[GreenKeys] My Second Dovetron

[William Wuttke]

My first Dovetron is a bare-bones MPC-1000R Mk II S/N R770, black front & rear panels & case, early BBP-100 and
no regenerator. It works pretty well after a few repairs.

I recently bought another MPC-1000R Mk II, S/N R032, but it has black front & side panels and blue rear panel, top, & 
bottom, late model BBP-100, and a TSR-500 regenerator. (The rear panels of the two units are quite different from one another.
1. It arrived with the loop filter capacitor bottom lead broken at the capacitor - replaced.
2. I has a non-standard (old standard) 3 pin oval power connector which I broke when trying to make a workaround
for the line cord. I bought a new connector, but was able to repair the original with a generous amount of epoxy.
( And I got the proper line cord.)
3. Next, I found that the loop current pot would not turn - the shaft was frozen - pulled apart and cleaned/lubricated.
4. The loop LED was burned out - replaced.
5. Had a couple of cold solder joints in the audio input circuit.
6. The AFSK monitor & switching functions of the BBP-100 were never enabled. Made a cable, installed 2 4066 ICs, but
it didn't work - worked OK from the front panel SEND/RCV switch but not from the REMOTE connector using the +15V
source on the back panel. The problem turned out to be that the 4.7K current limiting resistor for the +15V becomes
part of a voltage divider with the rest of the SEND circuit which puts approx. 10 VDC on the control pins of the 4066.
The 4066 requires 11VDC on the control pins. (It looks like the original 14066 was spec'd at 11 volts min., but typically
triggered at 8.25VDC.) I put a 2.7K resistor in parallel with the 4.7K and resulted with 12+ volts at the control pins - Fixed!
Now the cross-led display works both in receive and transmit - neat feature.
7. The AFSK switching function didn't work after getting the +15V sorted out. The problem was the switch on the BBP-100
itself. Spring tension keeps contact spring fingers pressed up into the plastic handle assembly. I guess over the years, the
spring tension just gave out. I bent the contact spring fingers a little, reassembled the switch, and all works again. (However,
this is a function that I'll probably never use - I keep the AFSK output ON even during receive because it's easier to check
my radio input level.) And, it doesn't really turn the AFSK all the way off during receive. The circuit parallels all 4
CMOS switches to "ground" the AFSK signal during receive giving an approximate resistance of 30 ohms,
which attenuates the signal a lot, but does not turn it off.
8. Modified the AFSK output circuit to give a variable, higher level output (did this on both units).
9. Made an "interface" to use RS-232 on the transmit side (TXD & RTS) using TLP222 solid state relays. It all fits inside
a DE-9 backshell. On the first unit, I can use RS-232 transmit data, but, in order to use the regen capability on the second
unit without modification, I need to use the loop for transmit data. RTS is only needed for the AFSK monitor. I key the
transmitter with my computer interface program.

It was fun getting everything working correctly.....or at least to my satisfaction.

Now I can use it to transmit CQ and see my signals on RBN or WebSDRs or kiwiSDRs and maybe get lucky once in awhile
to have someone respond to the CQ. Since the first of the year, I've only had RTTY QSOs with a handful of people.

Bill
KE3BK