Grey Bell Stancor A-3801 clone by Mercury Magnetics

Express, Liverpool, Rocket, Dirty Little Monster, etc.

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

Post by RJ Guitars »

M Fowler wrote:
redshark wrote:RJ I hope the specs of the PT are according to the specs of the Stancor P-8378 cause then that will be a PT that can be used with rocket, express or Liverpool!! including the recto 5v tap.

:D
Yes that Stancor has dual HT secondary and would work well.

One thing I do not find when thumbing through the Stancor transformer book is a PT that does not have a 5v filament winding except for vary low mA rating PT's.
you guys are onto something interesting here... It sorta looks like if a guy had a STANCOR P-8378 power transformer he would indeed have the one size fits all Wreck transformer. I don't have the hard evidence to support it but I wouldn't be surprised if this is what was used or similar to what was inside those early Rockets...

One thing that I did hear from my TW history connection was that the STANCORS were not consistent in quality and some had a tendency to overheat. This combined with the fact that they were no longer in production would be good inspiration for KF to work with Pacific to develop the standard Wreck trannies we are familiar with now. I just can't figure out any reason why he would not have had them add the 5V tap, but maybe it would make sense if I knew the whole story??

In my discussions with Patrick at MM in cloning the A-3801 tranny he did mention that it was not really a very well made transformer. Might explain the reason why KF said he would listen to each one and sort them by their characteristic sound - something like "bluesy, jazzy, etc.."
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by RJ Guitars »

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

Post by hitchcaster »

vox are kinda like tweeds In that modern voltages seem to not be be the sweet spot...... some builders of vox are hip to this and order vox PT's that account for this and aren't exact clones.... but give the B+ you would of gotten back in the day
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Mercury Magnetics rj-3801 clone is here

Post by RJ Guitars »

Finally, It has arrived.... I received the prototype Output tranny from MM and finished my test platform just in time to give it a listen. I built a test platform just for quick swapping amp modules or transformers and it turned out to sound excellent... http://ampgarage.com/forum/viewtopic.php?t=25030

From the onset it was a very good sounding tranny. The amp sounded great with the previous Heyboer OT and the MM did not disappoint in any way. Ultimately, I'll make up a thorough table or some sort of comparison graphic since i have about 10 different OT's to test. However, in the meantime, the MM passed the first set of tests with flying colors. Briefly I'll say it is a strong full sound and added more clean headroom to the Express than I have ever heard. I'll fill in more details in time. Patrick at MM did tell me to run it hard for at least 48 hours and then it would "break in". I'm not sure what all happens but I figure if it means it gets better with time it can only be a good thing. I tried to make a recording of it but my gear was inadequate and I had to order a preamp and USB interface... hopefully I'll get get clips done at some point.

I also received the original Stancor A-3801 that I sent them to clone. After a few hours pf playing through the MM clone, I swapped it out for the original. This might not be a surprise to everyone but it was to me... they don't sound exactly the same. One big difference I identified was that the original did not offer the same headroom as the clone. I'll do more characterization as time allows...

The MM sounds so good that I'm going to go forward with the first large order. Anyone who wants to order one with this first order I'll make them available for $145 delivered in the US. I'll adjust the cost for foreign shipments - I think it will add $35 or $40 to the cost. Several guys have already indicated they want one and I'll leave this option open for a few days if anyone wants to add their name to the list.
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by Mark »

Looks good RJ, I suppose the ticket is to run the amp for those 48 hours and compare the transformers again. Perhaps it is worth looking at some of the comments on the 18 Watt forum, I believe people were trying to clone an old transformer with a narrower bandwidth than having a new transformer. I haven't heard a comparison so it is hearsay.

Which Heyboer transformers have you compared the Stancor and the Mercury transformer to. I've heard the Marstan Express transformer is quite good, was that part of your comparison?

What I find a little odd is Mercury already have a Trainwreck transformer set. Did you ask Patrick how it differs from what they already offer?

No point in reinventing the wheel as they say.
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by Colossal »

Very cool report RJ. Your findings are interesting. I am using Mercury's other OT on my latest build and it too has slightly more headroom, killer full sound, and great clarity.
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by M Fowler »

Nice looking transformers rj, thanks for all your hard work on this.
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by Cantplay »

Just curious.. Same thickness and number of laminations on the core?

Were you given any choices of steel type for the lams?

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

Post by rooster »

Let me ask the obvious, they reproduced the odd-ball taps as well? It looks like they did but I wonder why you had them bother? Was this all about dead-nutz-on clone then?

At any rate, glad to hear about the added headroom. You do need to make some recordings!
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by RJ Guitars »

hitchcaster wrote:vox are kinda like tweeds In that modern voltages seem to not be be the sweet spot...... some builders of vox are hip to this and order vox PT's that account for this and aren't exact clones.... but give the B+ you would of gotten back in the day
I saw this note back when you posted it and was in agreement at the time but got busy and didn't respond back. I do believe it is really true and significant. I routinely get 124 or 125 volts out of the socket here and I'm not sure but what the power quality ( http://www.merrenaudio.com/power_quality ) is better than it was back in the day as well.

