Everyone have a happy and amplified holiday season!
Stay tuned and tubed!
Stancor transformer
Moderators: pompeiisneaks, Colossal
Re: Stancor transformer
I'm building the current limiter this weekend. Just want to make sure I don't light myself up like a Christmas tree when testing it. It would be bad form to electrocute myself whilst cooking the Christmas ham.
Everyone have a happy and amplified holiday season!
Stay tuned and tubed!
Everyone have a happy and amplified holiday season!
Stay tuned and tubed!
Re: Stancor transformer
Maybe someone will say otherwise, but I don't think a limiter is necessary at this stage. Without a load, there will be virtually no current flowing. If the PT has a short, it is already gone and a limiter won't make a difference.
If you feel you must have it, that's fine. However, you will have to power up the PT without the limiter to get accurate readings.
If you feel you must have it, that's fine. However, you will have to power up the PT without the limiter to get accurate readings.
Specs for unknown Stancor power tranny
So, after opening the transformer, I learned that it is a Stancor pc-8412. I found the specs and have posted them here.
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Re: Stancor transformer
Primary windings are 117v-60 cycle.
another photo with wiring specs
Here's the wiring specs for the tranny.
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Re: Stancor transformer
So, check your line voltage and then you'll have a clear idea of what it will do. For example, if yours is typically 122V, then 122/117= 1.043. Voltages will be a little bit high. This is only a problem for the filament supplies. In this example, I wouldn't characterize is as a problem at all. You'll get around 5.2 and 6.5 or 6.6. If you don't like the high B+, which could be in the range of 550-590V depending on type of rectifier, use a choke input which will drop it down below 400V. This is actually a nice place to be for most Octal power tubes, but a little high for 6V6.
Line voltage
My voltage off the outlet is 120.4
I'm currently looking for another builder in my area to help with the amp build but, in the meantime, and considering the leads on the PT, what amp would this work with? I'm guessing that because it came from an Oliver amp, it may go well with an Ampeg but, I'd like to see if I could build a Fender style, possibly that Super Reverb. The only problem I see is that the PT from the SR has an extra red/blue lead which seems to go to the bias control.
I'm currently looking for another builder in my area to help with the amp build but, in the meantime, and considering the leads on the PT, what amp would this work with? I'm guessing that because it came from an Oliver amp, it may go well with an Ampeg but, I'd like to see if I could build a Fender style, possibly that Super Reverb. The only problem I see is that the PT from the SR has an extra red/blue lead which seems to go to the bias control.
back-biasing
I'm seeing that I may need to install an input transformer/choke to lower the 400-400 voltage. Also, I saw that there are a few schematics for building a back biasing board to make up for the lost bias tap.
Alternatively, I could just sell the damn thing and buy a new transformer.
Alternatively, I could just sell the damn thing and buy a new transformer.
Re: Stancor transformer
Due to the high voltage on the secondary, I don't think it will fetch the best price. The good news is that you've got 200mA available, which is very promising for a ~50W or less amp. IMHO, choke input is the way to tame this. With choke input, you'll drop voltage and have over 300mA available opening up a world of possibility.
This looks promising at $57: https://www.edcorusa.com/cxc125-5h-300ma or you can look at the Hammond 194G at ~$24, but only good for 250mA ;-}. 159R or 159T are also possible for ~$20 and ~$30 respectively.
I'm not sure what your concern is about bias voltage. Just take the bias voltage from the 400 volt wire and reduce it Marshall-style. It works fine.
I would look for a choke. On a monetary basis, I think that is where you will come out best.
I wouldn't mess with back-biasing, bucking, zeners, etc. This is really quite simple and you have a really nice PT there.
I think you are see this as an uphill effort. I think it is straight downhill to the chassis!
This looks promising at $57: https://www.edcorusa.com/cxc125-5h-300ma or you can look at the Hammond 194G at ~$24, but only good for 250mA ;-}. 159R or 159T are also possible for ~$20 and ~$30 respectively.
I'm not sure what your concern is about bias voltage. Just take the bias voltage from the 400 volt wire and reduce it Marshall-style. It works fine.
I would look for a choke. On a monetary basis, I think that is where you will come out best.
I wouldn't mess with back-biasing, bucking, zeners, etc. This is really quite simple and you have a really nice PT there.
I think you are see this as an uphill effort. I think it is straight downhill to the chassis!
