The Amp Garage

I cannot tell if you were making a joke or not... Sorry - No, I wasn't trying to be funny, just applauding your pragmatism! :) What I SHOULD have written was.....HOW do you figure for a resistor with a value high enough to render it inconsequential while the amp is being played.? :) As already allu...

C Moore wrote:How do you figure that value.?
So that it will be high enough to be inconsequential when the amp is being played..

^ Spot-on!



(Actually you can get all technical about leakage currents, but that's as good an explanation as I've ever heard, and is probably The Truth )

Dries wrote:

Tillydog wrote: Are you holding the guitar when you do this?

Yes I am...

IMVHO, that's why you're getting feedback - I don't think it's a "fault" as such. Without a cover over the bottom of the chassis it'll be much worse.

Dries wrote:I have a TW Express clone ... When you touch the OT or go close to a output tube, it starts oscillating with a loud squeal.

Are you holding the guitar when you do this?

I had a filter cap installed with the polarity orienteded incorrectly. ON the schematic it is C18. i also see that resistors r28 and r29 are burnt up. C18 reversed would overheat R28 & R29. I very much doubt that any other damage would have been caused, especially as you switched it off quickly (R2...

What do you mean by straggling wire ? (sorry my english is not very good) Sorry: I mean the loose strands of wire that aren't soldered - near the biggest arrow on the right hand side. Did you 'tin' (=put solder on) before you tried to fit the wire through the hole? That can makes things more diffic...

... it was a mess trying to solder them to tube socket.. I'm sure you're on it, but just in case: IMO you need to clean up all those solder splashes and straggling wires, or these things *will* haunt you. Best way I've found to deal with 'big' wires is to cut them really cleanly (needs a good quali...

M Fowler wrote: none of them are bright today. WTF.

Happened to me once, too. Spent a few days swapping parts.

The part that fixed it?

New guitar strings!

...can build it exactly as I marked it on the scheme..? Yes. Make sure you get the chip with the UBE suffix. It is a logic chip, but early(-ish?) CMOS is quite good as a linear amplifier. The reason it uses (relatively) high currents is that it's operating in class A! :) (It'll still not use much m...

Well it definitely *was* a radio...

The big pulley is mounted on the tuning capacitor.

lpresnall wrote:..the 220K's are Red, Red, Orange, verified....

I do hope you mean Red, Red, *Yellow* (or Red, Red, *Black*, Orange)

+1 for better photos.

IMHO, the most likely problem is an ultrasonic oscillation. The circuit is notoriously fickle! My suggestions... Get the grid wires all tight to the chassis - in particular where you have pin 2 of the PI running near the wire from pin 6 and where the wire to pin 2 of V2 (with the green dots) is up i...

chrisq206 wrote:I'd like to have mine be a little tighter and Marshallesque for crunchier rhythm sounds any ideas?

For better or worse, I found that reducing the coupling cap between the 2nd & 3rd stages tightened the bass up no end - maybe try 1n5 or 1n8 instead of the 2n?

YMMV!

... now it works perfectly with all three speeds. I can't thank you all enough for all your help! Great stuff! The Amazon controller works as you describe - you would need to provide a decent DC supply for it - I would strongly recommend that you ditch the AT and use a conventional transformer for ...

Okay, I remember now, I have measured the voltage going to the field and the armature. With power on, the field is energized with 116vdc. With both relays engaged, the armature gets about 72vdc. With either relay engaged by itself, the armature gets 0vdc. I'm hoping the bridge rectifier is the culp...