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Pilot sp-210 power supply P-10 schematic

bobbyonions

bobbyonions

AK Member
I was wondering if anyone out there had a schematic for the P-10 power supply that came as an option with the sp-210 to run it stand alone.

There have been multiple inquiries on the Pilotone group on yahoo with barely a response. It seems like that group is more interested in following current market value for pilot stuff than helping owners with technical questions.
 
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Bobby -- If you cannot find one, it would not be hard at all to reverse engineer a design for one. That would certainly get it operational on its own, unless of course you are looking to absolutely build/repair the original item.

Dave
 
Yes, that would work as well. I know a few folks here on AK have built them. Maybe someone who has will contribute their plans. If so, I know of at least two other guys on that Pilot site that are looking for this too.
 
I have a PS-less 210 also and would be interested.

Did not know there was a Pilotone Yahoo group. I have 5 Pilot pieces; will check it out!
 
kirk57 said:
I have a PS-less 210 also and would be interested.

Did not know there was a Pilotone Yahoo group. I have 5 Pilot pieces; will check it out!
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Yeah, it's been around for several years. Like I said though, most info there seems to be about how much the stuff's worth. Some buying and selling going on there too I suspect.
Some strong advocates there for keeping all the old original leaky wax and oil caps in these units too. They do have some schematics on file as well. You should check it out.
 
I built a power supply for an SP-210 a while back but failed to draw up the schematic for it. What I built was based on a schematic I found elsewhere, with a couple of changes to the filament supply.

I've got parts to build another and good intentions to get around to it in the not far distant future. When I finally carve out the time for it, I'll make a point to document it carefully.

Maybe someone else will beat me to it in the meantime...
 
To build an external power supply should not be terribly difficult. Here's some information and guidelines that will help, from info taken from the 210 schematic, and that of an SA-260.

The heater supply for the 210 needs to be provided from the secondary of a 24 vac CT transformer, that can provide at least 1 Amp. It must have a CT connection, as the 210 employs a internal conventional full wave rectifier circuit to convert this AC power to DC for all of the filaments. On the preamp plug, the 24 vac is connected to pins# 1 & 3, while the CT is connected to pin# 2. I believe Radio Shack even sells an appropriate transformer to use for this purpose.

The pilot lamp on the 210 is connected to pins# 10 and 11, and requires 6.3 vac at 150 ma. If you are trying to keep your 210 all original, this will require a small (say 300 ma) 6.3 vac transformer on your external supply to power this lamp. Another option would be to install a similar base 24 volt version of the bulb, and simply use the AC power as provided to pins 1 & 3 for the heater supply to power this lamp as well. There is an additional option to power the original 6.3 volt lamp that will be explained in a moment.

For B+ requirements, the preamp operates off of well filtered 150 vdc, with the B+ applied to pin# 7, and ground provided at pin# 9. The preamp requires 10 ma of power at this voltage level. When connected to an SA-260, this power is basically derived from a 300 vdc source from within that amplifier, which is then used to power the preamp through a 15K 2W resistor. 10ma of current flowing through this resistor produces a 150 volt drop, meaning that the 300 volt source has been reduced to 150 volts to properly operate the preamp. For your external supply, a transformer providing say 250-0-250 vac (for SS rectification) or 265-0-265 vac for tube rectification (a 6X4 would be fine) would work perfectly in a conventional full wave rectifier circuit to provide about 300+ volts of B+, that could then be filtered and dropped along the way down to 150 vdc for the preamp. If you use a tube rectifier, you power transformer will also require a 6.3 vac winding to power this tube's heater -- which could also be used to power the original pilot lamp as well if the original bulb is used. The high voltage winding of this power transformer would only need to be rated at a very low, say 25 madc, although a higher current rating would not hurt anything. If you use a tube rectifier, the 6.3 volt winding would need to be rated at 1 amp to handle the tube and pilot lamp.

Finally the AC switch of the 210 appears across pins# 4 & 5 of the preamp power cord. You could use this to turn the external power supply on and off. A fast-blo 3/4A fuse would protect both the high voltage power transformer, and the heater supply transformer.

With this basis then, it would then be a simple matter to use a C-R-C-R-C filter from the output of the rectifier, to filter and drop the B+ appropriately down to 150 vdc when the preamp was connected. The Cs could all be 40 mfd or so, and the Rs both 10K 2 watt resistors. These resistor values will be close, but could then be tweaked as needed to target 150 vdc when the preamp was operating. It would also be a good idea to place a 100K 1/2 watt resistor across the output of the filter, to provide for a bleeder to ultimately discharge the supply, should it ever be turned on without the preamp connected.

These components should all be readily available at the usual parts houses. I know this is not an actual schematic to build from, but if you follow these principles, you should be able to construct a suitable power supply for the 210 in relatively short order. Good luck!

