yaesu: FT-101, finals replacement

From www.mods.dk, author not known:

There will come a time when the finals in your FT101E will need replacing. These transceivers were originally equipped with 6JS6C tubes manufactured by NEC.
This tube's properties are slightly different from the 6JS6C tubes available today from American tube manufacturers. By the way, don't bother looking for tubes made by NEC. They got out of the business several years ago.

In order to use the "American" variety 6JS6's, a simple modification to the neutralization circuit must be made to the final section of the transceiver.

The modification consists of replacing the fixed value 100 pf 1000 VDC mica capacitor with a 10 pf 1000 VDC mica capacitor. This capacitor, C125, is in series with the 10 pf variable neutralizing capacitor off of the plate circuit.

If this modification has not already been completed on your rig, be sure to use a mica or silver mica of at least 1000 VDC. Do not substitute a different type, because the heat in the final compartment will change the value, and your tubes will fail prematurely. Also, be very careful to keep all leads short and in exactly the same orientation as the original capacitor.

Before reneutralizing, open the variable neutralizing capacitor all the way to minimum engagement and follow the neutralizing instructions in the manual. While dipping the plate, remember to adjust the neutralizing capacitor for equal value meter reading peaks (IC position) on both sides of the dip when tuning the "Plate" control.

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DR OM Eilert, I think this information has also been published in England, in the RSGB Technical Topics book in around 1978.I also seem to recall an article a few years ago, pre-internet, in the RSGB magazine Radio Communication,giving details of using 6146B valves as replacements, with suitable valveholders, as these are proper transmitting valves, instead of over-run colour TV line-o/p valves, which were never used in the UK anyway, except in amateur transceivers. Then more recently, Svetlana producing an EL509/EL519 type which may be useable.

So, it looks like there are a few ways to keep these rigs ("FT101- the rig that Yaesu made, but also the rig which made Yaesu") going for anothe 3 decades! 

73,Martin(G8UWM)

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