Silvertone 1484 restoring advice

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Silvertone 1484 restoring advice

Postby k4444k on Thu Mar 02, 2017 12:49 pm

hi there,
My 1484 has finally having problem after having it for 8 years. The tone is fine when playing chords but when playing single note it sounds like there are some slap back delay/very rapid tremolo (osciallating) like sound which used to be just a solid single note sound.
I want to get it restored and perhaps improved with some mod.
I've been reading all the posts here on the forum and don't seem to find a post that properly listed out all the restoration/modification that can be be done for the amp. So maybe it's a good idea to have a thread like that for any future references.

So what would be the usual restoring job to be done to these amps ?
what are the usual modification that people would do to these amps ? (I probably want to keep the tone as original as possible but I do want it to have more low end)

I'm in Asia and there are no tech that has serviced any silvertone amps before. Therefore I might need some clearer explanation so I can tell the tech guy.

Thank you very much for any input !
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Re: Silvertone 1484 restoring advice

Postby stratele52 on Thu Mar 02, 2017 4:51 pm

1- Put know good tubes if needed.
2- Check and adjust bias for output power tubes,
3- Put new filter caps . Use good quality one. F & T or Malory Sprague Atom ; 25,10,5 mfd, 450 volts
4- Amp may also need new bypass caps on tubes's cathode ; 25 mfd, 25 volts
5- improvement for quiet amp is to install new shorting input jacks as you can see on every Fender amps schematic


Schematic here;

http://schems.com/bmampscom/silvertone/ ... ne1484.pdf
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Re: Silvertone 1484 restoring advice

Postby k4444k on Fri Mar 03, 2017 8:00 am

thank you very much, looks like there is a 'correct' schematic which has the correct diagram of the tremolo circuit:
http://www.silvertoneworld.net/amplifiers/1484/1484_schematic.html

and what would be the correct bias reading for the output power tube ?
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Re: Silvertone 1484 restoring advice

Postby stratele52 on Fri Mar 03, 2017 9:06 am

If you ask what is the bias may be you never do that before ?
Be careful, tube amps have lethal voltage that can kill you

Bias; check plate voltage first,
Schematic show 475 volts and with 6L6GC tubes, you may read 44 milliamp on each 6L6's cathode
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Re: Silvertone 1484 restoring advice

Postby k4444k on Fri Mar 03, 2017 7:57 pm

thanks again for your reply. I will get a tech to work on the amp so i guess he can just get all the information from the schematic ?
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Re: Silvertone 1484 restoring advice

Postby stratele52 on Fri Mar 03, 2017 9:35 pm

How to bias a amp is basic knowledge for a amp tech, It is not write on schematic. If your tech don't know, run away from him, he may damage your amp .
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Re: Silvertone 1484 restoring advice

Postby JJman on Sat Mar 04, 2017 12:17 am

The schematics referenced do not show that the bias is adjustable. A mod would be needed which would make sense to do.
-If it says "Vintage" on it, it isn't.
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Re: Silvertone 1484 restoring advice

Postby stratele52 on Sat Mar 04, 2017 12:28 am

JJman wrote:The schematics referenced do not show that the bias is adjustable. A mod would be needed which would make sense to do.



It is the case of many amps and it is easy for a amp tech to change a resistor value to adjust bias.

And to mod with pot for more easy bias adjustment.
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Re: Silvertone 1484 restoring advice

Postby k4444k on Sat Mar 04, 2017 5:30 pm

it would be quite challenging as I have to translate all these terms into their language. may i ask how to bias affect the amp ?
also is there anyway to make the 1484 have more low end ?
again, thank you very much for the inputs.
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Re: Silvertone 1484 restoring advice

Postby stratele52 on Sat Mar 04, 2017 6:27 pm

Under-biased amps will lack punch and the tubes will run noticeably hotter.s
Shorter tubes life.

Over-biased amps will sound thin and brittle, with the tube running too cool for proper performance.
A correctly-biased amps will sound clean and tight at moderate volume, then at higher volumes break up and distort musicaly
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Re: Silvertone 1484 restoring advice

Postby zarfnober on Tue Mar 14, 2017 1:23 pm

tubesandmore.com sells a replacement cap can, its a 20-10-10, so the last cap is 10mfd instead of 5mfd, but it fits and is same size as original. Also, you need to replace ALL of the electrolytic caps. Assuming all other components are within spec, you'll notice a real difference in a recap.

PM sent to k4444k.

Rocco
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Re: Silvertone 1484 restoring advice

Postby Slam on Wed Mar 22, 2017 12:13 am

I have restored a couple dozen of these amps, i usually find them in the worst condition but to me they're worth bringing back from the dead. After working on so many of these amps i developed a step by step approach that has been very successful to making them sound there best. If you are worried about it losing it's collector value then carefully remove the parts and save them, my approach is for reliability.

The first things are basic such as cleaning pots and switches, tightening all ground connections including input jacks , checking and tightening all tube sockets, three prong cord and installing an output jack.
The red Planet caps get replaced, the red bypass caps are usually still good but better to just replace those while your in there. All diodes get replaced with 1n4007 diodes. Surprisingly the 20 10 5 cap can is usually still doing it's job but gets replaced just to eliminate surprises. 20 10 10 is fine and i have used a 30 20 10 with great results. You can tuck in separate caps inside the chassis but this will take some planning as space is tight.
This is when the 100k 1/2 watt dropping resistor gets changed to a 1 watt, it was undersized and always goes bad, the 68k dropping resistors get changed but 1/2 watt is fine here.

