Pilot SA-232 new to me
- Thread starter HBTim
- Start date
HBTim
Really encouraging to hear you prefer your Pilot
SA-232 to your Fisher SA-100.
Encouraging because I have a Pilot 232 "Stereo Plus" 3 Channel "Curtain of Sound" amp that I never completed.
It was moved to the back burner when a Fisher SA-100 came along. Then a Fisher SA300B came along and the Pilot went on the back burner again.
Every so often I think about selling the Pilot "for parts, as is" but curiosity has "kept me hanging on."
After reading how happy you are with your Pilot, I'm encouraged to eventually complete that project.
Thank you.
Really encouraging to hear you prefer your Pilot
SA-232 to your Fisher SA-100.
Encouraging because I have a Pilot 232 "Stereo Plus" 3 Channel "Curtain of Sound" amp that I never completed.
It was moved to the back burner when a Fisher SA-100 came along. Then a Fisher SA300B came along and the Pilot went on the back burner again.
Every so often I think about selling the Pilot "for parts, as is" but curiosity has "kept me hanging on."
After reading how happy you are with your Pilot, I'm encouraged to eventually complete that project.
Thank you.
HBTim
Critical listener of beer fizz
Do it... finish it. Do not sell it!!
HBTim
Critical listener of beer fizz
Yup... me too.
In time. Right now I'm enjoying the music.
One great thing about a new component revealing things never heard before in a recording is that I get to discover my record collection all over again.
HBTim
Critical listener of beer fizz
Oh man, you said it.
Dswankey
Lunatic Member
While replying to another thread earlier I came across this, just thought I would add this and in no way is this a critique of @twiiii opinion
http://www.earlytelevision.org/pilot_history.html
oldtexasdog
Well-Known Member
Superman541
Well-Known Member
To my ear, tube amps just sound better. Way better, overall. Among tube amps, Pilots are notably sweet-sounding. Among Pilots (or any other brand) EL84-type output tubes are known to kick butt in the fidelity department. Finally, the output section of an integrated amplifier makes a big difference in sound quality and separate power amps sound better, often enough. And so....it is unsurprising the OP had an out-of-body experience with this Pilot amp. I have a Pilot 602 receiver which uses EL84s and I wish I had more Pilot gear.
Rolling 12AX7a and 12AU7s is always fun. There can be sound differences.
Rolling 12AX7a and 12AU7s is always fun. There can be sound differences.
The way I heard it put from a guy who repaired a lot of tube amps was that Marantz and McIntosh stuff had better build quality than Pilot, but Pilot was on par with both as far as sound.
HBTim,
Nice Pilot SA-232. I used to have a pair of Altec 604-8G speakers and I found that the combination of the Altec speakers and the Pilot SA-232 was unbelievably good.
Gold VS Silver: I always assumed that the gold units, that included the tube cage, were sold as stand alone units. The silver version was part of a console system where the amplifier was out of sight and there was no need for a tube cage. Also as a console amplifier, there was no need for the four Ω speaker taps because the designers knew that the console speakers were eight to sixteen Ω.
Heat: The SA-232 runs hot. There are no ventilation holes in the chassis. Over time the insides of the chassis gets hotter and hotter. In the two examples I own, both show signs of heat stress and all the HV capacitors have failed. I recommend using replacement electrolytic capacitors rated for 105˚C or better.
Nice Pilot SA-232. I used to have a pair of Altec 604-8G speakers and I found that the combination of the Altec speakers and the Pilot SA-232 was unbelievably good.
Gold VS Silver: I always assumed that the gold units, that included the tube cage, were sold as stand alone units. The silver version was part of a console system where the amplifier was out of sight and there was no need for a tube cage. Also as a console amplifier, there was no need for the four Ω speaker taps because the designers knew that the console speakers were eight to sixteen Ω.
When the amplifier is used stand alone without the Pilot preamp there is a eleven pin plug that needs to be fitted into the eleven pin socket. The plug accomplishes two things: 1) completes the AC connection to power up the amplifier and 2) engages a resistor load to make up for the current (approximately 10mA) that would have been used by the preamplifier, if it were connected. If one examines the SAMS schematic, one can see that R92 (6800Ω) and R97 (15kΩ) are the load resistors. The resistor load is needed to drop the supply voltage for the 145V source that feeds the 12AU7 front end. If the preamp is connected, the R97 load resistor is disconnected and draws no current. If the preamp is not used, the two resistors are connected and draw the equivalent preamp current. The power transformer sees the same HV power supply load if the preamp is connected or not. The preamp filament current is provided by a separate tap on the power transformer.
Heat: The SA-232 runs hot. There are no ventilation holes in the chassis. Over time the insides of the chassis gets hotter and hotter. In the two examples I own, both show signs of heat stress and all the HV capacitors have failed. I recommend using replacement electrolytic capacitors rated for 105˚C or better.
