Yaesu FT-101ZD page

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12BY7A Driver board PB-1714A

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The driver board amplifies the SSB/CW signal and feeds it to the PA. The driver uses a tube (12BY7A) for delivering the necessary power, and the tube is also used in the automatic level control circuit (ALC). Part of the output is available at a connector at the back, for use with transverters or other purposes. Tuning is done with the same inductive tuning unit, that is used by the RF board. The inductive tuning allows a constant output over a greater range. The heater of the tube is switched by the heater switch on the front. By using this switch during longer receiving-only periods, the tube will last much longer, and there is less heating up.

  Here's an interesting problem I spent the better part of the afternoon trying to find in a customers FT-101ZD.  I get the unit from the customer full of dirt hardly working and barely receiving.  Cleaned up the switches and controls and the unit started to receive, the transmitter was still dead in part due to resistors having been cut on the rectifier "B" unit PB-1968 by the last rocket scientist who tried to fix it.  After repairing the rect "B" unit and replacing several resistors we are ready for a test of the power supply. Plugged it up, turned it on and Poof smoke!  First I thought the filter capacitors were bad, so I pulled them out and the power supply smoked again with the caps out of the set.  Time to move further into the set. Removing the 300 volt line that goes further into the rig prevented the rect "B" unit from smoking.  Disconnecting wiring all the way back to the 12BY7 driver unit PB-1714 we could remove the problem and stop the unit from smoking. Taking a very good light and a good magnifying lens to the driver unit revealed nothing visible to the eye.  Hooked up the driver unit again and ~ poof more smoke back on the rect ":B" unit.  No choice but to pull the driver unit and try and figure out what is going on.  In the case of the FT-101ZD the 300 volt supply going to the driver unit feeds directly to the plate of the tube and pin #7 of the tube socket.  Sounds easy enough unless you're the one having to do the troubleshooting.  There was nothing there that would cause the power supply to keep burning up. SO ONE WOULD THINK.  Using an ohm meter on the circuit revealed a low resistance to ground, but there was really nothing on the driver unit PB-1092 that would have gone short, no capacitors mounted on the driver unit plate circuit to go bad. So I pulled the driver unit out of the transceiver and this is what I found.   A carbon track from Pin #7 directly to ground at the center of the tube. Spent a good part of the day looking for this one!  A replacement tube socket and a half hour later putting everything back together and we were up and running.  How can you ever be bored with ham radio as a hobby when you learn something every day. (W4CLM)

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The trimmer boards The inductive tuning unit The Driver board position


The Power Amplifier PB-1715A

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The Power Amplifier, consists of two 6146B heavy duty transmitting tubes, the input filter and the output filter. The output filter delivers the RF signal to a suitable antenna. The impedance from the antenna has to be between 50 and 75 ohms unbalanced. A Antenna with a different impedance at the feed point can be used, but there must be a matching device between the transceiver and this feed point. The same goes for other antennas with a lower impedance such as magnetic loops and others. The 6146B PA tubes are very rugged, and can deliver around 100 -120 Watts output depending on the band of operation, by a input of 180W in the SSB and CW mode. In AM mode the maximum input power is 45 Watt. This is due the fact that the SSB signal has just one sideband, which has only 25% of the power factor of a AM signal, so the tubes can deliver in SSB 4x the power of a AM signal, at the same dissipation. It is never a good idea to push the PA to the limit, it is much better to run the PA with powers around 150W input in SSB/ CW, the tubes will last much longer, and the difference at the receiving station is minimal. You will be surprised how many DX stations can be worked with low power. It all depends on an effective antenna, band conditions and operating skill, and not only big power: you have to double your power output to make a S-point difference at the receiving station!


Beware of what lurks beneath your next purchase! In short "Breaker 19"

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From the W4CLM vault of horror stories comes this one about an FT-101ZD that was used on eleven meter AM a bit too long! Almost hard to tell, it could have been the work of a .22 Cal bullet, but the sad fact of the matter is that excessive current and long periods of key down time can easily result in damage like this to any amateur transceiver that is used by a careless operator.  The mess in this rig also took out the main power supply transformer.  The rig was eventually repaired and put back into amateur service.




