Welcome, Guest. Please login or register.

September 24, 2020, 11:07:50 PM

Login with username, password and session length

Recent Posts

 

Author Topic: Old tube guitar amp upgrade  (Read 8675 times)

frank2

  • Regular
  • **
  • Posts: 14
  • Chip Points: 0
    • View Profile
Old tube guitar amp upgrade
« on: February 01, 2011, 11:13:14 PM »
Hi guys! I am new to this forum, i have done several project for audio, but more in hifi. I am a guitarist for about 14 years. I have found in a basement a old forgotten amp by an old tenant. I have identify the combo witch i remove the head. It seem to be a Gar Gillies amp. I have try it, it sound sooo good.... and soooo loud! too loud to be honnest... Anyway, the tube still work but they are in bad shape and of course, the pot make a lot of pop.

My question is: the electronic inside is old, is there part that have improved and would be a good idea to change, like cap? I will change the pots and tube, probably add a gain channel by building a "real mc tube" drive that could be switched. A new enclosure too... Your input are welcome, here is some pic of the beast:




DJPhil

  • Master
  • ***
  • Posts: 96
  • Chip Points: 16
    • View Profile
Re: Old tube guitar amp upgrade
« Reply #1 on: February 02, 2011, 05:32:06 AM »
Interesting find!

I'd definitely consider changing out the main filter cap. Have you worked with multi-element caps before like the one in the big aluminum tube? The first time I worked on older tube gear that one threw me for a loop! I know I've seen a site somewhere where they discuss restuffing them with modern electrolytics to retain the same look. Pots, jacks, and tubes aside, the rest is probably just fine.

There is one thing that caught my eye, attached below. Did someone hack together a fix for the fuse? That looks extremely unsafe! If it were me I'd go through and insulate all the flying component leads so they had no chance of shorting out on something, though I'm a bit paranoid.

Keep us posted on what you decide to do. :)

joecool85

  • SSGuitar Admin
  • Legendary
  • ******
  • Posts: 3319
  • Chip Points: 991
  • SSG Creator
    • View Profile
    • thatraymond.com
Re: Old tube guitar amp upgrade
« Reply #2 on: February 02, 2011, 05:49:05 AM »
Phil has it right.  It sounds like you have experience working on tube amps, if not, be VERY careful - they carry lethal doses of electricity.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

frank2

  • Regular
  • **
  • Posts: 14
  • Chip Points: 0
    • View Profile
Re: Old tube guitar amp upgrade
« Reply #3 on: February 02, 2011, 09:37:18 AM »
No i don't have any experience with tube amp exept for owning many, but i never service them. I have build several chipamp, active crossover and electronic volume. I know about the lethal voltage, i will identifie where the hi voltage pin are on the tube socket and follow the path. But an accident can happen so fast... Is there a way to draw the current stock in the cap?

I also haven't work with multi-element caps, i would not mind to have something that do the same job, even if it don't look the same. I consider to make an enclosure out of copper, with a mirror finish.

I don't know the history for the fuse, but i agree with you!

I have another question, that amp don't have any bypass. So i will add one. There is two way that i can see this work, i don't know witch is good: the switch can turn off the signal path or it could turn on the heater. Witch one is the good way?

Thank you for your help!

Frank Thompson

bry melvin

  • Elite
  • ****
  • Posts: 168
  • Chip Points: 13
    • View Profile
    • Recent Album
Re: Old tube guitar amp upgrade
« Reply #4 on: February 02, 2011, 10:45:52 AM »
weber and others have replacement cap cans DO not use NOS . There is a shelf life and they'll not be good.

Bypass? not sure what you mean  Standby? Standby switch goes on the HI V winding of the transformer. You WANT the tubes to warm up first.

Discharging cap. You discharge the HV from the caps at the cap to ground preferably through a resistor so no big arc. Carefully. Google the procedure.

EVERYTHING you do inside that amp before discharging you do with one hand...the other in your pocket. No rings or watches on your person either.

While rebuilding you CAN install a bleeder resistor. Take a look at power supplies of newer tube amps  (like a valve junior or such)
The amp will then start to bleed down as soon as you shut it off.

While working it helps dissipate if you leave the amp ON...and shutit off via a power strip.

There are quite a few tube amp hoby sites that discuss safety... You might want to research that a bit.

Oh and one more thing for the AMP's safety....Tube amps are opposite Solid state....they self destruct with an open speaker circuit. You MUST have a speaker connected if you power it up with tubes in it. (and yes to voltage gets high 3-500 even with the tubes out)

Bill Moore

  • Regular
  • **
  • Posts: 35
  • Chip Points: 4
    • View Profile
Re: Old tube guitar amp upgrade
« Reply #5 on: February 02, 2011, 11:06:32 AM »
I had a couple of old tube amps I worked on last year with the cap cans. They are availlable, but pricey. I bought a capacitance meter from AES, (about $45), so I could check the cans, and didn't replace either. It's also handy to determine values in the box of parts we all have.

frank2

  • Regular
  • **
  • Posts: 14
  • Chip Points: 0
    • View Profile
Re: Old tube guitar amp upgrade
« Reply #6 on: February 02, 2011, 11:11:57 AM »
Yes i was talking about stand by, thank you.

So the only dangerous cap that have to be discharged is the multi-element cap?

Thank you for the advice, i will take great care with them. I have buy a book on tube amp on amazon, it is called
"the guitar amp handbook" by Dave Hunter.

