January 24th, 2012, 01:02 AM
Interested in recreating a Silvertone 1481 with vintage spec Mercruy Magnetics transformers.
I love that dirty Jack White tone and want to get something along those lines at a much lower wattage. I already have a hot rod deville which is great but I can't crank it on stage, it is just too loud. So I was thinking use that for cleans and crank this on stage.
January 24th, 2012, 01:41 AM
I think the 1481 is a great amp. It doesn't sound the same as the 1485 that Jack uses. the lowest wattage silvertone that does sound close to it would be the 1483 with the speaker choke removed(basically what makes it a bass amp). it doesn't have the reverb or trem but the overall sound is there.
January 24th, 2012, 05:17 AM
I was pretty sure it wouldn't be quite the same, different circuit etc. I thought about a 1483 with the choke removed, not that fussed about reverb and trem anyway. They would be nice but I will build some nice external units if I want them. The reverb in the 1485 sucks anyway. I love Jack but I still want my own sound and I have heard some clips of the 1481 that sound pretty awesome. Good wattage for practice and cranked amp on stage.
I am really tempted to do the 1483 mostly because of the two channels but I think it will be too loud for really cranked sounds on the small stages I play on.
January 24th, 2012, 05:19 AM
Don't spose anyone knows what the secondaries would be on the 1481 power transformer? Also if someone could explain how to calculate the secondaries needed that would be great. I don't really want to just buy Mercury Magnetics replicas.
January 24th, 2012, 10:13 AM
The 1481 has a very simple primary transfomer. It has one primary winding and two secondary windings.
The MINIMUM required outputs of the secondary for a 1481 design are;
1.) B+ supply
One centertaped step-up secondary winding putting out 185-0-185 (370 volts AC) no load. That's a winding ratio of 3:1 on modern 120vac line power. Using a 6X4 rectifier tube and a 6V6 loaded class A and including the draw of the preamp tube, your B+ at the first filter stage should draw about 40ma total, and 35 ma at the frist stage. That means a drop down to about 330-345 volts DC at B+ plate supply. This amp is class A so that load will be constant.
Note that this value is the same B+ value as the 1482's power section. (no voltages are listed on my 1481 schematic...but I wouldn't be surprised if the 1481 Class A and the 1482 Class AB1 amps are the same transformer. This would be typical of Silvertone ) and 345 is certainly fine for a 6V6. drawing 35ma, it should make about 6 watts with 12 percent distortion.
The other secondary winding you need is:
2.) Filament supply:
One filament tap wound to supply 6.3vac +/- 10% at 1.32 amps load. (The transformer winding company will understand) A 2 amp filament rating would be good for reliability (You need a little safety margin here) Be sure to specify your expected filament load at 6.3 vac. Exact filament voltages are very critical to long tube life. Silvertone didn't care so much; You will since you are going to put NOS tubes in this thing (you ARE going to put NOS American tubes in her, right? :-)
Now, if it were me getting a custom transformer wound, I would go ahead and specify an extra 5V filament tap as well, just in case you wanted to use a 5Y3 rectifier instead of the 6X4.
That's it. Should work fine. Specify your desired mounting style ("through chassis" or "on chassis" mounting) your lead lengths, and you should be ready to solder.
January 24th, 2012, 02:54 PM
Thanks for that.
Of course NOS American made tubes! :) Hopefully I won't blow them up.
So this would be an appropriate PT?
The 369ex one. I need the 240v primary.
I am afraid I have a few more questions. On this person's schematic:
They have higher voltages on the transformer secondary, namely 250v on each plate. Why is this?
Secondly, How have they calculated an input impedance for the output transformer of 6.6k ohms? Also would a 7k ohm transformer which I have easy access to be close enough for rock and roll? I could of course use the Hammond 1760H with a 6.6k ohm primary but that is a lot of iron for a very small amp and I am paying for a centre tap I don't need. Could use it in future amps maybe :grin: The more iron in the output transformer, supposedly the tighter the bass yeah? Also wouldn't burn when pushed like the original Silvertones.
January 26th, 2012, 06:50 PM
January 26th, 2012, 07:41 PM
Could be worthwhile watching Fleabay as chassis for these do come up periodically and would probably be cheaper that trying to put one together from parts. Consider the 1482 also about 14 watts, in a solid cab theese roar.
January 26th, 2012, 08:01 PM
I built a 1482 clone in a solid cherry cab. Used Heyboer trannies. Wonderful little thing!
January 26th, 2012, 08:24 PM
What were the values on the heyboer transformers?
January 26th, 2012, 08:30 PM
I used the ones spec'd for a tweed deluxe. 5y3 rect, worked out great.
January 26th, 2012, 08:37 PM
Still think I am going to go with the 1481 so I might have to do some maths to calculate primary on the output transformer. Usually a 6v6 demands about 5000 ohms in class A but for some reason the aforementioned schematic has 6.6k ohms and I am worried I have made a mistake.
January 26th, 2012, 09:53 PM
Those old silvertones do sound nice. Really crappy pasteboard-like cabs and speaker baffles and thin very bendable chassis, though. I have worked on a couple, totally rebuilt a 1482 someone tried to make a PA (or something) out of. The 1482 had a replacement speaker with a HUGE ceramic magnet that pulled almost all the screws through the baffle. A nice wood cab and you would have great handwired amp.
Interesting how an artist can make a forgotten amp popular (and expensive). Before Jack White, no one would be could dead playing one (or at least admit it, that I knew of). I can remember when Stevie Ray made the price of a vibroverb double.
I was in a music shop back in the 70's. There was an old Fender Tweed deluxe sitting in the corner for like 50 bucks. The guy said to me, "You don't want that thing, too much distortion, we took it on a trade". What goes around, comes around. Keep your bell bottoms guys, they'll be worth a fortune some day.
January 26th, 2012, 11:32 PM
7k primary impedance will be fine for a 6V6 run at 345 B+ IF it is a purpose built SE transformer.
You'll want a purpose built SE transformer, not a PP transformer with a CT. PP trannies are built differently, and do not function well when used as as SE transformers. This is because they have no air gap built into them to minimize transformer core magnetism - since by nature the center tap design neutralizes the excess magnetic field in a PP design, it does not need the air gap typical of SE transformer.
Yes, the 369EX tranny will be ideal. Has a bias tap you won't need, but that won't hurt anything.
Sounds like fun! Build away!
January 26th, 2012, 11:54 PM
Thanks for all the help guys.
I am still looking into pt's because I am trying to find one at a reasonable cost that does the hight voltage. There is a nice and cheap Amp Maker transformer but it only produces about 250v once rectified, usable but I would like to run it a bit hotter. I am only 17 so I have no first hand experience from when Silvertone amps were considered second rate amps but personally, I think I probably would have always like that nasty garage rock sound. Even back in the day I think I would have liked it and a Silvertone would have been one of my choices to achieve it. Even before Jack made it famous.
Definitely going to build a proper cab though, this thing needs to take a bit of abuse. I am going to stick a Jensen reissue P12r into it.