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PAØPGA's FT-101ZD Internet purchase

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The PA with 6146A and 6146B tube

The “skilfully repaired” PA

The creative relay solution and choke

The PA now, after reconstruction


The rebuilt PA with 6146A tubes

Hints and Kinks by PAØPGA

In this section I will give facts and thoughts, that I have collected from all over the net. When sources are known, I will mention them, because to hold your FT-101ZD in an excellent condition is only possible when all real amateurs, share their knowledge and experiences. That’s still the first rule for a Ham in my opinion. Of course are all tips free to use, but using them is always at your own risk. If you don’t have the knowledge or technical skill, then please let the lids of your set closed, it is always better to have a good working transceiver then a perfect heap of junk. Never try to be smarter than the HF engineers of the design Lab, there is almost always a good reason that things are done the way it is. Most modifications are small, and are additions for a specific reason, not a complete rebuild of the set. So have said that, we start with a collection of tips:

Switching the fan: When the rig is mostly used on receive, there is no need to let the PA cooling fan run continuous. I switch the fan with the heaters On/Off switch: Pick up the 12V of the heater circuit at the accessory socket at the rear of the transceiver and rectify it with a diode and a suitable capacitor. Use the DC voltage to switch a small relay. I used a small 12V reed relay with 1 contact. Use a suitable series resistor to limit the current. With the relay contact you can now switch one 100 Volt connection to the fan socket. I made this modification 25 years ago, and it works still as a charm. There is room enough in the back of the transceiver to mount the relay and the couple of small parts you need in a neat manner.  Source: PAØPGA

Improving second Double Balanced Mixer: On the AF board is the double balanced mixer, D02 to D05, they are 4x 1S4007. Replace these with 4x Motorola MBD-702 diodes and the adjust VR01 and TC02 for the best carrier balance. It should be possible to null the carrier almost completely. Source: G3TJP

First mixer overload (only FT-101ZD MK2 and MK3, board PB-2154, used after run 17xxxx,) RF board: Improve the dynamic range of the first mixer by modifying the T-Pad attenuator on the input as follows: Change R8 (120R) to 36R, change R9 and R10 (10R) to 27R. Reset overall gain on IF board using VR02, which is the source load of Q15. Source: G3TJP

Improved Fine-tuning: Shunt the clarifier control with a 4k7 or 5k6 resistor, then recentre its action by adjusting VR01. This mod reduces the control’s range. Source: G3TJP

Tips from "ZL" Kiwi land, On 10 meters the transmitter takes off on HF or with the transverter being used. The problem is poor solder connections and ground points around the 12BY7. Resolder all connections on and around the 12BY7 board. Source: ZL3MH

Fault blows main fuse every 0.5 to up to 6 hours and is not the 6146’s flashing over. There are vertical type caps in PB-1968 and the internal fluid runs down and arc across the narrow gap in the caps (300 Volt screen supply, a common problem in TV sets). Replace caps C1001, C1002, C1003 and C1004, they are all 10uF/450 Volts. Source: ZL3MH

Replace the 1000pf condensor from the plate of the driver tube to the grids of the 6146B’s. This a precautionary measure, as the FT-101 series had problems here. Source: ZL3MH

The Noise Blanker stops working sometimes. It appears to be a poor solder connecton on plug pins of the Noise Blanker/ Fixed channel board. The fix is to solder around the connections of the board. Source: ZL3MH I had the same type of dry joints in the cable connectors of the audio board, and the cable connectors of the IF board, there where several pins with craters around. See picture. This gives all kinds of curious problems. Resoldering is the cure. Source: PAØPGA

The transmitter stops working: The band change switch is in two parts. It is joined where it goes to the 6146B compartment from a steel shaft to a fiber shaft. This connection comes loose, and the bands do not line up properly. It is a good precaution to mark the shafts with a (Sharpie) marking pen and tighten the screws on the band switch extension. I heard from a FT-101ZD technician having spent days tracking this one down. Source: ZL3MH

FTV-250 and FTV-650B on the FT-101ZD: The FT-101ZD is designed for the FTV-901 series of transverter via the 11-pin accessory socket. The Plate, screen and bias voltages are not always wired to the accessory socket. This is needed if you want to run the FTV-650B 6-meter transverter that is designed for the earlier FT-101 series. Especially the MK3 model did not have the above wiring. Both the FTV-250 and FTV-650B can be used with this mod on all FT-101ZD’s.  Source: ZL3MH

Finally before you begin any service on your equipment: Get the proper user and service manuals for the equipment that you have, and make yourself familiar with the working of the circuits. The manuals for the FT-101Z and ZD, and other Yaesu communication equipment are on the Fox Tango club, in PDF format, free to down load, (well, a small donation is very much appreciated, to keep things rolling), so there is no reason to start without them. Special recommended is the very extensive Maintenance Service Manual, with around 200 pages, which is not only very interesting, but gives all information on boards, voltages, trouble shooting lists and in general all information to keep your FT-101ZD in a first class condition.


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