VMARS ####

V.M.A.R.S.

The Vintage and Military Amateur Radio Society

THE "DX200" LINEAR AMPLIFIER

– an unauthorised and very rare Heathkit product?

by Roger Spear, G4BXM

The "DX 200" (as I call it) started life as a rather over-restored and rusty DX40 that was bought for a couple of pounds at a BARTAG rally some years ago.

It was in such poor condition that when a better example, complete with VFO came my way (illustrated), I had a fresh look at the "over restored" version and decided that dismantling was the kindest option. However, having removed the modulator, it occurred to me that the parts left might form the basis for a linear. I retained the 500v HT transformer and added another 350v transformer in place of the choke for screen and bias supplies, retaining part of the tank circuitry (the original anode tuning

Re-arranged front panel of "DX200"

DX40 and VF1U
The DX40 has long been regarded as a much maligned and sorry younger brother to the DX100, but I have found it to be an interesting rig. And if G3LEO's fine transmissions are anything to go by, then there's nothing wrong with the economical method of modulation that was seen as the DX40's worst feature - relegating it to a "CW only" Tx.

The VF1U looks a bit like an OXO tin but is in fact very stable, well built and copper-plated internally.

condenser still seems to handle the 200 or so watts). However, I replaced the coil and in doing so, discovered the original had been installed back to front, putting the taps in the wrong place probably indicating the reason for the bad performance (and disposal) in it's "DX40" state.

I could fit about three 807's in the remaining space, as well as the stabilisers, and Hey Presto! - it worked very well, with the unmodified DX40 as driver. The series-gate modulation looks a bit like sideband, and, unlike steady AM, doesn't overstrain the poor old bottles, even at 200 watts.

Interior of "DX200"