[Drakelist] R-4A PTO - transistors substituted?
Looking at the transistors in this PTO, I'm 99.9% sure someone replaced them: they are both marked NSRS / 2018, with the / being a line break. I'm sort of thinking that Drake used different parts for the oscillator and buffer for a good reason. Aside from this maddening frequency-shifting and crummy audio, the frequency calibration is still good. What are the chances that using the wrong transistors could be the source of all this grief? Steve Wedge, W1ES/4 I can't complain, but sometimes I still do. - Joe Walsh If the above message appears, it came from Steve's Son of Laptop!___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R-4A PTO - transistors substituted?
Steve - I've looked in a LOT of PTOs, and I've never seen anything but a 2N3858 in the Buffer and either a 2N3858 (early) or 2N706 (late) in the oscillator. No other changes required with either oscillator transistor. The '3858 is just about extinct, but the 2N706 is still a common transistor. Defective transistors have definitely been known to cause the kind of frequency changes you're seeing. So while they may even be a 'later' modification than factory built, and may even be a suitable substitute, they can still fail just like the originals. By the way, if you look at the PTO schematic, the FSK 'shift' terminal is connected to the output of the oscillator stage. This allowed you to _SHIFT_ the PTO frequency by up to 850 Hz by adding a cap from this terminal to ground. So variations in the Buffer transistor CAN dither the frequency. And yes, it does. I think transistors were about the third thing down on the list once you get through the lubrication, mechanical and ground faults. I know you said you were short on components, but '706s are cheap from Mouser, or if you can find a couple of 2N3904 (everywhere!) transistors you could try them just to see. They may not work perfectly, but if the PTO becomes stable you'll know. Watch the basing on whatever transistors you use. Seems like they are all different these days! 73, Garey - K4OAH Glen Allen, VA Steve Wedge wrote: Looking at the transistors in this PTO, I'm 99.9% sure someone replaced them: they are both marked NSRS / 2018, with the / being a line break. I'm sort of thinking that Drake used different parts for the oscillator and buffer for a good reason. Aside from this maddening frequency-shifting and crummy audio, the frequency calibration is still good. What are the chances that using the wrong transistors could be the source of all this grief? ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R-4A PTO - transistors substituted?
Or even a 2N. Between the 2N3858, 2N3904, and 2N, the fT / GBP, hFE, and C in/out parameters are reasonably identical. Probably the biggest variant will be the hfe value across samples, but I agree with Garey to give it a shot. The PTO is only running at 5 MHz. During college, I worked for an engineer who's philosophy was to replace with 2NAnyThing that worked. He certainly knew the widely different transistor parameters, but his point was that in many general purpose switching, amplification and oscillating circuits, 2NAnyThing is often an adequate substitute, taking into account the need to watch for NPN, PNP, FET, etc. configurations. Paul, W9AC - Original Message - From: Garey Barrell k4...@mindspring.com To: Steve Wedge w1es1...@earthlink.net Cc: drakelist@zerobeat.net Sent: Sunday, July 24, 2011 2:45 PM Subject: Re: [Drakelist] R-4A PTO - transistors substituted? Steve - I've looked in a LOT of PTOs, and I've never seen anything but a 2N3858 in the Buffer and either a 2N3858 (early) or 2N706 (late) in the oscillator. No other changes required with either oscillator transistor. The '3858 is just about extinct, but the 2N706 is still a common transistor. Defective transistors have definitely been known to cause the kind of frequency changes you're seeing. So while they may even be a 'later' modification than factory built, and may even be a suitable substitute, they can still fail just like the originals. By the way, if you look at the PTO schematic, the FSK 'shift' terminal is connected to the output of the oscillator stage. This allowed you to _SHIFT_ the PTO frequency by up to 850 Hz by adding a cap from this terminal to ground. So variations in the Buffer transistor CAN dither the frequency. And yes, it does. I think transistors were about the third thing down on the list once you get through the lubrication, mechanical and ground faults. I know you said you were short on components, but '706s are cheap from Mouser, or if you can find a couple of 2N3904 (everywhere!) transistors you could try them just to see. They may not work perfectly, but if the PTO becomes stable you'll know. Watch the basing on whatever transistors you use. Seems like they are all different these days! 73, Garey - K4OAH Glen Allen, VA Steve Wedge wrote: Looking at the transistors in this PTO, I'm 99.9% sure someone replaced them: they are both marked NSRS / 2018, with the / being a line break. I'm sort of thinking that Drake used different parts for the oscillator and buffer for a good reason. Aside from this maddening frequency-shifting and crummy audio, the frequency calibration is still good. What are the chances that using the wrong transistors could be the source of all this grief? ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R-4A PTO - transistors substituted?
