[Milsurplus] The Navy MAK project

[Robert Downs]

I say again, the more or less 6V equivalent to the 12A6 is the 6K6, which
has a 300 mA heater.  The 6V6 heater is 450 mA.

 

Have you tried substituting an FT-243 crystal for the DC-34/35”

 

Robert Downs

 

From: milsurplus-bounces at mailman.qth.net
[mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Ray Fantini
Sent: Thursday, July 18, 2019 08:29
To: Military Radio Collectors Association; MMRCG at groups.io; Military Surplus
Mail List
Subject: [Milsurplus] The Navy MAK project

 

Ok, here is a question for the Brain Trust. Been working on the MAK project
for a while now and now have a radio that works well on the original
channels. The highest current channel is 3.00 MHz

I am including my latest drawing that shows the modified Heathkit HP-13
power supply that provides the B+ and HV for the radio. I am running the
radio at reduced voltages of 165 for B+ and 400 for the HV and getting an
output of around ten watts into fifty ohms.

The new problem is I can only get HCU-6 rocks and the radio uses something
that looks like a DC-34/35, built an adapter and tried to get the
transmitters oscillator up and running but no joy, I can take a crystal that
was for the receive channel on 3.0 MHz that’s at 3.455 and that crystal
worked in the transmitter and it ran on 3.455 with no issue so the question
is what’s the difference between the two crystal types? And what can I do to
adapt the 12A6 oscillator to get it to work? Think maybe the old series huge
crystals had more capacitance and possibly a padding capacitor may help but
have not tried that yet. Spent most of last night building the adapter and
when it did not oscillate was too late to mess with it. 

The plan would be to build something into the crystal adapter and not modify
or change the original design of the radio. Don’t want to result to
installing an external chip oscillator and want to try to keep this using a
crystal.

Can this be an issue with the 12A6 not having enough gain? Think the 12A6 is
just a twelve volt version of the 6V6 and they make great crystal
oscillators. 

Also it’s not clear from my drawing but the oscillator stage uses tuned
slugs to set the oscillator frequency and you peak the tuning coil by
reading the grid drive via the ¼ plug on the front of the radio.

Wasted a lot of time using a HV supply that was grounded and a separate Bias
supply and having all sort of issues with getting the modulation right and
lots of additional stuff to make it work and finally looked at the original
design where the dynamotor had the negative side of the HV supply used for
providing Bias and microphone voltage and did the same thing with isolating
the HV supply and found the radio works a lot better, just goes to show that
sometimes the original design is better then what you can hack together and
thinking that I can  maybe find an equal solution to this crystal problem
but just can’t see finding any of the original DC-34 rocks for 3885.

 

Ray F/KA3EKH

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