Re: Stancor transformer
Phil_S wrote:Due to the high voltage on the secondary, I don't think it will fetch the best price. The good news is that you've got 200mA available, which is very promising for a ~50W or less amp. IMHO, choke input is the way to tame this. With choke input, you'll drop voltage and have over 300mA available opening up a world of possibility.
This looks promising at $57: https://www.edcorusa.com/cxc125-5h-300ma or you can look at the Hammond 194G at ~$24, but only good for 250mA ;-}. 159R or 159T are also possible for ~$20 and ~$30 respectively.
I'm not sure what your concern is about bias voltage. Just take the bias voltage from the 400 volt wire and reduce it Marshall-style. It works fine.
I would look for a choke. On a monetary basis, I think that is where you will come out best.
I wouldn't mess with back-biasing, bucking, zeners, etc. This is really quite simple and you have a really nice PT there.
I think you are see this as an uphill effort. I think it is straight downhill to the chassis!
Thanks Phil! I have been researching an input choke to install. I'm thinking of taking on the Super Reverb as a build for these trannys. I have most of the components and a few sets of turret and fiberboard. I also think, as we all know, building an amp from scratch is no overnight endeavor. Once I get the PT layout finalized, it's definitely downhill to the chassis. If the Super Reverb isn't doable, there's a nice amount of amps I have on the back burner to build.
Thanks a ton for the input! It's really appreciated.
Re: Stancor transformer
Eric,
You've got some research to do on this to figure out if you can make that PT work for your particular build. The SR calls for 465VDC at the center tap of the output transformer. I don't think there's anything magical about hitting the nail on the head with that voltage, but you don't want to get too far away from it either. I'm guessing you can go 10% under (about 420) and not notice that much of a difference, but I don't know for sure. I'd be reluctant to go 10% over as that is > 500V, meaning cap ratings, tube ratings, wire ratings, etc. all take on more importance at that higher number.
I think I'd start with rectifier tube specs, and I'd consider solid state with choke input, too. I don't have the experience or knowledge to work out all the options.
One way to do this is to mock up the power supply. Actually build it on a bread board, including tube sockets, choke, caps, bias supply, output transformer, speaker load, etc. Plug in the tubes and see what you get. You can use screw-down terminal strips to cut down on soldering, particularly the wire ends on the transformer, which you don't want to sacrifice unnecessarily.
In my view, there is nothing holy about any particular design. You can go wherever you want with it within reason. It may not be the amp someone else designed, but you might get a perfectly wonderful result (or not) depending on the particular deviation.
Is this your first scratch build? Just take your time. In my view, any successful project is 80% planning and 20% doing.
Here are a couple of things I keep going back to for rectifiers. You might also want to download Duncan's power supply tool. http://www.duncanamps.com/psud2/
You've got some research to do on this to figure out if you can make that PT work for your particular build. The SR calls for 465VDC at the center tap of the output transformer. I don't think there's anything magical about hitting the nail on the head with that voltage, but you don't want to get too far away from it either. I'm guessing you can go 10% under (about 420) and not notice that much of a difference, but I don't know for sure. I'd be reluctant to go 10% over as that is > 500V, meaning cap ratings, tube ratings, wire ratings, etc. all take on more importance at that higher number.
I think I'd start with rectifier tube specs, and I'd consider solid state with choke input, too. I don't have the experience or knowledge to work out all the options.
One way to do this is to mock up the power supply. Actually build it on a bread board, including tube sockets, choke, caps, bias supply, output transformer, speaker load, etc. Plug in the tubes and see what you get. You can use screw-down terminal strips to cut down on soldering, particularly the wire ends on the transformer, which you don't want to sacrifice unnecessarily.
In my view, there is nothing holy about any particular design. You can go wherever you want with it within reason. It may not be the amp someone else designed, but you might get a perfectly wonderful result (or not) depending on the particular deviation.
Is this your first scratch build? Just take your time. In my view, any successful project is 80% planning and 20% doing.
Here are a couple of things I keep going back to for rectifiers. You might also want to download Duncan's power supply tool. http://www.duncanamps.com/psud2/
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Re: Stancor transformer
Definitely my first scratch build. Here's what I was thinking of doing in regards to input choke placement. I found this on the web.
