After looking at GB Ron's schematic it was as I have found on other
Larcans....the gate bypassing is horrible. That needs a .01, 0.1 and a 1uF
on the FET side of the adjustment pot . This needs to be a "broadband"
bypass as modulation frequencies will "remodulate" the FETS and there will
also be low frequency instabilities because the FETs have a truckload of
gain at HF and audio frequencies.
73
Fred K1FMS
On Fri, Oct 25, 2024, 9:12 AM David Olean <k1whs@metrocast.net> wrote:
> I am pretty sure that all of those other Larcan amps are working
> reasonably well. The one that went to Good Buddy Ron had a hex put on
> it in an attempt to cancel the hex that GB Ron put on me and K3SK. I
> learned that trick from a Jamaican girl friend last year. I met her in a
> bar in Berwick. She was driving taxi.
>
> I would add that you should never buy an MRF151G from China. They are
> all made out of Chinesium and will not work. Most likely relabeled
> junk. Only buy it from a reputable source here in the US of A. I have a
> FM TX that has 2 X MRF151Gs in it. I was going to put it on 144, but
> decided to save it for the FETs. I am working on two more amplifiers
> here. One is a 1000 watt unit and the other is a 1500 watt unit for
> KF0M. I am adding filtering and VSWR protection circuits. That is one
> of my winter projects.
>
> I am wondering if the problem is a parasitic oscillation that
> intermittently appears. The 500 watt amp has a similar bias bypass as
> the 1500 watt amp. I believe it is a .01 chip. Possibly adding a .001 in
> addition might be a good idea. Maybe a chip on the drain rail as well. I
> am just guessing here.
>
> Dave K1WHS
>
> On 10/24/2024 12:03 PM, Ron Klimas WZ1V wrote:
> > Thanks to all who replied.
> > If anyone else got a self-igniting amp like mine from Good Buddy Dave,
> > Here's the link to the correct schematic so you can repair it:
> >
> > https://www.mmra.org/larcan/15kWhidocs.pdf
> >
> > Replacement non-exploding chip caps are available from Mouser,
> > the values on the output network of each FET are -
> > 30 pF in parallel with 27 pF, 39 pF x2, and 6.8 pF,
> > example Kyocera 800B270JT500XT for the 27 pf.
> >
> >
> https://www.mouser.com/c/passive-components/capacitors/ceramic-capacitors/mlccs-multilayer-ceramic-capacitors/multilayer-ceramic-capacitors-mlcc-smd-smt/?capacitance=27%20pF&voltage%20rating%20dc=500%20VDC
> >
> > There is no reason these caps should have shorted and burned up.
> > I suspect I was just unlucky and got a Larcan lemon.
> > Just a heads up on the FET's - they are all not created equal,
> > SRF3943-2 was the original part, beware of Chinese fake knock-offs.
> >
> > 73 Ron WZ1V
> >
> > ----- Original Message -----
> > From: David Olean <k1whs@metrocast.net>
> > To: newsvhf@mailman.qth.net, vhfcontesting@contesting.com, "222
> >> 222Activity@groups.io" <222Activity@groups.io>
> > Date: Wed, 23 Oct 2024 15:05:51 -0400
> > Subject: Re: [NEWSVHF] 222 activity night
> >
> >> Wow, Ron that is quite a list and I see a new call or two there, which
> > is great. It is funny how the power level works. When I went from 170
> > watts on 2M to 1500 watts I was sure that my grid totals would soar
> > during the contest. They did not. All I saw was an increase in the # of
> > contacts made. That sure surprised me. 120 watts will still do a lot of
> > work!! I worked 15 of the 20 stations that you worked. I missed N2SLO,
> > WB2ONA, K and W1GHZ. Other stations worked here include N1GYT, WA1LWC,
> > K3SK and two others for the same total of 20 QSOs.
> >
> > The excitement of the evening was working WA3EOQ on CW. We set up a sked
> > and I saw a big blip just off frequency and about 20 dB out of the
> > noise. I tuned it in and it was Howard calling me on CW. I gave him a
> > 559 and he passed along a 569. I never missed a dit, and that was the
> > strongest I have ever heard him on a Tuesday night. Knowing that things
> > might be up a bit down the coast, I tried FT8 with K3SK. He decoded me,
> > and I could tell he was there, but did not decode him. Normally we
> > hardly ever makea contact on FT8. We switched to Q65B-30 and worked
> > quickly. -22 here and I was -20 there as I recall. By about 00:50the
> > East Coast was quiet so I quit and listened on 28 MHz for a few minutes.
> > Between about 01:15 and 01:30 I could work JAs and VKs on FT8. I saw no
> > CW activity. Imagine JAs coming in so late in the evening. The SSB HF
> > contest will be Bedlam I am sure.
> >
> > I was really having fun hearing actual QRM early in the evening. There
> > were QSOs on top of QSOs. In short it was a huge amount of fun. Why
> > can't a VHF contest provide the same excitement? That is an
> > interesting question.
> >
> > 73
> >
> > Dave K1WHS
> >
> > On 10/22/2024 9:00 PM, Ron Klimas WZ1V wrote:
> >
> >> Limped along at 120 Watts on 222 tonight, but logged:
> >> WB2VVV FN41, WA2LTM FN20, K1PXE FN31, WA3NUF FN20,
> >> WB2ONA FN20, K1WHS FN43, N2SLO FN30, AA2SD FM29,
> >> KC1DWH FN31, W1AIM FN34, W1GHZ FN34, N1SV FN42,
> >> WA3EOQ FM09, WA3SSG FN20, K2RMX FN20, WA1RKS FN32,
> >> WA1MBA FN51, WB2RVX FM29, and K3TUF FN10.
> >> Anyone know where I can find a schematic and or parts list
> >> for a Larcan High Band VHF 500 Watt driver amp ?
> >> Having tough time repairing by guesswork.
> >>
> >> 73 Ron WZ1V
> >>
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