[600MRG] Homebrew Tube Transmitter

[Edward R Cole]

Adding to Mike's advice, couple questions:

Are you only going to run CW?  If considering 
digital modes then running in AB linear is needed.
Will you only use a xtal?  If not then converting 
the GAG7 into a driver stage would be best:
Probably would remove the variable cap and maybe 
the output tuned tank and only use capacitive 
coupling to the 807's.  Their output is a 
classic  pi-network which values will need tweeking to work at 475-KHz.

Replace the xtal with a coupling cap to drive.  A 
low level all-mode transmitter? or digital VFO for CW only.

I would guess 0.1 uF will work for bypass caps.

The 807 stage alone could be a good starting 
point for a 100w amp to use with low power 630 
transverters.  I guess 10w drive would be 
required.  Or convert the oscillator stage to a linear driver amp.

Replace bead board with shielded enclosure.

GL

73, ED - KL7UW

At 06:45 AM 1/28/2018, Michael Mussler wrote:
>Goody,
>It is feasible to convert HF tube rigs to the 
>new 630m band. Paul W0RW modified an old DX-100 
>for use on 600m. I modified a home-brew 2m 
>amplifier for 630m service that runs a pair of 6146 tubes in the PA.
>
>In addition to reworking the grid and plate tank 
>circuits I replaced the plate choke with 
>something more appropriate to the 630m band (4 
>mH, > 200mA) and scaled up the values of the 
>coupling and bypass capacitors. The cabinet 
>dimensions will prove to be a limiting factor. 
>Consider use of iron powder core toroids in 
>place of air wound coils for the plate and grid 
>circuits to solve the space problem. I had 
>success with Amidon red cores (T-225A-2). Select 
>a core size that can handle the current levels 
>involved. Running about 120 watts input the core 
>I use remains relatively cool.
>
>The vacuum tube approach is less efficient than 
>the solid state devices many are using, but on 
>the plus side tubes are relatively forgiving of 
>antenna VSWR changes. I’ve got over 20,000 
>hours on this amplifier in WSPR and beacon service.
>
>Good luck and hope to hear you on the new bands!
>73
>Mike, AI8Z
>ex WD2XSH/12
>
>
>
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73, Ed - KL7UW
   http://www.kl7uw.com
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