Silvertone 1391 Project

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by SLBlues, Jan 28, 2008.


  1. SLBlues

    SLBlues Member

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    So instead of building an amp kit, I decided to get this 1391 and learn a little about amps while resurrecting it. I should have checked on the availability of schematics because I can not find one anywhere. Help? The amp does work, but, the volume is very low even for a 5 watt output IMO. I assume all the caps need to be replaced and want to do that. I am having some difficulty identifying the resistor values, especially what watt resistorss to use. I want to update to a grounded power cord. I have attached a couple of photos for you experienced guys to check out for me. A quick search for caps did not find all the 600V caps needed. Any ideas of sources would be appreciated. Does the Planet Lyticap 2x10 450V need to be replaced with the same thing or can I use two 10uf 450V caps in its place? And the Sangamo Dry 50mfd 25v can I just use a 50uf 25V Sprague Atom? The two components with the ??? I assume are resistors? What type are they? Thanks for taking the time to check this out.

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  2. Jaybird03

    Jaybird03 Member

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    This is a schematic for a Silvertone model 1392. Often the models that are close together are very similar. It is possible that the difference in the 1391 and 1392 was only in speaker size and price. The tube complement is the same in this case. Good luck! I have 2 Silvertone amps that I really love.
    http://www.schematicheaven.com/bargainbin/silvertone_1392_1956-58.pdf
     
  3. SLBlues

    SLBlues Member

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    Thanks, JB, however, the 1392 has 2 6v6's power tubes and 12ax7s instead of a single 6V6, 6X5GT and a 6AU6 in the 1391. A Silvertone 1481 is closer to the 1391 but still not exactly the same. Can anyone tell me if the resistors are 1/4, 1/2, or 1 watt?
     
  4. PRNDL

    PRNDL Member

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    Don't worry. It's a single-ended amp. You can't get much simpler than that!

    If we compare this with the well-known Champ, we'll find that the 1391 has only one gain stage from the 6AU6, whereas the Champ has two with a 12AX7.

    The solution is to replace the 6AU6 with the 12AX7 and add another gain stage.

    Of course, since many of those companies are no longer in business.

    At this point, you'll want to figure out how to proceed.

    Many people replace all of the components (resistors and capacitors), and others like to use the old ones to retain the original tone (and save money).

    You could keep the point-to-point wiring and put in some or all new components.

    It's also possible to put in a Champ circuit board with all new components, which is easy to do and almost guaranteed to work without much hassle. You'll have to take careful measurements to make certain it will fit.
     
  5. jh45gun

    jh45gun Member

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    If it was me I would buy a preloaded 5F1 champ board from Ken @ Turretboards.com (now called Watts) http://www.turretboards.com for 65 bucks and learn from that. That is what I did for a 5e3 build and a old zenith chassis from an old mono phonograph. The amp works great. What you will have to do is measure to make sure the board will fit which it should and order 3/4 standoffs so the board will fit over the tobe sockets. With out looking it up I do not know off hand how many pins that 6au6 is so if does not fit into a 9 pin socket then you need to get one of those to and replace the socket so a 12ax7 would fit. That way you will have a champ clone for little money and for a first build an easy project. All you would have to do then is wire the heater wires for the new tube socket and then follow a champ layout to wire the board in and hook up the pots,jacks ect. Just my opinion but I decided to do this for my 5e3 build instead of buying individual parts or a complete kit and I found this was easier to do and not that costly. It makes it nice if you have the chassis and iron and tubes/sockets already which you do compared to having to buy a complete kit.
     
  6. Jaybird03

    Jaybird03 Member

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    I reloaded a Silvertone 1430, which had no power transformer with the circuit from the Kalamazoo model 1 and the amp is really sweet sounding and looks great in the old Silvertone cab. I stayed with PTP and was able to fit it on the existing Chasis.
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  7. SLBlues

    SLBlues Member

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    Thanks for the information guys. Installing the Champ Loaded Board is an interesting option. What other components would have to be replaced to make that deal work? Can I retain the original PT and OT? What about the
    6X5GT tube?

