to try a few more samples before any of it is meaningful. That's always the first step in publishing good science... if you can't repeat it then it's kinda like it never happened the first time.

since the last report I installed one of my vintage TRIAD S60-A OT's (same as Stancor A-3801). It sounded very similar to the Stancor that MM rewound as well as the Pacific K&M analog unit.... decent sounding with a lower saturation threshold.

I have about a half dozen left to test then I'll do some repeats.
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by Zippy »

rooster wrote:But this reminds me of a conversation I had with Gregg Levy not too long ago. He stressed that Kenny would order his OTs in sets of 10 and then have a friend come in and assess them for magnetic voodoo. The man changed and eventually Gregg became #3 for a brief time. All were described as having the 'touch' to sense something different regarding the magnetism of the OT.

So this is odd, but as I thought about it, if the manufacturer fired these individual pieces up for test - putting a current through them - then its possible the steel would have a slight magnetic charge to it. And make no mistake, using a magnometer of the type used to check for magnetism used in studios with tape machines, a used OT will easily display a magnetic field. But what if they didn't put current them? Well, then I think they would just arrive as steel and copper - no magnetic charge to them. So is/was every piece given a current test? I dunno. After use in an amp however, an OT will be magnetized. Will it change it's character? I dunno.
If you pass DC current, then yes, I'd agree that you could influence the volume fraction of aligned magnetic domains. If, however, you pass AC current, that would randomize the domains, leaving a residual magnetic bias due to hysteresis. Which is preferable?

It would be interesting to read the magnetic character of a new OT and compare that with measurements taken after "break in" - especially if one correlates an audible change to the OT only.
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by rooster »

Zippy, yeah, where's a lab that would do this?

BTW, this is the magnometer (more correctly called a 'magnetometer'!) I was referring to. It shows N and S and can also show gauss strength. Every studio using tape had one in the day. The transformer in the pic is a used ToneSlut example...
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