Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Jack_Hester on February 27, 2014, 07:22:17 pm
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I have been looking over the spec sheet on the G6A relay series. I'm curious as to how long of a period would one of these relays be on, at a time. Typically, when used in some of the recent amp designs, for switching the Overdrive in and out. But also, in other amp applications, as well.
The reason I ask is in reference to the last page of this sheet, which states:
●Long-term Continuously ON Contacts
Using the Relay in a circuit where the Relay will be ON continuously for long periods (without switching)
can lead to unstable contacts because the heat generated by the coil itself will affect the insulation,
causing a film to develop on the contact surfaces.
We recommend using a latching relay (magnetic-holding relay) in this kind of circuit. If a single-side
stable model must be used in this kind of circuit, we recommend using a fail-safe circuit design
that provides protection against contact failure or coil burnout.
The whole spec sheet file is too large to attach.
Comments, please. Thanks.
Jack
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There you go thinking again Jack. :laugh: Good question.
As far as the text you posted I remember KOC saying in a TUT book that make relays that are sealed with a special gas and have gold plated contacts? I think a relay like that will help fight that film thing from happing. Although I think he was talking about arcing form turn on/turn off? :think1:
Brad :icon_biggrin:
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I have been looking over the spec sheet on the G6A relay series. I'm curious as to how long of a period would one of these relays be on, at a time.
About as long as ther amp is left on. Probably not more than a few hours at a time. I would guess the data sheet is more worried about months.
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There you go thinking again Jack. :laugh: Good question.
As far as the text you posted I remember KOC saying in a TUT book that make relays that are sealed with a special gas and have gold plated contacts? I think a relay like that will help fight that film thing from happening. Although I think he was talking about arcing form turn on/turn off? :think1:
Brad :icon_biggrin:
Yep, I do a lot of that. Mainly because the short-term memory is sorely lacking these days. I'm just waiting for my interface to be perfected, so that I can back myself up. Thanks for the TUT source. Someday, I'm going to try to get to those manuals. I sure wish they were available on Kindle. Then, I could read them during lunch, at work.
About as long as the amp is left on. Probably not more than a few hours at a time. I would guess the data sheet is more worried about months.
Long term is what I was thinking about. Being from a power plant environment, we have them that can stay energized as long as a year. A rare few, longer.
This little, sealed relay had me wondering about the coil, and how robust it might be. I hadn't given consideration to the contacts, being as the signal that they have to handle is so weak. That is, until I read the spec sheet cautions.
I just recently received some from Doug, for experimenting. The spec sheet gives the part number for the magnetically latching model. I haven't chased that source, as I want to play with Doug's relays first.
Speaking of Kindle books, I believe one of yours is available on Nook (Barnes & Nobles). Are there any plans for yours to be available on Kindle? I would like to have your literature available electronically. Sorry for getting off on that tangent.
Thanks to both of you for your feedback. Have a good one.
Jack
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I saw same caution/warning, and was interested in, same as you. I have 5,6,9,& 12V. relays, and a number of clear bodied, larger, multi pin/contact relays (higher voltage), and contemplating options toward new build.
Clear ones I have are obviously heavy use, ATT type, and seem like might be a touch loud-click seems pretty audible.
my 1st high gain build, so a little more to worry about.
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I have a number of Potter-Brumfield 'clear' relays, that have an octal base. I would be a bit leary of these for this type application, as I think that they may pickup all kinds of noise. Standing up and unshielded. Plus, noise may come from the coil(s) if not DC and filtered. I have nothing on which to base this concern, as I haven't tried them in this type of application. Mechanically latched (or magnetically latched) would be used in a scheme where the coil is pulsed, or momentarily energized, to latch or unlatch. That should eliminate any coiled induced noise, particularly AC energized ones. These P-B are very loud when they operate, though this may not be an issue if buried inside a chassis/cabinet.
I can prove or disprove any relay concerns, when I have a breadboard in place. I'll post my findings when I do. Thanks for your response. Have a good one.
Jack
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Here are a couple of switching ideas.
The Self-Maintained scheme uses 6 of the model relays that Doug sells. If you will note relay contacts R1a and R2a, these would typically be time-delay-pickup (TDPU). But as this model relay doesn't have them available, I drew them as instantaneous contacts. Knowing that some relay contact-racing may occur. Also note, the PB switches are momentary, not maintained like you would find in most footswitches. I plan to try this scheme with Doug's relays, when time permits.
The Mechanically Latched scheme uses 6 relays, also, though I don't believe that these are in Doug's inventory. He can confirm this. Same brand and beginning model number. I used individual momentary PB's for this scheme, as I haven't had time to give thought to a single PB strategy. I had already been jotting notes and making these sketches, for a while.
Anyway, take a look, and I'll do more when I can. Have a good one.
Jack
Side Note: I know that all of this can be done easier with a solid state scheme. Where's the fun in that?
Note: 09Mar14 - See Reply 11, below, for latest drawing with a few mods. Same revision.
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No one caught my error on the Mech-Latched scheme. The Master Reset PB tie between allows for all to be Reset at the same time, no matter the source. I've removed it for now.
