All the circuits are working and are shown here no particular order. The plans for the next few months is to operate this radio on the 80M and then the 40M ham bands. The goal is to have at LEAST one confirmed QSO per band ~ but secretly I want to WAS and some DX too.
|KD6VKF Mk-VII Paraset - Top View|
The method to wiring this radio was done in stages. I started with the power supply and voltage divider (lower left of the photo) I wanted to test the linear regulator for the 6.3V filaments as well.
The only real issue I had with these circuits was the linear regulator would not start with all three tubes! The large current drain of the three cold filaments turning on caused the regulator not to work. I had to wire the switch to supply constantly power to the regulator and switch the output.
|KD6VKF Mk-VII Paraset - Bottom View|
The 6V6 TANK circuit power input turned out to be a busy little junction. I used plenty of RED Teflon tubing on the leads here.
|KD6VKF Mk-VII Paraset - Transmitter Power Close up|
Note: the new solder tag I added in the lower left of the photo. This two-tab tie point was added because the switch did not have lugs, but only two insulated wire leads.
The transmitter circuits were actually the last I wired in. The first tests with the 3.5 color burst and 7040 QRP crystals were disappointing, no oscillations or output. Tuning of the original circuit was very high due the smaller inductance of the TANK coil. Fortunately I had an 8MHZ crystal, or I would have thought the circuit was dead. I plugged it in attached the dummy load and tuned it up to full brightness on the lamps. I added a parallel capacitance to the low range 100pF and 3.5 MHz oscillates just fine now. The 40M crystals actually do oscillate, it is just at the very end of the TANK cap and too weak to make the bulbs glow. I will need to fix that later but I will only use 3.5 MHz crystals to start with.
|KD6VKF Mk-VII Paraset - TX Power and Caps|
The internal key works fine. I wired the EXT key Jack in parallel and used the "RING" connection as a ground point.
|KD6VKF Mk-VII Paraset - Transmit Side + Key|
|KD6VKF Mk-VII Paraset - Transmitter 6V6 Tube and Crystal Socket|
The internal key was described in an earlier post. Here it is wired into the transmitter's circuits. The contacts were changed to semi-tubular rivets, set wit the Tandy snap tool. Also with some washer spacers were added for better continuity and contact spacing from the original contacts. The copper braid ground contact to the arm was made from some fine wire de-soldering braid:
|KD6VKF Mk-VII Paraset - Internal Key|
The crystal socket was fabricated from two RCA type jacks mounted on a small fiber board. This allowed the sockets to seat behind the panel. Since ground connection was compromised by the hole repair, a solder tag was used to make the ground connection more reliable. The solder lugs were swapped to above the socket and the EXT Key jack was a convenient ground tie point for some components since it was well grounded.
|KD6VKF Mk-VII Paraset - External Key Jack|
The gimmick capacitor (BLUE wires below) has a few more turns than the original. I thought the added feedback capacitance may help when using smaller crystals, and it is easier to remove turns than to add. The two lamps were connected to the TX coil GREEN for AERIAL and RED for TANK Circuit. I found that a 2V flashlight bulb works best for the Aerial indicator while the 6V bulb glows brightly in the Tank circuit.
|KD6VKF Mk-VII Paraset - Transmit Coils and Gimmick|
The actual second circuit built was the receiver. I decided since it was the most complex in terms of the number of components I would build and test it before the transmit circuits.
When a new telescope is made, the firs time it is used astronomers call it "first light". The "first sound" for this set was pretty un-eventful. I hooked up the power, warmed up the 6SK7 tubes, plugged in the headphones and...nothing! Tinkered with the Regen control a bit and then was just going to try a sweep with the signal gen when I noticed the problem; the phones were connected to the wrong jack!
When connected to the "Phones" jack static came rushing in and a few twists of the dial and ...a SW Broadcast! I think the first heard station was: Radio Havana Cuba International, but the tuning was just short of the 40M and 80M ham bands:
As you can see due to the "Q" of the tuned circuit with the smaller than normal coil inductance used in this circuit was making for a narrow bandwidth, which has restricted the tuning range. I could not listen to CW that night, but I tuned around and had a great time listening to some international broadcasters, some utility SSB stations, and WWV on 5.0MHZ was almost centered at 50 on the scale.
I then made the tuning graph by setting the dial on the 10's (0-100) and tuning a signal generator, not coupled to the receiver, until it was heard on the set.
|KD6VKF Mk-VII Paraset - Receiver Side View|
The receiver was "band spread" for 80M. After I found the resonance frequency of the coil / tuning cap I thought it would be a strait forward tuning job, I calculated the required capacitors; one for parallel to increase the overall capacitance, and one in series to reduce the tuning range ...simple?
|KD6VKF Mk-VII Paraset - Receiver - With Band spread Caps for 80Meters|
[Note-- the colorburst crystal frequency is marked w/ red diamond]
I came up with some interesting band options in the process, which prompted me to put a small metal disk that I could put a rotary switch for multi-band operation! This can be seen to the Left of the crystal socket and EXT Jack in this view:
|KD6VKF Mk-VII Paraset - Transmitter Side Ext Key and Tank Circuits|