Using 5Watt PA on 6 and 2meters. #5wPA

Phil Crockford

Has anyone done mods to use the 5Watt PA on the lower VHF bands 6 and 2meters?
The assembly instructions hint that is may work on those bands.
The suggestion of substituting the IR510 for the RD15HVF1 I have done.
I am about to embark on modification to improve the O/P above 28Mhz and wondered if anyone had already done mode to the kit.
I am aware that the operation will be reduced below 28Mhz as a result.
Any input from someone who has tried this would be appreciated.


Curt wb8yyy


do a search here naming that device - see what is reported here - it makes sense that device may do VHF better.  also try search the web with U3S and that device name as well.  of course someone has likely reported on it. 

73 curt


IRF510 will work at 6m, but not at 2m.

For 2M you need the RD15VHF1.

Please reply on list so we can share.
No private email, it goes to a bit bucket due address harvesting

Timothy Fidler

Phil for the  RD15HVf1 you will have to "twist the pins" on G  and S it is I believe . People who have made PCB drafting errors of this type have reported losses at HF NOT VHF  of 0.3 dB from this.  Error -the instructions say this was allowed for , I was thinking of the 10 W linear kit. Seems that this kit has a dual pad arrangement.

2. Deleted. 

3. Almost all high performance amps at VHF use PTFE insulated wire in their OPT cores.  IN fact a lot above 6m use 1/4 wave Coax TE transformers which is a big change and a hard to get bit of kit in small qty. This makes them only semi broad band. Delete comment on Coax transformers for a class C amp design. Refers to cl B PP.

4.  I believe this kit uses type 43 Ferrite cores nominally Yes , FT50-43.  That is magnificently lossy even at 15Mhz.  You  will be able to get type 61 to work at 6m This has been proven in many real designs. Typically a PPull amp using the RD16HH (nb sixteen) and  using type 61 OP cores will produce 8 W out on 6m when it produced 16 W out on say 20m .  your mileage may vary but be prepared for as low as say 3W out after changin out the ferrite.  The best solution is to use a type 61 ferrite which has the same AL as a single FT 50-43.  If you used an FT140-61 which is massive c'w the original  then you are still short on AL , 150 versus  440 for the previous part.  (see Kitsandparts or Toroid king website for this data ) Possibly the cleanest soln is two off FT114-61 stacked and epoxied  end to end for an AL of 150 now up the turns by root (440/150). That gives you a multiplier onturns of 1.7 which, looking at the photo is probably feasible.  Will a type -61 ferrite work at 150 Mh? .  The Fair rite catalogue 14 show data - see the multiaperture core page. For a type 61xx 202 core the indications are the core Will work at 150 Mhz - the XL has dropped only about 10 percent over the 50Mhz value but is going south rapidly to wards zero impedance.  THe equiv curve for a type 43 material core shows it unusable as a practical RF transformer  above 80 Mhz.

5. If you are to get this to work on 2 m then the BS170 will almost certainly require change out .

All the information on its DS indicate that performance above 50 Mhz is problematical .  Sod's law is that there is no equivalent really as an industrial (cheap item ) that will work well at 144 Mhz.  There are some RD06 devices you could look at -they are going to be expensive to get in one offs from a reputable supplier . All the datasheets for these Mitsi mosfets are on the RFParts  (USA) site. 

 RD15HVf1 with a small bias based on the standard 5V type of cct  (adjustable to about 2.4 VDC  ) which implies a coupling capacitor might be an easiest case (procurement ) replacement for the BS170. Or after looking at threshold voltages on the respective DS  and what the BS170 is currently seeing you might be able to do just a simple twisted pin replacement. This is not beautiful for VHF and you potentially could get all sorts of instability issues (happy thought for the evening ).  Gate inductors of three turns of Cu wire on a 100 ohm  Carbon resistor body have been known to help in that case (at HF- mileage may vary).

This sort of (analogue)  circuit potentially can produce 8 W RF when RD16HH is used at HF.  possibly you might go as close as 5 W at VHF with optimised components.  I have no idea if the drive cct can run at 144 Mhz. HC 595 - HCmos logic - 40 Mhz clock rings a bell. Are you running it with the AT Tiny 84 and how fast can that run it ??.  it sounds  to me that 144 Mhz might be a non starter on the digital side - perhaps the frequency comment in the text refers only to what the PA could do on the anal. side and with massive re-engineering.. ... over to you , pilot.

Timothy Fidler

Tim in ZL back again.  As far as the OPT is concerned , I have had a look at optimising it  at 80 Mhz as a half way house between 6m and 2m. Type 43 material as per previous is death to RF at such frequencies. 
I came t the conclusion that a FT50-61 would do the job with 0.9 x the current winding scheme. This is based on real test data on coax suppression cores  , not just simple AL values.  This is on the basis of presenting to the Drain of the MOSFET the same approximate primary Z as it saw at 10 Mhz with the original FT50-43 core. I had to use some min frequency design basis and without calculations from the designer available to me 10 Mhz was a good number between  3 Mhz and 28 Mhz as a mean design point.  The data I used was based on Farrite Cat 14 datasheets and also the AL values shown on the Toroid King  technical pages.  These latter data relate to Amidon toroids I believe and  Am and Fairrite use the same material but different ID and through  dimensions for the same inch series cores.  Engineering basis in due course - written up in my diary.