Use any heavy-duty 250V switch.
Typically same-as your Power switch.
Yes, 350V is "over rating". But a "250V" switch is expected to stand LARGE surges and currents and arcing. Vacuum-cleaner motors, incandescent lamp filaments, etc. The secondary of a PT is not an "infinite source" and doesn't abuse the switch nearly as much as most loads the switch is designed for. Fender and Marshall used 250V switches for many decades, few failures.
Typically same-as your Power switch.
Yes, 350V is "over rating". But a "250V" switch is expected to stand LARGE surges and currents and arcing. Vacuum-cleaner motors, incandescent lamp filaments, etc. The secondary of a PT is not an "infinite source" and doesn't abuse the switch nearly as much as most loads the switch is designed for. Fender and Marshall used 250V switches for many decades, few failures.
@intensate - multiple threads on the same topic have been merged.
Diodes are cheap insurance
Except that we beat the heck out of valves in most (western) guitar amps and they fail far more often than in "normal" usage.
Indeed the very first mod in Premier guitar's Immortal Amp series is exactly this: diodes in series with your rectifier.
Except that we beat the heck out of valves in most (western) guitar amps and they fail far more often than in "normal" usage.
Indeed the very first mod in Premier guitar's Immortal Amp series is exactly this: diodes in series with your rectifier.
output transformer turns ratio /impedance?
Hello all
The amp design I am working on,I used a doner chassis that came complete with the mains transformer and output transformer along with ec83 pre and el84 output in push pull
It was a diy build from way back when
The output transformer I assumed was a match and has 2 output impedance's of which I wanted to find out if they were say 4 and 8 ohm etc
I put 4.7ac into 1 of the sec pairs and got 189vac on pri
so 189/4.7 =40.21 turns ratio
40.21x40.21 =1616 then x 4 ohms = 6464 or 8 ohms 12928
the 2nd pair 192/4.7 =40.85
40.85x40.85=1668 x 4 ohms =6672
and 8ohms 53376
I am confused as this doesn't match what push pull el84 need and I am not so confident with my maths either
On measuring the pri there are 3 wires ,1 being center tap.I measured across the 2 and not the center tap ,did this make the readings I have ?
also my multi meter ac settings are 600 and 200vac only?
Thanks all
Hello all
The amp design I am working on,I used a doner chassis that came complete with the mains transformer and output transformer along with ec83 pre and el84 output in push pull
It was a diy build from way back when
The output transformer I assumed was a match and has 2 output impedance's of which I wanted to find out if they were say 4 and 8 ohm etc
I put 4.7ac into 1 of the sec pairs and got 189vac on pri
so 189/4.7 =40.21 turns ratio
40.21x40.21 =1616 then x 4 ohms = 6464 or 8 ohms 12928
the 2nd pair 192/4.7 =40.85
40.85x40.85=1668 x 4 ohms =6672
and 8ohms 53376
I am confused as this doesn't match what push pull el84 need and I am not so confident with my maths either
On measuring the pri there are 3 wires ,1 being center tap.I measured across the 2 and not the center tap ,did this make the readings I have ?
also my multi meter ac settings are 600 and 200vac only?
Thanks all
My figures say 13,350; 13k not 53k.
All the rest looks OK.
Are you sure the "4.7VAC" stays at 4.7V when connected to a low-impedance winding? Did you measure that with the transformer connected?
Two windings making 189V and 192V is very odd. You expect them to be the same, or very different, not 2% different.
Indeed - you need to do your switching up stream of the rectifier.
Switching DC power above 12V is a specialist activity: in AC any arc-over shuts off every half cycle. In DC the arcs never have to stop.
I have a 200W amp on the bench with 70V rails; fried output transistors and speaker protection relays welded shut.
Even 12V will melt a switch if it's badly designed. Ask anyone with a '70s British car with electric windows or sunroof.😡
Hi PRR I measured the 4.7 with no load and not connected to the op transformer thanks I will try it loaded with op transformer
Hi PRR
I re did the mesurements under load
Under load the transformer reads 4.6 v ac and I re did the volt readings and it seems both secondarys give an output of 190.2 vac on pri
so its not clear to me which ones are 4ohm and 8 ohm?
thanks for any help
I re did the mesurements under load
Under load the transformer reads 4.6 v ac and I re did the volt readings and it seems both secondarys give an output of 190.2 vac on pri
so its not clear to me which ones are 4ohm and 8 ohm?
thanks for any help
It would seem like I have 2 4onm taps?
And el84 need an 8k transformer so I may need to get one?
And el84 need an 8k transformer so I may need to get one?
6.6k is fine for el84's. I doubt you have 2 four ohm taps. Is there a code stamped into the bell of the transformer? That may help determine the make and color code.
just had a loo inside the bells ,nothing written
only markings are 1100 on top
pink and yellow are one winding,blue and oronge other set
only markings are 1100 on top
pink and yellow are one winding,blue and oronge other set
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only thought I had was to feed a 1khz 500mv p p signal from my scope into its sec and measure volt at pri? to see if I get different readings
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