dumb questions of the day, perhaps?

[jimipage]

I've been studying the Wreck schematics and layouts found here and at blueguitar for quite some time and I'm on the verge of taking the plunge and building one. I have some questions, though:

1) why is there no resistor shown from the input jack to the first triode grid? The symbol looks like some sort of hangman's noose -- what does it mean?
2) I've also observed in the schem's that there is an 820ohm resistor from the volume to the second triode's grid, but I can't find it on the layouts. Can anybody explain this?
3) I'm thinking about using a choke in place of the 1.5k 25W resistor in the power supply. It seems that from what I've read here it would be OK to do so, but I'd like to know the pro's and con's.
4) pro's and con's of using a tube rectifier, say a 5u4, instead of diodes?

Any help is appreciated -- thanks!

[d95err]

1) why is there no resistor shown from the input jack to the first triode grid? The symbol looks like some sort of hangman's noose -- what does it mean?
2) I've also observed in the schem's that there is an 820ohm resistor from the volume to the second triode's grid, but I can't find it on the layouts. Can anybody explain this?
3) I'm thinking about using a choke in place of the 1.5k 25W resistor in the power supply. It seems that from what I've read here it would be OK to do so, but I'd like to know the pro's and con's.
4) pro's and con's of using a tube rectifier, say a 5u4, instead of diodes?

I haven't built a TW (yet) but I'll try to answer some questions:

1. Some of the designs posted have an input grid stopper resistor, some does not. The input resistor is not strictly necessary, but it can help to prevent oscillations and radio frequency interference.

2. The 820 ohm resistor is also a matter of taste. It's so small, the effect is probably very subtle, and some builders appear to have skipped it.

3. Not sure about the effect of a choke. Better filtering (less hum), and it may effect the transient response of the circuit (also a matter of taste I guess).

4. A tube rectifier would give lower voltages (less headroom) and some sag, when pushed hard. Cons would be a more complex circuit, bigger transformer required, possible failure of the rectifier tube and, depending on taste, the compression of transients (sag).

You can very easily simulate a tube rectifier by adding a resistor (perhaps 50-150 ohm). Add a switch, and you can get the best of both worlds. I haven't tried this myself, but some tube amp gurus say the effect is indistinguishable from a real tube rectifier. You'll find lots of sag resistor discussions on this and other amp building forums.

[Turmoil]

The hangmans noose indicates a shielded cable grounded at one end.

Tim

[dobbhill]

In some cases, that shield may be connected to B+, or elsewere.
See Liverpool.
D