For when I build my own guitar:



Slowed down the tremelo on my GA-8T

Cool! It worked! I doubled one of the .047 uf caps and the tremolo slowed down - a lot. At first I did the cap that is closest to the Depth pot and sure enough, this seemed to increase the depth. Now that I moved it to the first cap the depth seems "shallower". I might go to a .033 instead because it's almost too slow, now. Also, the signal sort of gets "lost" at the fastest speed. Maybe I should increase the values of all 3 caps?

I also went back to the original linear taper 500K pot on the Speed control and I like it better.


Good Tremolo Info

Good Tremolo info

The technology of phase shifters and flangers



Audio circuits to build - cool links to tons of projects

I tried the 500K audio pot and (as I suspected it would) it changed the variation of speed to a logarithmic sweep, but the slowest is till the same speed and the fastest is still the same speed. I want to make it slower on the lowest setting. If this makes the highest setting slower, too, that's okay.

I found some info on the web:

Slowing down the tremolo

...that describes a tremolo circuit comprised of three different-value caps, and suggests changing one out for a slightly larger value to slow things down. However from my schematic it looks like my amp has three same-value caps and uses resistors to vary the signal. Or am I just reading the schematic wrong?

Things are real tight inside the amp, and someone squirted glue all over when they replaced some caps, plus the old round caps are all lying down underneath a row of resistors, making them difficult to see.

Here's some more info from http://www.blueguitar.org/new/text/threads/from_dave/tremelo_reverb/trem%20slowdown.txt:

In a typical fender circuit, there are three capacitors in the phase shift network. The deluxe reverb circuit shows a .022uf (connected to the plate of V5A), then a .01, followed by another .01uf. By increasing the value of one or more of these caps, the oscillator frequency can be slowed down. Try doubling the size of the .022 cap, by simply paralleling another one across it. Tack solder, and check the results. Not slow enough? Add capacitance to the .01's. In some instances, the old caps may have drifted down in capacitance. Complete changeout using film types may be a wise investment.

Usually, I find that replacing one of the .01 caps with a .022 slows the tremelo down sufficiently. In situations where I decide to replace all three caps, the small metallized polyester caps (such as the blue Xicons) fit easily between those four eyelets.

I would like to add.. some fenders have a weak trem. and some models use a 100ohm resistor and some use a 47ohm resistor ..changing to the 47 ohm gives it more..intensity.

Info useful for Andy's Magnatone Troubador


Some more Magnatone info here

The story on the famous Magnatone Vibrato

Some tech info on the Magnatone vibrato circuit and "varistors" and some more

Amp Info Archive

This is a good tech resource: http://xoomer.virgilio.it/augiuliv/amps/

Well, I got the GA 18T sounding a lot nicer, now. I bought a pair of used 6BM8's from Audio Pro and plugged them in and the amp was like a new beast. It was still a bit gravelly so I swapped thru a few 12AX7's until i found one that sounds nice and clean. There was some buzz/hum at first but playing the amp more seems to have reduced that effect.

Now I want to get the tremolo to oscillate more slowly. At it's slowest it seems reasonable, but anything about 1 or 2 is much too fast. I figure there's some resistor or cap values I cvan tweak to change this, but haven't found much info on the net so far. This might be relevant but applies to a Fender:

...it can't be slow enough!

A guy on Tubes Asylum recommended changing the 500K linear pot out for a 500K audio pot. It seems to me that this might change the range of speeds, but the lowest speed would still be the same, since it's a 500K pot. Or maybe I'm thinking about it backwards... I need to learn more about how tremolo works.


I'm researching information on this amp I'm working on. It's a Vega 120, and it was made in Boston, MA. It has a beautiful cabinet. I'll post a pic this weekend. I haven't been able to find out too much, yet, but here's a start:




Good summary of tubes and their applications

I'm deciding whether to buy a Gibsonette GA 8T guitar amp from a friend. It's not a GA 5T but it does have tremolo so I'm checking it out.

Right now it sounds gravelly at any volume and the tremolo does not work. I have it on loan for a couple of days to try to figure out what's wrong with it and then I can decide if I want to buy it.

