New guy just getting started

[sliberty]

I am new here, and new to TW's. I have built a few other amps though (5e3, 5f2a, P1, Spifire), so I would describe myself as an informed hobbiest (certainly not an experienced tech). I have lots of elementary questions. Any help would be appreciated.

1. I noticed that the TW's don't have a 68k input resistor like just about everything else on the planet. What gives? Is that a gain-helper?

2. I printed out the stack of schematics (A0 through A9k). Boy am I confused now. Which should I build?

3. What are the PT specs?

4. What are the OT specs?

5. Why are some parts shown in red?

6. Why is the bias supply shown in blue?

7. What voltages should I expect to see at key places in the amp?

OK, thats a start. I plan to gut an old blue Univox head, and use it as a platform for my TWE. I'll start with the mechanical stuff (emptying and cleaning the chassis, etc) while I continue to study the circuit and ask questions.

Thanks in advance for any help you can provide.

Steve

[v00d00blues79]

You may want to search this forum for hte Kelly schematic. This one is reportedly really close to how Francesca was built, but wil a few component values being different. Starting with the Kelly schematic, the layout Richie corrected and the Francesca pictures, that should get you in the ballpark of a really killer amp.

The transformer specs:

Power Transformer
o Primary: 120V
o HV Taps: 300 - 260 - 0 - 260 - 300 (300mA)
o Heater Tap: 6.3V (7.5A)
o Rectifier Tap: 5V (3A)

Output Transformer
o Primary: Dual 5200 / 6600 Ohms
o Secondary: 4 / 8 / 16 Ohms
o Watts: 35 (conservatively)

This was taken from http://toneslut.com. Moose sells these transformers.

Hope this helps.

Andy

[jblues]

"input resistor" (68 k is part of dynamicsor lack thereof) in the trainwreck it's not there to give better sensitivity to playing hard or soft....if you put it in you loose sensitivity and a little treble. colors on schematics indicate parts that are verified "black ones" parts that are in the fender princeton that first wreck was built in place of old circuit, some such thing a comparison "blue parts" the bias in particular is a fender princeton bias i believe....we don't know if the first wreck used this or if it was changed...back a few years ago ppl were still trying to get the info on the trannies ...so you guys have everything you need to do this now...these amps were not all alike however since ken fine tunes stuff to players taste (much like we'll do to suit our likes dislikes)...one thing is important though the thing is bright for a reason to cut through a band with a lead tone and to, at lower volumes than a 100 watt marshall, feed back with lower gain no buzzy fuzzy sound here.

[paulruby]

1. I noticed that the TW's don't have a 68k input resistor like just about everything else on the planet. What gives? Is that a gain-helper?

68K is a hold-over from the first tube circuits ever designed, befor guitar amps. It's purpose is to form an RC filter (the C is the tube's grid capacitance) to filter any radio frequency making it's way into the amp.

But, it has a down side in guitar amps, especially those using solid state recto and large first filter caps (like a wreck). Guitar amps have a lot of gain so will amplify noise that gets to the grid of the input tube very well. The solid state recto dumps very large spikes of charging current into the first filter cap every 8ms, which causes radiated radio noise (the familiar 120hz buzz every guitarist has heard).

With the 68k grid resistor, despite blocking radio coming in from outside your amp via the guitar cord, the input tube grid node is now high enough impedance to directly pick up this radio noise that is inside your amp. And you hear buzz. This is a very common problem for folks building wrecks, including me.

So, leave out the 68K grid resistor. If you hear external radio (literally a radio station coming through the amp) then add a ferite bead around the line from your input jack to the input tue.

- Paul

[mlp-mx6]

One other thing that worked for Fender, but was not optimal, is that those 68K resistors were not mounted directly to the grid pin, but on the input jacks. Optimal placement of the "grid stopper" resistor is DIRECTLY on the tube pin.

Look at some of the gut shots of Dumbles and you'll see a terminal strip in front of the preamp tubes, with resistors running from the strip to the tube pin - this is MUCH better placement of those resistors.

(I am not intending to contradict Mr. Ruby, just intending to explain that while what Fender did worked for Fender in a relatively low-gain amp, it is not optimal - especially for a high-gain amp..)

Michael