I will now do a quick check on all the resistors down the preamp tubes to make sure nothing has gone open or shorted or way out of tolerance, these resistors were pretty cheap and it's easy to just want to change them all. This is up to you, i usually change the plate resistors and upping them to 1 watt is never a bad idea.

I would say lets get to the reverb later but there is always an issue here that effects the rest of the amp. The 27k plate resistors on the 6fq7 furthest from the cap can should have been 1 watt and are almost always fried, this is the major reason the reverb doesn't work in these amps anymore. If you have a problem with both volume controls sounding scratchy, the two .02uf caps leading from this tube to the reverb pan are probably leaking because of these resistors failing. Changing these to .047 will help with the sound of the reverb, which should be working again at this point. If not i can tell you a few other things to try and tricks that can be done to improve the reverb.

Now i check across the choke with an ohm meter and see if you have around 500 ohms, anything close to 0 or 1 meg means this must be replaced. I use a 4 henry choke with a 500 ohm winding rated at 50ma.

It is now safe to put in a set of good tubes and check some voltages. The voltage coming out of the choke should be around 350vdc. There are two 330k resistors coming from the 100uf 50v bias cap that tie to a pair of .02uf coupling caps, check the voltage to ground at the two points where the 330k resistor ties to the caps, each side should be around -37vdc give or take. This is your neg bias voltage for each power tube.

The amp should be sounding pretty darn good at this point but the preamp voltages should be checked again to make sure nothing is dragging it down.

These amps are getting popular and hopefully this information will help a few people out.
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Re: Silvertone 1484 restoring advice

Postby k4444k on Thu Apr 06, 2017 1:03 pm

Again, thank you very much for your input.
I have translated the process and send it to the tech with the schematic.
Let's see how it turns out. I would be really surprised if the reverb is working again.
xiexie!
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Re: Silvertone 1484 restoring advice

Postby vez on Sat Oct 07, 2017 4:54 am

Slam wrote:I have restored a couple dozen of these amps, i usually find them in the worst condition but to me they're worth bringing back from the dead. After working on so many of these amps i developed a step by step approach that has been very successful to making them sound there best. If you are worried about it losing it's collector value then carefully remove the parts and save them, my approach is for reliability.

The first things are basic such as cleaning pots and switches, tightening all ground connections including input jacks , checking and tightening all tube sockets, three prong cord and installing an output jack.
The red Planet caps get replaced, the red bypass caps are usually still good but better to just replace those while your in there. All diodes get replaced with 1n4007 diodes. Surprisingly the 20 10 5 cap can is usually still doing it's job but gets replaced just to eliminate surprises. 20 10 10 is fine and i have used a 30 20 10 with great results. You can tuck in separate caps inside the chassis but this will take some planning as space is tight.
This is when the 100k 1/2 watt dropping resistor gets changed to a 1 watt, it was undersized and always goes bad, the 68k dropping resistors get changed but 1/2 watt is fine here.

I will now do a quick check on all the resistors down the preamp tubes to make sure nothing has gone open or shorted or way out of tolerance, these resistors were pretty cheap and it's easy to just want to change them all. This is up to you, i usually change the plate resistors and upping them to 1 watt is never a bad idea.

I would say lets get to the reverb later but there is always an issue here that effects the rest of the amp. The 27k plate resistors on the 6fq7 furthest from the cap can should have been 1 watt and are almost always fried, this is the major reason the reverb doesn't work in these amps anymore. If you have a problem with both volume controls sounding scratchy, the two .02uf caps leading from this tube to the reverb pan are probably leaking because of these resistors failing. Changing these to .047 will help with the sound of the reverb, which should be working again at this point. If not i can tell you a few other things to try and tricks that can be done to improve the reverb.

Now i check across the choke with an ohm meter and see if you have around 500 ohms, anything close to 0 or 1 meg means this must be replaced. I use a 4 henry choke with a 500 ohm winding rated at 50ma.

It is now safe to put in a set of good tubes and check some voltages. The voltage coming out of the choke should be around 350vdc. There are two 330k resistors coming from the 100uf 50v bias cap that tie to a pair of .02uf coupling caps, check the voltage to ground at the two points where the 330k resistor ties to the caps, each side should be around -37vdc give or take. This is your neg bias voltage for each power tube.

The amp should be sounding pretty darn good at this point but the preamp voltages should be checked again to make sure nothing is dragging it down.

These amps are getting popular and hopefully this information will help a few people out.

There is either an error on my amp or an error on the schematic from Silvertone World. My amp has R31 connecting where R30 meets R32. In otherwords my amp has R30, R32, R31 and C14 all connecting at one point. Let me know if this is the same on your amps please. if so its an error on the schematic.
Thank you, Rick
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Re: Silvertone 1484 restoring advice

Postby vez on Sat Oct 07, 2017 12:16 pm

vez wrote:
Slam wrote:I have restored a couple dozen of these amps, i usually find them in the worst condition but to me they're worth bringing back from the dead. After working on so many of these amps i developed a step by step approach that has been very successful to making them sound there best. If you are worried about it losing it's collector value then carefully remove the parts and save them, my approach is for reliability.

These amps are getting popular and hopefully this information will help a few people out.

There is either an error on my amp or an error on the schematic from Silvertone World. My amp has R31 connecting where R30 meets R32. In otherwords my amp has R30, R32, R31 and C14 all connecting at one point. Let me know if this is the same on your amps please. if so its an error on the schematic.
Thank you, Rick

All right, now that I've looked at other schematics floating around the Internet, I see that they have it right, that is, they show these component, R30, R32, R31 and C14 all joined, but, they show mistakes with the tremolo. This schematic seems to be cursed.
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