It uses a 12AX7 pre, a 5Y3GT rectifier, and 2 6BM8 power tubes.

So far: I replaced the 12AX7 w/ no effect. I swapped the power tubes left to right (I don't have replacements) and it sounds even worse (squeals).

I found this at Schematic Heaven: Gibson GA 8T schematic

...fortunately I have a much clearer version from a book.

Here's some stuff from this cool amp troubleshooting page:

Ugly sounding distortion can take several forms.

Harsh grainy sound
Output tubes biased 'way too cold
Rubbing or torn speaker cone
Rarely, the amp can be oscillating ultrasonically and still get some sound through, with a harsh, ugly sound.

Sound cuts out or squawks on loud notes
Failing coupling capacitor
Failing plate resistor, cathode bypass cap, cathode resistor or grid resistor
Intermittent ultrasonic oscillation

Muffled or constricted sound
Failing preamp tube; find the offending section by tube swapping and see if a good tube fixes the problem
Low signal tube bias is pushing it into saturation or cutoff. Measure operating voltages on the preamp tubes. The problem section will have tube pin voltages that are 'way off normal.
Failing coupling capacitors from the preceeding stage.
Failing plate resistor, cathode bypass capacitor, cathode resistor, or grid resistor
Power supply problem; a dropping resistor may have drifted far from it's nominal value, changing the power supply voltage enough to cause this.

Faint out of tune sound on every note
Excessive power supply ripple, usually indicating that the power filter capacitors are going bad. This can also be caused by speaker cones and voice coils with problems so they just rub slightly, too.

I also posted the problems on Tubes Asylum.

Good source for some rare tubes


Chassis kits

Mission Amps "Scholar" kits

Parts sources for 5E3 project:

WeberVST - chrome 5E3 chassis and eyelet board, P12Q speaker
MojoTone - power transformer, output transformer, tubes, misc hardware
Bruce Collins/Mission Amps - circuit components
Parts-Is-Parts - tolex and grillcloth

(I got these links here: http://www.kilback.net/homebrewtweaks/amps/amps.htm - this page also has a useful .xls parts checklist and lots of good details).


Vintage Hammond Organ Grill Cloths

The same guy makes these beautiful amps

HOMEBREW: Tweed 5E3 Deluxe - step by step instructions, layout, schematics, parts, cabinet plans

Great page of DIY amp links

House of Jim - Tube amp info and parts (eyelet boards, etc)


Gibson GA-6


Stella V 200 based on GA-6

Custom Input Jacks

From meo@rru.com Tue Mar 26 10:37:58 CST 2002
Article: 404226 of alt.guitar.amps
Date: Tue, 26 Mar 2002 07:32:02 GMT

If your amp has more than one input jack per channel, you can set it up so that each jack has a different flavor - different volume attenuation and tonal response - simply by using different value resistors.

Look at almost any old Fender or Marshall, and you'll find 68K inputs. Gibson used all sorts of values, from 47K to 220K. Magnatone was partial to 47K, Vox used a variety but especially liked 100K, and HiWatt seemed to like none at all. Ampeg was one of the earlier to mix them, for instance using a 100K (with a .005u bypass cap) for the bright input and a 47K for the normal input.

You can try any values you like. I recommend at least one input having no resistor, just a wire straight to the grid of the first preamp. Then try a mix of resistors on the others.

I just finished rebuilding a Gibson GA-6 that's a cross between a 5C3 and a 5D3 tweed Deluxe, but now with cathode biased preamps. This amp has a single "mic" input on one channel, and three "instrument" inputs on the other. I left the mic input with no resistor; this is an incredibly quiet, full sounding channel. I set the other three jacks up with 100K, 47K, and 22K resistors, and each jack has a very distinct flavor now. I also added a 1M resistor across the #1 input jack. (This is the only shorting jack on this channel.) You can also experiment with these resistors that go across the jacks, but don't go real low (say, 220K) or real high (say, above 5M).

Using a (non-shorting) 1/4" plug in the #1 slot while using the #2 or #3 jack changes things up, too, by cutting out the short to ground so that the 1M resistor kicks in. *Lots* of possible input sounds here, folks!

NOTE: changing resistor values will affect channel input noise as well as volume and tone.


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