5E3 Standby?

[stephenhartley]

Hello - I've just joined the forum and I'm new to amp building (although I've been playing through old valve amps for years)

I'm building a 5E3 based amp with a standby replacing the ground switch.

I've looked at other Fender tweeds in the Gerald Weber book and they have a 05 600v cap from the standby switch to ground.

Can anyone tell me what this cap does. Is it ok to use this for a standby mod for a 5E3?

[TransLucid]

that may be to reduce arcing when the switch is thrown, to increase switch life.

[stephenhartley]

Thanks for that

[Wittgenstein]

Are you sure those schematics aren't showing a ground switch rather then a standby? The original Fender 5E3 layout diagram (see attachment) shows that cap "death cap" on the ground switch going to chassis. This was used to reduce hum when the old 2 prong cord was plugged in the wrong way. Since you will be using a 3 prong cord with ground, you will not need this. You can do like you said, and make it standby switch instead. TBH, standby is really not even needed on this amp as the 5Y3 rectifier takes longer to warm then the 6V6's and 9 pins, but I used it on my 5E3 build just to fill the hole on my chassis. I attached the Weber layout, which uses a standby for reference.

[stephenhartley]

Thanks for that - the standby on the tweed bassman for example uses that cap. Thanks for the Weber schematic - it's useful for comparison. I've bought the Mission tone mod as well and I've built a cab with 2 8" & 2 6" speakers.

I'm working towards building a scaled down 4x8 Bassman which is is a bit more compact and portable.

I'll try and put some pictures up of my 5E3 when it's finished

[ThermionicScott]

I have an idea that'll save you the cost of a standby switch.

- Scott

[stephenhartley]

Wha's that?

I've finished all the soldering today, but I don't dare turn it on yet. Going to check through it all first

[Wittgenstein]

I've finished all the soldering today, but I don't dare turn it on yet. Going to check through it all first

Pics? =)

[cminor9]

Wha's that?

I've finished all the soldering today, but I don't dare turn it on yet. Going to check through it all first

My bet is that He was gonna tell you that you don't need one. You really don't. Unless you just want one, then go for it. I have built 5e3s with and without. Doesn't matter. If you do add one, then I'd put in on the OT center tap rather than on the b+.

[stephenhartley]

Yeah, I'll try and work out how to put pics up. I've made the chassis out of aluminium channel & sheet. It's in the same style as Fender Tremolux, Bassman etc - i.e hanging upside down.

I've already done the standby switch. If I build another, I'll try and use the space for some kind of attenuator switch for getting low volume with decent distortion.

[ThermionicScott]

My bet is that He was gonna tell you that you don't need one. You really don't. Unless you just want one, then go for it. I have built 5e3s with and without. Doesn't matter. If you do add one, then I'd put in on the OT center tap rather than on the b+.

- Scott

[vavlehead]

that cap is known as the "death cap". And should be removed if you are using a 3 prong AC line. As you should be.

EDIT: oops sorry looks like Witt has already addressed this.

[stephenhartley]

5E3 biasing via Tx tap

I had a little mishap building my first ever amp & unfortunately I blew up the mains transformer - oops! (I've learnt a lot from it & won't do it again)

I've got a replacement which has a 70v tap. The bloke I bought it off tells me it's for biasing the output valves.

Can anyone tell me how to adapt the standard Fender Tweed Deluxe 5E3 circuit to accomodate this and incorporate a biasing pot?

[Jazz P Bass]

The 5E3 is a cathode biased amp.
That being so, you do not have a need (cannot use) a bias pot.
The 70Vac tap in this case is redundant.
Cap the leads & tie them off.

[stephenhartley]

Thanks for that. I'm going to put a 1 ohm resistor in series with cathode resistor (as suggested on here on another thread) to measure current