I am fairly new to electronics and to building amps. I’m building a stock El Cheapo Amp as my second build and have some questions about the power supply. The schematic I have is the one drawn up by Dave of Planet 10.
I’ve read all the threads I can find on it on this, and other sites. I know that the recommendation is for the following transformers and chokes from Allied Electronics:
part # 967-2343 Triad N77U transformer - B+ supply $33.80
part # 967-8019 Triad VPS24-1800 - 12V heater supply and 12V to B+ booster $15.68
part # 967-1004 Triad C-24X Choke, - 1H 50 Ohms 240 mA for B+ supply $7.73
part # 227-0034 Hammond 6K27VF - B- and 6.3v heater. $14.73
Total cost $71.94
I’ll build the stock amp first before trying to modify it.
Power Supply Questions:
1) I understand B+ should be about 350v for the 12AT7 to behave well. I tried simulating this in psud and didn’t get beyond 335v. Is that what I should get from this version of the power supply?
2) The B- supply is built off the 125v tap on the Hammond transformer?
3) I’m not quite sure how to wire in the second transformer, the B+ boost. Is it as simple as putting it in parallel with the B+ output, observing the polarity of the windings?
4) So that I can check the power supply without a load, what should the B- voltage be?
I’ll be using the Dynaclone Z565 PP-UL output transformers from Triode.
Thanks for your help.
rus
I’ve read all the threads I can find on it on this, and other sites. I know that the recommendation is for the following transformers and chokes from Allied Electronics:
part # 967-2343 Triad N77U transformer - B+ supply $33.80
part # 967-8019 Triad VPS24-1800 - 12V heater supply and 12V to B+ booster $15.68
part # 967-1004 Triad C-24X Choke, - 1H 50 Ohms 240 mA for B+ supply $7.73
part # 227-0034 Hammond 6K27VF - B- and 6.3v heater. $14.73
Total cost $71.94
I’ll build the stock amp first before trying to modify it.
Power Supply Questions:
1) I understand B+ should be about 350v for the 12AT7 to behave well. I tried simulating this in psud and didn’t get beyond 335v. Is that what I should get from this version of the power supply?
2) The B- supply is built off the 125v tap on the Hammond transformer?
3) I’m not quite sure how to wire in the second transformer, the B+ boost. Is it as simple as putting it in parallel with the B+ output, observing the polarity of the windings?
4) So that I can check the power supply without a load, what should the B- voltage be?
I’ll be using the Dynaclone Z565 PP-UL output transformers from Triode.
Thanks for your help.
rus
Attachments
1) Either is fine, your line voltage varies more than that. The input circuit is
self adjusting due to the current source and negative supply.
2) Yes, the one labeled Allied. It's a FWB hybrid rectifier.
3) Can you restate the question more clearly?
4) The Hammond's secondary is 125VAC, and open circuit voltage is around -165VDC.
Last edited:
I checked Allied out today and VPS24-1800 is not available. Fortunately, the VPL24-2000 will substitute and it is available.
Allied has changed stock numbers. Phooey!
70218190 = N-77U
70218219 = VPL24-2000
70218145 = C-24X
70009000 = 6K27VF
The VPL24-2000 has a pair of "12" V. windings. 1 of those windings is used to energize the heaters of the O/P tubes and the 12AL5. The 2nd winding is wired in series with the 120 V. O/P of the N-77U. Phasing is important as 1 arrangement boosts the net O/P, while the 2nd reduces (bucks) the net O/P. (120 + 12) (2) = 264. (264) (21/2) = 373.4, which (even after losses) is sufficient.
BTW, put ferrite beads on the heater power wires, close to the VPL24-2000. Keep crud from getting into the signal, via the heaters.
The Triad "iron" works for both "120" and "240" VAC mains. The 6K27VF is "120" V. only and builders with "240" V. mains need to come up with an alternative for energizing the B- rail.
Allied has changed stock numbers. Phooey!
70218190 = N-77U
70218219 = VPL24-2000
70218145 = C-24X
70009000 = 6K27VF
The VPL24-2000 has a pair of "12" V. windings. 1 of those windings is used to energize the heaters of the O/P tubes and the 12AL5. The 2nd winding is wired in series with the 120 V. O/P of the N-77U. Phasing is important as 1 arrangement boosts the net O/P, while the 2nd reduces (bucks) the net O/P. (120 + 12) (2) = 264. (264) (21/2) = 373.4, which (even after losses) is sufficient.
BTW, put ferrite beads on the heater power wires, close to the VPL24-2000. Keep crud from getting into the signal, via the heaters.
The Triad "iron" works for both "120" and "240" VAC mains. The 6K27VF is "120" V. only and builders with "240" V. mains need to come up with an alternative for energizing the B- rail.
Excellent. Triad has been "monkeying" with parts #s.
See VPS24-1800-B. IIRC, a 3rd item used to show when searching on VPS24-1800.The Z565 is the "Gold Standard" for "El Cheapo" builds. Bandwidth and power handling are good. Triode/UL mode switches or straight forward UL mode "finals" are options the nice "iron" provides.
Eli,
I also would like to build your clever “El Cheapo”, but I would like a clarification on the design output of the power supplies without monkeying around with everchanging part numbers. Please tell for the record what B+ and B2+ is intended to be.
Thanks,
Francois
Questions re El Cheapo Design
I guess Eli Duttman is off-line. Could anyone else provide answers? Especially builders of the El Cheapo amp. Is it worth building, or should I look for another design?
