Hello and Help (Silvertone 1448 Amp/Guitar)

[gfell15]

Hello everyone!  I'm Greg and I've been poking around these forums for quite a while but had never found a need to post, so this is my first one.

I've been scouring the internet looking for a little more information, but I can't seem to find what I need or I'm just not understanding it, so I'm hoping you fine, knowledgeable folks can help me out!

I recently re-discovered a Silvertone/Danelectro 1448 Amp-In-Case and Guitar I've had since I was a child.  The guitar seems to function, though I think the output jack is a little lose, so I'll have to look at that someday.  The amp, however, only buzzes.  Doesn't seem to register any input, either the guitar that matches it or my known good guitar.  I would greatly love to get the amp working again, as it used to belong to my late uncle and he left it to my family when he passed.  Unfortunately, this is my first adventure in the wide world of Tube Amp Repair, but I feel it's simple enough and is a great place to start.

So, I guess what I'm looking for is a little guidance on where I should start in repairing this thing.  I believe the buzzing is being caused by the old electrolytic capacitor which should probably be replaced (is that correct?)  How can I test the tubes to verify those are functioning?  And everytime I read about the 1448 Amp there is someone who says it's unsafe and I'll probably kill myself if I plug it in (which I've done several times).  Why exactly do they say that and what should I do about it?

Any help is greatly appreciated.

[TIMBO]

Hi gfell, welcome aboard. Yeah, I wouldn't touch it till a few more learned guys here take a look first. If this is the amp you are talking about http://www.el34world.com/charts/Schematics/files/silvertone/silvertone_1448.pdf there is some pretty funky things going on in that circuit that I cant comment on, so hopefully someone will give some guidance on what to do. Thanks 

[DummyLoad]

very unsafe. it needs an isolation transformer and what describe, new filter caps. a 50VA isolation transformer should do the job.

a friend has one in pristine condition - tone? bleh! they are nostalgic above all, and that's my opinion of course, so please take no offense.

respectfully,

--pete

[gfell15]

Hi guys, thanks for getting back to me!

@Timbo, yes, that is the amp I am describing.  I have seen the schematic a few times now, and I'm starting to understand the way everything is lining up inside.

@DummyLoad, from the videos on youtube, I really like the tone, though I'm sure it's not for everyone.  Of course, we'll see how I like it when I get this one working again, but it's more about an introduction to tube amplifiers and getting something back in playable condition for the memory of my uncle.

So about installing the 50VA Isolation Transformer?  I believe I have seen a schematic to add one of those to the 1448, but I can't seem to locate it this morning.  What does the Isolation Transformer do that this amp currently is not doing?

[stratele52]

very unsafe. it needs an isolation transformer and what describe, new filter caps. a 50VA isolation transformer should do the job.


--pete

+1

[sluckey]

What does the Isolation Transformer do that this amp currently is not doing?

It will prevent you from getting shocked, possibly hurt pretty bad. As is, one side of the power cord connects indirectly to chassis. Your guitar strings are also connected directly to chassis. Playing barefoot on a concrete floor will get you shocked.

The isolation transformer "isolates" the power cord from the chassis. And when you also use a three conductor power cord with the green wire connected to chassis, that shock hazard is removed. See attached schematic.

It's an easy mod to this amp, at least on paper. But with the amp in the case design it may be tough to physically fit the transformer neatly in the case.

[gfell15]

Awesome.  Thank you for the crystal clear explanation and providing the schematic!  I will certainly see what I can do with this.

[gfell15]

Well, it's been awhile, but I finally got around to ordering an Isolation Transformer and getting installed.  Followed the instructions you all provided and guess what!?  Nothing exploded!!

The amp fires up and all the tubes light up and glow a pretty orange but all I get is a light buzz from the speaker (same symptoms the amp had before the Iso Transformer install).  My guess was capacitors, in particular the large electrolytic tube shaped capacitor.  Does anyone have any other suggestions or something I should check?

Thanks! 

[silverfox]

Introduction to tube amp troubleshooting.

I don't know how much experience you have with electricity and troubleshooting so this may be information you are already aware of. However, no one here would want to feel in any way connected with your demise should you start following a test procedure and get animated electrically.

