Question on zener placement to

18watt-specific Tech Talk - Building, Fixing, Parts, Mods...

Moderators: CurtissRobin, colossal, zaphod_phil, Daviedawg, Graydon

bvayling
Occasional poster
Occasional poster
Posts: 120
Joined: Sat 03/30/13 12:53 am

Question on zener placement to

Post by bvayling »

reduce the B+ voltage. Searching on the site, I think I get the basics. My B+ of 360V at pin 3 of V6 is about 15V higher than I'd like it to be. So 3 x 5.6 V 5W zeners in series seems to be in order.

Reading through the material, it seems I can put these three in line with the wire going from the capcan terminal to the board with the stripe side of the zeners facing back to the capcan. Is this correct?

If the placement is correct, will suspending them in the air be enough to cool them?

Thanks.
Bernard
2 x

User avatar
JMPGuitars
Super Duper Admin
Super Duper Admin
Posts: 1981
Joined: Tue 09/18/12 8:00 pm
Location: South Central, MA
Contact:

Re: Question on zener placement to

Post by JMPGuitars »

Sounds like you've got a good handle of what you're doing here. The 5W rating is overkill (which is a good thing), especially when you're using 3 Zeners to do the voltage dropping, so heat shouldn't be an issue.

I would be more concerned with vibration. If it's a short distance to the board from the cap can, then it's all good. If not, I'd use a terminal strip in between to give it stability.
0 x
'I installed a skylight in my apartment yesterday... The people who live above me are furious.' - Steven Wright
Web Design: DolceVittoria.com
Guitars / Amps / Effects: JMPGuitars.com
(anti)Social: Facebook · Instagram
Items for Sale

bvayling
Occasional poster
Occasional poster
Posts: 120
Joined: Sat 03/30/13 12:53 am

Re: Question on zener placement to

Post by bvayling »

Cool, thanks for the feedback Josh. I’m sure when I open it back up i’ll figure some thing out.
Cheers!
0 x

User avatar
zaphod_phil
Builder, Admin
Builder, Admin
Posts: 14993
Joined: Wed 03/19/03 2:00 am
Location: YYZ

Re: Question on zener placement to

Post by zaphod_phil »

bvayling wrote:
Wed 04/15/20 10:58 am
reduce the B+ voltage. Searching on the site, I think I get the basics. My B+ of 360V at pin 3 of V6 is about 15V higher than I'd like it to be. So 3 x 5.6 V 5W zeners in series seems to be in order.
Reading through the material, it seems I can put these three in line with the wire going from the capcan terminal to the board with the stripe side of the zeners facing back to the capcan. Is this correct?
Correct - except the stripe side of all the zeners need to point towards your OR, not the filter cap can.***correction that was meant to say "OT" not "OR" :-(
0 x
Nature abhors a clean tube amp

bvayling
Occasional poster
Occasional poster
Posts: 120
Joined: Sat 03/30/13 12:53 am

Re: Question on zener placement to

Post by bvayling »

Thanks Phil.
I thought I understood it but obviously need to do some more reading and retention on zeners.

I had even copied what you just said from a 2011 thread into my notes.....I need to slow down and process better. (Hits self on head.)
0 x

geoff 1965
Frequent poster
Frequent poster
Posts: 718
Joined: Mon 01/04/16 3:52 pm

Re: Question on zener placement to

Post by geoff 1965 »

just for confirmation,looking at this symbol which side has the grey/silver band on a zener diode?
zener diode.jpg
You do not have the required permissions to view the files attached to this post.
0 x

User avatar
zaphod_phil
Builder, Admin
Builder, Admin
Posts: 14993
Joined: Wed 03/19/03 2:00 am
Location: YYZ

Re: Question on zener placement to

Post by zaphod_phil »

The pointed end with the bent bar across it, is the stripe side.
0 x
Nature abhors a clean tube amp

bvayling
Occasional poster
Occasional poster
Posts: 120
Joined: Sat 03/30/13 12:53 am

Re: Question on zener placement to

Post by bvayling »

zaphod_phil wrote:
Thu 04/16/20 12:29 pm
bvayling wrote:
Wed 04/15/20 10:58 am
Correct - except the stripe side of all the zeners need to point towards your OR, not the filter cap can.***correction that was meant to say "OT" not "OR" :-(
Thanks for the clarification, I was getting even more confused...
For peace of mind at this point, I am guessing that when you say OT, you mean the final destination in the chain of the current flow? (Since the wire in question goes to the board.)
0 x

User avatar
JMPGuitars
Super Duper Admin
Super Duper Admin
Posts: 1981
Joined: Tue 09/18/12 8:00 pm
Location: South Central, MA
Contact:

Re: Question on zener placement to

Post by JMPGuitars »

bvayling wrote:
Fri 04/17/20 8:22 am
zaphod_phil wrote:
Thu 04/16/20 12:29 pm
Correct - except the stripe side of all the zeners need to point towards your OR, not the filter cap can.***correction that was meant to say "OT" not "OR" :-(
Thanks for the clarification, I was getting even more confused...
For peace of mind at this point, I am guessing that when you say OT, you mean the final destination in the chain of the current flow? (Since the wire in question goes to the board.)
The issue in clarity here is that I don't know that either of you are speaking about the same method of dropping the voltage. "After the 1st filter cap" can be vague. Maybe a reference diagram would be helpful.
0 x
'I installed a skylight in my apartment yesterday... The people who live above me are furious.' - Steven Wright
Web Design: DolceVittoria.com
Guitars / Amps / Effects: JMPGuitars.com
(anti)Social: Facebook · Instagram
Items for Sale

geoff 1965
Frequent poster
Frequent poster
Posts: 718
Joined: Mon 01/04/16 3:52 pm