The SA-260 has the same setup with the load resistors. Don't have the 232 schematic handy, but on the 260 it uses a pair of 15k for that. With the jumper plug in place it ends up wasting about 10ma of current to put the voltages where they should be. I expect the 232 is a similar amount. I would have figured about half that based on whats in the 210. Either way, its not enough current to cause the supply to be massively oversized. I do like that they designed the thing so the voltages were the same whether the preamp was plugged in or not though. Most amps did not.
Mike Stehr
Poverty Audio
.
Hi Mike,
Thank you so much for the schematic. I spent a fair amount of time looking on the internet for a schematic and came up with only a very blurry, very difficult to read copy.
Thank you.
Mike Stehr
Poverty Audio
Hi Mike,
Thank you so much for the schematic. I spent a fair amount of time looking on the internet for a schematic and came up with only a very blurry, very difficult to read copy.
Thank you.
No problem...I'm rebuilding a SA-232 currently and went through the same thing...a blurry unreadable Sams schematic.
Undeterred, I scrounged harder. I lucked out and came across the original SA-232 schematic in pdf, and I'm glad I did.
Keep in mind the Sams schematic shows a little higher voltages than the Pilot schematic for some reason.
Unloaded, with 117VAC input, my PS transformer measures 305VAC on each secondary leg.
What I'm unfamiliar with is they only have one 270 ohm screen resistor for each push-pull pair, with one resistor on the blue primary side, with the other push-pull pair having the resistor on the brown primary side.
They just wire the OPT's B+ to a screen pin, and then run a 270 ohm resistor to pin 9 of the other tube.
It would seem to make a indifference in screen voltage...maybe it's a balance sort of thing. I have no idea...
The center tap of the 6.3 volt winding has .047uF cap, and 39K resistor to ground. The schematic indicates 25 volts at this cap and resistor.
From there, a 330K resistor goes in series to the phase inverter plate resistors.
The 100K plate/anode resistors for the phase inverter are 5%.
Is this some sort of a bias scheme for the inverter tube? (diode bias?)
Mike
Is it built like the schematic shows? That is strange. Normally I'd expect one resistor per screen, or one that was common to both but not this. Best guess is its some sort of stability mechanism but why they put them on opposite sides per channel is beyond me. If they were doing it for some sort of balance deal it would seem it needs to be on the same leg on both channels.
The center tap connection to ground is to provide a reference but fix it positive relative to ground to limit heater-cathode voltage and to reduce hum. If the heater is positive relative to cathode its less likely to pick up hum. The other common way of doing this is tying it to the output tube cathodes. Serves the same purpose. The 330k and 39k simply form a voltage divider, has nothing to do with biasing the tubes and its definitely not a diode.
The center tap connection to ground is to provide a reference but fix it positive relative to ground to limit heater-cathode voltage and to reduce hum. If the heater is positive relative to cathode its less likely to pick up hum. The other common way of doing this is tying it to the output tube cathodes. Serves the same purpose. The 330k and 39k simply form a voltage divider, has nothing to do with biasing the tubes and its definitely not a diode.
I am glad you did too. I am also currently servicing / rebuilding a pair of SA-232.
The Pilot specifies 115VAC on the chassis, however; both the SAMS and the Pilot schematics indicates117VAC line voltage test conditons.
The SAMS shows that the 270 ohm resistors are optional. My guess is that they are there to stop parasitic oscillations.
gadget73's post explains well the reason for the 25V bias on the filaments.
Yes, this is a puzzle.
Since the amplifier was designed to operate at 115VAC line voltage and today's line voltage is a bit higher (typically about 123VAC here), I have made a couple of changes to my Pilots. I have added a CL-80 and increased the cathode bias resistors from 120Ω to 150Ω.
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@HBTim , Nice Pick UP!! congrats. Pretty clean looking 232 you have.
Years ago when I finally got tired and bored of listening to sand gear (SS) and got into valves, the Pilot 232 was one of the first items I picked up. As long as your speakers are not too demanding or too spiky an impedance curve, should sound quite good.
Also the 232 creates a pretty good glue bond joint between your rear end and the seat. (i.e. weak bond joint if you are listening - get bored after 10 min and shut the gear off). The better the glue bond joint the more natural the music has become.
Years ago when I finally got tired and bored of listening to sand gear (SS) and got into valves, the Pilot 232 was one of the first items I picked up. As long as your speakers are not too demanding or too spiky an impedance curve, should sound quite good.
Also the 232 creates a pretty good glue bond joint between your rear end and the seat. (i.e. weak bond joint if you are listening - get bored after 10 min and shut the gear off). The better the glue bond joint the more natural the music has become.