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Old 3rd March 2009, 03:12 AM   #1
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Default SS power supply.

I have questions about a power supply i`m building. Please bear with me as i`m pretty green at this. When using PSUD do i enter the full voltage of both windings of my transformer 300-300 i.e, 600v or 300v? I`m using uf5408s in a fullwave configuration and then CLCLC to try to achieve my 350v. Also how many ma should i enter for the constant current for the amp. It`s an RH807 set amp which uses a 12at7 driver and 2 807s as a stereo amp.
Steve.
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Old 3rd March 2009, 10:30 AM   #2
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First question's easy - you use 300v. That way, if you should ever want to switch to a single winding with a bridge rectifier, you don't need to change anything except the rectifier config,

Second one needs someone who knows 807 operation in SE. My guess for 350v on the plate would be 65mA per tube, giving total current for the stereo amp of 130mA. (For practical purposes, you can ignore the 12AT7's current.)
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Old 3rd March 2009, 04:01 PM   #3
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Csteve,

One of the first amps I built was the RH 807SET. (I used 1625's because I have a bunch and its the same tube just dif base and heater voltage.)

The one thing was I could not get their design to match anything on the 807 Triode strapped curves I have? The schematic I have (the only one I can find by "google") I think deliberately leaves out the DCR of the OPT so we do not know the ACTUAL Plate Voltage. So anyway I made my own Operating Points and was reasonably happy with the results.

Attached is a nice 807 Plate curve plotted with what I suggest as the OP's. I ASSUMED you are using a 6K OPT impedance?

I used pretty much what I am attaching here but with lower OPT impedance (was what I had)

I am not sure of your tech knowledge so at the risk of being redundant. The PURPLE line is the load line. Io is the "Idle Current" =48.7mA so 2x that for the load in PSUD = 97.4m

The B+ needs to be the total of Vp+Cathode Bias and the voltage drop thru the OPT.
(300+24+???) Use a VOM to measure the DCR of your primary on the OPT. From there use Ohm's Law to find the Voltage Drop
(I*R=E) or .0487*????=Voltage Drop

Once you have the total for your B+ you can play with PSUD
Change the load to a Constant Current of 97.4M use the "Fullwave SS" rectifier and the 300V (measure the "Off Load" voltage and the DCR of the primary and secondaries and input into the tranformer spec's the numbers for 1 side of the transformer)

You will also need the DCR's of the chokes. Use the VOM for those also. I think you will need an RC pole in there just before the load. I suggest that you calc the CLCLC based upon what you have for Caps and Chokes. Then add an RC filter for each side. Take the voltage at the 97.4 mA load and then ohms law will tell you what R you need to drop to the B+ @ 48.7mA
(Voltage from PSUD@97.4mA - B+ needed Voltage)=Needed Drop
Needed Drop / .0487 = Resistor Value
use maybe a 100-150uf Cap there and you should be on your way.

I am sorry if all this was redundant, again I do not know how much knowledge you have.

BTW The 12at7 input will give you more than enough gain assuming 1V in. If your source is higher than this then I suggest a volume control at the input.

another BTW I built with no NFB and liked it that way so you might try different values on the Rfb
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Old 3rd March 2009, 08:03 PM   #4
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Quote:
Originally posted by ray_moth
First question's easy - you use 300v. That way, if you should ever want to switch to a single winding with a bridge rectifier, you don't need to change anything except the rectifier config,

Second one needs someone who knows 807 operation in SE. My guess for 350v on the plate would be 65mA per tube, giving total current for the stereo amp of 130mA. (For practical purposes, you can ignore the 12AT7's current.)
Thanks Ray. There seems to be a variety of ways to do this. I`m going with SS diodes because i can`t seem to get the required voltage with tube rectifiers from a 600 ct trans.

Quote:
Originally posted by coldcathode
Csteve,

One of the first amps I built was the RH 807SET. (I used 1625's because I have a bunch and its the same tube just dif base and heater voltage.)

The one thing was I could not get their design to match anything on the 807 Triode strapped curves I have? The schematic I have (the only one I can find by "google") I think deliberately leaves out the DCR of the OPT so we do not know the ACTUAL Plate Voltage. So anyway I made my own Operating Points and was reasonably happy with the results.

Attached is a nice 807 Plate curve plotted with what I suggest as the OP's. I ASSUMED you are using a 6K OPT impedance?