    What about just replacing the 6AU6 with a 12AX7 and putting in some new caps?

    Thanks for your help and suggestions.
     
  8. jh45gun

    jh45gun Member

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    Yea the origional OT and PT should work it did with my project I would have to look at a champ board. The Champ amp takes a 5y3 rectifier not sure if yours would work or not maybe some one else can let you know on that. From what I see on the layout the only thing you would need for extra parts is a 1 meg resistor for the input jack to ground and the volume pot is 1 meg and it looks like it has a switch on it too for the power though I would suspect you could wire a normal 1 meg pot and use a separate on off switch. Otherwise every thing is on the board you need. Like I said you would need to order some 3/4 inch standoffs to keep the board above the tube sockets also. 4 of them and I had Ken drill 6 holes in the board instead of 4 so I had more mounting options since you are mounting it on a chassis that is not designed for that board. I had no issues finding a suitable place to drill enough holes to mount the board and from the looks of that chassis you should not either. PRNDL said you could use the champ board so I would think your rectifier would work or he would have said so. I would ask PRNDL to be sure.
     
  9. DefaultII

    DefaultII Member

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    Actually, what you should do first is fix the thing and then decide if it's necessary to build a Fender with it.
     
  10. DefaultII

    DefaultII Member

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    [​IMG]


    Remove the cap soldered to the fuseholder. Replace the two conductor cord with a grounded cord. Replace the electrolytic caps with new ones. Two 10 mfd, 450 volt caps are fine. Replace the 50 mfd 25volt cap with the same. Remember to drain the filtercaps (the 450 volt ones) by grounding the positives with a screwdriver. I guarantee that it'll be safer and sound better after this, and it'll be cheaper that ruining the collector value by Fenderizing it. If you really don't like the tone, look for a harp player. They love amps with lower amplification in the front end.
    Tubewise, a 6x5 is not a 5y3. there isn't likely to be a 5 volt winding on this power transformer. No 5 volt winding = cheaper tranny.
     
    Last edited: Feb 16, 2010
  11. Jerry Glass

    Jerry Glass Member

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    I'm going to agree with DefaultII and suggest that you just recap the amp and go with that for now. Leave the existing resistors and coupling caps in place unless they need to be replaced. You will need two 10uF @ 450 volt electrolytics and a 50uF @ 25 volt electrolytic. Both are stock Sprague values and can be sourced from Mouser as well as several other sources.
     
  12. DefaultII

    DefaultII Member

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    Make it easy on yourself, if this is going to be your first project! Incidentally, it looks similar to the silvertone 1331, with the exception of the 6au6 being subbed for the earlier octal pentode. It even has that funky trimmer capacitor that yours has. http://www.schematicheaven.com/bargainbin/silvertone_1331.pdf
     
  13. Keyser Soze

    Keyser Soze Member

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    The 6AU6 is a 7 pin mini tube, you would need to open up the hole in the chassis to sub in a nine pin. You could probably run a champ board off of the voltage supplied by the 5x6, but overall I'd agree with DefaultII - there is no reason to trash a perfectly good amp.

    You also probably don't need to mess with those blue coupling caps - at least wait until you replace the electrolytics and the power cord.

    If the amp still doesn't sound good after that, then start looking for other issues (those tubes might be suspect also.)

    I have a Champion 600 clone (not a re-issue) it is a 6V6 single ended amp with one 6SJ7 tube (pentode, but wired as a triode) so it is somewhat similar to your amp. Mine is really only about 3-4 watts tops, and does not break up with single coils even when dimed (does get pretty thick though). One gain stage into a single power tube is going to sound very tame as compared to a Champ.

    Cool little amp.
     
  14. donnyjaguar

    donnyjaguar Member

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    Silly question, but is this amplifier useful for anything? The size of that output transformer looks a little small to be of much use for anything.
     
