5F6A kit "issues". Help me, PLEASE!

[frpax]

Hello amp dudes and dudettes!

So, based on my excellent experience in converting an old Hammond organ into a 6V6 Plexi a couple of years ago, I've been itching to do something else.
After MUCH deliberation, I decided to  get the Hoffman 5F6A kit. Just the amp & chassis and all the small parts, no cabinet or speakers as I'm planning on something a bit different.

Today, everything arrived (with the exception of the Output Transformer-- it is out of stock) and I've noticed some pretty glaring inconsistencies. So, I humbly come to you experts to help me out with some stuff:
1. The Hoffman wiring diagram (layout) shows the tone stack as Treble/Mid/Bass. The actual chassis is Treble/Bass/Mid (like the original Bassman was). WHY?
2. The Hoffman layout shows only 2 input jacks---the chassis has the normal 4. So is the Hoffman layout showing 2 as 1 Normal and 1 Bright? How do I wire it up for the 4??
3. The Hoffman layout shows just one speaker output jack---chassis has 4. How do I wire up for 4??
4. The Hoffman layout has no Ground Switch, yet the chassis has the hole for it and the kit came with one. What do I do here??
5. The Hoffman turret board has no holes for the stand offs. I can drill some, no problem. But it also looks as if I need to drill the chassis as well. The holes that are in the chassis, that look to be what should accommodate the board, are too far apart for the size of the board I got. Just seems weird to me.

So, am I missing something? Am I an ignorant fool and ordered mismatching parts, somehow?

Please help me out here!

Many, many thanks!!

~Frank

[tubenit]

Frank,

The first thing I would do in your situation is print off the original 5F6-A Bassman layout  AND  the Hoffman 5F6-A layout and study the differences in how they are wired up.  Since the chassis is a duplicate of the original chassis,  it would be useful to look at the original layout which may easily answer some of your questions.  I've added another link that has a good layout drawn that you can print out also.

https://el34world.com/charts/Schematics/files/Fender/Fender_bassman_5f6a_layout.gif

https://el34world.com/Hoffman/files/Hoffman_5F6A.pdf

https://www.tedweber.com/media/kits/5f6a_layout.jpg

1)  OK,  so just change the wiring.  Easy to do.  Look at the original layout.  And look at this layout.
     https://el34world.com/Hoffman/images/5f6aOld.gif

2)  Look at the original layout.  Look in Hoffman's Library of Information at how to wire low/high input jacks.
     https://el34world.com/charts/CommonHookups.htm

3)  Look at the original layout.  You can also look at the schematic and layout here:
     https://www.tedweber.com/media/kits/5f6a_layout.jpg

    AND again, Hoffman's Library of Information is incredibly useful and Doug created that as a wonderful resource just for the very kind of
    questions.   Look at " 4 speakers parallel and series wiring diagram"

    https://el34world.com/charts/Charts.htm

4)  Assuming you are using a 3 prong plus and not a two prong plug like original,  I am thinking that you don't need that. So one way to plug the
     hole is get a piece of chrome sheet metal and put it on the inside of the chassis to "cover" the hole using small screws or perhaps epoxy or
     silicone.

5)  So, drill the holes that are needed and move on.  No big deal.  IF the chassis is a duplicate of the original and drilled for the original board and
     you're using a Hoffman board. Then adapt. 

You can make this work.  There is great information available if you look for it & the forum members are super helpful when you get stuck.  Hoffman's layouts are tried and true and they are very quiet at idle.  He has thought them out well & it's a great approach.

Some of building is also the mindset you bring.  Some of it's a mental thing.  We create mental pictures of the way things "should be" and it's easy to get flummoxed trying to figure out how to accomplish that.  For example,  do you need 4 input jacks?  You might because of "jumpering" but IF you don't then don't use all 4.  You can plug the holes with plastic inserts or put pieces of chrome sheet metal inside the chassis.

Stick with a "can do" attitude!  You can be successful with this and have a phenomenal amp that you enjoy for yrs and yrs.

