Tube amp mayhem

Shmoopie

Senior member
Messages
1,582
This friend of mine has an old silver tone amp in a case,  its a 35 watt class A or A/B with just a volume knob an on switch and a Five inch speaker.
He says its starting to sound "fuzzy"
We are planing on getting a new speaker, but where would I/we find a 5 incher
I suggested replacing the tubes, except they are hard to find rare tubes. (will get back to you on the models) already found a replacement 12AU6 for the preamp.

Then I thought, why not get a bigger speaker (12 inch), make a new cab, and make it into a combo amp instead of a case amp.

any suggestions? We do have to stick to a budget (lame)

Thanks in advance
  -Schmoopy
 

jackthehack

Senior member
Messages
5,630
That's probably a 5 watt amp, does it look like this:

http://www.retrothing.com/2007/12/guitar-week-sea.html
 

Jedi Ninja

New member
Messages
4
Here are some pictures of it.

DSC01579.jpg

DSC01580.jpg
 

Shmoopie

Senior member
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1,582
yeah, but is said it was more than five, and we're having some technical difficulty posting pics i take that back
 
R

RLW

Guest
25 watts is the power draw, not the output. I doubt if that amp could put out 5 watts with a 100 mph tailwind, probably closer to 1.

Be very careful where you poke your fingers, that design is my least favorite to work on. High voltage pretty much everywhere.
 

jackthehack

Senior member
Messages
5,630
YouTube video of some schmuck demo'ing the same guitar/amp. You'd think he'd put on something different than his Oreo cookie boxer shorts to make a video to link to the eBay page....


<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/poxRomtf_x8&hl=en"></param><embed src="http://www.youtube.com/v/poxRomtf_x8&hl=en" type="application/x-shockwave-flash" width="425" height="344"></embed></object>
 

Shmoopie

Senior member
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1,582
i hate that guitar with a passion, the worst tuners ever. But the amp is great, he uses a metal muff with top boost, and an epiphone lester.

So any suggestions on where to get the tubes, or the speaker, or how to discharge the amp, so we don't DIE, or how to replace the tubes and speaker?
 

jackthehack

Senior member
Messages
5,630
All those tubes are available from thtubedepot.com; are there any markings on the transformer? All the speakers in the world are available from http://www.parts-express.com/wizards/speakerwizard.cfm?raid=1&rak=replacement_speakers.

 

Jedi Ninja

New member
Messages
4
Sir SchmoopY said:
i hate that guitar with a passion, the worst tuners ever. But the amp is great, he uses a metal muff with top boost, and an epiphone lester.

So any suggestions on where to get the tubes, or the speaker, or how to discharge the amp, so we don't DIE, or how to replace the tubes and speaker?

Actually Elliott the problem with the tuners where that the nuts weren't screwed in all the way so now its really easy so now it shouldn't take us 3 hours to re-string it again.
 

-CB-

Senior member
Messages
5,427
Schmoo... brothers... all...

The amp is about THREE watts on a good day.  Its a take off on the classic audio sections used in table radios of the 40's and 50's, known as the AA5 or "All American Five".  Five being the number of tubes used in the radio.  The heaters are 50v, 35v and 12v giving a heater string of about 100v, able to take a bit more.  They may have a resistor there to help with keeping the overall voltage in line with 117 volt wall current.  There is no power transformer because of this, only a rectifier and output transformer.  Everything in the amp was designed for one thing: CHEAP.  Yay Silvertone and Sears....

The 50C5 is run 3watts, class A, single ended.

The 35W4 is the rectifier, run as a half wave

The 12AU6 is the preamp

I've not seen this amp, but I know the problem.  It may be the speaker, whose cone has become unglued from the coil former.  But, its more likely to be in serious need of new capacitors.  The tubes are probably fine, as they're stressed little in use.  The caps go bad even if the amp is not played... so #1 job - RE-CAP.  That will probably restore 90percent of the amps oomph, clarity and headroom.  Then, address issues as they're still present in the amp.

Forget new tubes for now.  Forget speakers.  Concentrate on making the capacitors right.  And by right - you need similar sized physically as well as electrically.  Dont cheap out on the recap.


 

Shmoopie

Senior member
Messages
1,582
thats good to hear I guess, but now the problem at hand is how to work on it with out getting zapped?
bout how much would capacitors cost?
 

-CB-

Senior member
Messages
5,427
zapped... just make a dezapper - test lead, 20k 1w resistor, wire if needed, alligator clip, shrink wrap

Assemble as follows:

Test lead, short piece of wire, resistor with shrink wrap to insulate it (use 2 layers), wire about 18 inches long, alligator clip.

Clip to ground, touch the plus side of all the caps.  Then use your meter to check the voltages.  Repeat as needed.

