Building fender 6g15 from scratch

nkg · 15th June 2010, 03:27 PM

Hi All
I am building a Fender 6G15 from scratch I can buy clone power transformer but would prefer to have separate heater supply to switch on first before B+ as it a silicon rectifier . The circuit diagram doesn't give voltage of power tranny secondary only 300 volts after the half wave rectifier and I am at a loss as how to find the RMS voltage of the of the secondary if someone could help with the math as I would prefer to get one wound . The second question I don't understand why did fender used 3 diodes in series as half wave rectification .
Thanks Nigel

firechief · 15th June 2010, 05:15 PM

I took the liberty of attaching the sch. better for people to comment.

gain-wire · 15th June 2010, 08:23 PM

If I recall correctly, you divide the unrectified voltage by the square root of 2. this gives you your RMS voltage, but bear in mind this is a LOADED voltage, what you want will have to be slightly higher than that. So take 300V, subtract roughly 3 volts for the rectifier diodes, so you have 303V peak divided by 1.414 equals 214.3V RMS.
Now you can find the turns ratio if you need to.

Also, don't worry about that B+, it will work even if it's off by as much as 30%.
two more volts or three less volts is no problem. The only thing you have to worry about is exceeding any maximum voltages like the capacitor voltages or Plate voltages.

The reason why you see a chain of diodes of early circuits like this is because Germanium diodes didn't have a very high Vforward max. So, they put a few in series to increase the overall Vf rating of the whole rectifier.
With Si diodes, it's not a problem, at least not with 1N4006 or 4007 in your case.

Enzo · 16th June 2010, 12:25 AM

Instead of a separate heater supply, just add a switch to the B+ winding. A standby switch so to speak. Main power on starts the tube heaters, then flip teh B+ switch.

But that is really not necessary. The tubes are under no stress. After all, these things have been around 50 years without burning up tubes, so I doubt they would start now.

firechief · 16th June 2010, 12:56 AM

OK This thread is going in the right direction,. Gain-Wire is right about the B+ and the diodes, and Enzo is right about not needing a seperate filament transformer. Nigel, got any part's yet?
Bob

Printer2 · 16th June 2010, 05:04 AM

LC Capacitor-Input Filter

nkg · 16th June 2010, 11:51 AM

Hi
Thanks for your replies . I have made the chassis I got an accutronics tank the valves and caps and ordered the opt and choke . I was going to switch the power on via 2 switches the first turns on the heaters the second switch is wired to to the first switch so no matter which switch is flicked on first the heaters will always come on first I saw this idea in the tube amp forums I understand tubes are rugged little critters but they are all nos and getting expensive and ss diodes do come on with a bang unlike tube rectifiers but wanted to try keep it as original a possible . I am making this to go with my pro junior which I have rebuilt to make it harp friendly .
Thanks again Nigel

gain-wire · 17th June 2010, 02:59 AM

Quote:

Originally Posted by nkg

Hi
Thanks for your replies . I have made the chassis I got an accutronics tank the valves and caps and ordered the opt and choke . I was going to switch the power on via 2 switches the first turns on the heaters the second switch is wired to to the first switch so no matter which switch is flicked on first the heaters will always come on first I saw this idea in the tube amp forums

euh... I don't want to dissappoint you, but no, the heaters will not come on first in one of the possible situations. That is if you flick the Hi-Voltage switch first then the Main switch, the heaters will come on at the same time as the Hi-Voltage, which is what you were trying to avoid. Not that it's bad, but true, I'd rather have my eleven seconds thank you before someone drags me out of bed.

It will however prevent the user from turning on the Hi-Voltage alone.

Quote:

Originally Posted by nkg

I understand tubes are rugged little critters but they are all nos and getting expensive and ss diodes do come on with a bang unlike tube rectifiers but wanted to try keep it as original a possible . I am making this to go with my pro junior which I have rebuilt to make it harp friendly .
Thanks again Nigel

Original in what way? do you mean looks or functionality?

nkg · 18th June 2010, 01:53 PM

No gainwire you won't disappoint me because if you think about it the mains and the heater transformer are wired to first switch . When the first switch is turned to the on position and the second switch is wired to the first switch and it is in the off position then there can be no current to the second switch and seeing the second switch provides current to power transformer there is no B+ voltage .
And to answer your second question original as in functionality as the 63 reverb is still regarded as the better design than the reissues .
Nigel

Enzo · 19th June 2010, 05:12 AM

Then why add the non-original power switching system?

