[Novice-Rigs] Re: GB> Transmitter project

[Brian Carling]

Speaking of running all three of the old novice bands of the day,
how about some 15m Novice band CW activity this spring?
As part of the activity weekend it would be really good to get on 
21.100 to 21.200 mega-sickles. Use it or lose it, I say!

72ube de AF4K

( I just invented that - "72UBE" - I wonder if it will catch on?!)

See you MOPA fans on the air!!!

On 29 Jan 2005 at 7:48, N2EY at aol.com wrote:
 
> In a message dated 1/28/05 11:47:16 PM Eastern Standard Time, mjsilva at swfla.rr.com writes:
> 
>     use a single B+, 
>     hence the two tubes in parallel to get a reasonable amount of power out of 
>     the TV transformer.
>     
>     I'd guess that the single biggest reason that was done was to avoid having 
>     to make a full wave bridge rectifier out of tubes. 
> 
> 
> The main reason was simplicity. McCoy was looking to build a dead-simple MOPA at absolute 
> minimum cost, that a beginner could build with a minimum of tools. The only mandatory 
> metalwork is three tube socket holes, a power plug and a meter hole, plus the top shield (which 
> can be cut with heavy scissors). While 350 volts can kill you stone cold dead, it's not as 
> dangerous as 700 volts, too.
> 
> Yet the rig would work all three Novice bands of the day, run almost the old Novice power limit, 
> and be expandable when the General was earned. The design is TVI-proofed, capable of 
> multiplying the xtal or VFO used, metered, and doesn't use any trick circuits, critical adjustments 
> or unobtanium parts (except perhaps the coil forms and Miniductor, but they're easily replaced 
> with homemade equivalents).
> 
> In followup articles, W1ICP describes a 150 watt amplifier to follow the 65W rig, a modulator 
> based on the surplus MD-7 (back when you could get MD-7s for $10!) and even "An Easy To 
> Build VFO". The basic FWCT power supply evolves into a bridge/economy supply - 6DE4s were 
> TV tubes, remember...
> 
> Nowadays with 
>     
>     semiconductor rectifier costs down in the noise this is not an issue (unless 
>     one of blasphemy!). So perhaps the biggest reason for one B+ rather than 
>     the economy hookup is gone. That's not to say that the economy hookup has 
>     no other costs (more filter caps), but those are pretty cheap too. 
> 
> 
> Filter chokes. Bleeder resistors.
> 
> 
> It also 
>     
>     precludes using BC-spacing (receiving) variables for the TUNING cap. 
>     Depending on what one has in the junk box that might be a bigger 
>     consideration than the filter caps.
> 
> 
> Also bypasses and coupling caps.
> 
> In the end, it comes down to cost. Which is less costly - an extra 6BG6G, socket, cap, bypasses 
> and parasitic suppressor, or all the components needed to have two levels of B+?
> 
> There's also the advantage of additional plate dissipation in the final. You can probably run a 
> single 6BG6 at 65 watts if you have 600-700V plate voltage available. But you better be good 
> tuning it up!
> 
> 73 de Jim, N2EY