Cost of caps depend on which they used, but generally... unless it used some weird "can cap", think in terms of under $20,  Weird can caps, think $30 to $40 maybe if its really weird and odd.
 

jimh

Senior member
Messages
1,344
Sir SchmoopY said:
thats good to hear I guess, but now the problem at hand is how to work on it with out getting zapped?
bout how much would capacitors cost?

One thing you can do is switch it off while still playing the guitar.  You should hear the volume and audio 'quality' die as you play the notes, chords are good.  This is draining the power supply caps, as you are using up the energy they store without topping it back up (cos the amp is not switched on any more) in layman's terms

Leave it plugged into the wall socket but SWITCHED OFF for at least 30minutes before you do any work.  This should make sure any residual charge stored in any of the caps has a chance to dissipate.

THEN UNPLUG IT BEFORE YOU DO ANYTHING ! ! ! !
Again, leave it for half an hour....

Double check that it is unplugged, and then remove the cover.  Without touching anything if you can get away with it, carefully note the types, sizes/value (electrically speaking), the size (physically speaking), and the orientation (this is important, as some capactiors are Polarized, ie they only work in one direction, they'll be marked on one side/end or have an arrow with a minus-sign). 
Then get down to your local electronics shop, and purchase the up to date equivalents of what is in there.  Radio Shack should be able to help you, or there will be thousands of places on the web that'll do this sort of stuff.

Should'nt need to pay more than a dollar or so for each part.  Maybe a couple of dollars for the bigger power supply caps.

Again.....and I stress......MAKE SURE IT IS UNPLUGGED.  Carefully de-solder each cap and replace with the new one, being careful to note the orientation.

If you are inexperienced with electronics, have someone with you (but not touching you) around in case if you do fry yourself, then there'll be someone else to tell you that you are stupid, and then call you an ambulance.

If you are at all unhappy with doing this, stop and leave it alone.  These things can KILL you.  Take it to a pro.  Any decent music shop should be able to point you to an amp tech.

Sorry if I'm sounding patronising or teaching you to suck eggs,  But I just dont want you to die.

 
R

RLW

Guest
> THEN UNPLUG IT BEFORE YOU DO ANYTHING ! ! ! !

It's amazing how easy that is to forget. One benefit of working on tube amps, you completely lose your fear of wall sockets.
 

jimh

Senior member
Messages
1,344
RLW said:
> THEN UNPLUG IT BEFORE YOU DO ANYTHING ! ! ! !

It's amazing how easy that is to forget. One benefit of working on tube amps, you completely lose your fear of wall sockets.

I speak from experience when I say .....Once you've taken a belt, you wont EVER forget to unplug it again.  I was lucky.  Just had a tingling sensation in my hand for about 6 hours.

Could'a been Waaaaaaayyyyyyy worse.... :eek:
 
I

ildar

Guest
jackthehack said:
YouTube video of some schmuck demo'ing the same guitar/amp. You'd think he'd put on something different than his Oreo cookie boxer shorts to make a video to link to the eBay page...

Or at least tune the f'ing guitar.
 

-CB-

Senior member
Messages
5,427
jimh said:
Sir SchmoopY said:
thats good to hear I guess, but now the problem at hand is how to work on it with out getting zapped?
bout how much would capacitors cost?

One thing you can do is switch it off while still playing the guitar.  You should hear the volume and audio 'quality' die as you play the notes, chords are good.  This is draining the power supply caps, as you are using up the energy they store without topping it back up (cos the amp is not switched on any more) in layman's terms

No.... No.... and No!

Switching off is not the way to do that.  I was very hesitant to say... but will now since this came up.

SWITCHING off will not always do the trick, since it many times will disconnect the B+ voltage and you still have charges there.

However - UNPLUGGING the amp while on will sort of... maybe... discharge it enough to not kill ya.  The switch is still on, and no matter the amp design, you'll have B+ connected with switch (power AND standby) in play positions.

But CAUTION - doing that trick will not guarantee you have no residual.  A lot depends on the tubes, and how hot they are.  The tubes will conduct as long as the heaters do their thing.  If the tubes are not up to full temperature, then the decay will be less, and the residual charges will be greater.  Its a crap shoot. 

So  STILL TEST THE AMP WITH YOUR MULTIMETER - FOR HIGH DC VOLTAGES, BEFORE YOU STICK YOUR GUITAR LOVING FINGERS IN THERE

Anything higher than just a few volts and you need to bleed down.

Also know, that capacitors creep back up (electrochemical) and WILL zap ya later.  I've had this happen numerous times, where the caps will creep back up slowly... to a rather large voltage like maybe 200vDC.  And - thwack!  They getcha.  Sorta like a spark plug wire.
Amp men know that if you're going to be in an amp for a long time, you ground out the B+ supply, so it cant creep back up.
 
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