5E3 - Why No Bleed Resistor to Drain B+?

[haashole]

I'm about to start a 5E3 build, and, in preparation, have looked at many layouts/schematics for it, from various vendors. I've noticed that none of them have added a bleed resistor to the first filter cap.

This is only my third build, but I was under the impression that such a bleed resistor was always a good idea for safety reasons.

Could someone please shed some light on why none of these re-drawn layouts have added a bleed resistor?

-John

[MWJB]

Just use a jumper wire from V1 pin 1 or 6 to the chassis when working on the amp, this will drain the caps and you can visually confirm it's in place. Remove the jumper when powering up.

If making your own board there's nothing to stop you using a totem pole arrangement at the first filter cap, with smoothing resistors bypassing the caps (see Super Reverb schem) IF you can find caps small enough (perhaps relocate the cathode resistor & cap if using an off the shelf board?). This will drain your caps when you power down.

[Enzo]

Sure it is a good idea, but it doesn't do anything to aid the performance of the amp. SO a lot of people leave them off. I am careful to make sure the caps are discharged when I work on something, or at least I remain aware there is a held charge. All depends on what I am doing. It offers little safety to the amp user, it mainly serves to protect a technician working on it.

Resistors may not cost a lot, but when you can eliminate thousands of them on your production line, they add up.

[Paul P]

Is it possible that not having a bleed resistor is easier on a tube rectifier ?
Without the resistor the filter caps remain charged and there isn't an rush
of current everytime you turn the amp on.

I like the idea of a bleed resistor getting rid of all the high voltage before
I open up my amp, though I wouldn't count on it having worked. It's
just one safety device against a stupid mistake.

Paul P

[haashole]

Thanks for the replies, and thanks MWJB for the pointer to the Super Reverb schematic, I'll check that out.

It certainly makes sense to me why Fender didn't include a bleed resistor, due to added cost over thousands of units, but I was curious about the the current kit providers. For example, my last build was a 18W LiteIIB, and the original Marshall schematic from which this amp was derived, did not include a bleed resistor. But, some of the kit suppliers' layouts I've seen for this amp have incorporated a 220R 2W bleed resistor across the first filter cap. I haven't seen a similar thing done with the 5E3 kits. This made me wonder if there was a reason why.

So, Enzo, you say "it doesn't do anything to aid the performance of the amp", but does it do anything to detract from the performance of the amp?

I am building my own board, so if there is no adverse effect in including a bleed resistor, I'd like to do it. Sure, I could clip one in place when working on the amp, but either way I'm going to verify there is no/low B+ with the DMM before diving in, so a permanent bleed resistor would just be more convenient for a tweaker like myself.

Thanks again for the replies, I'm psyched to build this amp. I've never played thru a 5E3, or anything close, really, so I'm eager to hear my Gretsch make it growl.

-John

[dobsont]

I was about to put a bleed resistor in mine but I noticed that the voltage drops right off when I hit the switches anyway, much like it has one. Switch to standby with a meter on b+ -- the voltage drops right out. I think it's because the dinky 16uf caps don't really hold much charge and the decaying signal out of the guitar is enough to quickly use up all they have.

I could be wrong, but this is how mine behaves.


(ps 5e3 + gretsch = happy)

[haashole]

I was about to put a bleed resistor in mine but I noticed that the voltage drops right off when I hit the switches anyway, much like it has one. Switch to standby with a meter on b+ -- the voltage drops right out. I think it's because the dinky 16uf caps don't really hold much charge and the decaying signal out of the guitar is enough to quickly use up all they have.

I could be wrong, but this is how mine behaves.


(ps 5e3 + gretsch = happy)

Thanks for that input. Good point about the 16uf caps. I did add a bleed resistor, but I may unsolder one end as an experiment to see how quickly mine drains without it.

I just powered her up for the first time a couple days back, and am still tweaking/debugging it. It's still on the bench, and haven't build a cab yet, so removing the bleed resistor would be an easy experiment.

It sounds great - I think I'm gonna really like it once I figure out what tube I like in V1. I have a strat down by the bench so I've been using that and haven't run the Gretsch thru it yet. Gonna have to do that tonight.

John

[dobsont]

I'll share my experience so far on tubes -- you're totally right, it's a big deal.

I'm running a tung sol 12AV7 in v1. Somehow I happen to have 4 or 5 of them around. 12au7 is WAY low gain, but I didn't mind how it sounded -- alright, but not much volume. I don't have any 12ay7s to try, but the 12av7 is very close (and just a little cooler, IIRC).
12at7 and 12ax7 are too hot for my taste (I like a lead sound ala gene vincent/bill haley. Setzer is about as hot as I get it. Also do some neck p/u Lightnin' Hopkins type stuff). I can't seem to really get there with those tubes.



Try 'em all.

[haashole]

Thanks for the tube suggestions, I don't have a 12AV7, I'll have to look into that.

I have a 5751 that I plan to try, and there some folks over at the Tele forum that really like the 6072 which I'll have to look into acquiring.

http://www.tdpri.com/forum/amp-centr...highlight=5751

[dobsont]

I don't know much about those tubes -- I'll have to look them up (and look through my collection -- might have some). Thanks for that. I'm very happy with my 12av7 -- it gets me the keerangy-spanky cleanish-but-verging sound I was after.

But now I'm taking us pretty far OT...

Maybe somebody else will chime in about those 16uf caps...

[Billy R aka DynaFreak]

It's not that the caps dont hold a charge or that you have residual guitar signal. It's that hot tubes continue to conduct current long enough to drain the voltage to a safe level. That let Fender save a resistor.