5e3 Build - Pilot light in standby hole?

[teletrizz22]

Hello all, long-time lurker here! Building a 5e3 with a NFB switch and pre-phase inverter master volume. This amp will eventually look a lot like RobRob's 'RobRob Deluxe' with the exception of the lead channel mod and with a split ground bus instead of a single unified bus. Based on the advice of some great builders, my current goal is to build a working 5e3 with minimal modding before going too crazy. I have a good amount of experience with electronics, guitar pedals and guitar wiring, though this is my first amp project.

I've populated the turret board and have attached some pictures if any of you more experienced builders out there are willing to check my work. The board is from Hoffman, and includes a set of extra turrets on the input side of the board to help facilitate the lead channel mod if I eventually end up wanting to give it a try. Other than that, it's pretty much a stock 5e3 board to my knowledge.

PT and OT are Heyboer and most of my components came from a 5e3 parts kit from tube audio supply.

Anyways, the main reason for this post is for me to ask this question: anyone ever tried putting the pilot light in the standby hole? I know there is potential for some hum to get picked up by the heater wires, though I'm hoping that with very clean wiring, it can be done without introducing any noticeable hum. How did I get here? Well, I had decided to put the master volume pot in the pilot light hole to make wiring a bit shorter, and to keep the early signal path away from the PT, though while I was planning this all out, I hadn't fully considered the downsides of putting the pilot light in the standby hole. Oops. As you can see, due to my negligence, I've already drilled the standby hole out, so I'm hoping to make this work! The pilot light housing does clear the PT quite easily (by a few millimeters), though I figure I may want to insulate the pilot light housing where it is prone to touching the PT's metal plate.

What do you guys think? Am I overthinking this, or is this a terrible idea that I will regret immensely? Hahaha. Would it make sense to flip the PT in this case? Let me know your thoughts. Still not too late to change plans.

 

[chas.wahl]

My "no experience with this" opinion: there's no juice flowing in the pilot light's metal frame, and the heater wires come out of the PT anyway, so I'd say it should work out OK, so long as you try to keep other wiring away from the greenies. I'm assuming that the frame is "close-not-touching" the transformer bell end. You could rotate the frame if it is touching.

 

[dan40]

I don't see any issues. Both the PT and pilot light are carrying AC voltage so there shouldn't be any noise penalties by installing the light over the PT.

 

[Lowerleftcoast]

You already drilled out the hole. You are committed... or should be. hah.

Now go drill a hole for the power cord ground.

And.. welcome to TDPRI.

 

[teletrizz22]

Going for it! Thanks for the reassurance y'all. I will update this thread with the build process! Going really well so far.

 

[teletrizz22]

Finished the heaters. How's it looking?

Going to wire all the pots and switches later this week, screw the OT into place then drop the turret board into place!

 

[chas.wahl]

If you don't mind a comment about your heater wiring: The hum reduction that twisting wires together develops is because it keeps the two conductors that you've used black and white for in closest possible proximity to each other continuously (the twist only physically enforces the proximity, there's nothing magical about twisting per se other than that). So, twisting the black and the white wires, apart from each other (the all-white and all-black twisted runs at tube sockets) don't really accomplish this, because the black and white conductors are separated. Compare Merlin Blencowe's examples of this in his Heaters article.

I fully understand that heater wiring doesn't always get twisted, and works just fine; that some people fly the wires over the sockets; and that Fender actually used the chassis as one of the conductors for the heaters in early amps (with wires from socket terminals soldered directly to the adjacent chassis metal) -- different strokes for different folks. But if you're drinking the twisting kool-aid, might as well know how to best achieve it: twist the different colored wires as far as possible, rather than separating them.

 

[Paul G.]

I've done it when I had a master volume. It's fine.

 

[teletrizz22]

Thanks to y’all who have given me feedback so far. I cleaned up my V1 heater wires a little bit and decided to leave the rest. They look nice and I don’t expect any issues.

Wanted to share some progress photos. I’m going to test voltages pretty soon here once I have some free time. Have pretty much checked everything that I can with it unplugged, everything is looking good so far! I would appreciate anyone who wants to check my wiring.

To put it simply, this 5e3 build is basically a RobRob Deluxe without the lead channel mod and 10% power mod. I’ve removed the standby switch, and am using a split ground bus scheme (some of the jumpers are below the board, as displayed in previous photos). Master volume is in place of the pilot light, and the pilot light has been moved to the standby hole, which was the original reason I started this thread haha.

You guys are great and I’m very excited to be a part of this awesome community!

 

[chas.wahl]

PLEASE IGNORE:
While maybe it doesn't matter that much, as long as we're nit-picking: polarity between different preamp tube heater supplies should ideally be reversed, see https://www.tdpri.com/threads/heaters-phase-and-polarity.708937/ esp. post #5 by @robrob.

