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Author Topic: Yaesu FT101EE vs FTdx401 power output question  (Read 846 times)

Posts: 362

« on: November 16, 2017, 11:08:26 AM »

I own a Yaesu FT101EE and only recently had a chance to use a FTdx401. The 401 is capable of twice the input power of the 101, 560 watts PEP vs 280 watts PEP for the 101. Both use two sweep tubes in the final, 6KD6's for the 401 and 6JS6's for the 101.

Both these tubes seem to have about the same plate dissipation ( 33 watts for the 6KD6 vs 30 watts for the 6JS6 ). Sweep tubes were not designed for RF service so I was wondering if there is some unstated characteristic that allows twice the power input to the 6DK6's over the 6JS6?

Posts: 153

« Reply #1 on: November 16, 2017, 05:38:45 PM »

I can't answer your question directly, but maybe someone with a deeper knowledge of tube and/or Yaesu history can do so.  However, I've recently restored an FTDX-560, which is the same as the FTDX-401 in all but a few minor aspects.  The restoration went well and perhaps few comments about the radio's performance might be useful to you.

Part of the overhaul involved installation of some NOS 6KD6 PA tubes and, with that done, I get an honest 300W CW output, at least on bands below 10m.  As I recall, the PA plate current is pretty high at that setting, maybe 800 mA or so from memory.  My HT is a bit higher than 600V, so the input power could well be about 500W or a bit more.  The PA runs decidedly toasty at full output and I wouldn't run it at that level for any length of time.  (I see some early modifications to *increase* the power output!  But I guess tubes were cheap in those days).

The real kicker is the SSB IMD performance.  At full output (300W PEP), with a two-tone input, the best I could get was IMD3 of about -20 dB, relative to one of the two RF output tones. When I checked the manual from about 1969, the "distortion products" spec is -25 dB, and that would almost certainly be relative to the PEP output, using the convention of the day.  That yields a 6 dB better spec than the modern one so I concluded that an FTDX-560 could well be within spec with an IMD3 of -19 or -20 dB, measured according to the modern convention. Specifications aside, the PA at full power is clearly unsuitable for modern band environments and, when I run the transceiver at selected times, I don't go above about 120W PEP. I've also increased the idle current by about 10 mA or so. With that, I can get an IMD3 of a bit better than -25 dB.

I notice that the FT101E specs give the "distortion products" as better than -30 dB, again no doubt stated according to the PEP reference level.  In any event, it looks like Yaesu did produce a somewhat cleaner follow-up to the early FTDX series and maybe part of that was just throttling back to sensible levels.  As a matter of interest, what key-down PA current do you get with your FT101?  I also wonder about the relative screen voltages in the two radios but a quick check leads me to think they are similar at 160/170V.

While the FTDX-560 is no rival for my Collins S-line or modern radios the receiver is quite OK and actually sounds good.  Just don't plan on working any 10m DX without some external help.

73, Peter.
« Last Edit: November 16, 2017, 05:44:34 PM by VK6HP » Logged

Posts: 362

« Reply #2 on: November 16, 2017, 06:25:19 PM »

I suspect you have actually answered the question, LOL! I read a commentary that the ARRL actually tested the IM3 of the FT101 and a comparable rig with parallel 6146's. The FT101 measured at -34 dB and the 6146 rig at -37 dB. Not sure if the reference is the old or new though. If I find that article again I will post it here.

The FT101 manual states to keep key down current to 330 mA or less from 80-15M and less than 280 mA on 10M to prevent spurious radiation. I usually keep it to 300 mA and 260 mA, respectively. The bias current is set to 60 mA ( for both tubes so .03A * 700 VDC = 21 watts at the plate ). The plate voltage is supposed to be around +600 VDC but mine measured more like +700 VDC dropping to +650 VDC key down. So .3 x 650 = 195 watts. Assuming 65% efficiency = 127 watts out.

What is the factory idle current for the FTdx560?

P.S. Like your call. I started my career at HP in Palo Alto.

Posts: 153

« Reply #3 on: November 16, 2017, 09:55:00 PM »

The recommended bias current for the FTDX-560 is 50 mA (25 mA per 6KD6).  As I mentioned, increasing it to 60 mA improves the IMD situation noticeably, at not too much dissipation penalty. 

Yes, with similar plate and screen voltages, and a 2 to 1 plate current factor, it does look like a significant change between models was in how hard the PA is driven.

As your numbers are from the ARRL, they will certainly be relative to PEP (i.e., the old convention).  The League was (is?) one of the last bastions of that convention. I'd also assume that the 6146 reference PA might have been a basic type.  With my Collins and Kenwoods (both having some negative feedback) IM3 after careful setup and tuning is closer to -40 dB, in the new convention.

HP have a great history but my call choice was pragmatic: I wanted a two letter call when I moved to VK6 but my original (and very underutilized) VK7 letters weren't available, so I reversed the order.

Seems like you're all set with the FT101E now, after the glitch diagnosis etc.  I've called a halt to the FTDX-560 work since it's operating well.  I was on the lookout for a CW filter but, with the aging in the SSB crystal filter, I've slightly tweaked the BFO crystals to compensate.  Getting everything to line up with the passband of a CW filter might need more work than was justified.  I only started the restoration because of nostalgia: my first "real" rig as a teenager was a second-hand FTDX-401.
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