*Note - my secondary readings would be the 400-400v
*Note - my secondary readings would be the 400-400v
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Re: Stancor transformer
If your PT is actually putting out 410-0-410 (estimated from your line voltage), that is +13.9% and will give you B+ or 500VDC. If you can figure out how to drop this 5-10%, you might be in good range for a SR build.
Maybe it is time for the Zener trick. It's been discussed here. Search for it.
Maybe it is time for the Zener trick. It's been discussed here. Search for it.
zener trick
I saw a few things on it, one which showed two diodes and another which had four. Here's my interpretation.
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Re: Stancor transformer
Don't look to complicate this. Both tubes and solid state or diodes. They do the same thing, but voltage will be different. Use one or the other, not both. Solid state diodes will give the most voltage.
That picture with the CLC input filter shows B+ is 122% of input voltage (440/360) with the 5V4 rectifier. Your PT is spec'd at 117 for line voltage. You have 120.4 (this changes by the hour/minute/day) which is +3%. That's where I get 410 from which everything else flows. The math is totally linear.
You want to build a SR, which uses a pair of 6L6 tubes. The SR schematic indicates B+ is 450 (depends on which schematic, but close enough.)
Do the math. You get 500V. That's too high. Too high for the SR, too high for the tubes.
Look at that rectifier tube chart. Also look at the tube spec. http://tubedata.itchurch.org/index.html
http://tubedata.itchurch.org/sheets/049/6/6L6GC.pdf
Look at the 6L6GC data sheet, Class AB2, typical operation. Max plate current is 205mA (need to add screen current to this) and maximum plate voltage is 500. You've got to figure out where your intended build lands on the curve and stay within the limits. You also need a rectifier that has adequate mA capacity.
That rectifier sheet is curiously accurate for all the short cuts it takes. It says the multiplier for 5V4 is 1.2. If that will give you 500V, backsolving for the secondary gives us 417V...really close to 410.
So, ideally, you need to choose a rectifier that can handle more than 200mA and only has a multiplier of 1.1, which should give you B+ of about 458 in the model you show (darn close, and as good as it gets.) It also needs to be one you can find. I might seriously think about using two 6AX5GT to get the mA rating needed. Rectifier filaments should be on their own winding. Your PT doesn't have an extra 6.3V winding, so you'll need to add an extra PT that provides 6.3V @ 2.4A. Oops, 6AX5GT has an input limit of 350V. That won't work. You see...you need to find your way.
I'm not sure I've filled in all the blanks here. These are some basics of the power supply. You'll need to decide what route you want to take and if you think that PT is viable for what you want to do.
That picture with the CLC input filter shows B+ is 122% of input voltage (440/360) with the 5V4 rectifier. Your PT is spec'd at 117 for line voltage. You have 120.4 (this changes by the hour/minute/day) which is +3%. That's where I get 410 from which everything else flows. The math is totally linear.
You want to build a SR, which uses a pair of 6L6 tubes. The SR schematic indicates B+ is 450 (depends on which schematic, but close enough.)
Do the math. You get 500V. That's too high. Too high for the SR, too high for the tubes.
Look at that rectifier tube chart. Also look at the tube spec. http://tubedata.itchurch.org/index.html
http://tubedata.itchurch.org/sheets/049/6/6L6GC.pdf
Look at the 6L6GC data sheet, Class AB2, typical operation. Max plate current is 205mA (need to add screen current to this) and maximum plate voltage is 500. You've got to figure out where your intended build lands on the curve and stay within the limits. You also need a rectifier that has adequate mA capacity.
That rectifier sheet is curiously accurate for all the short cuts it takes. It says the multiplier for 5V4 is 1.2. If that will give you 500V, backsolving for the secondary gives us 417V...really close to 410.
So, ideally, you need to choose a rectifier that can handle more than 200mA and only has a multiplier of 1.1, which should give you B+ of about 458 in the model you show (darn close, and as good as it gets.) It also needs to be one you can find. I might seriously think about using two 6AX5GT to get the mA rating needed. Rectifier filaments should be on their own winding. Your PT doesn't have an extra 6.3V winding, so you'll need to add an extra PT that provides 6.3V @ 2.4A. Oops, 6AX5GT has an input limit of 350V. That won't work. You see...you need to find your way.
I'm not sure I've filled in all the blanks here. These are some basics of the power supply. You'll need to decide what route you want to take and if you think that PT is viable for what you want to do.