5F10 FUN

screefer

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Greetings.
So I'm like a drop of water on a hot stove with this attempt.
A quick recap.

Plan A.
Build a Harvard with stock values (305 v. etc.) to yield clean Cropper tones. I had previously built a Mojotone 5F2a with split buss and carbon comps.
Sounds great, dead quiet to 9.

So I step-drilled out a 5F2a chassis and ordered parts. My first choice for PT was a Hammond 290CAX but then decided on a 290AX
because of less extra wires and lower weight. ( the CAX is rescheduled)
OT is Hmd. 1750E.

I had gotten great advice and knowledge from this earlier thread..


Plan B.
I see this thread...https://www.tdpri.com/threads/hasty-draft-a-single-ground-5e3-your-review-please.1098306/
Theoretically quieter, eh?
I'm thinking, maybe I'll employ a single bus because the 5f10 is higher gain, push/pull and twice the wattage than the 2a.
Again I get wonderful input from this thread.

I stake a board by eyeball from this one but decide to go with only two inputs like my 2a...
1651788475774.png
IMG_1621.JPG


..and make a #14 gauge single buss attached at the input end of the chassis. Isolated under the lamp.


IMG_1706.JPG




Then I discover DIYLC, and get straightened out here ...https://www.tdpri.com/threads/diylc-help-needed.1099269/.
so...
Plan C.
DIYLC enabled me to make a shorter (by 3/4") board that won't have to be shoehorned around the lamp.
IMG_1743.JPG

It also, as you all know, makes planning and editing so easy!!

All along I am endeavoring to study grounding ala The Valve Wizard and Rob's page. I'm making slow but real progress.
My decision to have only one ground point to the chassis via the bus requires isolating all jacks, the tag strip voltage divider, and 1 ohm bias resistor solder lugs off the socket bolts.

I realize that lots of Harvards have been built with quiet results with split busses, etc., but Mr. Blencowe makes a pretty good case for only one ground to the Chassis.

Sailing along, and then my research leads to Rob's Optimized 5E3 layout...

1651790960715.png


Hmm...
Plan D.
Why not 'optimize' my 5f10 layout?

1651843269457.png


This will require staking another board but not a big deal. (I obviously need the practice [chuckle])
I have drilled out the jacks for two Switchcraft 1029 shoulder washers apiece and dry fitted the 1 ohm resistor solder lugs with 6-32 shoulder washers. Need to cut a longer 6-32 bolt and add a steel washer. No continuity to chassis so they seem to work.

IMG_1737.JPG

I am reading Merlin's grounding treatise and do not understand it all but here is a quote that I think I understand and why I wish to go this route...

"Bad habits may also be reinforced by our familiarity with circuit diagrams that show
components terminated with ground symbols. This makes for tidy diagrams, but it is
easy to forget that current actually flows in a loop, so if it comes from some power
source or generator then it must somehow find its way back again, via ground.
Ground is, therefore, ‘the other half of the circuit’, and not some electrical blackhole
into which current disappears never to be seen again, even though some
diagrams seem to imply this.
Valve amplifiers are fairly noisy even at the best of times, but bad grounding is a
serious contributor, even in many commercial amps. Sometimes it is difficult,
practically, to follow an ideal ground scheme, and there is always the temptation to
connect something to whatever bit of ground wire or chassis happens to be nearest,
and hope for the best. Sometimes we will get away with this, especially in small,
low-gain amplifiers, but readers of this book are probably beyond that level and will
want to do things properly."

I am on the entry level but I do wish to do things properly.


If your great minds can expose any minor crimes or fatal flaws, in my 'plan D layout, please add your thoughts.
It will be greatly appreciated.
:)
 
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SacDAve

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I built the Optimized 5E3 I'd build another one
 

screefer

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I built the Optimized 5E3 I'd build another one
I have read your post a few times.
Interesting heater wiring.
Stunning cab!!
 

King Fan

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@screefer, great journey of research, reading, and revising… and even better, all before you build!!!

Tiny detail, would it work to bridge the .0047 cap back from the tone ground lug to the volume pot ground lug? Rob:

C95F278F-3E26-46EE-9D12-F2A564BF3AAF.jpeg
 

screefer

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Tiny detail, would it work to bridge the .0047 cap back from the tone ground lug to the volume pot ground lug? Rob:
I will defer to Rob as I had done with the pot ground point. In a previous post, LLC, had recommended that ground point.
I'm glad that nothing else raises concerns?

DIYLC is a game changer for me!

great journey of research, reading, and revising… and even better, all before you build!!!
So much fun! And even better, turns out the guitarist I jam with has a 40 years ago history of electronics study in school. He has shown interest so I sent him Merlin's Grounding page. He stopped in an hour ago on his way to town and said he downloaded Merlin from page one (Rob's page too) and started reading. He said lights came FLASHING on and, to make a long story short, he plans to build Rob's Champ micro. We plan to go through Merlin from page one together and see what happens. He's got the long lost education and I've got the enthusiasm.
I credit you as the spark!!

Thanks

Revised

1651855782677.png
 

Lowerleftcoast

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Note where the nodes are located. I have shown them in red and blue on your layout and I also show the corresponding pins of the tubes in the same red and blue.
Blencowe suggests having the nodes together.

EDIT: The speaker ground node is with the red (last filter cap) because the 5F10 Global negative feedback terminates on the 12AX7 which is powered by the red (last filter cap) node.

Inked1651855782677_LI.jpg
 
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screefer

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Note where the nodes are located. I have shown them in red and blue on your layout and I also show the corresponding pins of the tubes in the same red and blue.
Blencowe suggests having the nodes together.