Funny, I don't recall you working for me during college :-) 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Paul Christensen wrote: Or even a 2N. Between the 2N3858, 2N3904, and 2N, the fT / GBP, hFE, and C in/out parameters are reasonably identical. Probably the biggest variant will be the hfe value across samples, but I agree with Garey to give it a shot. The PTO is only running at 5 MHz. During college, I worked for an engineer who's philosophy was to replace with 2NAnyThing that worked. He certainly knew the widely different transistor parameters, but his point was that in many general purpose switching, amplification and oscillating circuits, 2NAnyThing is often an adequate substitute, taking into account the need to watch for NPN, PNP, FET, etc. configurations. Paul, W9AC - Original Message - From: Garey Barrell k4...@mindspring.com To: Steve Wedge w1es1...@earthlink.net Cc: drakelist@zerobeat.net Sent: Sunday, July 24, 2011 2:45 PM Subject: Re: [Drakelist] R-4A PTO - transistors substituted? Steve - I've looked in a LOT of PTOs, and I've never seen anything but a 2N3858 in the Buffer and either a 2N3858 (early) or 2N706 (late) in the oscillator. No other changes required with either oscillator transistor. The '3858 is just about extinct, but the 2N706 is still a common transistor. Defective transistors have definitely been known to cause the kind of frequency changes you're seeing. So while they may even be a 'later' modification than factory built, and may even be a suitable substitute, they can still fail just like the originals. By the way, if you look at the PTO schematic, the FSK 'shift' terminal is connected to the output of the oscillator stage. This allowed you to _SHIFT_ the PTO frequency by up to 850 Hz by adding a cap from this terminal to ground. So variations in the Buffer transistor CAN dither the frequency. And yes, it does. I think transistors were about the third thing down on the list once you get through the lubrication, mechanical and ground faults. I know you said you were short on components, but '706s are cheap from Mouser, or if you can find a couple of 2N3904 (everywhere!) transistors you could try them just to see. They may not work perfectly, but if the PTO becomes stable you'll know. Watch the basing on whatever transistors you use. Seems like they are all different these days! 73, Garey - K4OAH Glen Allen, VA Steve Wedge wrote: Looking at the transistors in this PTO, I'm 99.9% sure someone replaced them: they are both marked NSRS / 2018, with the / being a line break. I'm sort of thinking that Drake used different parts for the oscillator and buffer for a good reason. Aside from this maddening frequency-shifting and crummy audio, the frequency calibration is still good. What are the chances that using the wrong transistors could be the source of all this grief? ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R-4A PTO - transistors substituted?
