Pilot SA-232 new to me
- Thread starter HBTim
- Start date
Mike Stehr
Poverty Audio
Yeah. I'm used to seeing one screen resistor for each output tube, usually with a filter cap.
Usually, they use a filter cap with a dropping resistor for the screen of each output tube.
Correct me if I am wrong, but from what I understand is the screen voltage on the output tube uses dropping resistors to lower the voltage/dissipation
of the screen compared to the anode/plate.
Where under certain conditions, the screen dissipation/voltage can exceed that of the anode.
I'm guessing it depends how the PP pair is set-up and biased.
Yup...Kudos for gadget73. He's always here to help answer questions...thanks.
My wall voltage is around 121-122VAC. I plan on getting a CL-80, and have been pondering increasing the cathode resistors to 150 ohms.
The 270 ohm doesn't drop enough voltage to be significant. Its mostly there to de-tune the circuit that forms between the screen and filter cap. Its been explained far better elsewhere but basically under the wrong conditions it can cause arcing in the tube. Thats why I don't get the single resistor, it doesn't seem like it would work quite right. Maybe @dcgillespie has some insight? Dave has a whole lot more tube experience than I do.
the article that explains the use of screen stopper resistors
Techniques To Maximize Power Tube Life (tronola.com)
the article that explains the use of screen stopper resistors
Techniques To Maximize Power Tube Life (tronola.com)
HBTim
Critical listener of beer fizz
Quick little funner'ness. I have a buddy coming over on Friday the 3rd. We plan on doing some slippy swappy amp madness.
I have a newly acquired Fisher 202t that I cannot wait to hear. What a lucky find. I would not have even known anything about this amp if not told about them. Apparently it is a 400C pre with a tuner. Very cool and not many made. Just making sure all is up to spec before stretching its legs. Get pic up later of it it. Quit the looker.
Also, we will have a mod'd Marantz 8, and the aforementioned gear in the earlier posts with the 400CX2, SA-100/300, and, of course, the Pilot. I will be using newly found Speakerlabs K-Horn's, or "K'"?? Anyway, the Klipschorn clone. Cabs are nothing special and needs a lot of work but they sound amazing. I will also have some Cornwall's in the mix as well. This will be fun.
I will check back in with some pics and impressions on how the Pilot holds up against the healthy guests.
I have a newly acquired Fisher 202t that I cannot wait to hear. What a lucky find. I would not have even known anything about this amp if not told about them. Apparently it is a 400C pre with a tuner. Very cool and not many made. Just making sure all is up to spec before stretching its legs. Get pic up later of it it. Quit the looker.
Also, we will have a mod'd Marantz 8, and the aforementioned gear in the earlier posts with the 400CX2, SA-100/300, and, of course, the Pilot. I will be using newly found Speakerlabs K-Horn's, or "K'"?? Anyway, the Klipschorn clone. Cabs are nothing special and needs a lot of work but they sound amazing. I will also have some Cornwall's in the mix as well. This will be fun.
I will check back in with some pics and impressions on how the Pilot holds up against the healthy guests.
trainbuftony
Electron Herder
Oh fun!
These events are so fun and memorable.
Good friends, good music, and a wide variety of amplification.
It will be interesting to know what you agree and disagree on...
These events are so fun and memorable.
Good friends, good music, and a wide variety of amplification.
It will be interesting to know what you agree and disagree on...
I will look forward to hearing your report.
Tim, you crack me up! I have both a 101T and a 202T and they're both amazing. My 202T is fully restored and sounds fantastic.
I got the Pilot bug when I purchased a decrepit "portable" (giant) turntable with amp inside for $10 at a picker sale. It was a Pilot SA 1060A. The cabinet was trashed, the turntable an unexciting Garrard but the front end was this tiny little Pilot stereo tube amp. Brought it up on a variac, everything worked and it sounded fantastic. Got my attention in a hurry. I've since picked up a number of Pilot pieces and found the 232 is one of my most enjoyable. Would love to be a fly on the wall at the shootout on the 3rd....
I got the Pilot bug when I purchased a decrepit "portable" (giant) turntable with amp inside for $10 at a picker sale. It was a Pilot SA 1060A. The cabinet was trashed, the turntable an unexciting Garrard but the front end was this tiny little Pilot stereo tube amp. Brought it up on a variac, everything worked and it sounded fantastic. Got my attention in a hurry. I've since picked up a number of Pilot pieces and found the 232 is one of my most enjoyable. Would love to be a fly on the wall at the shootout on the 3rd....
This thing originally had long legs and could be connected to a companion speaker. There are a few threads on AK about it-all glowing comments about the amp. You're not wrong about the heft. It was sitting on the ground, which was wet. The cabinet was moldy, falling apart. Not sure what made me open it up and look inside but boy was I surprised.
MadcapLaughs
Active Member
Hey a bit off topic, but I have a pilot SA 232 tube amp and have used several preamps with it over the past few years, but I really want to get a matching pilot preamp. However, there is a small annoyance that I can’t seem to confirm why these pilot preamps have them:
I listen to a ton of mono records and I get a lot out of using a built in mono sum function on my preamp (Mono A+B). However, most pilot tube products seem to only include mono channel A or mono channel B as two separate functions. My simple question is, if you select one of these functions, are you still getting the benefits of a traditional mono sum function when playing LPs on a stereo cartridge or is there some other archaic application for this switch selection? It’s simply a deal breaker if there isn’t any benefit during mono playback on my stereo system and no I won’t buy a mono cartridge or use a Y cable as an alternative. Thanks guys!