My questions:
1. Are the two schematics posted in #1 the most recent version of this design?
2. What are the intended voltages marked B+, and B2, as well as the negative CCS voltage?
Mr. Duttman was kind enough to provide suggestions for how to implement cheap transformers to power the amp, but I can’t find specific directions as to the design volages.
I have a pet peeve of schematics that list B+, B2, etc, etc. and not give the intended value of the voltage.
I guess Eli Duttman is off-line. Could anyone else provide answers? Especially builders of the El Cheapo amp. Is it worth building, or should I look for another design?
My questions:
1. Are the two schematics posted in #1 the most recent version of this design?
2. What are the intended voltages marked B+, and B2, as well as the negative CCS voltage?
Mr. Duttman was kind enough to provide suggestions for how to implement cheap transformers to power the amp, but I can’t find specific directions as to the design volages.
I have a pet peeve of schematics that list B+, B2, etc, etc. and not give the intended value of the voltage.
Since you're having trouble finding info. that's been provided several times, here it is again.
The needs of the 12AT7 splitter/driver rule the roost, with regards to the B+ rail. The 'T7 triode sounds good with 200 to 220 V. on the plate and an IB of 3 mA. 150 V. get dropped in the 50 Kohm load resistors. That plus 200 for the plate = 350. "Check valve" decoupling between B+ and B2+ exhibits a low drop, < 2 V. So, 355 to 360 V. is an "ideal" B+ rail voltage.
The situation with the B- rail is different. What's needed is enough volts to operate a CCS plus what's required to provide compliance with the I/P signal. 40 V. are plenty. The 6K27VF B- trafo was selected for reasons of cost. After hybrid bridge rectification, over 100 V. are present at the CRC filter's I/P. Remember, the CCS is set for 6 mA. Notice the voltage drops in the 5 Kohm resistor and (particularly) the 10 Kohm carbon film thermal isolation resistor. If a different transformer with a "shorter" rectifier winding voltage was employed, the thermal isolation part's value gets adjusted. Reduction to as little as 100 Ω could be correct.
The needs of the 12AT7 splitter/driver rule the roost, with regards to the B+ rail. The 'T7 triode sounds good with 200 to 220 V. on the plate and an IB of 3 mA. 150 V. get dropped in the 50 Kohm load resistors. That plus 200 for the plate = 350. "Check valve" decoupling between B+ and B2+ exhibits a low drop, < 2 V. So, 355 to 360 V. is an "ideal" B+ rail voltage.
The situation with the B- rail is different. What's needed is enough volts to operate a CCS plus what's required to provide compliance with the I/P signal. 40 V. are plenty. The 6K27VF B- trafo was selected for reasons of cost. After hybrid bridge rectification, over 100 V. are present at the CRC filter's I/P. Remember, the CCS is set for 6 mA. Notice the voltage drops in the 5 Kohm resistor and (particularly) the 10 Kohm carbon film thermal isolation resistor. If a different transformer with a "shorter" rectifier winding voltage was employed, the thermal isolation part's value gets adjusted. Reduction to as little as 100 Ω could be correct.
Thank you very much, mr. Duttman!
I can understand that you get tired of answering the questions again and again, I am sorry. It would be a good idea to include the voltages on the schematic.
In defense I have searched for this information and had not been able to find it. Please explore for yourself what bewildering list of topics you get when you search for “El Cheapo” on diyaudio.
I can understand that you get tired of answering the questions again and again, I am sorry. It would be a good idea to include the voltages on the schematic.
In defense I have searched for this information and had not been able to find it. Please explore for yourself what bewildering list of topics you get when you search for “El Cheapo” on diyaudio.
Many years ago there was a large "El Cheapo" thread on another forum, which was deleted unfortunately.
jeff
Use the 275 VAC trafo. CLC filter the B+. The 1st filter cap. will be small, just enough capacitance to keep the rail voltage up. A 6 H. Triad C-14X choke should be both adequate and affordable. Lots of capacitance goes in the reservoir position. A film cap. could be feasible in the 1st position.
The cathode bias resistor value changes, when 6BQ5/EL84 "finals" are employed.
Would your have a Mouser recommendation for the heater ferrite beads? The choice is endless.
Also if I put beads on the 6.3v ac heater lines should I also have a small cap to ground or line2line to give a path for the crud to go?
The ferrite beads referred to in the quote are intended to keep artifacts generated in voltage doubling process from sneaking into the tube heaters. Remember, a 12 VAC winding is boosting the B+ rail voltage, while the 2nd 12 VAC winding sharing that lamination core is feeding signal tube heaters.
In the configuration using a FW rectified toroid power trafo and CLC filter, substantial artifacts rate to be absent.
Ferrite beads on the primary wires of all power trafos, to suppress trash riding on the AC mains, should be sufficient. You want large, chamfered (to avoid insulation knicking), beads with a central opening large enough to allow at least 1 loop of wire to fit.
You are correct about "wading" through Mouser's site being a PITA. Jim McShane should have what you need and perhaps some other stuff you can use.
In the configuration using a FW rectified toroid power trafo and CLC filter, substantial artifacts rate to be absent.
Ferrite beads on the primary wires of all power trafos, to suppress trash riding on the AC mains, should be sufficient. You want large, chamfered (to avoid insulation knicking), beads with a central opening large enough to allow at least 1 loop of wire to fit.
You are correct about "wading" through Mouser's site being a PITA.
Jim McShane should have what you need and perhaps some other stuff you can use.- Status
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