 

[sds1]

While maybe it doesn't matter that much, as long as we're nit-picking: polarity between different preamp tube heater supplies should ideally be reversed, see https://www.tdpri.com/threads/heaters-phase-and-polarity.708937/ esp. post #5 by @robrob.

I don't completely follow what he's saying there, first he says ideally the phasing is flipped for each subsequent gain stage, then he reminds us in a dual triode package this is impossible. Got it. Then he says ideally swap phase between dual triodes -- I'm not sure if this means each tube should be out of phase with the subsequent?

Later in the thread he seems to say he is mindful of keeping phase consistent across all the preamp tubes.

I reckon you understand Rob to be saying that @teletrizz22 should swap the heater phase on one of those preamp tubes?

 

[chas.wahl]

PLEASE IGNORE:
It seemed to me that @robrob's advice was that you can't alternate polarity between the two triodes of a preamp tube (they share a pin for heaters), but you can (and ideally should) alternate polarity between two different tubes. Made sense to me.

 

[Lowerleftcoast]

check my wiring

I didn't see this ground wire under-board. Check for a connection.

 

[teletrizz22]

It seemed to me that @robrob's advice was that you can't alternate polarity between the two triodes of a preamp tube (they share a pin for heaters), but you can (and ideally should) alternate polarity between two different tubes. Made sense to me.

Interesting discussion. I will look into this and try to wrap my head around it! I wired everything in phase just because that seemed to be the most common approach to a 5e3 when i was researching heater wiring. I enjoy learning all of the nit-picky optimal circuitry stuff however so thanks for pointing these things out chas. I probably won’t change the polarity unless I have problems since I’d probably have to run new heater wires from V2 to V1 and I really don’t want to do that at this point haha.

 

[teletrizz22]

I didn't see this ground wire under-board. Check for a connection.

View attachment 1056625

Good catch, definitely missed that one! Thanks for your discerning eye, probably saved me a good deal of trouble, though I do hope that I would have been thorough enough to notice that during my final inspection before plugging in.

So can I just run a wire to the ground bus wire above, or would it be better to float a wire over to the B+3 filter cap negative terminal? Looks like you are suggesting the negative side of B+2 which I suppose makes sense since these are the power tube grid leaks. Standard 5e3 layout on Rob’s site grounds those grid leak resistors on the preamp side. Will it make much a difference either way?

 

[sds1]

It seemed to me that @robrob's advice was that you can't alternate polarity between the two triodes of a preamp tube (they share a pin for heaters), but you can (and ideally should) alternate polarity between two different tubes. Made sense to me.

I look forward to Rob clarifying since that advice is in conflict with all other recommendations I've come across, including on Rob's website:

Build an Amp

How To Build a Tube Amplifier

robrobinette.com

 

[Lowerleftcoast]

So can I just run a wire to the ground bus wire above, or would it be better to float a wire over to the B+3 filter cap negative terminal?

The wire should connect to the cap I have shown.

The wire can go over the components but it might look better to go under the components, if there is room (laying on top of the board). Alternatively, the wire could be routed to the top edge of the board, if you think that would look more elegant.
Your choice.

EDIT: Don't let Rob's placement of *this* ground throw you. His layout does not show it grounded with the node it belongs to. It belongs with the power tubes not the preamp circuit. The only DC flowing here is from the control grid of the 6V6 tubes. It is not much current but this current does not need to be near the sensitive preamp tubes.

 

[chas.wahl]

I look forward to Rob clarifying since that advice is in conflict with all other recommendations I've come across, including on Rob's website:

Build an Amp

How To Build a Tube Amplifier

robrobinette.com

I'm embarrassed -- that reference does apparently conflict with the one I made above (a post of his in 2017). So now I don't know what to think about the phase for successive preamp stages. I apologize for bringing it up. Where else is it covered, by others?

 

[sds1]

I'm embarrassed -- that reference does apparently conflict with the one I made above (a post of his in 2017). So now I don't know what to think about the phase for successive preamp stages. I apologize for bringing it up. Where else is it covered, by others?

I don't think you should feel bad, what you stated here caught my attention but I definitely see why you said it. It's because that is what Rob said here:

swapping the phase between dual triodes is the best way to do it

I don't know how to interpret that any differently than you did. You could be right. That's why I say I look forward to Rob clarifying. He knows stuff.

It's good that you brought it up, although I guess we kinda jacked up this guy's thread a little. Sorry @teletrizz22

 

[teletrizz22]

The wire should connect to the cap I have shown.

The wire can go over the components but it might look better to go under the components, if there is room (laying on top of the board). Alternatively, the wire could be routed to the top edge of the board, if you think that would look more elegant.
Your choice.

EDIT: Don't let Rob's placement of *this* ground throw you. His layout does not show it grounded with the node it belongs to. It belongs with the power tubes not the preamp circuit. The only DC flowing here is from the control grid of the 6V6 tubes. It is not much current but this current does not need to be near the sensitive preamp tubes.

Got it!