For the oscillating device in the LO I would add noise to the list of what to look for in a transistor. This varies a lot from type to type and even from maker to maker. For example, the 2N is not exactly the world's quietest transistor. To just check to see if that osc transistor is the root of the problem, then free subsitution is fine. Otherwise stick to a device that was designed for RF service, which is different than a device designed for general saturated switching. I know this from experience; my company was a transistor manufacturer in the past. Dennis AE6C On Sun, Jul 24, 2011 at 2:20 PM, Garey Barrell k4...@mindspring.com wrote: Funny, I don't recall you working for me during college :-) 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Paul Christensen wrote: Or even a 2N. Between the 2N3858, 2N3904, and 2N, the fT / GBP, hFE, and C in/out parameters are reasonably identical. Probably the biggest variant will be the hfe value across samples, but I agree with Garey to give it a shot. The PTO is only running at 5 MHz. During college, I worked for an engineer who's philosophy was to replace with 2NAnyThing that worked. He certainly knew the widely different transistor parameters, but his point was that in many general purpose switching, amplification and oscillating circuits, 2NAnyThing is often an adequate substitute, taking into account the need to watch for NPN, PNP, FET, etc. configurations. Paul, W9AC - Original Message - From: Garey Barrell k4...@mindspring.com To: Steve Wedge w1es1...@earthlink.net Cc: drakelist@zerobeat.net Sent: Sunday, July 24, 2011 2:45 PM Subject: Re: [Drakelist] R-4A PTO - transistors substituted? Steve - I've looked in a LOT of PTOs, and I've never seen anything but a 2N3858 in the Buffer and either a 2N3858 (early) or 2N706 (late) in the oscillator. No other changes required with either oscillator transistor. The '3858 is just about extinct, but the 2N706 is still a common transistor. Defective transistors have definitely been known to cause the kind of frequency changes you're seeing. So while they may even be a 'later' modification than factory built, and may even be a suitable substitute, they can still fail just like the originals. By the way, if you look at the PTO schematic, the FSK 'shift' terminal is connected to the output of the oscillator stage. This allowed you to _SHIFT_ the PTO frequency by up to 850 Hz by adding a cap from this terminal to ground. So variations in the Buffer transistor CAN dither the frequency. And yes, it does. I think transistors were about the third thing down on the list once you get through the lubrication, mechanical and ground faults. I know you said you were short on components, but '706s are cheap from Mouser, or if you can find a couple of 2N3904 (everywhere!) transistors you could try them just to see. They may not work perfectly, but if the PTO becomes stable you'll know. Watch the basing on whatever transistors you use. Seems like they are all different these days! 73, Garey - K4OAH Glen Allen, VA Steve Wedge wrote: Looking at the transistors in this PTO, I'm 99.9% sure someone replaced them: they are both marked NSRS / 2018, with the / being a line break. I'm sort of thinking that Drake used different parts for the oscillator and buffer for a good reason. Aside from this maddening frequency-shifting and crummy audio, the frequency calibration is still good. What are the chances that using the wrong transistors could be the source of all this grief? __**_ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/**mailman/listinfo/drakelisthttp://mailman.zerobeat.net/mailman/listinfo/drakelist __**_ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/**mailman/listinfo/drakelisthttp://mailman.zerobeat.net/mailman/listinfo/drakelist __**_ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/**mailman/listinfo/drakelisthttp://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R-4A PTO - transistors substituted?
Dennis - And watch those reverse breakdowns too!! :-) The 2N is the 6L6 of the transistor world. No matter how much you abuse them, they just keep going 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Dennis Monticelli wrote: For the oscillating device in the LO I would add noise to the list of what to look for in a transistor. This varies a lot from type to type and even from maker to maker. For example, the 2N is not exactly the world's quietest transistor. To just check to see if that osc transistor is the root of the problem, then free subsitution is fine. Otherwise stick to a device that was designed for RF service, which is different than a device designed for general saturated switching. I know this from experience; my company was a transistor manufacturer in the past. Dennis AE6C On Sun, Jul 24, 2011 at 2:20 PM, Garey Barrell k4...@mindspring.com mailto:k4...