Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Snake5150 on October 20, 2024, 09:43:01 pm
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Using 2 jacks on an output secondary for 8/16 ohm.
When cable is plugged in should there be continuity between tip to ring.
And one tap can be open as long as the other is being used or should the un used tap go to ground?
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Your built : One jack on 8 ohms output and one jack on 16 ohms output
With a speaker cable plug in on ANY jack you should read output transformer secondary winding in ohms, fews ohm.
No tap ( tip ) to ground on any jack any time .
What I see on Univox I fixed, a switch and 2 jacks on each output ;
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The OT secondary is a not very long length of fairly thick wire. So it, and any taps from it, will have low resistance.
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What I see on Univox I fixed, a switch and 2 jacks on each output ;
Was there a problem with the schematic snippet you posted that required fixing? Or did you just modify the design to your liking?
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What I see on Univox I fixed, a switch and 2 jacks on each output ;
Was there a problem with the schematic snippet you posted that required fixing? Or did you just modify the design to your liking?
This is the original schematic of the amp as built by Univox . I have not modified or retouched anything.
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Using 2 jacks on an output secondary for 8/16 ohm.
When cable is plugged in should there be continuity between tip to ring.
He wants to know about 'continuity between tip to ring', not ohms. Why???? :dontknow:
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Using 2 jacks on an output secondary for 8/16 ohm.
And one tap can be open as long as the other is being used or should the un-used tap go to ground?
Yes, you can leave a secondary tap open when using the other tap.
No, do NOT ground any un-used tap. That will short the OT's secondary to ground.
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Using 2 jacks on an output secondary for 8/16 ohm.
When cable is plugged in should there be continuity between tip to ring.
He wants to know about 'continuity between tip to ring', not ohms. Why???? :dontknow:
I has .8 ohms from tip to ring with the secondary’s connected. I was just trying to clarify my setup as to not damage the transformer
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Using 2 jacks on an output secondary for 8/16 ohm.
When cable is plugged in should there be continuity between tip to ring.
He wants to know about 'continuity between tip to ring', not ohms. Why???? :dontknow:
I has .8 ohms from tip to ring with the secondary’s connected. I was just trying to clarify my setup as to not damage the transformer
I was replying pdf64. I'm was not asking you 5150.
You 1st asked about 'continuity between tip to ring' now you give an ohms measurement.
I posted why about that I have no idea why your asking about 'continuity between tip to ring'.
On an OT the secondary is as pdf64 wrote, a heavy gauge wire with only a few turns around the OT's core. On your OT they wound enough to get to an 8 output, they tapped it, then they finished the wind to get a 16 ohm output. So it's all 1 wire with a tap at a portion of the whole wind at 8 ohms. The OT's secondary has 'fly leads' connected to the start and finish of that wind and the 8 ohm tap is a 'fly lead' too. The start and finish, 2 ends of the wind, those 2 fly leads go to the output jack. So when you plug in a cord into the output jack, that cords wires become extensions of the fly leads which are extensions of the secondary wind. So if you test for continuity from the tip to the sleeve, your meter will say yes, you have continuity from tip to sleeve.
Why? Because it's all 1 wire.
Now why you want to know that to protect your OT I have no clue.
And your .8 ohm measurement should tell you there's also continuity from tip to sleeve.
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Using 2 jacks on an output secondary for 8/16 ohm.
When cable is plugged in should there be continuity between tip to ring.
He wants to know about 'continuity between tip to ring', not ohms. Why???? :dontknow:
I has .8 ohms from tip to ring with the secondary’s connected. I was just trying to clarify my setup as to not damage the transformer
I read 1 ohms with a Fluke meter. so your reading is good.
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I has .8 ohms from tip to ring with the secondary’s connected.
This is not clear at all.
What do you mean by "with the secondary’s connected." Connected to what? To each other? What secondaries?
With your OT that has an 8 and 16 ohm secondary, you can either connect the 8 ohm tap to a non shorting 1/4" jack and the 16 ohm tap to it's own non shorting 1/4" jack or use a large body, able to handle the current, switch to switch between either tap.
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Using 2 jacks on an output secondary for 8/16 ohm.
When cable is plugged in should there be continuity between tip to ring.
He wants to know about 'continuity between tip to ring', not ohms. Why???? :dontknow:
I has .8 ohms from tip to ring with the secondary’s connected. I was just trying to clarify my setup as to not damage the transformer
I was replying pdf64. I'm was not asking you 5150.
You 1st asked about 'continuity between tip to ring' now you give an ohms measurement.
I posted why about that I have no idea why your asking about 'continuity between tip to ring'.