With respect and good will,  Tubenit

[pompeiisneaks]

You already got great answers, I just wanted to add two things. 

A. Dougs Bassman is meant to be slightly different than the original, he's done something to the inputs for example, to get you a slightly different channel than the original, (different cathode cap and resistor, the original shared them).   Etc.  The idea is to build something like one, but with more.

B.  The reason the diagrams only show one pair of input jacks, is that you wire both sets up identically.  The Bass channel gets two jacks, one wired in Hi one in Lo mode.  Then you repeat the exact same process for the Normal channel. There are some great documents out there that explain how the Fender Lo/Hi jacks work, you should read up on it to understand it, one of them is by Sluckey here on the forums.  read it here: http://www.sluckeyamps.com/misc/Amp_Scrapbook.pdf (Go to page 8) or read up from the description of another forum member, Rob Robinette here: https://robrobinette.com/How_Fender_Input_Jacks_Work.htm

Should help fill in the gaps on why/how you use 2 input jacks, and with very slight wiring changes you get quite a different sound/feel from them.  As tubenit stated, though, you could just choose to use a 33k resistor and a 1m resistor to ground and only use 2 inputs, one per preamp section so you can choose which you want quickly and move on (but the 'jumpering' is worth it alone in my opinion.  Which is putting a small jumper cable between the two inputs so you can play both at the same time on one guitar.)

~Phil

[frpax]

Frank,

The first thing I would do in your situation is print off the original 5F6-A Bassman layout  AND  the Hoffman 5F6-A layout and study the differences in how they are wired up.  Since the chassis is a duplicate of the original chassis,  it would be useful to look at the original layout which may easily answer some of your questions.  I've added another link that has a good layout drawn that you can print out also.

https://el34world.com/charts/Schematics/files/Fender/Fender_bassman_5f6a_layout.gif

https://el34world.com/Hoffman/files/Hoffman_5F6A.pdf

https://www.tedweber.com/media/kits/5f6a_layout.jpg

1)  OK,  so just change the wiring.  Easy to do.  Look at the original layout.  And look at this layout.
     https://el34world.com/Hoffman/images/5f6aOld.gif

2)  Look at the original layout.  Look in Hoffman's Library of Information at how to wire low/high input jacks.
     https://el34world.com/charts/CommonHookups.htm

3)  Look at the original layout.  You can also look at the schematic and layout here:
     https://www.tedweber.com/media/kits/5f6a_layout.jpg

    AND again, Hoffman's Library of Information is incredibly useful and Doug created that as a wonderful resource just for the very kind of
    questions.   Look at " 4 speakers parallel and series wiring diagram"

    https://el34world.com/charts/Charts.htm

4)  Assuming you are using a 3 prong plus and not a two prong plug like original,  I am thinking that you don't need that. So one way to plug the
     hole is get a piece of chrome sheet metal and put it on the inside of the chassis to "cover" the hole using small screws or perhaps epoxy or
     silicone.

5)  So, drill the holes that are needed and move on.  No big deal.  IF the chassis is a duplicate of the original and drilled for the original board and
     you're using a Hoffman board. Then adapt. 

You can make this work.  There is great information available if you look for it & the forum members are super helpful when you get stuck.  Hoffman's layouts are tried and true and they are very quiet at idle.  He has thought them out well & it's a great approach.

Some of building is also the mindset you bring.  Some of it's a mental thing.  We create mental pictures of the way things "should be" and it's easy to get flummoxed trying to figure out how to accomplish that.  For example,  do you need 4 input jacks?  You might because of "jumpering" but IF you don't then don't use all 4.  You can plug the holes with plastic inserts or put pieces of chrome sheet metal inside the chassis.

Stick with a "can do" attitude!  You can be successful with this and have a phenomenal amp that you enjoy for yrs and yrs.

With respect and good will,  Tubenit

VERY good advice! And THANK YOU for taking the time to respond!

I absolutely have a CAN DO attitude! Just sometimes I need to be pointed in the right direction.

[frpax]

You already got great answers, I just wanted to add two things. 