@mindspring.com wrote: Funny, I don't recall you working for me during college :-) 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com http://www.k4oah.com/ Paul Christensen wrote: Or even a 2N. Between the 2N3858, 2N3904, and 2N, the fT / GBP, hFE, and C in/out parameters are reasonably identical. Probably the biggest variant will be the hfe value across samples, but I agree with Garey to give it a shot. The PTO is only running at 5 MHz. During college, I worked for an engineer who's philosophy was to replace with 2NAnyThing that worked. He certainly knew the widely different transistor parameters, but his point was that in many general purpose switching, amplification and oscillating circuits, 2NAnyThing is often an adequate substitute, taking into account the need to watch for NPN, PNP, FET, etc. configurations. Paul, W9AC - Original Message - From: Garey Barrell k4...@mindspring.com mailto:k4...@mindspring.com To: Steve Wedge w1es1...@earthlink.net mailto:w1es1...@earthlink.net Cc: drakelist@zerobeat.net mailto:drakelist@zerobeat.net Sent: Sunday, July 24, 2011 2:45 PM Subject: Re: [Drakelist] R-4A PTO - transistors substituted? Steve - I've looked in a LOT of PTOs, and I've never seen anything but a 2N3858 in the Buffer and either a 2N3858 (early) or 2N706 (late) in the oscillator. No other changes required with either oscillator transistor. The '3858 is just about extinct, but the 2N706 is still a common transistor. Defective transistors have definitely been known to cause the kind of frequency changes you're seeing. So while they may even be a 'later' modification than factory built, and may even be a suitable substitute, they can still fail just like the originals. By the way, if you look at the PTO schematic, the FSK 'shift' terminal is connected to the output of the oscillator stage. This allowed you to _SHIFT_ the PTO frequency by up to 850 Hz by adding a cap from this terminal to ground. So variations in the Buffer transistor CAN dither the frequency. And yes, it does. I think transistors were about the third thing down on the list once you get through the lubrication, mechanical and ground faults. I know you said you were short on components, but '706s are cheap from Mouser, or if you can find a couple of 2N3904 (everywhere!) transistors you could try them just to see. They may not work perfectly, but if the PTO becomes stable you'll know. Watch the basing on whatever transistors you use. Seems like they are all different these days! 73, Garey - K4OAH Glen Allen, VA Steve Wedge wrote: Looking at the transistors in this PTO, I'm 99.9% sure someone replaced them: they are both marked NSRS / 2018, with the / being a line break. I'm sort of thinking that Drake used different parts for the oscillator and buffer for a good reason. Aside from this maddening frequency-shifting and crummy audio, the frequency calibration is still good. What are the chances that using the wrong transistors could be the source of all this grief? ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R-4A PTO - transistors substituted?
Thanks, Garey - Yeah - I've seen that they're only about a buck-seventy-five on Mouser. I think that this is where I'm going next. Just in case this doesn't work out, which capacitors are the ones with the negative temp coefficients? I suspect the 3000 pF would be one of them. Steve Wedge, W1ES/4 I can't complain, but sometimes I still do. - Joe Walsh If the above message appears, it came from Steve's Son of Laptop! - Original Message - From: Garey Barrell k4...@mindspring.com To: Steve Wedge w1es1...@earthlink.net Cc: drakelist@zerobeat.net Sent: Sunday, July 24, 2011 2:45 PM Subject: Re: [Drakelist] R-4A PTO - transistors substituted? Steve - I've looked in a LOT of PTOs, and I've never seen anything but a 2N3858 in the Buffer and either a 2N3858 (early) or 2N706 (late) in the oscillator. No other changes required with either oscillator transistor. The '3858 is just about extinct, but the 2N706 is still a common transistor. Defective transistors have definitely been known to cause the kind of frequency changes you're seeing. So while they may even be a 'later' modification than factory built, and may even be a suitable substitute, they can still fail just like the originals. By the way, if you look at the PTO schematic, the FSK 'shift' terminal is connected to the output of the oscillator stage. This allowed you to _SHIFT_ the PTO frequency by up to 850 Hz by adding a cap from this terminal to ground. So variations in the Buffer transistor CAN dither the frequency. And yes, it does. I think transistors were about the third thing down on the list once you get through the lubrication, mechanical and ground faults. I know you said you were short on components, but '706s are cheap from Mouser, or if you can find a couple of 2N3904 (everywhere!) transistors you could try them just to see. They may not work perfectly, but if the PTO becomes stable you'll know. Watch the basing on whatever transistors you use. Seems like they are all different these days! 73, Garey - K4OAH Glen Allen, VA Steve Wedge wrote: Looking at the transistors in this PTO, I'm 99.9% sure someone replaced them: they are both marked NSRS / 2018, with the / being a line break. I'm sort of thinking that Drake used different parts for the oscillator and buffer for a good reason. Aside from this maddening frequency-shifting and crummy audio, the frequency calibration is still good. What are the chances that using the wrong transistors could be the source of all this grief? ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R-4A PTO - transistors substituted?