That will be a long term project anyway, like 2 or 3 month, i am preparing myself to enter at university in civil engineering, so study and work take a lot of my time. But i can't help it, i like electronic project :P


@Bill Moore: yes i have listed every resistor and cap, so if anything burn, i will be able to know the value..

frank2

  • Regular
  • **
  • Posts: 14
  • Chip Points: 0
    • View Profile
Re: Old tube guitar amp upgrade
« Reply #7 on: February 02, 2011, 12:42:58 PM »
is there another name for multi element capacitor? I don't find them on digikey..

bry melvin

  • Elite
  • ****
  • Posts: 168
  • Chip Points: 13
    • View Profile
    • Recent Album
Re: Old tube guitar amp upgrade
« Reply #8 on: February 02, 2011, 01:04:54 PM »
digikey mouser etc won't carry those. They are obsolete by today's designs

Look at http://tedweber.com/ They call them cap cans you might also look at antique radio supply  (tubesandmore .com)

can you still read the values on that can....You'll need to do that and make a little schematic before you take that off!

there may be up to 4 different capacitors in that can I can't tell for sure from the picture.

It would probably be a good idea to do a complete schematic and layout drawing before taking anything apart.

Look at the layouts and schematics on the tedweber amp kit site to see what I mean.

If you can't find a can that matches you COULD use some of the modern 2 capacitor cans like JJ makes...But you NEED a detailed schematic before you start modifying things.

bry melvin

  • Elite
  • ****
  • Posts: 168
  • Chip Points: 13
    • View Profile
    • Recent Album
Re: Old tube guitar amp upgrade
« Reply #9 on: February 02, 2011, 01:20:29 PM »
Quote
I have buy a book on tube amp on amazon, it is called
"the guitar amp handbook" by Dave Hunter.

That is a pretty good book...but doesn't give you overhaul advice...just background theory (abridged for musicians) It DOES have a project amp build...but he says if it doesn't work at first take it to a technician.

The book is worth having and reading though.


You would want to discharge each elemet of the can, and any other electrolytics just to be sure... only takes a few minutes..

Replacing wires make sure you have 600V wire...a lot of stores only have 300V hookup wire these days (like radio shack) buy several colors so you don;t get confused. And annotate a layout .


get someone to test your tubes before you buy new ones.

what ARE the two power tubes?


frank2

  • Regular
  • **
  • Posts: 14
  • Chip Points: 0
    • View Profile
Re: Old tube guitar amp upgrade
« Reply #10 on: February 02, 2011, 10:44:48 PM »
It is writen:

SPRAGUE
made in canada
TO-236

MFD    V.D.C
40        450
40        450
30        400
20        350

85 celcius   WKG C5


I will do the shematic before, that is a good idea. I will have time anyway before i have all the part and the new enclosure done.

The power tube are two 6V6
the preamp is a 12ax7 and a 12au7

frank2

  • Regular
  • **
  • Posts: 14
  • Chip Points: 0
    • View Profile
Re: Old tube guitar amp upgrade
« Reply #11 on: February 02, 2011, 11:11:42 PM »
I have found one on a site name "vibroworld" do someone know it?

https://www.vibroworld.com/parts/tech15.html#cans
at 60% of the page, it is labelled " 40/40/30/20 ", sorry, i can't do a direct link...

Or there is this one that is close, i don't know if it is acceptable:

http://www.tubesandmore.com/scripts/foxweb.dll/moreinfo@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?item=C-EC4020X2-525

what do you guys think?

DJPhil

  • Master
  • ***
  • Posts: 96
  • Chip Points: 16
    • View Profile
Re: Old tube guitar amp upgrade
« Reply #12 on: February 03, 2011, 02:55:41 AM »
what do you guys think?
At those prices I'd leave the old one there, disconnected, and wire in some brand spanking new caps. It'll look the same unless you open up the guts. Folks here can give you better advice than I can about what exactly to use. Assuming they're all used in the filter their capacitance value isn't really important, just the working voltage (WV). You can pick up a 47uF (nearest standard value nowadays) 450WV electrolytic cap for one or two dollars US.

Definitely trace out a schematic before removing anything, or you'll regret it later. Mark the wires and make good diagrams. If you do swap out the caps for modern electrolytics, make absolutely sure you don't hook them up backwards. They'll only take maybe five or ten volts if hooked up backwards before they split their casing and vent capacitor blood all over the place, sometimes with great violence. I always turn away when applying power to a new creation for the first time as I was once nearly blinded by boiling capacitor electrolyte.

Regarding books, I think the best one I've read about valve amps was Jack Darr's "Electric Guitar Amplifier Handbook". I don't know if you can even buy it anymore, but I know it's out there on the internet somewhere in pdf form. It's sort of aimed at the electronics shop repairman as a guide to guitar amps.

Just my opinions, hope it helps some. :)

frank2

  • Regular
  • **
  • Posts: 14
  • Chip Points: 0
    • View Profile
Re: Old tube guitar amp upgrade
« Reply #13 on: February 03, 2011, 10:10:07 PM »
thank you, i have done a first draw of the schematic, it is a lot of work.
I will look it back tomorrow to see if it is accurate, now i am at the beer state for the night... ;)

Jack1962

  • Elite
  • ****
  • Posts: 249
  • Chip Points: 4
    • View Profile
Re: Old tube guitar amp upgrade
« Reply #14 on: April 11, 2011, 12:18:34 PM »
Unless the multi-tap cap is bad I wouldn't replace it , but if you really want to check Hoffmans website , or CE