How much experience do you have working on a electrically powered device?

Most tube amplifiers will use voltages much higher than the one you are considering troubleshooting BUT, even the line level voltages present in your amp can kill you or cause a secondary injury if you were to get a shock and fall off the chair or similar.

It only requires 3 watts of power passing through your heart in order to cause cardiac arrest and death.

Rule one: Keep one hand in your pocket or at your side, behind your back or otherwise out of contact with the circuit and or chassis you are diagnosing if it has power going to it.

Always double check to be certain the power is off before you attempt to change a part or move the chassis or otherwise manipulate the assembly. It's easy to get wrapped up in the process and forget a circuit is energized.

If you have a power strip with an illuminated switch that would provide a quick indication that the circuit could be energized or plug a small device such as a lamp or LED clock into the power strip too. That will tell you power is going to the amp just by looking at it.

You most likely will need a Volt-Ohm meter. Do you have one?

Do you know how to solder, de-solder?

Consider now if perhaps it would be expedient to bring it to a service shop instead. However if you are interested in learning more about tube amps proceed on.

Okay, several people including yourself seem to believe it's the silver can shaped capacitor.

You should also look for obvious signs of burnt components for a clue to the problem.

Remove the chassis from the guitar case. Take a photo of the component side and post it here for review. Try to figure out how you will remove the capacitor if it is bad. The cap should be either attached with a circular clamp, soldered to the chassis or will have some metal tabs that that pass through the chassis and have been twisted to secure the can to the chassis.

Silverfox.

[gfell15]

Hi Silverfox, thanks for checking in.

Yes, sorry, I never explained anything about my background.  I've been working on small electronics (vcrs, computers, XBoxes, Playstations, anything with a circuit board, etc) for awhile now.  Soldering and desoldering things isn't difficult.  Most of my troubleshooting of capacitors has been "Oh, look at that, it's burnt and the top of the can is popped up.  I'll replace that one."  Unfortunately, I'm not seeing any of that here, so I'm looking to learn some new tricks and get this amp working again.  However, I've never worked on anything with tubes.  I mean, fundamentally it's all electricity, but there's all that mysticism around tubes!

To answer your questions, yes I can solder/desolder, I understand electricity can and will kill me, and I have a Multimeter.

The only reason I suspect it's the big red capacitor is only because someone else suggested it while I was doing my research.  I did not perform any troubleshooting up to this point because I was told I would likely kill myself without the Isolation Transformer in place.  That's taken care of now, so I'm off to the next step.  Here are my before and after pictures pre-Isolation transformer and Post-Isolation Transformer.  (Here's hoping I did it right and don't get flamed for being a knucklehead!)

[sluckey]

Does anyone have any other suggestions or something I should check?

Tubes first.

[gfell15]

Tubes first.

That would probably be easiest.    But is there a way to tell if the tubes are good at all?  They turn on and glow orange once power is going.  These tubes are most likely original tubes from the early 60s.

[sluckey]

Substitution was the best way to check tubes when that amp was new. Still is today, but tubes are not a commonplace item now days. If you love that little amp you need a spare set.

BTW, replacing that red multi-cap is also high on the to do list. Speaker may be shot too.

[terminalgs]

I repaired one of these last year that had the exact same symptoms.    The culprit was the big red multi-cap 100/50/30. sourcing an exact replacement might be tricky, but you can use 3 individual caps instead.   since the 100uf and 50uf are 150V caps, they are cheap.   a 47uf will work in place of the 50uf, and  a 22uf or 25uf in place of the 30uf if you can't source exact caps.

[gfell15]

Awesome!  Glad to know I'm on the right track.  I plan to test the speaker by some other means in the very near future, but it was on my list of possible issues, and I'll look into replacing that cap and tube.  I'll keep you posted!

Thanks for the help, you guys rock!

[HotBluePlates]

Tubes first.

That would probably be easiest.    But is there a way to tell if the tubes are good at all?  ...

If it were in my hands, I'd measure d.c. voltage at all tube pins.

