Silvertone 1484 reverb mod please help!

[chrisq]

hi all!

I found this thread on here:

http://www.el34world.com/Forum/index.php?topic=9951.0

"Silvertone Spring Reverb tank mod:
Use a short 3-spring reverb with 800 ohms input: 8EB2C1B.

First build a tank driver:
Re-wire the reverb driver tube as a follower: remove connections to Pin 2 and wire Pin 2 to Pin 7.
Connect one end of a 1.5uf 250V cap to the cathodes. the other end goes to the reverb tank input.

Now fix the reverb recovery circuit: Jumper the 560K resistor and remove the resistor (and sometimes capacitor) that connect to Pin 2 of the reverb recovery tube. Reason is, these parts make a voltage divider that kills the signal. Install a 220K resistor from Pin 2 to ground as was done in AB763."

I'd really like to do this mod.  I don't know the full values of the parts to order.  what watts, does anyone know offhand?  Also, what is AB763?

So... Which 220k resistor? 

I guess I need a more step by step.  This is summed up quite a bit.

Please help!

[smackoj]

I remember reading about the Silvertone model 1484 in Gerald Weber's tube amp book "All About Vacuum Tube Guitar Amplifiers" which is available on-line and likely on ebay too. On page 211 he has a re-print of an article he wrote titled, 'World Class Vintage Tube Amp Tone for under a Grand" In the article he states that the reverb on these amps (the 1484 and 1485) is very poor and 'cannot be made right without extensive rewiring'  So, I guess if I was to offer advice on your question, I would ask you if you are sure this is what you want to do?  I had the model 1474 for about 5 days and resold it because the materials and hodge podge wiring made me not want to even start on the thing. Seriously, I studied the scheme and other material sources, and all the while looking at the guts, and I threw in the towel on that dude. Weber also notes in his article that a buyer should "avoid" the model 1474 for bias problems and other remarks. I agreed with his thoughts within days.

I would suggest considering adding vibe, trem, dig delay, surf ghosts or what have you via a decent pedal (many avail.) OR, if you want to stick with the building part of a true reverb for this amp, consider a stand alone reverb build such as the Fender stand alone or similar. There is a bunch of top notch help in the 'Archives' here about the stand alone reverbs....lots of members have built them.  There is also some good info in the Archives about the 'One Tube Reverb' which may be an option for you to wedge a different circuit into your chassis? I will defer to the Big Guns who moderate this forum to read your scheme and comment about what types of wiring changes would have to be done to make your amp have it's own spring pan, driver and recovery phase that works properly.  Here is the link to the layout for the stand alone Fender Reverb:
http://www.el34world.com/charts/Schematics/files/fender/REVERB_6G15.pdf

The 'AB763' is a very popular Fender amp design that was considered a Blackface circuit? (they used that same design with different ouput transformers to build lots of famous amps; Super Reverb, Bandmaster etc. ) Lots of home builders use that model for their builds. Those all originally came equipped with reverb and vibrato in the circuitry so that could be another option if you decided to "go long" and build a whole new amp from the chassis up?

I hope this gives you some ideas in your quest to turn that Silvertoner loose.

 

[chrisq]

I'm pretty sold on a 1484.  I'm not sold on the mod.  I don't hate the existing reverb, unlike everyone else.  I play very garage-ish Indie rock (not White Stripes... but The Aislers Set, early Kinks), i'd just like a little clarity and less feed back, i use a Domino Dawson (with Epi p90's) and feedback is already an issue.   

I really dislike footpedals,  and really hate digital reverb (even holy grails).   I use an 60's Olsen Fuzz Master and a tuner.  I really like on board reverb.  I've been playing a '66 Epiphone Electra.  But it is proving to small for some venues I'm playing.  I hate Fenders (i've owned vintage twins, princetons, champs).  My favorite amp I own is my Silvertone 1452 (actually it's my prized position, the Hornet is my main guitar as well).  I wish I could make a 40 Watt version with reverb. 

This just seemed like a fairly straight forward mod that would ad a little better reverb and have it be in the case.  I like the little 3 spring verb.   

I'm also a working musician.  I'm not/can't shelling/shell out as much as an amp for a Fender Reverb tank.

I'm very stuck in the past, I hate new gear.

So does the aforementioned mod look false?

[SoundmasterG]

That reverb thank that they suggest to use is 9 1/2 inches long...where will you fit that in the existing head cabinet?

http://www.tubedepot.com/rt-8eb2c1b.html

If you do a search from a couple years back you will find a thread by me talking about the mods I did to my brother's Silvertone 1484 which included adding the AB763 Fender reverb circuit, transformer, and reverb tank to my brother's amp. In order to make it fit (that was a larger tank than the one your mod suggests) we had to make a new head box that was taller. It works fine and the amp sounds great with that Fender Reverb on it. If I had to do it again, I would probably just build a clone of the Fender outboard reverb as it would be easier and more versatile to use it with other amps that don't have reverb like my AC30. The Silvertone 1484's wiring and layout sux. The stock reverb isn't bad, but is sort of weak and cheesy sounding, and often fails.

Greg

[smackoj]

<This just seemed like a fairly straight forward mod that would ad a little better reverb and have it be in the case.  I like the little 3 spring verb.   

I'm also a working musician.  I'm not/can't shelling/shell out as much as an amp for a Fender Reverb tank.

I'm very stuck in the past, I hate new gear.

So does the aforementioned mod look false? >

What I am trying to say, is that people with much experience say "IT" is not just a 'straight forward mod' to do what you want to do. So, the preparation, planning stage of the mod (where we are at now) concludes that this is NOT going to be simple, one afternoon fix 'em up mod.