On an OT the secondary is as pdf64 wrote, a heavy gauge wire with only a few turns around the OT's core. On your OT they wound enough to get to an 8 output, they tapped it, then they finished the wind to get a 16 ohm output. So it's all 1 wire with a tap at a portion of the whole wind at 8 ohms. The OT's secondary has 'fly leads' connected to the start and finish of that wind and the 8 ohm tap is a 'fly lead' too. The start and finish, 2 ends of the wind, those 2 fly leads go to the output jack. So when you plug in a cord into the output jack, that cords wires become extensions of the fly leads which are extensions of the secondary wind. So if you test for continuity from the tip to the sleeve, your meter will say yes, you have continuity from tip to sleeve.
Why? Because it's all 1 wire.
Now why you want to know that to protect your OT I have no clue.
And your .8 ohm measurement should tell you there's also continuity from tip to sleeve.
I was just trying to verify the conditions that should exist with the wiring attached. The secondary taps are wired to the jack showing .8 ohms between ring and tip. I understand my vocabulary is quite lacking. I was just trying to make sure things seem correct
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Hi,, Willabe was alluding to using an impedance selector switch. Personally this is the way to go. Then you can wire your OT outputs to the switch and select between them, and wire your outputs with a switchcraft 12a speaker jack and paralleled switchcraft 11 aux jack as done on countless Fender amplifiers. Then if the amp is turned on and operated with no speaker plugged in by mistake, the OT is protected.
These switches are smaller and work great https://www.tubesandmore.com/products/switch-rotary-1-pole-3-position-0 (https://www.tubesandmore.com/products/switch-rotary-1-pole-3-position-0)
I've installed this exact switch into many of my amps to ustilize the OT multi-taps out. The amp becomes more versatile and then can usually use any speaker cabinet available.
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He only has 2 taps, that rotary switch has 3 positions. I was thinking a SPDT switch. Like the Carling used for the Fender ground switch. Big body, can handle the OT secondary's current.
Doug sells them in his on line web store.
https://hoffmanamps.com/MyStore/catalog/parts7.htm
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yes that would work well
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He only has 2 taps, that rotary switch has 3 positions. I was thinking a SPDT switch. Like the Carling used for the Fender ground switch. Big body, can handle the OT secondary's current.
Doug sells them in his on line web store.
https://hoffmanamps.com/MyStore/catalog/parts7.htm
I really don’t have room for a big rotary. A the idea of a spdt is great, I have plenty also. But is 5amp 250vac enough? At this point I know yall are like “ this mf” . I know enough to sound good and hurt myself what can I say.
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I like to use a separate speaker output socket for each OT tap.
Then there's one less thing to fail.
So with 2 taps then at least 2 sockets.
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I like to use a separate speaker output socket for each OT tap.
Then there's one less thing to fail.
So with 2 taps then at least 2 sockets.
And you never forget to plug one or ther other in? This whole no transformer load open circuit thing might have me over spooked. I have 1 cabinet, don’t play shows. I may be over thinking it. I don’t have room for the rotary and only have 8 and 16 ohm taps. Was gonna just run jacks for each. Only reason I want both is because I could theoretically require the cab to run 16. Not that I would people have suggested either way, and functionally both would work. Odds are I won’t open short the tranny but ya never know.
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2 output jacks works fine too.
Just leave a speaker cab plugged in all the time. When you move it, plug the cab back in.
You can turn an amp on without a speaker hooked up to it, just can't play anything into the amp.
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Hi,, Willabe was alluding to using an impedance selector switch. Personally this is the way to go. ........
Answer #1 schematic show what to do .
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Tbh I would just wire it for 8 ohms. If one day you end up owning a 16 ohm cab you can always revisit the amp wiring.
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I like to use a separate speaker output socket for each OT tap.
Then there's one less thing to fail.
So with 2 taps then at least 2 sockets.
And you never forget to plug one or ther other in? This whole no transformer load open circuit thing might have me over spooked.
I fit a safety back up load resistor across one of the sockets, eg 470R on the 16 ohm output, as per the Vox AC50 https://el34world.com/charts/Schematics/files/Vox/Vox_ac50_1.pdf
This pretty much eliminates the possibility of the OT secondary being unloaded, open circuit. And should provide enough of a load to prevent damage in the short term, without excessively wasting power or affecting the amp's response.
My understanding is that an intermittent open circuit, eg dodgy speaker cable / connector / switch, when the amp is working hard, is the worst case scenario for a valve amp.
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... should there be continuity between tip to ring.
The OT secondary is a not very long length of fairly thick wire. So it, and any taps from it, will have low resistance.
He wants to know about 'continuity between tip to ring', not ohms. Why???? :dontknow:
When I didn't know any better, I thought my meter's Continuity setting amount to "a beep for 0Ω/short-circuit."
Turns out many meters beep for a resistance <100Ω (or something similar).
In my youthful ignorance, I would have thought I made a wiring mistake & created a short-circuit somewhere.
These days, I know that I need to understand how my test gear makes its test, what values to expect in my circuit, and consider the ways my circuit will cause my test gear to mislead me. That is, a Continuity Test will give confusing results around a very low-resistance circuit that's properly wired.