Non CT Bias Supply Questions

[sluckey]

They do have a certain eye appeal for tube circuits. And they are available in 9 pin noval also. Different operating voltages and different time delays. They don't glow but they do get warm. You can find those for half that price. I just linked to the first one I saw.

[pdf64]

If you want to really get obsessive about protecting this 10 watt homebrew amp, consider using an old thermal time delay relay. Looks like an octal tube. Use the STBY switch to control 120V to relay heater...

I think it would be protecting the tubes from a non-applicable hazard:D
To paraphrase p65 of RCA 'Transmitting Tubes' application guidance book http://www.tubebooks.org/tubedata/tt4.pdf if a tube requires that its cathode be heated prior to HT being applied to its plate, then the manufacturer's information for that tube will note details for the constraint.
eg see http://www.mif.pg.gda.pl/homepages/fran ... 6/6383.pdf and http://www.mif.pg.gda.pl/homepages/fran ... 5/575A.pdf
I've never seen such a constraint noted on any tube info for tube types used in guitar amps.
The 83 mercury vapour rectifier used in the 5F6 seems the most likely candidate, but no, not even that seems to have it.
It seems to be limited to a very few, mostly obsolete by 50s, power tubes and rectifiers.
Of course standby can help with dodgy circuits such as the direct coupled cathode follower, where HT on a cold tube could cause a problem.

[sluckey]

I think it would be protecting the tubes from a non-applicable hazard:D

I totally agree. I'm not really obsessing about this.

[Littlewyan]

As cool as that delay is, I don't have room for another valve.

I'm going to simply short out one side of the standby switch so half of the secondary winding is always connected. The bias circuit will always be on then.

As its a Marshall circuit it does have the cathode follower you speak of. There is a workaround for cold cathode followers but as I've got the standby switch I will just use that.

Here is a few photos of it by the way.

[xtian]

Pink tone wire! Build looks great. What are those yellow coupling caps?

[Littlewyan]

Why thank you sir. Yes I found that pink wire has better tonal qualities when used for tone controls...............Just kidding, Marshall often used pink wire so I copied .

The coupling caps are Vishay 1813 caps. Very good and quite cheap to buy. I think Marshall use them in their handwired amps. Beware their leads aren't that long. The ones Marshall use seem to be larger so not sure if they're just higher voltage caps or if they use a slightly different model cap.