Either get the full mod layout and instructions as the fella before me said was avail in the Archives, source the parts and get after it, or think seriously about the Fender style stand alone unit. I say "fender style" to ensure you it is not about building an entire fender amp. If you are low on funds, I could send you a free chassis from an old tube radio you could use for the stand alone. I'll even throw in a couple necessary tubes for the build for free....just pay shipping.....maybe 15 or ? to ship?

 

[tubenit]

I don't know if you looked in the SCH files but there has been a 1484 reverb mod DRAFT idea there for yrs. I attached a SCH schematic that you can use to keep track of mods with your amps.

http://www.el34world.com/Forum/index.php?topic=593.0

SoundMasterG helped me with the original (non reverb) schematic values and drawing.

I probably would the reverb mod as I drew it first and then if that wasn't what I wanted, I'd move it one gain stage closer to the input.

With respect, Tubenit 

[DummyLoad]

tubenit, the 150pF caps you show on top of the bass pot in the tone network are 1.5nF on the original. just wondering if the 150pF shown in the posted schematic are intended use values. lastly, PS nodes B C D are shorted to ground on the B side of the choke.

respectfully,

--pete

[tubenit]

Hey DL,

THANKS for saying something! I am always appreciative of your contributions to the forum! 

I had a terrible awful time trying to read the "original" 1484 schematic on the internet.

IF you would, PLEASE,  can you edit the SCH version attached and correct it any place that it is needed?  I would be appreciative of that.  I've actually never played a 1484 or had the chance to look inside one.

Thanks, Tubenit

[DummyLoad]

...edit the SCH version attached and correct it any place that it is needed

happy to do so. file attached.

--pete

[tubenit]

DL,

THANKS, man!  I always appreciate your help. I'll let the thread run a little longer and then update the SCH file with your correct.

With respect, Tubenit

[DummyLoad]

I've actually never played a 1484 or had the chance to look inside one.

they sound decent. 

Silvertone 1484 + 1446 Cris Isaac Model Demo01

their guts are nasty - typical danelectro.

pic search

[chrisq]

hi!

Thanks for all the info!  I took apart the stock reverb.  One of the contacts that the springs sit on had come loose.  I glued it back, change the tension of the spring and reverb!  The best sounding I've heard on one of these amps.  I think the spring being tightened cleaned up the wateryness a bit. 

Now i'm in another pickle.  I'm trying to put a 3 prong plug.  I know what the modern plug ends are, i know the green goes to the transformer bolt, i DON'T know which is which on the original plug.  Also in the photo is the yellow cap the death cap?

Can some one point to which is hot? 

[sluckey]

It's unclear in that pic if that cap is the death cap, but the death cap will be connected to the ground/polarity switch. However, when you correctly install the 3 conductor power cord, the term 'death cap' no longer applies. That cap simply becomes a safe line filter. It always was just a line filter but when you connect the chassis to earth via the green wire, the cap becomes safe.

The hot wire is not established in the original 1484 since one power cord wire connects to the power switch and the other power cord wire connects to the fuse. I would rewire the new power cord such that the black wire connects thru the fuse to the power switch. But you don't really have to do that. The absolute easiest way to replace that power cord would be to cut it off leaving 2" pigtails still connected to the circuit. Then connect the new black wire to one pigtail and connect the new white wire to the other pigtail. Green goes to chassis. Leave the ground switch and cap as is. It may still be useful if you have noisy power lines.

[chrisq]

awesome!

Just to clarify.  I have two white lines that run from where the outlet is.  they run to the ground switch.  one white that runs to the power switch,  and one black one that runs to the fuse.

Black to fuse, white to power switch, green to ground?

[sluckey]

If you don't want to do the pigtail idea then unsolder the old power cord and connect the new power cord EXACTLY where the old cord was connected. Connect the new black where the old black was connected. Connect the new white where the other old black was connected.

[chrisq]

Thank you!  It worked perfectly!  Sounds great, nice and quiet.  Even the original caps are quiet.

This thing is flawless... it looks brand new inside and out!

[nichesound]

 1484 reverb troubleshooting:
Doug Circuits
Silvertone used undersized plate resistors on the 6CG7. 125V across a 27KΩ resistor is .58WATTS, and Silvertone used 1/2-WATT resistors. If the voltage at the plate of the 6CG7 is close to 320-340V instead of 215V, the resistor has failed. Similarly, this can also be an indication that the tube has failed.
 
 The major difference between the M13 and the 1484 circuit is that the Silvertone "Tank" takes a push pull signal from a phase inverter that the 6CG7 (V2) provides in para-phase arrangement. The 6CG7 is a
 
 Can this circuit be easily modified to accept a common Hammond style tank?
 
 If we remove the voltage divider (R47 & R48), and instead let V2B's grid be tied to V2A's grid, both triodes will produce a signal in the same phase as the each other (instead of inverted). We can then tie the two signals together at the tank inside of the coupling caps, and send that signal to the tank.
 
 The current produced should be reasonably strong. This parallel arrangement of triodes is similar the M13's paralleled 12AU7, and the plate resistors are load enough that it should produce a strong current to drive the tank.
​The amperage draw does not change for the pair of triodes, so it'll have no effect on the power supply.
 
 R40's 560K will need to be reduced (or eliminated). R26's 560K values might need to be tweaked to get the wet/dry mix right. Otherwise, this would work!
 
 Another note about the 1484
 
 The other weak spot is the power transformer arrangement. These used an odd-ball power transformer (PT) that had two secondary 150V windings. They used voltage doubler rectifier circuits and stacked the two on top of one another to make the 480V of B+ to power the amplifier.
 
 I have searched for this article to add a tank reverb and found it...hope this helps anyone who wanted to add a tank to their Silvertone Amps....good luck...Johnne in Clallam Bay WA.