Jack
Note: 09Mar14 - See Reply 11, below, for latest drawing with a few mods. Same revision.
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There are several types of mechanical latching relays. The 'dual' coil type like you show requires a momentary voltage applied to one coil to latch the relay in one position. Then it requires a momentary voltage applied to the other coil to latch the relay in the other position. You must have two separate momentary switches to operate this relay unless you use some of the contacts to steer a single pushbutton to either coil.
Another type has a single coil but uses a rotary cam with a high and low position to open or close the contacts. Pulse the coil once and the cam rotates to close the contacts. Pulse the coil again and the cam rotates to open the contacts. Similar to the pull chain switch on your ceiling fan. Requires one momentary switch for on/off operation.
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The spec sheet for the G6A relay that Doug offers is too large for attaching. So, I put it where it can be downloaded:
www.terra-glide.net/pgms/en-g6a.pdf (http://www.terra-glide.net/pgms/en-g6a.pdf)
Take a look at another type latching relay that they show towards the end of the sheet. One coil, and when polarity is swapped to the coil, the relay changes states. At least that's how I interpret their drawing. I'm not going to chase that one, yet.
My drawing (as it's shown) will have timing issues, without TDPU contacts available.
When I'm in a position to do hands-on experimenting, I won't have to rely on the what-ifs of drawing. For now, I'm just proposing ideas that will need refining, the end result hopefully having one momentary switch to step through each channel. And, a master reset/unlatch, that can serve as a form of Standby to quieten the amp. If that's needed.
Thanks for looking and please continue to give it thought. Have a good one.
Jack
Side Note: I meant to show the PB switches as Momentary. I'll fix that on updates, as they come.
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Decided to combine the two drawings into one file. Defined the PB switches as Momentary. Other than that, they are unchanged, but there will be more refining to come.
Jack
Note: 09Mar14 - See Reply 11, below, for latest drawing with a few mods. Same revision.
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I added a Master Reset to the Mechanically-Latched scheme, so that there would be no link to the other channels.
Plus, I added a picture to each scheme, taken from the spec sheet. Now, you can see the actual relay layout to compare with my drawing.
The relay picture for the Self-Maintained scheme is of the one that Doug sells.
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I have been looking over the spec sheet on the G6A relay series. I'm curious as to how long of a period would one of these relays be on, at a time. ...
●Long-term Continuously ON Contacts
Using the Relay in a circuit where the Relay will be ON continuously for long periods (without switching)
can lead to unstable contacts because the heat generated by the coil itself ...
Aren't you overthinking this a bit?
The warning basically says, "Don't use a relay where the long-term default position is an energized relay."
Only you know what is your most-likely setting. That said, how many thousands (millions?) of devices are out there with relays, and you don't waste time worrying if you're in one setting or the other too long.
If it's worthwhile to offer a switch, then you'll probably find you're in each setting a similar amount, if averaged over a long-enough time. Even if you think you'll be in an ON setting more often, you're not likely gonna use these in a high-current situation where the warning will matter (gotta have big current to get big heat, right?).
And if it's a big enough worry (possible noise or lifetime issues), then you'd switch to solid-state switching circuits that will outlast any relay. Of course, if you provide a socket for each relay, you can just change them if they get noisy or have questionable performance.
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Aren't you overthinking this a bit?
The warning basically says, "Don't use a relay where the long-term default position is an energized relay."
Only you know what is your most-likely setting. That said, how many thousands (millions?) of devices are out there with relays, and you don't waste time worrying if you're in one setting or the other too long.
If it's worthwhile to offer a switch, then you'll probably find you're in each setting a similar amount, if averaged over a long-enough time. Even if you think you'll be in an ON setting more often, you're not likely gonna use these in a high-current situation where the warning will matter (gotta have big current to get big heat, right?).
And if it's a big enough worry (possible noise or lifetime issues), then you'd switch to solid-state switching circuits that will outlast any relay. Of course, if you provide a socket for each relay, you can just change them if they get noisy or have questionable performance.
Yes, to the overthinking part. Comes from too many years around overworked relays (power plant), and resolving those issues.
In the late 80's, we started retrofitting much of the relay logic with PLC's, though it's practically impossible to replace them all (relays, that is). Then, almost at the same time, we started replacing our boiler controls (analog) with digital, computerized systems. That's when we found out that a large number of the relays had to remain, for current carrying capabilities.
We're now on our second generation of Distributive Control Systems, and are now able to replace relays with direct I/O that can handle the current. And, we're removing the PLC's, as troubleshooting is easier through the DCS.
My point is, I read spec sheets often, because I need to know that what I'm using as a retrofit can do the job. I recently bought some of the G6A relays from Doug, and downloaded the spec sheet for them, getting the bonus info with it, about the other models. That's what led me to working on a relay scheme for switching, with self-maintained (energized, continuously) and latched (momentary energization). None of this if probably practical. But, if I put it out (like thinking out loud), it may find it's way into something practical.
Not knowing the kind of use that these little relays may get, in signal switching applications, I go for worse case. That's when I tend to overthink. Please bear with me.
Have a good one.
Jack