Re: Question on zener placement to

Post by geoff 1965 »

yeah this is confusing to me now,the 18V zener on this triwatt is showing the stripe side towards the rectifier not the OT?
TriwattSchematic12.pdf
so for instance if i place a zener to drop B+ between the can cap filter and OT then the stripe/band side goes to the OT.
You do not have the required permissions to view the files attached to this post.
0 x

User avatar
JMPGuitars
Super Duper Admin
Super Duper Admin
Posts: 1981
Joined: Tue 09/18/12 8:00 pm
Location: South Central, MA
Contact:

Re: Question on zener placement to

Post by JMPGuitars »

The stripe goes towards the voltage source.

The vagueness is in the actual placements of the Zeners considering that "after the first filter cap" could literally mean any point from between the first two filter caps to the end of the B+ line (which would be silly, but you get my point).

In your example of the Triwatt schematic, D5's stripe is pointed towards the voltage source (which is correct), but it is also before the 1st filter cap. The issue here is that it won't drop voltage as efficiently. In my experience the voltage drop could be as low as 50% of the Zener rating in that position. I do it anyway for logistical reasons, but it's not ideal.
0 x
'I installed a skylight in my apartment yesterday... The people who live above me are furious.' - Steven Wright
Web Design: DolceVittoria.com
Guitars / Amps / Effects: JMPGuitars.com
(anti)Social: Facebook · Instagram
Items for Sale

geoff 1965
Frequent poster
Frequent poster
Posts: 718
Joined: Mon 01/04/16 3:52 pm

Re: Question on zener placement to

Post by geoff 1965 »

yeah Josh i followed that triwatt orientation with the stripe towards the rectifier except i've placed it between the 1st filter and output transformer as ZP says they are more efficient here.i'm trying to add a pic but my laptop is'nt reading the card!
it's working and dropping the correct voltage.
003.JPG
You do not have the required permissions to view the files attached to this post.
Last edited by geoff 1965 on Fri 04/17/20 2:46 pm, edited 1 time in total.
0 x

bvayling
Occasional poster
Occasional poster
Posts: 120
Joined: Sat 03/30/13 12:53 am

Re: Question on zener placement to

Post by bvayling »

It seems to me placing the zeners after the filter cap and before the voltage goes to the board makes the most sense.

From what I’ve read, a zener will drop voltage regardless of orientation but will drop it‘s full rated voltage only if placed with the stripe facing “back” towards the voltage source.

I think Phil is using OT as a form of providing direction, as in the voltage comes from the capcan and ultimately winds up at the OT. If I am trying to reduce the B+ It has to be done before it gets to the board, no?

I’ve been wrong before.
0 x

User avatar
JMPGuitars
Super Duper Admin
Super Duper Admin
Posts: 1981
Joined: Tue 09/18/12 8:00 pm
Location: South Central, MA
Contact:

Re: Question on zener placement to

Post by JMPGuitars »

bvayling wrote:
Fri 04/17/20 10:14 am
From what I’ve read, a zener will drop voltage regardless of orientation but will drop it‘s full rated voltage only if placed with the stripe facing “back” towards the voltage source.
Zeners only drop the rated voltage in one direction. If you orient them the wrong way, they work as a standard diode. For example, a 15V diode will likely drop only about .7V if not oriented correctly.
0 x
'I installed a skylight in my apartment yesterday... The people who live above me are furious.' - Steven Wright
Web Design: DolceVittoria.com
Guitars / Amps / Effects: JMPGuitars.com
(anti)Social: Facebook · Instagram
Items for Sale

User avatar
zaphod_phil
Builder, Admin
Builder, Admin
Posts: 14993
Joined: Wed 03/19/03 2:00 am
Location: YYZ

Re: Question on zener placement to

Post by zaphod_phil »

geoff 1965 wrote:
Fri 04/17/20 9:23 am
yeah this is confusing to me now,the 18V zener on this triwatt is showing the stripe side towards the rectifier not the OT?
TriwattSchematic12.pdf
so for instance if i place a zener to drop B+ between the can cap filter and OT then the stripe/band side goes to the OT.
I'm fascinated that we're using the Triwatt as an example here, as that is actually one of my own amp designs (with much borrowed from Dave Reeves' original Hiwatt designs) :)

The zener orientation in that schematic is indeed correct, pointing the opposite direction to the rectifiers, D1 -D4. I must now apologise for saying the zener stripe ends should point towards the OT. As some folks now know, I am recovering from a brain injury, due to a combination of brain surgery and radiation treatment. So I often get these mind glitches (aka "brain farts" :lol:), as well as short-term memory losses.

What I really did wrong in the Triwatt design was to place the zener in between the rectifiers and the 50+50uF cap can, C20. I realized my error when testing voltages on the bench, and found that instead of dropping 18V, it was dropping something like 12V, IIRC. However, that drop turned out to be exactly what was wanted, so we left the zener right there in the final design :).
1 x
Nature abhors a clean tube amp

Post Reply