Steve - No, typically they are smaller values. The TC caps are some of the ones with asterisks (*) beside them. Those are the selected caps, picked at final test. It's certainly possible that the 3000 or 90 pF ARE TC though. The small disc ceramics caps that are TC type have the top half 'dipped in paint', and the color indicates TC. The tubular _glass_ caps have a complex, colored dot pattern. The capacitance value is often Body - End - Dot for the capacitance value (first - second significant figures and third multiplier) and typically the rest of the dots specify either a third significant, or TC, or There is a set of tables in the back of the ARRL Handbooks that explain a lot of the codes, or I'm sure they're on the internet. So far though, all the PTOs that I've had to replace devices in have resulted in good linearity. I don't think the active device has much of an effect on TC, it's mostly the relationship between the coil's, form, core, capacitance. Don't overheat anything in there, and be sure to let it cool to room temp before becoming concerned about TC. WATCH the device basing 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Steve Wedge wrote: Thanks, Garey - Yeah - I've seen that they're only about a buck-seventy-five on Mouser. I think that this is where I'm going next. Just in case this doesn't work out, which capacitors are the ones with the negative temp coefficients? I suspect the 3000 pF would be one of them. Steve Wedge, W1ES/4 I can't complain, but sometimes I still do. - Joe Walsh If the above message appears, it came from Steve's Son of Laptop! - Original Message - From: Garey Barrell k4...@mindspring.com To: Steve Wedge w1es1...@earthlink.net Cc: drakelist@zerobeat.net Sent: Sunday, July 24, 2011 2:45 PM Subject: Re: [Drakelist] R-4A PTO - transistors substituted? Steve - I've looked in a LOT of PTOs, and I've never seen anything but a 2N3858 in the Buffer and either a 2N3858 (early) or 2N706 (late) in the oscillator. No other changes required with either oscillator transistor. The '3858 is just about extinct, but the 2N706 is still a common transistor. Defective transistors have definitely been known to cause the kind of frequency changes you're seeing. So while they may even be a 'later' modification than factory built, and may even be a suitable substitute, they can still fail just like the originals. By the way, if you look at the PTO schematic, the FSK 'shift' terminal is connected to the output of the oscillator stage. This allowed you to _SHIFT_ the PTO frequency by up to 850 Hz by adding a cap from this terminal to ground. So variations in the Buffer transistor CAN dither the frequency. And yes, it does. I think transistors were about the third thing down on the list once you get through the lubrication, mechanical and ground faults. I know you said you were short on components, but '706s are cheap from Mouser, or if you can find a couple of 2N3904 (everywhere!) transistors you could try them just to see. They may not work perfectly, but if the PTO becomes stable you'll know. Watch the basing on whatever transistors you use. Seems like they are all different these days! 73, Garey - K4OAH Glen Allen, VA Steve Wedge wrote: Looking at the transistors in this PTO, I'm 99.9% sure someone replaced them: they are both marked NSRS / 2018, with the / being a line break. I'm sort of thinking that Drake used different parts for the oscillator and buffer for a good reason. Aside from this maddening frequency-shifting and crummy audio, the frequency calibration is still good. What are the chances that using the wrong transistors could be the source of all this grief? ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R-4A PTO - transistors substituted?