15th June 2010, 03:27 PM	#1
nkg diyAudio Member Join Date: Jul 2004 Location: perth	Building fender 6g15 from scratch Hi All I am building a Fender 6G15 from scratch I can buy clone power transformer but would prefer to have separate heater supply to switch on first before B+ as it a silicon rectifier . The circuit diagram doesn't give voltage of power tranny secondary only 300 volts after the half wave rectifier and I am at a loss as how to find the RMS voltage of the of the secondary if someone could help with the math as I would prefer to get one wound . The second question I don't understand why did fender used 3 diodes in series as half wave rectification . Thanks Nigel

15th June 2010, 08:23 PM	#3
gain-wire diyAudio Member Join Date: Nov 2004 Location: NCR	If I recall correctly, you divide the unrectified voltage by the square root of 2. this gives you your RMS voltage, but bear in mind this is a LOADED voltage, what you want will have to be slightly higher than that. So take 300V, subtract roughly 3 volts for the rectifier diodes, so you have 303V peak divided by 1.414 equals 214.3V RMS. Now you can find the turns ratio if you need to. Also, don't worry about that B+, it will work even if it's off by as much as 30%. two more volts or three less volts is no problem. The only thing you have to worry about is exceeding any maximum voltages like the capacitor voltages or Plate voltages. The reason why you see a chain of diodes of early circuits like this is because Germanium diodes didn't have a very high Vforward max. So, they put a few in series to increase the overall Vf rating of the whole rectifier. With Si diodes, it's not a problem, at least not with 1N4006 or 4007 in your case. __________________ Trans-directional-servo-logamp non-zerocrossing autogain compressing thingamajig

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16th June 2010, 12:25 AM	#4
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	Instead of a separate heater supply, just add a switch to the B+ winding. A standby switch so to speak. Main power on starts the tube heaters, then flip teh B+ switch. But that is really not necessary. The tubes are under no stress. After all, these things have been around 50 years without burning up tubes, so I doubt they would start now.

16th June 2010, 12:56 AM	#5
firechief diyAudio Member Join Date: Sep 2008 Location: Near Seattle Wa	OK This thread is going in the right direction,. Gain-Wire is right about the B+ and the diodes, and Enzo is right about not needing a seperate filament transformer. Nigel, got any part's yet? Bob

16th June 2010, 05:04 AM	#6
Printer2 diyAudio Member Join Date: Apr 2010	LC Capacitor-Input Filter

16th June 2010, 11:51 AM	#7
nkg diyAudio Member Join Date: Jul 2004 Location: perth	Hi Thanks for your replies . I have made the chassis I got an accutronics tank the valves and caps and ordered the opt and choke . I was going to switch the power on via 2 switches the first turns on the heaters the second switch is wired to to the first switch so no matter which switch is flicked on first the heaters will always come on first I saw this idea in the tube amp forums I understand tubes are rugged little critters but they are all nos and getting expensive and ss diodes do come on with a bang unlike tube rectifiers but wanted to try keep it as original a possible . I am making this to go with my pro junior which I have rebuilt to make it harp friendly . Thanks again Nigel

18th June 2010, 01:53 PM	#9
nkg diyAudio Member Join Date: Jul 2004 Location: perth	No gainwire you won't disappoint me because if you think about it the mains and the heater transformer are wired to first switch . When the first switch is turned to the on position and the second switch is wired to the first switch and it is in the off position then there can be no current to the second switch and seeing the second switch provides current to power transformer there is no B+ voltage . And to answer your second question original as in functionality as the 63 reverb is still regarded as the better design than the reissues . Nigel

19th June 2010, 05:12 AM	#10
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	Then why add the non-original power switching system?

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