  15. DefaultII

    DefaultII Member

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    Yeah, it's an economy model tranny, but since you are only pushing maybe four watts through it, you don't need a big'un.
    Remember, these were the cheapest amps you could get at the time, so, if it made a noise, that was good enough.:D

    Good for us, because we can crank it at midnight and not tick off the neighbors
     
  16. Trout

    Trout Member

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    A heck of a lot of famous recordings were made by famous musicians with nothing more than a 4-6W amp. So, I would say heck yes as far as useful.

    If all else a good practice box.

    Antique Electronics has a dual section 10/10-450V for under 10 bucks should you want it to look semi original, part number [FONT=Arial, Helvetica, sans-serif][SIZE=-1]C-ET10-10[/SIZE][/FONT]
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    or as mentioned above, just use 2 Spragues.
    Same thing with the 50uf/25V<- I would use a 50uf/50V just for a better safety margin.

    The part labeled Arco 462
    is a mica trimmer capacitor, Arco 462/ GMA40200 10-80 pf $2.10
    This might be a source

    Part labeled ??? 2
    appears to be the cathode resistor 270 ohm 5W. Most certainly I would replace it along with the bypass cap. Those old long resistors drifted like crazy even when they were new.

    Part labeled ??? 1
    It looks like a 2.2M 1W, hard to tell in the photo on my crappy monitor.

    It will be a fun project, if it sucks, just sell it to a harp player, they blow anyway :rimshot
     
    Last edited: Feb 16, 2010
  17. Rockinrob86

    Rockinrob86 Supporting Member

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    Im going to give you some advice.

    You have a cool amp there, and a really simple amp there. Before you move forward at all, you need to learn more about amps.

    If I was you, I would pick up some books.

    My first book was this one http://www.amazon.com/Desktop-Refer...=sr_1_4?ie=UTF8&s=books&qid=1266379420&sr=8-4

    If you read through this and think about it, you will learn alot about your amp and how to troubleshoot it. You will not have questions about what wattage resistors you need for what section of the amp. You will know what capacitors need to be replaced. Many of those old caps will still be working fine. You need to know what kind go bad, and how to measure caps.

    The project you have is a very easy one to get that amp working right, if you learn some basics. Working on tube amps is far from rocket science once you get the basics down.

    and please dont convert that thing to a champ. There are only a certain number of those quirky old silvertones. There are infinite champ clones. When you learn more about amps (and build a champ for fun sometime. Maybe even out of an old tube radio, tv or something like that. many of those have the right transformers to do it) you will be glad you have that cool silvertone that you started on.
     
  18. SLBlues

    SLBlues Member

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    Wow, I had no idea this thread had been resurrected from 2008. I apologize for not responding to everyone in a timely manner. I still have this amp an have done nothing at all with it....yet. Thanks for all the great information on components and sources for them. I will get busy and order the stuff so I can get this thing up and running. Thanks again.
     
  19. Rockinrob86

    Rockinrob86 Supporting Member

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    btw, the book I listed doesnt cover your amp, but it talks about amps in general.

    I also ordered the tom mitchell book, and thought it was good, but it wasnt as useful to me as the weber book.

    This one was also very useful to me http://www.amazon.com/Guitar-Amplif...g-Amplifiers/dp/087930863X/ref=sip_rech_dp_10


    I think it also may help you to go through another amp you have that works, especially if it is pretty simple. I have a clark 5e3 deluxe, and I found that by looking at the schematic and following the wires in that amp I was able to piece alot together about how amps work
     
  20. SLBlues

    SLBlues Member

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    Thanks, I have the Dave Hunter book and have already ordered the Weber book as you suggested. I also have a 5E3 clone (Richter) and will have a look at it with a schematic when time allows. All this tube stuff is pretty interesting in that we studied vacuum tubes and their theory and operation in my HS Physics class(1961). As I remember I did very well with that stuff. However, most of it is long forgotten. I do not want to modify this amp from original. Just replace what is necessary and get it operating correctly. Thanks to everyone who has chimed in with information.
     

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