Dave
 
Dave, as usual you are a fount of knowledge! I sure appreciate your contribution to our community here.

The supply I built was pretty close to what you just described. Tube rectified and then LC filtered, but I used a 0A2 gas regulator tube to provide the 150V to the preamp.What are your thoughts on that approach? :scratch2:

Pictures here: http://www.audiokarma.org/forums/showpost.php?p=2578492&postcount=33
 
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Thank Dave. I've copied and saved your post for safe keeping should I ever be internet-less. And Redboy, thanks also and it's good to get some visuals. I'd love to see a build thread on your next power supply.

I have a question. If using the 210 with the 232 or 260 amps, is there an audible benefit to running a powered 210 pre over slaving off the amp's power? Or is the benefit really just being able to use the 210 with other equipment?
 
Redboy -- Thanks for the kind words! The VR tube approach you used is very neat. Its greatest benefit in this case is to keep the B+ stable in view of a changing AC power line source. It will certainly accomplish that task, but remember that dropping a rectified 300+ vdc to 150 vdc through a dropping resistor to power the preamp will supply regulating benefits of its own as well. That's because the preamp itself will act as a semi current regulator in the face of a changing voltage supply to it. That acts to help keep the voltage presented to the preamp fairly stable. Therefore, the overall results of a VR tube are somewhat limited here, but hardly a bad idea. Since a preamp operates class A through out, there is no benefit due to a changing load on the supply with the application of signal in the preamp, since current draw does not change with class A operation.

Bobby -- there is a very good benefit to powering the preamp from its own external supply, as audio systems where the preamp steals power from a power amp tend to be far more prone to motorboating, and otherwise generally undesirable coupling between the power amp and preamp circuits. Also, such a configuration is much more prone to ground loops as well. Building a dedicated separate supply for your 210 would be a very worthwhile improvement, besides making it more flexible with your other equipment.

Dave
 
dcgillespie said:
For B+ requirements, the preamp operates off of well filtered 150 vdc, with the B+ applied to pin# 7, and ground provided at pin# 9. The preamp requires 10 ma of power at this voltage level. When connected to an SA-260, this power is basically derived from a 300 vdc source from within that amplifier, which is then used to power the preamp through a 15K 2W resistor. 10ma of current flowing through this resistor produces a 150 volt drop, meaning that the 300 volt source has been reduced to 150 volts to properly operate the preamp. For your external supply, a transformer providing say 250-0-250 vac (for SS rectification) or 265-0-265 vac for tube rectification (a 6X4 would be fine) would work perfectly in a conventional full wave rectifier circuit to provide about 300+ volts of B+, that could then be filtered and dropped along the way down to 150 vdc for the preamp. If you use a tube rectifier, you power transformer will also require a 6.3 vac winding to power this tube's heater -- which could also be used to power the original pilot lamp as well if the original bulb is used. The high voltage winding of this power transformer would only need to be rated at a very low, say 25 madc, although a higher current rating would not hurt anything. If you use a tube rectifier, the 6.3 volt winding would need to be rated at 1 amp to handle the tube and pilot lamp.

Finally the AC switch of the 210 appears across pins# 4 & 5 of the preamp power cord. You could use this to turn the external power supply on and off. A fast-blo 3/4A fuse would protect both the high voltage power transformer, and the heater supply transformer.

With this basis then, it would then be a simple matter to use a C-R-C-R-C filter from the output of the rectifier, to filter and drop the B+ appropriately down to 150 vdc when the preamp was connected. The Cs could all be 40 mfd or so, and the Rs both 10K 2 watt resistors. These resistor values will be close, but could then be tweaked as needed to target 150 vdc when the preamp was operating. It would also be a good idea to place a 100K 1/2 watt resistor across the output of the filter, to provide for a bleeder to ultimately discharge the supply, should it ever be turned on without the preamp connected.

These components should all be readily available at the usual parts houses. I know this is not an actual schematic to build from, but if you follow these principles, you should be able to construct a suitable power supply for the 210 in relatively short order. Good luck!

Dave
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I have a PT salvaged from an old Fleetwood (Grundig) receiver. Here is part of the schematic showing the PT and power supply. The PT was supplying 280V after a SS full wave device and also has a 6.3V tap and two 3.15V taps. Am I reading this right and would this take care of the B+ source, pilot lamp, and tube rectifier heater V? How do I determine the amp ratings of these windings?
 

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Great thread

Thanks bobbyonions for starting it, I too have a 210 that needs a separate PS.
I am following along and appreciate everyone's input.

I have an old Phillips console that has a separate tube rectified PS that I was going to consider, just never got around to pulling it and seeing whether its a candidate.
 