Thanks, Garey - I've done loads of rework over the years, so hoping I won't mess up the basing (though I won't say that I've never messed it up). I'm ordering 3 each anyway. I used to have scores of 2N3904's but gave all my parts away when I moved five years ago. Not a big deal - Mouser has 'em for less than a quarter each. The shipping's going to cost me more than the parts :-) I was just figuring I can order some of the caps while I'm paying $7 for shipping anyway. I have no idea what these transistors are that are in there now. Someone must have had these around as generic NPN's and used them. Even though that 3000 pF cap is huge and funny-looking, am I right in assuming I could replace it with a standard SM one? Here's hoping replacing them takes care of the problem. 73, Steve Wedge, W1ES/4 I can't complain, but sometimes I still do. - Joe Walsh If the above message appears, it came from Steve's Son of Laptop! - Original Message - From: Garey Barrell k4...@mindspring.com To: Steve Wedge w1es1...@earthlink.net Cc: drakelist@zerobeat.net Sent: Sunday, July 24, 2011 6:24 PM Subject: Re: [Drakelist] R-4A PTO - transistors substituted? Steve - No, typically they are smaller values. The TC caps are some of the ones with asterisks (*) beside them. Those are the selected caps, picked at final test. It's certainly possible that the 3000 or 90 pF ARE TC though. The small disc ceramics caps that are TC type have the top half 'dipped in paint', and the color indicates TC. The tubular _glass_ caps have a complex, colored dot pattern. The capacitance value is often Body - End - Dot for the capacitance value (first - second significant figures and third multiplier) and typically the rest of the dots specify either a third significant, or TC, or There is a set of tables in the back of the ARRL Handbooks that explain a lot of the codes, or I'm sure they're on the internet. So far though, all the PTOs that I've had to replace devices in have resulted in good linearity. I don't think the active device has much of an effect on TC, it's mostly the relationship between the coil's, form, core, capacitance. Don't overheat anything in there, and be sure to let it cool to room temp before becoming concerned about TC. WATCH the device basing 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Steve Wedge wrote: Thanks, Garey - Yeah - I've seen that they're only about a buck-seventy-five on Mouser. I think that this is where I'm going next. Just in case this doesn't work out, which capacitors are the ones with the negative temp coefficients? I suspect the 3000 pF would be one of them. Steve Wedge, W1ES/4 I can't complain, but sometimes I still do. - Joe Walsh If the above message appears, it came from Steve's Son of Laptop! - Original Message - From: Garey Barrell k4...@mindspring.com To: Steve Wedge w1es1...@earthlink.net Cc: drakelist@zerobeat.net Sent: Sunday, July 24, 2011 2:45 PM Subject: Re: [Drakelist] R-4A PTO - transistors substituted? Steve - I've looked in a LOT of PTOs, and I've never seen anything but a 2N3858 in the Buffer and either a 2N3858 (early) or 2N706 (late) in the oscillator. No other changes required with either oscillator transistor. The '3858 is just about extinct, but the 2N706 is still a common transistor. Defective transistors have definitely been known to cause the kind of frequency changes you're seeing. So while they may even be a 'later' modification than factory built, and may even be a suitable substitute, they can still fail just like the originals. By the way, if you look at the PTO schematic, the FSK 'shift' terminal is connected to the output of the oscillator stage. This allowed you to _SHIFT_ the PTO frequency by up to 850 Hz by adding a cap from this terminal to ground. So variations in the Buffer transistor CAN dither the frequency. And yes, it does. I think transistors were about the third thing down on the list once you get through the lubrication, mechanical and ground faults. I know you said you were short on components, but '706s are cheap from Mouser, or if you can find a couple of 2N3904 (everywhere!) transistors you could try them just to see. They may not work perfectly, but if the PTO becomes stable you'll know. Watch the basing on whatever transistors you use. Seems like they are all different these days! 73, Garey - K4OAH Glen Allen, VA Steve Wedge wrote: Looking at the transistors in this PTO, I'm 99.9% sure someone replaced them: they are both marked NSRS / 2018, with the / being a line break. I'm sort of thinking that Drake used different parts for the oscillator and buffer for a good reason. Aside from this maddening frequency-shifting and crummy audio, the frequency calibration is still good. What are the chances that using the wrong transistors could
