I have a PT that I can't identify but reasonably sure the power will be sufficient. Question is, is the no-load voltage of 767 too high for the build? I could use a diode string on the center tap but is it too much? Also, I have a 50w OT with a measured primary of 6.272k @ 8ohms... Does this sound right? Should I just get new iron?
Tony
5B6 Build TX Questions
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dorrisant
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5B6 Build TX Questions
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Stevem
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Re: 5B6 Build TX Questions
Man that is way too much loaded or unloaded voltage if it's center taped!
Even a somewhat crappy PT will have 10% regulation so under max load you would still have some 680 volts and you have not rectified it yet which will kick that up by some 100 volts through that amps 5U4 recto!
The 5B6 amp uses filters rated at only 450 volts, can you say yike's!
767 volts Times the 1.2 for a 5U4 recto gives you over 900 volts.
In regards to that OT fender uses 4.2K primary on those 5881 output tubes, the 6K will work, but you be a tad down on power and the output stage will stay cleaner before clipping.
The output tubes will last a bit longer with the 6K if you tend to play the amp cranked all the time, in fact that OT will also work with 6V6 output tubes.
Even a somewhat crappy PT will have 10% regulation so under max load you would still have some 680 volts and you have not rectified it yet which will kick that up by some 100 volts through that amps 5U4 recto!
The 5B6 amp uses filters rated at only 450 volts, can you say yike's!
767 volts Times the 1.2 for a 5U4 recto gives you over 900 volts.
In regards to that OT fender uses 4.2K primary on those 5881 output tubes, the 6K will work, but you be a tad down on power and the output stage will stay cleaner before clipping.
The output tubes will last a bit longer with the 6K if you tend to play the amp cranked all the time, in fact that OT will also work with 6V6 output tubes.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: 5B6 Build TX Questions
You're getting 767 by measuring as across both secondaries ?if so I'm guessing around 465-470 with a 5u4
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dorrisant
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Re: 5B6 Build TX Questions
Yes... It would be listed as a 383-0-383 PT...
"Education is what you're left with after you have forgotten what you have learned" - Enzo
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Stevem
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Re: 5B6 Build TX Questions
Ok, 383 volts is better but still too high to get the true soul/ feel of that circuit!
That amp put out some 26 clean watts and you only need some 360 volts to do I that with a 6K OT.
You really do not want more than 400 volts of B+ which calls for a PT of no more than 330, or why build it in my mind.
That amp put out some 26 clean watts and you only need some 360 volts to do I that with a 6K OT.
You really do not want more than 400 volts of B+ which calls for a PT of no more than 330, or why build it in my mind.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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dorrisant
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Re: 5B6 Build TX Questions
Steve, if I can get that B+ where it needs to be then I should be ok. I have been looking at the amps Mark Fowler has been building and posting here. He used a 355-0-355 in one, I think. Also the Bassman from the Tony Zottola book suggests a 700v (350-0-350) PT in the BOM.
I just thought that the one I have is a bit high. I would like to put some Zeners between the center tap and ground. I'll have to do some more research about what values I can get away with there. I just picked up some 10v 5w Zeners. I don't know if they will work or not.
Tony
I just thought that the one I have is a bit high. I would like to put some Zeners between the center tap and ground. I'll have to do some more research about what values I can get away with there. I just picked up some 10v 5w Zeners. I don't know if they will work or not.
Tony
"Education is what you're left with after you have forgotten what you have learned" - Enzo
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dorrisant
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Re: 5B6 Build TX Questions
Double post
Last edited by dorrisant on Sun Sep 07, 2014 6:48 pm, edited 1 time in total.
"Education is what you're left with after you have forgotten what you have learned" - Enzo
Re: 5B6 Build TX Questions
The 350-0-350 MCI PT that I used for my 5B6 build was just over 800V unloaded with 124+V mains input, but loaded was right around 405V on the plates. I would use your PT with a minor change, for the the first filter cap use node two 40uF-80uF/350-500V caps in series with 220K balancing resistors.dorrisant wrote:I have a PT that I can't identify but reasonably sure the power will be sufficient. Question is, is the no-load voltage of 767 too high for the build? I could use a diode string on the center tap but is it too much? Also, I have a 50w OT with a measured primary of 6.272k @ 8ohms... Does this sound right? Should I just get new iron?