I listen to a ton of mono records and I get a lot out of using a built in mono sum function on my preamp (Mono A+B). However, most pilot tube products seem to only include mono channel A or mono channel B as two separate functions. My simple question is, if you select one of these functions, are you still getting the benefits of a traditional mono sum function when playing LPs on a stereo cartridge or is there some other archaic application for this switch selection? It’s simply a deal breaker if there isn’t any benefit during mono playback on my stereo system and no I won’t buy a mono cartridge or use a Y cable as an alternative. Thanks guys!
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congrats on your 202t, tim. what's its serial number, and does it have an mpx installed? i put up a post in the fisher forum where i'm trying to keep the data for known owners...https://audiokarma.org/forums/index...on-thread-and-roll-call.953758/#post-14664309
you might want to look at the pilot fa-690 (or 690a), iirc mine has the sum function.
HBTim
Critical listener of beer fizz
No MPX… sad about that… but I will get serial number this weekend.
however, my friend that is coming over this weekend has one. MPX unit that is. I will try to get pics and model.
MadcapLaughs
Active Member
From what I can tell there is no sum function on the 690 or 690a, only mono channel a (fm), and a separate channel b (am). Where is the typical A+B mono sum function? I dont understand why they only included two single channel options, in fact I'm not even sure what the purpose of that would be.
i dunno. mine is packed away, and i’ve never seen an operating guide…
Two comments I would offer to the party --
1. The single 270Ω screen resistor: As a cathode biased amplifier, the danger of output tube arcing from any circuit induced tendencies (i.e.violent transient oscillations) in the SA-232 is beyond remote. However, the more usual garden variety parasitic oscillations can still be present in any push-pull output stage using high Transconductance tubes like those in the 6BQ5 (or 7591) family of tubes, whether it is operated with cathode biased or fixed bias. These parasitic oscillations can form if the screen grids of the two tubes are connected directly together and powered from the same source. While using dual screen stoppers looks nice on a schematic and certainly gives the impression of a more balanced approach, in this application, only a single resistor is actually needed to do the job -- and it doesn't matter which grid it's connected to, either. The important point is that it's connected in at least one of the grids, which will then break up any tendency towards producing parasitic oscillations within a push-pull pair. The small value used is plenty big enough to do the job it's required to do, but hardly big enough to upset the dynamic balance between the tubes. The fact that they are in the opposite grid relative to each channel causes the two channels together to present a mirror image to the screen circuit (common to both channels), further helping to preventing any parasitic oscillations that might form due to the use of a common power supply to power both channels. A second screen stopper can be added in each channel if it causes any loss of sleep -- but that's about the only actual benefit it will provide in this case.
2. Use of one phono preamp of a stereo pair to provide for mono operation: Invariably, when this design feature was offered, it was to accommodate specifically a mono cartridge as was typically used in record changers for the purpose of playing 78 RPM records. During the time period this feature was offered, LP stereo recordings were understood to be played on a separate turn table, which of course offered higher playback quality than a changer could -- through a separate stereo RIAA input setting to accommodate the turntable.
Since no 78 records were recorded in stereo, the EQ for such records was only installed in one phono preamp (usually Channel A). To make the sound appear in both channels, units with this feature also invariably included a Mode switch, which then allowed the output of the one phono preamp with the 78 EQ to appear in both speakers. The same Mode switch also typically includes a mono setting, which then allows for combining the output of the two phono preamps (or any of the stereo inputs) in a traditional A+B format from both speakers.
I hope this helps!
Dave
1. The single 270Ω screen resistor: As a cathode biased amplifier, the danger of output tube arcing from any circuit induced tendencies (i.e.violent transient oscillations) in the SA-232 is beyond remote. However, the more usual garden variety parasitic oscillations can still be present in any push-pull output stage using high Transconductance tubes like those in the 6BQ5 (or 7591) family of tubes, whether it is operated with cathode biased or fixed bias. These parasitic oscillations can form if the screen grids of the two tubes are connected directly together and powered from the same source. While using dual screen stoppers looks nice on a schematic and certainly gives the impression of a more balanced approach, in this application, only a single resistor is actually needed to do the job -- and it doesn't matter which grid it's connected to, either. The important point is that it's connected in at least one of the grids, which will then break up any tendency towards producing parasitic oscillations within a push-pull pair. The small value used is plenty big enough to do the job it's required to do, but hardly big enough to upset the dynamic balance between the tubes. The fact that they are in the opposite grid relative to each channel causes the two channels together to present a mirror image to the screen circuit (common to both channels), further helping to preventing any parasitic oscillations that might form due to the use of a common power supply to power both channels. A second screen stopper can be added in each channel if it causes any loss of sleep -- but that's about the only actual benefit it will provide in this case.
2. Use of one phono preamp of a stereo pair to provide for mono operation: Invariably, when this design feature was offered, it was to accommodate specifically a mono cartridge as was typically used in record changers for the purpose of playing 78 RPM records. During the time period this feature was offered, LP stereo recordings were understood to be played on a separate turn table, which of course offered higher playback quality than a changer could -- through a separate stereo RIAA input setting to accommodate the turntable.
Since no 78 records were recorded in stereo, the EQ for such records was only installed in one phono preamp (usually Channel A). To make the sound appear in both channels, units with this feature also invariably included a Mode switch, which then allowed the output of the one phono preamp with the 78 EQ to appear in both speakers. The same Mode switch also typically includes a mono setting, which then allows for combining the output of the two phono preamps (or any of the stereo inputs) in a traditional A+B format from both speakers.
I hope this helps!
Dave
Separate FM and AM tuners within one unit were used for stereo broadcasts before a FM multiplex system was approved and implemented. One tuner would provide the left channel information (example channel A on FM) and the other tuner would provide the right channel (example channel B on AM). If one was not listening to a stereo FM / AM broadcast, one could use either the FM or AM tuner through both channels using the A to both channels or B to both channels mode.