Interesting.
Looking at example b., from input to rectifier on the bus, I see the input connected to chassis ground then I see V1's control grid and cathode grounds tied together and soldered to the bus near B+3. Then I see the same for V2 in between the latter and B+3. (grids going through pots to ground not shown?) Then B+3 itself. Heading towards B+2 node, I see speaker ground soldered on the quiet side of B+2 and then B+2 node and then V3 cathode and control grid(s) tied to V3 cathode ground and then to B+1 side of B+2 ???
This what I aimed for.

1651868857228.png


If I understand what you are saying then this would be the revision??

1651871297732.png
 

Lowerleftcoast

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Then B+3 itself. Heading towards B+2 node, I see speaker ground soldered on the quiet side of B+2 and then B+2 node and then V3 cathode and control grid(s) tied to V3 cathode ground and then to B+1 side of B+2
On page 273 of Blencowe's Chapter 15 on grounding he writes, "A separate wire (which does not need to be heavy gauge) should then run from the negative connection of the speaker jack back to an appropriate star. If global feedback is not used then this speaker ground wire should be returned to the power-amp star. If global feedback is used then the speaker ground should be returned to the local star of whichever stage the feedback happens to be applied to, which is usually the phase inverter (e.g., fig. 15.14)."

The 5F10 has the global feedback inserted at the first half, (triode), of the 12AX7.

If I am comprehending Blencowe, the correct place would be with B+3.

I am not willing to say the wire from the negative connection of the speaker must be connected at any particular node to avoid noise. On my builds, I do not isolate the speaker jack from the chassis. I have not had any issues. Imo, this wire has little DC current flow and has little chance of causing trouble.
If I understand what you are saying then this would be the revision?
Well the Vol pot ground should move to the last node. As you have seen with Blencowe, the bus should not have wires attached randomly along the bus, they cluster at each node.
If you haven't drilled the final board, explore ways to change layout. (You may decide this is as good as it gets.) If you have already drilled, imo, it is close enough.
 

screefer

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On my builds, I do not isolate the speaker jack from the chassis. I have not had any issues. Imo, this wire has little DC current flow and has little chance of causing trouble.
I wonder if anyone isolates the speaker jack? I'm just trying to be consistent with Merlin's practices. FBOFW
If you haven't drilled the final board, explore ways to change layout. (You may decide this is as good as it gets.) If you have already drilled, imo, it is close enough.
Final board not drilled. I will head back to Merlin with this new perspective.
Just so I'm clear this version...

1651879277139.png

... with the volume ground changed to B+3, would suffice if changing layout proves fruitless?

Thanks tons
 

Lowerleftcoast

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Looking good.

To make sure I know where the under-board wires go, I changed it to look like this.
(I found the 22k dropping resistor typo circled in red. You did this to test me, right?)

1651893107095-3.1.png

EDIT: Concerning grounding theory. I question whether the half wave rectifier reservoir capacitor (bias cap) should be included with the 2nd filter node. It seems to me that cap should ground with the B+ reservoir cap. (It is after all a reservoir cap for the bias supply and is not part of the B+ supply.) Blencowe's grounding article does not address the bias cap. The 6V6 220k grid leak resistors B+ current should ground with the 2nd filter cap, so, imo, the bias pot should ground with the 2nd filter cap. Others may have a different opinion.
 
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screefer

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To make sure I know where the under-board wires go, I changed it to look like this.
So cool! I haven't yet found how to flex a jumper wire. I wonder if a hookup wire can be edited to the same smaller size. I'll find out.
Here was what I had come up with but it doesn't address the confusing grid A lead.

1651934525272.png

(I found the 22k dropping resistor typo circled in red. You did this to test me, right?)
Lol!
No. When moving resistors around I duplicate and then delete the one in the way and then edit and reinsert. I misread the 220.:(
 

screefer

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Latest revision to de-confuse the under-board plate resistor connections with my new found trick. (thanks to LLC)
I'm going to stare at this for a day and then fire up the drill press.:)

1651942757851.png
.
 

Ronno25

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I don't mean to meddle with your plans but worth mentioning is that if you do have 3 inputs you can jump input 2 and 3 with a guitar cable and you get a different sound out of input 1. I'm not sure if you enlarging the chassis holes and using isolation would cause a spacial problem for this. I think this is one of the cooler tricks with a Harvard.
 

screefer

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I don't mean to meddle with your plans but worth mentioning is that if you do have 3 inputs you can jump input 2 and 3 with a guitar cable and you get a different sound out of input 1. I'm not sure if you enlarging the chassis holes and using isolation would cause a spacial problem for this. I think this is one of the cooler tricks with a Harvard.
Love meddling!
This is the first I've heard of this. I was under the impression that the third input was unnecessary because you could just use your guitar controls.
Have you a link to any sound clips? I'll do some digging.
Pretty sure there is room between the other two. I'd have to order:( another L12A tho...
 

Ronno25

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Love meddling!
This is the first I've heard of this. I was under the impression that the third input was unnecessary because you could just use your guitar controls.
Have you a link to any sound clips? I'll do some digging.
Pretty sure there is room between the other two. I'd have to order:( another L12A tho...
I'm not at home for the next two weeks or so otherwise I would record you a sound clip. The sound isn't a night and day difference, but it is notable, and it's fun to have a slightly different sound option. The jacks are tight together so you have to be very accurate with your hole placement.
 

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mrfitz98

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Latest revision to de-confuse the under-board plate resistor connections with my new found trick. (thanks to LLC)
I'm going to stare at this for a day and then fire up the drill press.:)

View attachment 980808 .

The bias cap is grounded twice? And there is a jumper going from the resistor hanging off the 6v6 sockets to ground? Both of those resistors are grounded, so that jumper seems redundant.
 




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