Tony
TM
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Stevem
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Re: 5B6 Build TX Questions
Well you will likely need more ten volt zener's than you think you do as they do not quite drop a full ten volts
You might want to check out the NTE brand of bolt down zener's in there 5275AK thru 85AK series as they go from 50 volt to 100 volt.
You have to drill a 5/8" hole to mount them, but they last forever as they use the chassis for a heat sink and are rated at 50 watts, overkill but you will sleep well!
You might want to check out the NTE brand of bolt down zener's in there 5275AK thru 85AK series as they go from 50 volt to 100 volt.
You have to drill a 5/8" hole to mount them, but they last forever as they use the chassis for a heat sink and are rated at 50 watts, overkill but you will sleep well!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: 5B6 Build TX Questions
If you use a large choke that will handle the entire amp and place it in front of the first filter cap you can lower the B+ about 50volts. I have done this a few times and it works well.
The world is a better place just for your smile.
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dorrisant
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Re: 5B6 Build TX Questions
Thanks to everyone for all the answers!
I did a lot more research and decided I'm going to use the 5w Zeners I have to dial it in for now. If all goes well, I will replace the 5w Zeners with a single chassis-mount type. I want to try something with the extra octal socket I will have left over, (has anyone used an octal tube for a Dumble type overdrive?)...
The chassis is a rust bucket. I want to get the circuit right, then I will pull the guts and have the chassis powder coated... Maybe not. I'm open to suggestions.
Let me know if you guys see any pitfalls or have any other suggestions.
Thanks again,
Tony
I did a lot more research and decided I'm going to use the 5w Zeners I have to dial it in for now. If all goes well, I will replace the 5w Zeners with a single chassis-mount type. I want to try something with the extra octal socket I will have left over, (has anyone used an octal tube for a Dumble type overdrive?)...
The chassis is a rust bucket. I want to get the circuit right, then I will pull the guts and have the chassis powder coated... Maybe not. I'm open to suggestions.
Let me know if you guys see any pitfalls or have any other suggestions.
Thanks again,
Tony
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"Education is what you're left with after you have forgotten what you have learned" - Enzo
Re: 5B6 Build TX Questions
Don't cover up all that mojo with powder coat!
Just rub it down real good with a good degreaser and clear coat it like a rat rod!!!
Just rub it down real good with a good degreaser and clear coat it like a rat rod!!!
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dorrisant
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Re: 5B6 Build TX Questions
Now that sounds cool!! Off to see what ideas I can get from the net... Glad I didn't sandblast it yet.RWood wrote:Don't cover up all that mojo with powder coat!
Just rub it down real good with a good degreaser and clear coat it like a rat rod!!!
Tony
"Education is what you're left with after you have forgotten what you have learned" - Enzo
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Stevem
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Re: 5B6 Build TX Questions
Krylon spray paints are very flexible, hold well and dry very fast so you can blast on 3 coats of flat clear in 2 hours at room temp and then pick it up without it feeling tacky, full cure as with any paint comes when it does not smell any longer!
In regards to the rusty PT core I would get some brush on automotive rust converter to change that rust into a primer and then brush on some testors moldeling type flat black over that.
In regards to the rusty PT core I would get some brush on automotive rust converter to change that rust into a primer and then brush on some testors moldeling type flat black over that.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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gui_tarzan
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Re: 5B6 Build TX Questions
This!RWood wrote:Don't cover up all that mojo with powder coat!
Just rub it down real good with a good degreaser and clear coat it like a rat rod!!!
--Jim
"He's like a new set of strings, he just needs to be stretched a bit."
"He's like a new set of strings, he just needs to be stretched a bit."