470 ohm resistor

[tdelucia]

Is the 470 ohm resistor a protection load when no speaker is plugged in?  I think so.

[sluckey]

Is the 470 ohm resistor a protection load when no speaker is plugged in?  I think so.

The 470 ohm resistor is a popular value. It has many uses. Your question is very specific. We need to see a schematic to give a specific answer.

[tdelucia]

It's on an older hoffman parts layout sheet for a 5e3. It's not on the website anymore. I have the older parts layout and it shows the 470 ohm resistor.  I also have the current parts layout and it doesn't show the 470 ohm resistor.  It's not on the schematic either.  All my voltages seem fine but I'm getting very low output from  the amp.  Real low.  I took an old 1x12 SS amp and converted it to a 5e3 tube.  I'm thinking it may be the OT?  Any thoughts?

[sluckey]

It's on an older hoffman parts layout sheet for a 5e3. It's not on the website anymore. I have the older parts layout and it shows the 470 ohm resistor.

Please show us the layout you are talking about.

[kagliostro]

On a BOM for the 5E3 that I've (by Hoffman) I can see 2 x 470R 3W

the Note say Screen

but the file is one year old or a bit more, so no one of the older version

Franco


p.s.: BTW there is one other thread with the same subject, I think one must be deleted

[EL34]

Why would there be a 470 ohm resistor on the speaker jack?

Makes no sense to me and I don't remember ever having a mistake like that on any of my layout drawings
It would be on a bunch of them if that was the case because I copy and paste things from one drawing to the next

As Sluckey requested, please post this layout drawing so we can see it

[tdelucia]

OK.  Lets just put this to rest.  I was just asking what the purpose of the 470 resistor was on the speaker jack on an older Hoffman parts layout diagram that I have.  The current parts diagram doesn't show it, nor does the schematic.  I thought maybe someone may have built the 5e3 with the older diagram ( maybe a few years old ), that could answer the question.

[jjasilli]

See, e.g.:


http://el34world.com/Forum/index.php?topic=18236.0



http://music-electronics-forum.com/t31452/

[sluckey]

OK.  Lets just put this to rest.  I was just asking what the purpose of the 470 resistor was on the speaker jack on an older Hoffman parts layout diagram that I have.  The current parts diagram doesn't show it, nor does the schematic.  I thought maybe someone may have built the 5e3 with the older diagram ( maybe a few years old ), that could answer the question.

I've been here over 10 years. None of Hoffman's 5E3 diagrams have ever had a 470Ω resistor on the speaker jack. You say you have a Hoffman diagram that does have a 470Ω on the speaker jack. Please show us that diagram. It's easy to attach a pic to your reply.

[tdelucia]

I was told this came from the Hoffman site.  I not that would explain some of the responses.

[EL34]

Nope, not my drawing
You can see what my drawings look like on the library page


They look like this

[tdelucia]

Yeah OK.  I was told it cam from the Hoffman site.

[kagliostro]

I've find the old version



and is clear that also the old version was very different from those you have

I would like to say that someone copied the basic layout and arranged it at his taste

Franco

[EL34]

That's a real long time ago
That's before I had Visio


I did those really old layout in Paint Shop Pro

[John]

To the original question: I assume that is a safety resistor meant to protect the OT if someone forgets to plug in a speaker to it and hits a power chord, or if you blow the speaker while hammering away. Plugging in the speaker basically makes that resistor "invisible" to the OT due to Ohm's Law. This is also assuming I read your picture right with my head cricked to one side. 

[Ed_Chambley]

Member Binwitt did a Princeton Reverb with the 470 attached. This drawing does not look like his work. I have seen builders use a 8 ohm 25 watt connected to a switching jack that works as a dummyload when the speaker is not plugged.
I never liked the idea for many reasons.

[sluckey]

I was told this came from the Hoffman site.  I not that would explain some of the responses.

That ain't a Hoffman drawing.

[tdelucia]

OK everyone.  Thanks for all the reply's.  I was told that it was an older Hoffman layout.  Anyway I thought the resistor acted as a dummy load.  I just wanted to confirm.  My main problem with my 5e3 build is very low output.  So I thought maybe not putting in the resistor may have something to do with my problem.  I checked my voltage and wiring over and over and can't seem to find anything that is not wired up correctly.  The amp is not putting out any reasonable volume.  I also changed out to different tube still the same problem.  Can anybody give me some place to look?  Or, what may be the systems of low volume?

[sluckey]

Can you show us a more detailed drawing? 640x480 ain't big enough to show the detail we need to see.

[EL34]

OK everyone.  Thanks for all the reply's.  I was told that it was an older Hoffman layout.  Anyway I thought the resistor acted as a dummy load.  I just wanted to confirm.  My main problem with my 5e3 build is very low output.  So I thought maybe not putting in the resistor may have something to do with my problem.  I checked my voltage and wiring over and over and can't seem to find anything that is not wired up correctly.  The amp is not putting out any reasonable volume.  I also changed out to different tube still the same problem.  Can anybody give me some place to look?  Or, what may be the systems of low volume?

Yes, you do this first and then report back
The highlighter on the layout is really important

[HotBluePlates]

You may also want to post large, clear photos of your build, so we can help you find any mis-wired or wrong parts.  Also note that only the main speaker jack should have an extra contact that touches the Tip contact (if your amp has those at all on the speaker).

Yes, the 470Ω on your drawing is the author's attempt to protect the amp in the event of no speaker.  They may have started with a Hoffman layout, but then they changed the drawing itself to look more like a literal, physical layout.  They also added at least that resistor, plus something illegible on the input stage cathode circuit.

[tubeswell]

470R is okay as an emergency no-load, 220R would be okay also. In the circuit, the resistor will be in parallel with the actual 4-8-16R speaker, and will make next to no difference to the reflected load.

[dude]

Why not just use a switchcraft shorting jack and be done with, but if you have an extension spk jack, make sure it's not a shorting jack.


al 

[HotBluePlates]

Why not just use a switchcraft shorting jack and be done with ...

Some have gotten to where they don't like that approach.

[sluckey]

Mystery solved! That drawing was done by forum member bnwitt. So that's the connection to Hoffman. Barry was very active here years ago when I first arrived and it's quite possible that he posted that drawing on the forum back then. So yes, it may have come from this site and no, it's not one of Hoffman's drawings.

I have the original Visio drawing that Barry gave me years ago when we were swapping drawings and shapes.

And yes that 470Ω resistor on the speaker jack is called a safety resistor on Barry's revision 2 of that layout.

And for Dude... The shorting jack works if the speaker cable is unplugged from the amp ONLY. The 470Ω resistor provides a degree of protection if the speaker cable is plugged into the amp but not connected to a speaker load. But it has to be wired correctly. Unfortunately, in that drawing, the 470Ω only provides protection if the speaker cable is not plugged into the amp, so may as well just connect the switch terminal to the ground terminal.

[EL34]

Thanks Steve
That splains that