If you clip your meter's black lead to the chassis and probe with the red lead, you will hear a little pop through the speaker when you measure the output tube plate voltage. You'll get a slightly bigger pop when you measure voltage on that tube's control grid (due to amplification of the disturbance). You should hear a similar pop at the 12AU6 plate, and a bigger pop when measuring the 12AU6 grid.

This will at least tell you the tubes are passing signal. Maybe they could be stronger, but they're at least doing the job. This should also help you figure out if the signal is being interrupted at the jack or the volume control, or if something later isn't working. For me, the "pop" working from output to input helps me find where a signal is interrupted.

[super&plexi]

if you need, and will pay shipping, I'll send you some NOS Mullard, Amphenol, & Telefunken tubes to keep/check it out with/spares, whatever........

O.K., just kidding, but I do have some oldies, that work fine, and you're welcome to a couple/3 if need be. think I even have one marked Harmony/Silvertone.  But can attest to the good quality of some sold by this site. Guess I'm saying get em from EL34 World 1st, but if not sure of being bitten  by 'the Tube Bug', I'd be happy to help out.

Oh yeah, a cardboard tube w/new caps inside is aesthetically almost indistinguishable from orig. heck, maybe one from toilet paper, paper towel.

Funny, was just looking at Gregory amps, (same problem/design) this morning. 

[PRR]

Big BUZZ (and extreme age and cheapness) would lead me to the main filter caps.

Tubes are _slightly_ less likely to be bad. Because tubes had to be made more carefully, and their materials are less likely to self-decay than old borax, foil, and paper. But lack of _any_ geetar sound does suggest more than just a filter cap.

Here again I'd look at the coupling caps into each G1. These also were the cheapest junk. Radio restorers routinely replace ALL wax-caps.... if not dead today, they die tomorrow or next month, and *can* take-out a tube with them.

[LHPcope]

Introduction to tube amp troubleshooting.

  The one thing I would add to this excellent list of do's and don'ts is that filter caps can hold their charge after the circuit is removed from power.  Make sure they are discharged before beginning any work or inspection of a circuit that you think is not energized.  Adding a + 1 meg resistor across all filter caps is a good trick to ensure they are discharged after power is removed.

[gfell15]

First of all, thank you all for checking out the post and laying down your input and ideas.  I greatly appreciate it!

Secondly, I've been busy (some call it lazy), so I haven't touched this thing since my last post.  But I am online now looking for new capacitors and scoping out tube prices.  I will keep you posted, albeit slowly, as to the progress of this project.

Thanks again!

[Platefire]

Hay Gfell15

Welcome to the forum. I got two silvertone 1482's, was my first amp as a teenager--well I'm 66 now I have scanned throught the previous post and didn't see where anyone recomended cleaning tube sockets, and pots with switch cleaner. Sometimes that can make a world of difference on amps thats been sitting up a long time. Looks like your on the right track with all the good previous advice. Hope you get it going soon but be aware--tube amp work is habit forming! Platefire

[Willabe]

cleaning tube sockets, and pots with switch cleaner.

There's 2 basic types of cleaners.

1. has a lubricant in it and is for pots (and switches) so you don't wear out the resistive track with the pots wiper.

2. has NO lubricant and is just for cleaning, use this type for tube sockets.

You don't want any lubricant left on the tube sockets.


            Brad     

[gfell15]

Hope you get it going soon but be aware--tube amp work is habit forming! Platefire

This was my plan all along!  I'm looking to find a hobby to work on other than playing video games and playing harmonica.

There's 2 basic types of cleaners.

1. has a lubricant in it and is for pots (and switches) so you don't wear out the resistive track with the pots wiper.

Would something like a Teflon lubricant/cleaner, similar to gun cleaners such as RemOil work? (trusted for many years in all my guns.  I guess I do have another hobby!)  Or any particular product you'd recommend for both lubricated and none-lubricated would be awesome.

[Willabe]

Would something like a Teflon lubricant/cleaner, similar to gun cleaners such as RemOil work?

I would say no but let some of the other guys say for sure.

You want a good electronics type cleaner. The lube kind usually has mineral oil in it?