Dave -- Your Grundig transformer will work just fine to power the 210, although I'm sure it will be overkill in the ratings department. To really know what the actual ratings of the windings are, you would need to add up the current required for all the heaters used in the original receiver, and know the B+ current draw of the receiver as well. However, in this case, that really isn't necessary. The fact that your proposed transformer is powering a receiver in the first place implies an RF front end, an IF amplifier, AF amplifier, and at least a power output stage. Almost any one of these stages will draw at least as much power as the entire 210 preamp will draw, so the transformer is more than capable. However, if you notice, there is no CT to the HV winding. Therefore, you will be required to use a SS bridge rectifier as shown on the schematic, and will not be able to use a tube rectifier option with this transformer. The 6.3 volt winding can still power the pilot lamp in the 210 however. Also of course, you will still need a 24 volt CT transformer to power the heaters in the 210 as well.

Dave
 
What are the pros and cons of solid state VS tube rectification in a power supply for the sp-210 preamp?

Here is the transformer and a vacated chassis from an old Lafayette bulk tape eraser. It's a cool box about 6" X 9". The top of the chassis is some sort of fiber glass or phenolic material. The bottom is steel and the box could be used upside down. It's already fitted with an on/off switch, pilot light and fuse holder. I've been saving this for a future DIY project.

I'm thinking this transformer and chassis are both overkill for the PS build size-wise. Maybe I should save this for a small amp or preamp down the road. What say ye all?
 

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The pros and cons of SS versus VT rectification can be broken down into two issues -- sonic, and technical.

The answer you get as to the sonic question will depend on who you talk to. Those answers are as varied as the people are, depending on the sonic differences they perceive that they hear.

From a technical standpoint, voltage from a SS supply will appear instantly. As a result, normally there will initially then be no current draw from the preamp to reduce the raw power supply voltage down to its normal operating value for the preamp proper until the tubes heat. Therefore, all the electrolytic caps involved -- both in the supply, and the preamp itself -- should be able to handle the temporary over voltage condition until the tubes establish normal current draw, which should take no more than 30 seconds.

However, because of the somewhat unique design of the 210, there is some current flowing in the preamplifier at the moment power is applied. As a result, with the dual 10K dropping resistors I suggested as a filter network, the 350 volt rating of the 210's internal electrolytic caps are adequate for an external supply that could surge to over 600 vdc! Therefore in this case, the only real concern with a SS supply is to make sure the first filter cap within it can handle any surge that might exist before the preamp tubes have fully warmed. The remaining caps down stream will likely be just fine during this interval due to the initial current that the preamp draws. However, good design practice would dictate that all the filter caps in the external supply be able to handle the full voltage of the supply. That way, they will not be over voltaged, even if the supply is operated without the preamp connected.

So, other than the cautions mentioned for the supply itself, using a SS supply with the 210 is of no real concern at all from a technical standpoint, which means the choice will boil down to sonic preferences, which means the choice becomes entirely personal.

Dave
 
I am considering building this power supply small enough to mount inside my wood cabinet that houses the 210 pre, much like the factory configuration. Does having the supply that close to the preamp negate any of the benefits of an outboard power supply? If they are close to each other will that induce noise?
 
It is possible for that to be a noise maker. It would depend on how well the transformer itself is shielded, how it is positioned relative to the most sensitive circuits of the preamp (i.e. phono preamps), whether a separate chassis is used, etc. I have an Eico HF-85 that I have completely disabled the original power supply in, and then built a small external power supply to operate it from. The supply sits behind and below the preamp, with a 4 foot connection cable to keep the supply out of proximity of the preamp. The result is that the preamp produces no hum at all, but only hiss when the phono level is advanced to full while driving the most sensitive power amp. If you're going to the trouble of building a separate power supply to operate the preamp with, then the goal should be zero hum under all conditions. If you plan to install the power supply in the same case where the preamp resides, use all available means to minimize any hum that effort creates.

Dave
 
resurrecting an old thread...

I was thinking of using the Steve Bench version 1 (150v) regulated supply for my SP-210 rebuild; I figured it would be pretty straight forward, and I could use the umbillical if I added a junkbox 24vct trans for the filament supply.

BUT... maybe not as straight forward as I thought. On the supply side of the umbilical, the 150v comes off of the 0A2 with just a small .02uf cap for noise. On the SP-210 side, there's a 40uf cap. With nothing in between but the umbillical... is that too much capacitance off of the VR tube?

Of course I could omit the 40uf cap, but I would rather leave the SP-210 circuit stock. I suppose I could stack an 0A3 and 0B3 for 165v, and drop the voltage w/ a resistor to isolate the VR tubes from the cap, but that seems kinda cheesey...
 
Bean -- placing a 40 uf cap in parallel with a VR tube will surely ruin it. You would want to isolate the preamp B+ input with at least 470 ohms of resistance between it, and the VR tube to prevent destructive oscillations from happening. In this instance, the use of a VR tube only works to maintain the B+ level in the face of a changing AC line voltage, as the current draw from the preamp itself is constant under all operating conditions.

Dave
 
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