Thanks for posting this up initially, it's something to consider when we set out to clone the specifications on a vintage amp.
Cantplay wrote:Just curious.. Same thickness and number of laminations on the core?

Were you given any choices of steel type for the lams?

John
In this case I simply asked them for an exact clone... I didn't give them any specifications although I think they probably have more info than I do on Stancor tranny build materials and protocol. I haven't talked to their technical people yet and I need to run this new tranny for bit before I really know what it's going to sound like... having said that, I'm skeptical that they matched the steel very closely... that can be a complex issue and you'll need a materials scientist to really understand all that matters in matching up the steel specifications... I don't know what they did in that regard. I'll have to look more closely at the two trannies to verify the number of lams but I did compare the stack thickness and it's pretty close. Lots of follow up to do on this for sure.
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by Zippy »

Before we go correcting for "vintage" voltages - what is "vintage"? If Ken was using old design PT, what voltage was he seeing in the day? Do notes exist regarding what B+ voltages he was seeing when designing/building these amps?

If we were rebuilding tweed Fenders, it'd be a slam dunk - or not. Many people prefer the way the amps play with vintage iron at today's voltages. Others would like to replicate the way they were intended to sound "in the day".

Sorry. Sometimes I think too much... :?
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Re: Grey Bell Stancor A-3801 clone by Mercury Magnetics

Post by RJ Guitars »

rooster wrote:Let me ask the obvious, they reproduced the odd-ball taps as well? It looks like they did but I wonder why you had them bother? Was this all about dead-nutz-on clone then?

At any rate, glad to hear about the added headroom. You do need to make some recordings!
Yup, they have all the taps on there. I am not sure what might change if you eliminate them... do they add extra wire at one end or the other to get those impedance's?? So i had them make it just like the original... I know everybody will cut those leads and tape them off.

Yeah, the results have been pretty easy to hear so far and a decent recording would give you the sounds to evaluate for yourself... just don't hold your breath, this is gonna take a while.
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Pacific K&M Analog Output Tranny evaluation

Post by RJ Guitars »

Today I swapped in the Pacific K&M Analog 25525 Wreck OT. It sounded similar to the Stancor in it's early breakup... maybe not quite as extreme. Overall the sound was a bit more complex and I'd say an improvement over the original Stancor. After playing through the MM clone, I would really like to hear this Pacific clean up a bit more so it could be used in more ways than rockin' the house. I know I have heard several really nice clean tones from Geetarpicker on his recordings and the MM reminded me a lot of those sounds where I think it would be hard to get there with this Pacific OT.

I am making up a spreadsheet with all these observations on it. I'll do a more extensive evaluation on each of these trannies before I am done with this project. After that I'll post the spreadsheet on the first page with my original post in this thread once I get it formatted and all the info on it. Right now I am just prepping each tranny by stripping back the leads and tinning them so I can quick swap each one in and out of the test amp.
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clones

Post by angelodp »

rj, you bring up some interesting notions about clones. Metal composition being one, and i would imagine the wire type and guage are also critical. What about glue and coatings. What about magnetic properties and flux patterns. In all things clone, how does one define a clone. I am not surprised that you are hearing differences in the original and the 'clone'. Since I started making pickups I have been amazed at the variations that are possible with a given pickup design, by changing even very small parameters... wind pattern, covers, magnet types, wire, wax, string,,,,, on and on. Hell, every amp I have heard, that you have made rj, sounds great.

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

Post by RJ Guitars »

Mark wrote:... Which Heyboer transformers have you compared the Stancor and the Mercury transformer to. I've heard the Marstan Express transformer is quite good, was that part of your comparison?

What I find a little odd is Mercury already have a Trainwreck transformer set. Did you ask Patrick how it differs from what they already offer?

No point in reinventing the wheel as they say.
I used a Heyboer HTS-9384 in the first test. It is also referred to as the 6.6K vintage tranny.

I haven't talked to MM engineering at all yet... that will be on my list though. I do have one of their TW-KF OT transformers here that I'll include in the comparison.

I don't have a Marstran or the Magnetic Components tranny yet... I just counted and at this point I have 16 different models and lots of duplicates to test.

---------

Yeah... thanks Ange. I am finding that transformer comparison is anything but simple or predictable. Every transformer I have used so far makes this amp sound entirely different... each with a strength and at least one sweet spot, but so far each has been entirely unique. I have duplicates of several of these and I'll be curious how unique each specific tranny of any one part number sounds... then there is that "break in" element, will they still sound the same or similar in a few days, a few weeks, etc..

I just swapped out the original Trainwreck OT from Pacific and it again sounds unlike any of the others. I can't crank it up until tomorrow so I don't know yet what it's going to sound like when I get it revved up.

I recall more than one person telling me of being in Ken's basement and he had a stack of transformers that he'd characterized with individual designations such as "jazzy", "bluesy", etc.. If the same phenomenon is still true in modern production, then it would seem that the actual outcome of an amp could vary wildly depending upon what transformer went in to it... even if we assume that all the other components are equivalent.
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