            Brad   

[silverfox]

gfell15: "Would something like a Teflon lubricant/cleaner, similar to gun cleaners such as RemOil work"

http://www.remington.com/~/media/Files/MSDS/MSDS-RemOil_Aerosol.ashx

RemOil does not contain Teflon. It does however contain several highly flammable compounds. It would also leave a film of oil. You want a compound that will evaporated after moving the contaminating substances away from the area of interest- The Carbon film and the metallic slide in the potentiometer.

RemOil may also be slightly conductive and could perhaps, cause an arc if used on the HT portion of a tube socket.

On the other hand, in applications where two or more parts of a mechanical assembly must smoothly operate at high speeds with no chance of malfunction, RemOil would be a good choice.

Helicopter Minigun in Action Firing Shooting Training Video Chopper Gunships Dillon M134 Gatling Gun

Happy Turkey Day All!

[gfell15]

Good points, wasn't thinking of the flammability of the product, just the cleaning and lubrication aspects.

Also, I don't know the exact chemical compounds included in the product, but it is called "Rem(r) Oil with Teflon(r) Lubricant".  That makes me reasonably certain there's some Teflon in there! 

Awesome video, too!  Thanks for that and the good reminder that some things tend to catch fire! 

[gfell15]

Two new developments/updates with this project.  Again, slow and steady, and I'll have this thing working someday!

I was trying to figure out a way to test the speaker to see if it and the transformer were still good.  I read on another Silvertone 1448 thread that you could test the speaker by touching a 9v battery to the wires.  I just happen to have a 9v and the speaker on my desk when I read it.  I touched it off and I am getting clicking.  According to the other post, that means the speaker is good.  Can anyone confirm that test here?

Secondly, I was looking into replacing the 100/50/30uF @ 150/150/25v capacitor.  I dug up another 1448 post where they mentioned a company that does custom capacitors.
The Hayseed Hamfest Co http://www.hayseedhamfest.com.  I sent them an email to inquire about price and here's part of the response I got:

Hi. Greg.  Thanks for writing.

We don't stock that cap, but we can produce one.  We don't charge extra for "one-off's".  The actual spec would be:

100-50-30 uF @ 160-160-50V and the price is $16.95 + $4.95 shipping and handling.

After pricing out other options I found that the price difference really isn't that much.  So I'm pretty sure I'm going to get this unit.  Plus, it will be more aesthetically pleasing to me mounted in the circuitry than having 3 random capacitors sitting there!  I won't likely get the capacitor until after Christmas due to backordering at HHC for their holiday orders, but again, this is most likely the option I will be taking.

[PRR]

> means the speaker is good.  Can anyone confirm

It makes noise. It isn't utterly dead.

That does not prove it is "good". It may rub, scrape. rattle, etc. Try it with another amplifier.

[PRR]

Contact cleaner and gun-oil are very different things.

Guns are supposed to oxidize. It's gonna happen, a mono-layer of oxide is a hard coating which resists wear and may lower friction. Many of the classic gun "finishes" are oxide or similar: good old bluing, phosphate, etc. Iron oxide isn't that tough, so we use oil on top, for lubrication and to reduce further oxidation.

Electrical contacts should NOT have oxide. Contact cleaners cut oxide. Some leave less or more film to retard new oxidation. The bad old "Tuner Cleaners" left great globs of oil-foam to soothe the poor mechanical action of low-price mechanical TV tuner switching. But there's several high-class contact cleaners which do the job without mess.

[gfell15]

I just hooked the speaker up to the inside of my Honeytone.  It actually sounded REALLY good!  I hooked the speaker up directly, cutting out the transformer.  When I hooked the transformer up to the Honeytone I got no sound, but I assume it's because the Honeytone doesn't work like that?

At least I know the speaker functions.  One more thing I can cross off the list. :)

[DummyLoad]

For cleaner use CAIG brand de-oxit

--pete

[silverfox]

Regarding the speaker- The schematic shows it should read 180 ohms. I don't think that would be an impedance reading. Rather an ohmic reading. Sounds like the speaker and tranny are fine.

Have you gotten the caps yet?

Silverfox.