A. Dougs Bassman is meant to be slightly different than the original, he's done something to the inputs for example, to get you a slightly different channel than the original, (different cathode cap and resistor, the original shared them).   Etc.  The idea is to build something like one, but with more.

B.  The reason the diagrams only show one pair of input jacks, is that you wire both sets up identically.  The Bass channel gets two jacks, one wired in Hi one in Lo mode.  Then you repeat the exact same process for the Normal channel. There are some great documents out there that explain how the Fender Lo/Hi jacks work, you should read up on it to understand it, one of them is by Sluckey here on the forums.  read it here: http://www.sluckeyamps.com/misc/Amp_Scrapbook.pdf (Go to page 8) or read up from the description of another forum member, Rob Robinette here: https://robrobinette.com/How_Fender_Input_Jacks_Work.htm

Should help fill in the gaps on why/how you use 2 input jacks, and with very slight wiring changes you get quite a different sound/feel from them.  As tubenit stated, though, you could just choose to use a 33k resistor and a 1m resistor to ground and only use 2 inputs, one per preamp section so you can choose which you want quickly and move on (but the 'jumpering' is worth it alone in my opinion.  Which is putting a small jumper cable between the two inputs so you can play both at the same time on one guitar.)

~Phil

Thank you for your comments and suggestions!

[frpax]

So, the kit came with 5 large caps that connect to the board. However, the kit did not come with a small board for those caps. So, I either need to make one or buy one. The original 5F6A had 4 caps, so if I were to buy one, it would need to accommodate 5. Any thoughts on this? I'll need to mount in vertically in the chassis so the dimensions need to be no larger than 3.5" x 2" (maybe 2.25" max). Does Doug sell one? I looked and didn't find anything, other than blank phenolic material.

[sluckey]

Doug likes to mount caps like this...

[frpax]

Doug likes to mount caps like this...

Is he grounding each cap to the buss ground on the back of the pots?

[sluckey]

The four gray caps are grounded to the pot ground buss. But the node A cap (big blue) is grounded at a PT bolt. Keep in mind that pic is an AB763, not a 5F6A, but the idea applies to your amp as well, ie, ground the node A caps at the same PT bolt that the red/yellow centertap is grounded, and ground the other caps on the pot ground buss.

Even if you put the caps on a board or use some other method to mount the caps you should ground the node A caps at the same PT bolt that the red/yellow centertap is grounded, and ground the other caps on the pot ground buss.

[frpax]

The four gray caps are grounded to the pot ground buss. But the node A cap (big blue) is grounded at a PT bolt. Keep in mind that pic is an AB763, not a 5F6A, but the idea applies to your amp as well, ie, ground the node A caps at the same PT bolt that the red/yellow centertap is grounded, and ground the other caps on the pot ground buss.

Even if you put the caps on a board or use some other method to mount the caps you should ground the node A caps at the same PT bolt that the red/yellow centertap is grounded, and ground the other caps on the pot ground buss.

Very good to know! Options! I like it!!

[frpax]

Question:

I want to wire up 4 input jacks like a vintage 5F6A, but Doug's diagram shows only 2. Looking at a "vintage" style layout, i can get some of it, but i'm still missing something.
Please look at the input jack area in the pic below and let me know if something is wrong and where I need to connect the "tips" to:

[frpax]

Also, is this method of grounding the speaker jack acceptable? Or major mistake?

[pompeiisneaks]

Rob Robinette's site has a good picture of how to wire up the 2 input jacks hi/lo version here:

https://robrobinette.com/How_Fender_Input_Jacks_Work.htm

as for the grounding of the speaker jack, that is not only good, but super important to ensure you don't destroy an output transformer.  The old school way was to count on the jack's connectivity to the chassis as the ground but those do come loose.  Having a separate wire that is soldered to a chassis point is a better guarantee you don't ever leave your OT secondary open and give it a better chance of getting roasted.  Grounded is still a possible damaging state, but much less so than open. 

