Thinking about building an El Cheapo PP. I have some vintage hammond 10k iron that might be good in it.
This air wired stuff has never worked out well for me. And I'm getting the hang of KiCAD. And so many years have passed that some of the parts don't make sense or aren't "cheap" at the moment, or not as cheap as other options.
For example if I'm using a pcb there's no reason not to use a small 2.5va 28v transformer to generate B-, and just lose those big power resistors. The RS transformer specified for heaters is obviously not available, etc.
There are cheaper options for most of the other iron than specified in the schematics I've seen, too.
Might call it El Huevón.
This air wired stuff has never worked out well for me. And I'm getting the hang of KiCAD. And so many years have passed that some of the parts don't make sense or aren't "cheap" at the moment, or not as cheap as other options.
For example if I'm using a pcb there's no reason not to use a small 2.5va 28v transformer to generate B-, and just lose those big power resistors. The RS transformer specified for heaters is obviously not available, etc.
There are cheaper options for most of the other iron than specified in the schematics I've seen, too.
Might call it El Huevón.
Things have changed, markedly, over 10.5 years.
A complete set of power magnetics can be ordered from Allied Electronics. Stock # 70218190 is the Triad N-77U main B+ part. Stock # 70009000 is the Allied 6K27VF B-/'T7 heater part. Stock # 70218344 is the Triad VPS24-1800 "12" V. heater power/B+ boost part. Stock # 70218145 is the Triad C-24X B+ filter choke.
In O/P "iron", the Dyna Z565 was/is the "Gold Standard", but it's not inexpensive. For triode wired "finals", Edcor's GXPP15-8K will get the job done, while allowing deeper bass extension.
A complete set of power magnetics can be ordered from Allied Electronics. Stock # 70218190 is the Triad N-77U main B+ part. Stock # 70009000 is the Allied 6K27VF B-/'T7 heater part. Stock # 70218344 is the Triad VPS24-1800 "12" V. heater power/B+ boost part. Stock # 70218145 is the Triad C-24X B+ filter choke.
In O/P "iron", the Dyna Z565 was/is the "Gold Standard", but it's not inexpensive. For triode wired "finals", Edcor's GXPP15-8K will get the job done, while allowing deeper bass extension.
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I do like Allied, but instead of the N-77U at $33.80 from allied, I was thinking the Hammond 186F20 from Mouser for $23.88.
The VPS12-2000 is a couple bucks cheaper than the VPS24-1800 and offers 6.3v and 12.6v. I was also considering using an SMPS for heaters, since a Mean-Well 12v 50w enclosed, isolated supply is only $11 from mouser.
Not sure what you mean by B+ boost. Were you suggesting using the 24v available from the VPS24 to make B-?
In another post from 2009 or something, I see where you said that most of the voltage in the B- supply is lost across the resistors, and only about -40v is needed.
The tube rectifier on the B- supply is about soft start, right? What if the B- transformer is connected to the output of the CL150 limiters?
A Tamura 3FS-328 is only $5.66 and offers 86ma of 28vac. Should give about 40vdc after a silicon FWB.
I'm curious if that would work well enough, since it would save several components. No tube, no socket, no heater power for tube, no wirewound resistors. Since I'm etching a board, the fact that it's a PC mount transformer isn't a problem. I already created the footprint for pcbnew.
The VPS12-2000 is a couple bucks cheaper than the VPS24-1800 and offers 6.3v and 12.6v. I was also considering using an SMPS for heaters, since a Mean-Well 12v 50w enclosed, isolated supply is only $11 from mouser.
Not sure what you mean by B+ boost. Were you suggesting using the 24v available from the VPS24 to make B-?
In another post from 2009 or something, I see where you said that most of the voltage in the B- supply is lost across the resistors, and only about -40v is needed.
The tube rectifier on the B- supply is about soft start, right? What if the B- transformer is connected to the output of the CL150 limiters?
A Tamura 3FS-328 is only $5.66 and offers 86ma of 28vac. Should give about 40vdc after a silicon FWB.
I'm curious if that would work well enough, since it would save several components. No tube, no socket, no heater power for tube, no wirewound resistors. Since I'm etching a board, the fact that it's a PC mount transformer isn't a problem. I already created the footprint for pcbnew.
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Voltage doubling a N-77U doesn't quite get "there", in terms of B+ rail voltage. The VPS24-1800 has 2X "12" V windings. Use 1 of those windings for heater power. The 2nd winding is phased up and wired in series with the N-77U's secondary. The composite gets voltage doubled. Put ferrite beads on the wires connected for heater power.
The very last thing you want, during start up, is for a 'T7 grid to go positive, with respect to its cathode.
The 12AL5 is an inexpensive way of ensuring small signal tube grid safety.
Huh. That is not shown on the schematic.
For just a couple dollars more than the current price for the N-77U i could just get a 100va 250vac toroid from antek. Shipping would be an additional consideration, but i could forego the voltage doubler. Yeah, i realize that voltage doublers move some noise out of the audible range.
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AS-1T250 would give me 400mA of 250vac and a pair of 3A 6.3v windings. $34.50 (literally less than $2 more than the N-77U) plus about $7 for shipping, and I could forego separate iron for the heaters. PSUD2 sim says it would do about 330vdc.
Or for the same price, AS-1T150 provides 660mA of 150v, keep the doubler supply, and get to 355vdc or so
Or for the same price, AS-1T150 provides 660mA of 150v, keep the doubler supply, and get to 355vdc or so
The schematic came before the FECs (field engineering changes) started.
Contact Jeff Yourison for all sorts of "goodies".The B+ rail should be about 355 V. That accommodates the needs of the 'T7 splitter/driver. The 'T7 triode sounds good, when 200 to 220 V. are on the plate and IB is 3 mA.
BTW, 2X Triad N-68X trafos with secondaries wired in parallel, instead of a N-77U, is a potential way to save some cash.
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