[gfell15]

I just threw the transformer wires on my multimeter and got a reading of ~190-200 Ohms.  Hopefully that seems about right, based on the 180 Ohms you pointed out on the schematic.

I just ordered the multi-sectioned tubular capacitor through Hayseed Hamfest not moments ago.  They informed me that they are very busy for the holidays and I may not see it until next year at the earliest.  But since I've been at this project this long a few more weeks for another part isn't going to kill me.  Hopefully that's the last piece I'll need though!

Thanks for checking in everyone, I appreciate it!

[PRR]

> When I hooked the transformer up to the Honeytone I got no sound

The HoneyTone is designed for a several-Ohm speaker.

The SilverTone speaker *alone* is several ohms so should work. (It did.)

The SilverTone speaker plus *transformer* is about 2,000 ohms audio impedance (~~200 ohm stray copper loss plus a couple Kohm reflected audio impedance from the speaker).

This "should" work BUT at about 8/2000 or about 1/25th of expected loudness. If the Honey's speaker is also engaged, you sure won't hear anything from the transformered speaker, maybe with your ear IN the speaker.

[gfell15]

Well.... I received the capacitor from Hayseed Hamfest.  It looks great, and was pretty clearly labeled.  Quite a bit different than the original red tube, but should work nicely.  Not sure how I'm going to get it mounted just yet, but I'll find something.  They sent a clip with the tube, but it doesn't actually fit the circumference of the capacitor, so that was a bit of a downer.

I hooked it up several months ago and unfortunately have all the same symptoms i've always had with this amp.  It kind of bummed me out so I put it off to the side for a few months.  Today I ordered a new set of tubes from TubeDepot.  We'll see if that provides any changes to this little amp that is quickly becoming more trouble than it's worth!

I also calculated it out, to get similar capacitors/resistors/etc for the entire amp from Mouser would only cost me rough $25 dollars.  I've considered doing that to see if I can build the amp on a turret board and get it working, but I'm still not sure I'll be going that route.

[TubeGeek]

Well.... I received the capacitor from Hayseed Hamfest.  It looks great, and was pretty clearly labeled.  Quite a bit different than the original red tube, but should work nicely.  Not sure how I'm going to get it mounted just yet, but I'll find something.  They sent a clip with the tube, but it doesn't actually fit the circumference of the capacitor, so that was a bit of a downer.

I hooked it up several months ago and unfortunately have all the same symptoms i've always had with this amp.  It kind of bummed me out so I put it off to the side for a few months.  Today I ordered a new set of tubes from TubeDepot.  We'll see if that provides any changes to this little amp that is quickly becoming more trouble than it's worth!

I also calculated it out, to get similar capacitors/resistors/etc for the entire amp from Mouser would only cost me rough $25 dollars.  I've considered doing that to see if I can build the amp on a turret board and get it working, but I'm still not sure I'll be going that route.

Our host, Doug Hoffman, has all the parts you'll need and his shipping is lightning fast.

[gfell15]

Our host, Doug Hoffman, has all the parts you'll need and his shipping is lightning fast.

That is good to know, TubeGeek.  Thanks for the info, I will definitely look into that... Because my battle continues!

So I got all new tubes and swapped them out.  I haven't changed anything since I installed the big capacitor.  I plug it all in, flip the switch... Everything continues to fire up, so that's good.  The humming that I had previously is now louder than ever though, but still absolutely no sounds coming from the input or adjusting the volume.

I will be attacking this thing with a schematic and a soldering iron this weekend, but if anyone has further troubleshooting tips, I'd love to hear it.

[gfell15]

Well, it appears I'm not cut out to be an amp tech right now.  I went ahead and bought some Mallory 150s to replace all the Sangamo Type 33 capacitors in the amp for about $5 plus shipping.


Now the amp turns on as before but I'm not getting any hum.  Just a little bit, but I think that's just electricity.  Regardless, still no input and I feel I've made things worse.


I'll probably put this project away until I know a little more about it, but I certainly won't be buying an amp kit to build anytime soon, that's for sure!

[PRR]

Did you measure tube pin voltages as was suggested some months back?

Good DC voltages do not ensure good audio, but bad DC voltages sure will harm the audio (yes, to silence).