~Phil

[sluckey]

Does this help with the four input jacks? (see pic)

Your speaker jack grounding looks exactly like Hoffman's drawing. It will work just fine. ***BUT*** Didn't you want to use four RCA jacks for the speaker jacks just like the original?

[frpax]

Does this help with the four input jacks? (see pic)

Yes!

Your speaker jack grounding looks exactly like Hoffman's drawing. It will work just fine. ***BUT*** Didn't you want to use four RCA jacks for the speaker jacks just like the original?

I'm going to go into a 2x12 combo cabinet.

[sluckey]

There's a photo of the dual jack wiring on this web page. Other useful stuff too. Worth a look...

     https://el34world.com/charts/CommonHookups.htm

[frpax]

Regarding the wiring to the heaters, I was following THIS:




But my board has 2 turrets for "heaters", so should it look like THIS, instead?

[PRR]

> THIS:... like THIS, instead?

What is the difference?

OK, the resistors are physically located at the lamp or on the board. But electrically the same.

[pompeiisneaks]

> THIS:... like THIS, instead?

What is the difference?

OK, the resistors are physically located at the lamp or on the board. But electrically the same.

Exactly.  No difference.  The net goal is to connect two 100 ohm resistors from each leg to earth.  Doesn't matter where it happens.

~Phil

[sluckey]

I would use big 18AWG from the pilot lamp directly to V5 pins 2 and 7. I would then use small 22AWG between the board and V5 socket.

However, if your PT filament winding has a center tap (usually green/yellow) on the filament winding, I'd just connect that to chassis ground and not connect the filament wires to the board.

[frpax]

I would use big 18AWG from the pilot lamp directly to V5 pins 2 and 7. I would then use small 22AWG between the board and V5 socket.

However, if your PT filament winding has a center tap (usually green/yellow) on the filament winding, I'd just connect that to chassis ground and not connect the filament wires to the board.

Like this?

[pompeiisneaks]

Yes, of course if it's not super clear here, those heater wires also have to chain across to all the tubes from there as well, note the tube pins that have the 'green' color are the pins that should be connected, one lead to each side (the pins 4 and 5 on the preamp tubes need to be jumpered and you connect just one side to those two the other to pin 9, this is only for 12A*7 tube types, you'd need to check for others on their respective data sheet for heater pins.)

~Phil

[frpax]

Yes, of course if it's not super clear here, those heater wires also have to chain across to all the tubes from there as well, note the tube pins that have the 'green' color are the pins that should be connected, one lead to each side (the pins 4 and 5 on the preamp tubes need to be jumpered and you connect just one side to those two the other to pin 9, this is only for 12A*7 tube types, you'd need to check for others on their respective data sheet for heater pins.)

~Phil

Yep. I got all the green heater wires all connected. Just need to go from V5 to the board.

[pompeiisneaks]

It looks like V4 is physically closer, so you could do a direct connection with a shorter run and less chance of interaction with other signal wires, but basically any of the tubes to those 100 ohms is fine.  Or as sluckey mentioned, if there's a Center Tap on the transformer, just ground that.  the 100 ohms are a 'virtual center tap'.

~Phil

[frpax]

Or as sluckey mentioned, if there's a Center Tap on the transformer, just ground that.

There is a Center Tap on the power transformer, which I do have grounded.



So with the center tap grounded, I needn't worry about going from the board to V4 or V5. Correct?

[sluckey]

wrong center tap.

However, if your PT filament winding has a center tap (usually green/yellow) on the filament winding, I'd just connect that to chassis ground and not connect the filament wires to the board.

[pompeiisneaks]

The winding you're talking about is the heater winding, the B+ winding's center tap is not the same thing as the heater winding.  The question was if the heater winding has a center tap :D

~Phil

[frpax]

wrong center tap.

Great! I was unaware of there being more than one center tap! 

[EL34]

I am late to the party here but I am guessing you did not look at all the documents listed under the particular board you have on the library page

If you did you would see all the options that are available when building any one of my boards
https://el34world.com/schematics.htm#Hoffman_5F6A_Bassman_