I used pretty much what I am attaching here but with lower OPT impedance (was what I had)

I am not sure of your tech knowledge so at the risk of being redundant. The PURPLE line is the load line. Io is the "Idle Current" =48.7mA so 2x that for the load in PSUD = 97.4m

The B+ needs to be the total of Vp+Cathode Bias and the voltage drop thru the OPT.
(300+24+???) Use a VOM to measure the DCR of your primary on the OPT. From there use Ohm's Law to find the Voltage Drop
(I*R=E) or .0487*????=Voltage Drop

Once you have the total for your B+ you can play with PSUD
Change the load to a Constant Current of 97.4M use the "Fullwave SS" rectifier and the 300V (measure the "Off Load" voltage and the DCR of the primary and secondaries and input into the tranformer spec's the numbers for 1 side of the transformer)

You will also need the DCR's of the chokes. Use the VOM for those also. I think you will need an RC pole in there just before the load. I suggest that you calc the CLCLC based upon what you have for Caps and Chokes. Then add an RC filter for each side. Take the voltage at the 97.4 mA load and then ohms law will tell you what R you need to drop to the B+ @ 48.7mA
(Voltage from PSUD@97.4mA - B+ needed Voltage)=Needed Drop
Needed Drop / .0487 = Resistor Value
use maybe a 100-150uf Cap there and you should be on your way.

I am sorry if all this was redundant, again I do not know how much knowledge you have.

BTW The 12at7 input will give you more than enough gain assuming 1V in. If your source is higher than this then I suggest a volume control at the input.

another BTW I built with no NFB and liked it that way so you might try different values on the Rfb
CC. Thanks for the detailed reply. I think i understand most of the details although i`m not familiar working with tube curves yet. I`ll work up a supply with what i have and report my progress. Many thanks. BTW how did you like the amp?
Steve.
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Old 3rd March 2009, 08:32 PM   #5
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Quote:
Many thanks. BTW how did you like the amp?
I liked it quite a bit. It was (aside from a 3 tube amp using the old american 5 tubes) the first amp I built.

I had to adapt because this is purely a "junkbox" type hobby and I had limited resources. With the lower load and smallish OPT's I could not get the power I want/need.

They sure are nice looking though and the amp (even though I have cannibalized parts from it) is still a conversation piece with guests.

I will say this though, it is the single most important reason that I continued in this "hobby" (read Obsession) I couldn't fill my workshop with sound but at the moderate level up close the sound was brilliant, like nothing I had ever heard in all the years of SS stuff and Car Audio I had. As a frame of reference I once had a Car Audio System in my VW GTI that was upwards of 1500Watts RMS, cost over $6,000 , most of the components were real "high end" stuff nothing you couldn't buy in a "Big Box" store. A/D/S, Nakamichi, Boston Acoustics, etc. Custom speaker locations in the kick panels (to keep "on-axis") etc etc. This was not a rolling "Boom Box" as a matter of fact there were only 2 x 12" subs. I listen to a variety of music so it was setup for clarity and sound stage etc.

The "sound" of the tube amplification with a decent set of speakers is really amazing.

Good luck and keep me posted.


Attached is a pic of the first protoype. The OPT's there turned out to be unacceptable because I think they were from a 70V system (junk yard finds) I since changed over to some 4K smaller tranny's from an old reel to reel amp and it sounded much much better.
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Old 3rd March 2009, 08:33 PM   #6
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Real Amps GLOW IN THE DARK!
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Old 5th March 2009, 12:42 AM   #7
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Ok, I think after reading up on this i think i`m going to try a hybrid bridge with uf5408s and a 5ar4. What do you think of this idea? I like the slow start capability and the voltage drop should be manageable with the ss diodes up front.
Steve.
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Old 5th March 2009, 10:58 AM   #8
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Sounds all right to me. I like hybrid bridges but prefer TV dampers as the tube diodes, to get the least voltage drop - and they're quiet in operation and cheap!
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Old 5th March 2009, 08:36 PM   #9
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Quote:
Originally posted by ray_moth
Sounds all right to me. I like hybrid bridges but prefer TV dampers as the tube diodes, to get the least voltage drop - and they're quiet in operation and cheap!
Thanks Ray. Could you recommend a damper diode to use? Preferably without a top cap.
Steve.
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Old 5th March 2009, 10:52 PM   #10
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I've used only the 6D22S, which I could certainly recommend, but which does have a top cap for the cathode connection and uses the rare magnoval base.

I know there are TV dampers that don't have a top cap but I don't know enough about them to know which ones to recommend. I'm sure other people here can answer that.
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