Yaesu FT101Z: the iconic amateur radio masterpiece of the 1980s
By Dorian Stonehouse (GW4MRM)
With valuable input from Bernard (GW0LDZ) and John David (GW0JDS)
I WAS very lucky, having been presented with this great transceiver by Bernard Garland, the amateur radio operator and tech guru who lives just up the road.
No strings
The donation had one condition attached to it, namely that I make the most of the rig, as he had no current plans to use it himself. I duly accepted the rider – thanks Bern!
The FT101ZD with the covers off
The photo below shows a pair of 6146 RF power amplifier output valves (top left), Drive board and valve (tube) (top centre), tuning slugs (below valve), premix local unit (top right), RF unit ( with three plugs connected), Premix unit (right – next to RF unit), IF unit (bottom right), rectifier B board (bottom left), capacitor board (directly above B board) and a large mains transformer.
Bottoms up!
The bottom reveals a sizable AF board (bottom left), rectifier A unit (bottom right), select switch board (halfway up left), bottom of the VFO unit, waver switches (just before top) and trimmer boards A, B and C (top centre)
Resurrected after many years
I connected the transceiver via a power meter to a dummy load, switched on and was immediately greeted with plenty of receiver noise. However, the power meter on my FC902 matcher (ATU) indicated zero RF power.
It had to be the usual suspects
Upon inspection, I could see (and smell) that the main smoothing electrolytic capacitors co1 and co2 (200uF), on the capacitor unit PB-69-A board, were bulged and needed changing. So, in went a new pair of capacitors:
I changed these capacitors years ago, and at that time had to hunt down a capacitor supplier. Nowadays, however, they sell electrolytic capacitor kits online for the FT101Z/D, which covers capacitors and other components likely to need changing.
Next I changed ALL the electrolytic caps in rectifier B unit PB-1968B :
Rectifier A unit PB-1967 has far fewer capacitors; and luckily the mains transformer (a beast of a thing) appeared intact and was worked okay:
Having changed all the capacitors I was going to, I left the old dear warm up in receive mode for about 30 minutes, as she had been in Bernard’s garage for several years.
The next step was to switch on the heater switch on the front panel and allow plenty of time for the 6146 PA valves (tubes) to warm up. I then switched to “tune” position and applied a very small RF drive to the grids to see what happened.
With more drive showing more RF power minus arcs and sparks, I continued with fine adjustment of: “preselect,” “plate” and “loading.”
The RF power meter on my FC-902 antenna matcher eventually read 100 watts RF power into the dummy load.
More notes on matching (tuning up):
Tuning method you may wish to try:
If you are a newcomer to valve (tube) transceivers, you may find it a tad awkward trying to find that tuning dip on the FT101Z IC mA meter. Moreover, the more time it takes to find the dip, the more strain is placed on those output valves (tubes). So, here is a method you may wish to try:
Forget “dip” and instead just carefully tune for max power and minimum SWR
When matching the FT101Z Power output/tank coils to the antenna load, first adjust (in receive mode) the “plate” for the wavelength of operation. Adjust “preselect” for maximum RF noise (mush):
With the heater switch on and allowing plenty of time for the valves to warm up, adjust the “drive” control (photo directly below) fully anticlockwise – left.
Next turn the “Mode” switch to “tune” (second photo below) and the “VOX Gain” switch to “MOX.” (This switch clicks when turned anticlockwise):
Advance the “drive” only slightly clockwise (outer ring above) and adjust “plate” and “preselect” to produce a small RF power output, as indicated on an antenna matcher (ATU).
Perform the above manoeuvre fast, to prevent any damage to the PA stage.
This means applying drive to the PA stage for no more than and few seconds at a time; before returning the “VOX gain” control to the “PTT” position.
When in the “MOX” tuning position, apply increased drive for a few seconds, while readjusting the “plate” and “preselect” for more power and minimum SWR for the drive applied.
The above method soon gives 100 watts RF power on my FC-902 power indicator with little SWR.
The “loading” position becomes intuitive after a while, as the control is adjusted for maximum output power. The “Drive” control is then turned off (fully anticlockwise), leaving only audio to produce the RF output.
And now for something completely different…
How to deal with those pesky waver switches:
Scratchy AF and RF gain controls (potentiometers) are a much-expected bane on a transceiver of this age.
In the “good old days” of Carbon tetrachloride (Carbon tet) a squirt on the tracks would have probably cured the scratchiness altogether. But with those effective cleaners now all banned, we are left with what we can get!
I tried many cleaning products on these wafer switches, but all except “Coldklene 111” failed (I think they call it “Coldklene 110” nowadays).
Even with “Coldklene” there is quite a procedure involved to get the switches really clean, and my preferred method is as follows:
Remove the two shields which partly cover the wafer switches. The switches are then soaked with Coldklene.”
keep rotating the band switch back and forth several times, so that the wafer switch wipers come into contact with respective contacts. Then leave the solvent to dry for a few minutes.
Rotate the wafer switches so that the wipers are fully accessible
Using a good quality no3 paintbrush (see above), saturate the brush with “Coldklene.”
Proceed with the wet brush to rub the wipers of each switch section, making sure that the solvent does not evaporate and taking care not to damage anything!
You may have to repeat the above operation several times before the wafer switches get close to being as clean as shown immediately above.
What about those pots then?
The AF gain (inner) and RF gain (outer) controls are equally susceptible to scratchiness. Therefore, in the ideal World, they should, therefore, be removed and submerged overnight in a small tub filled with “Coldklene.”
Pot removal, however, may be impractical for numerous reasons. Moreover, if the carbon tracks are just worn out, then a replacement is the only sensible way forward.
With the above in mind, the “poor cousin” method involves repeatedly saturating the potentiometer tracks with “Coldklene” and twiddling the pot controls back and forth until the scratchy audio disappears.
Moderate to good results are achievable with “Coldklene.” But please be aware that miracles may take longer!
Different photo aspects of this giant of the 80’s:
Trimmer boards A, B, and C:
NB fix unit:
IF unit:
Audio board with additional circuits :
Tuning slugs:
Large mains transformer:
PA board etc:
VFO unit and rear of front panel:
T
Second view IF Board, VFO and rear of front panel:
Premix unit (left), RF unit (right):
Linkage mechanism, driver valve etc:
Premix local unit:
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Thank you
Dorian.
[whohit]iconic amateur radio masterpieces of the 1980s [/whohit]