I'm building Pete Millett's "Engineer's Amplifier", and would like a little help in the power supply. I'm planning on running it at about 100WPC with 5kohm OPTs rated for 100W at 30Hz.
I'm planning on using 6HJ5 and 6GU5 tubes, so I'll need to supply about 10A of heater current.
The amplifier also uses a -60V bias supply with is supplied via 50-0-50 taps on the transformer Pete has spec'd for the stock build.
I am wondering if I got two of the original power transformers, if this is how I would wire them up (See attached). Would that be too much voltage? Did I draw that circuit wrong? I think the negative terminal on the cap for the B+ boost should go to the center tap of that transformer, and not to ground, and maybe it should be bigger.
Can you recommend a different way of accomplishing this, I would appreciate that too, as the 4 transformers alone for this are going to cost me over $600 Cdn.
Thanks
I'm planning on using 6HJ5 and 6GU5 tubes, so I'll need to supply about 10A of heater current.
The amplifier also uses a -60V bias supply with is supplied via 50-0-50 taps on the transformer Pete has spec'd for the stock build.
I am wondering if I got two of the original power transformers, if this is how I would wire them up (See attached). Would that be too much voltage? Did I draw that circuit wrong? I think the negative terminal on the cap for the B+ boost should go to the center tap of that transformer, and not to ground, and maybe it should be bigger.
Can you recommend a different way of accomplishing this, I would appreciate that too, as the 4 transformers alone for this are going to cost me over $600 Cdn.
Thanks
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> 100WPC with 5kohm OPT
The original is 20 Watts with 8K load. Not sure how you've scaled that to 100W 5K.
100W in 5K suggests 550V-600V main B+. I get that from 6550 data; 6550 is 42 Watt plate dissipation, considerable more than the nominal 17W of the sweep tubes. Yes, the sweep tubes will stand a lot more (the low rating is for sweep duty which is very hard to measure for Pdiss). And I guess you are planning four big bottles per channel?
> this is how I would wire them up
OK, you have stacked 340V on 340V to get near 700V, a bit more than you need. But double-voltage means double-current (and 8K:5K means more), 4X Power (in line with 20W-100W aim), but I don't see more current or more than 2X power.
Or do you do all this twice? (Four power transformers)
> transformers alone ...over $600 Cdn.
If I wanted 100 Watts on a budget, I would absolutely look to Fender 100W Replacement iron. They are sold very competitively. The target will be 450V-500V out of 4 6L6-size tubes (which may include those sweep-tubes, if not run steady half-Power). Much re-thinking needed to guess Vg2 needed and suitable Vg1.
The original is 20 Watts with 8K load. Not sure how you've scaled that to 100W 5K.
100W in 5K suggests 550V-600V main B+. I get that from 6550 data; 6550 is 42 Watt plate dissipation, considerable more than the nominal 17W of the sweep tubes. Yes, the sweep tubes will stand a lot more (the low rating is for sweep duty which is very hard to measure for Pdiss). And I guess you are planning four big bottles per channel?
> this is how I would wire them up
OK, you have stacked 340V on 340V to get near 700V, a bit more than you need. But double-voltage means double-current (and 8K:5K means more), 4X Power (in line with 20W-100W aim), but I don't see more current or more than 2X power.
Or do you do all this twice? (Four power transformers)
> transformers alone ...over $600 Cdn.
If I wanted 100 Watts on a budget, I would absolutely look to Fender 100W Replacement iron. They are sold very competitively. The target will be 450V-500V out of 4 6L6-size tubes (which may include those sweep-tubes, if not run steady half-Power). Much re-thinking needed to guess Vg2 needed and suitable Vg1.
Tubes are 6HJ5. Another member, Tube Lab, got 125wpc at 600V into a 3300ohm load. So my setup at close to 700V into 5k should be just under 100W.
The question was more if I had the wiring correct. Do I have the transformer wiring drawn correctly so that nothing blows up?
The 4 transformers I was referring to were the two output transformers and the two power transformers. I will look into the Fender iron, thanks.
The question was more if I had the wiring correct. Do I have the transformer wiring drawn correctly so that nothing blows up?
The 4 transformers I was referring to were the two output transformers and the two power transformers. I will look into the Fender iron, thanks.
I hope you won't wire your IEC socket as shown. It is dangerous to fuse both Live and Neutral because if the Neutral fuse blows first, the wiring on both poles of the primary become live!
> your IEC socket
Some IEC sockets ARE fused both legs.
While fused Neutral is banned in wall-wiring, INside an appliance "should" be safe because you will "always" disconnect the plug-socket before reaching inside. Or else be trained in safety.
Living in the US I would add that it "can't" matter, because Not/Neutral swaps are fairly common (though wrong). This also applies to Schuko systems, where H/N are indistinguishable, "line can connected to either pin of the appliance plug". I don't live there, but I could see why such systems might "require" fuse in both legs.
Some IEC sockets ARE fused both legs.
While fused Neutral is banned in wall-wiring, INside an appliance "should" be safe because you will "always" disconnect the plug-socket before reaching inside. Or else be trained in safety.
Living in the US I would add that it "can't" matter, because Not/Neutral swaps are fairly common (though wrong). This also applies to Schuko systems, where H/N are indistinguishable, "line can connected to either pin of the appliance plug". I don't live there, but I could see why such systems might "require" fuse in both legs.
Fusing both line and neutral is permissible under all safety standards I am aware of, and is preferred or even required by some standards for single-phase cord-connected equipment.
Why? Because there is no guarantee that line and neutral are not reversed, at the plug, or in building wiring. If they are reversed, then a single fuse does not protect against a short to ground.
A description:
Double Fusing or Fusing Both Sides of the Line | In Compliance Magazine
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