[Milsurplus] [MRCA] The Navy MAK project

[Ray Fantini]

FT-243 may be more what the oscillator wants, somehow I can't help but assume that the DC-34 construction has a bucket of internal capacitance due to the big plates and the like. That's why I was wondering about maybe padding the HCU-6 a bid but have to wonder what that will do to the frequency?

RF

From: Robert Downs [mailto:wa5cab at cs.com]
Sent: Thursday, July 18, 2019 1:15 PM
To: Ray Fantini <RAFANTINI at salisbury.edu>; 'Military Radio Collectors Association' <mrca at mailman.qth.net>; MMRCG at groups.io; 'Military Surplus Mail List' <milsurplus at mailman.qth.net>
Subject: RE: [MRCA] The Navy MAK project

Have you tried an FT-243 holder on a frequency in the vicinity to see whether or not it will work with either the 12A6 or the 12K8?  I have a few 3885 KC and 4340 KC pairs in the FT-243 holders.  They are actually for the BC-611.

Also, it would be more nearly correct to say that the 12A6 is a 12V equivalent to the 6K6 than the 6V6.  The 6V6 has a heavier heater than the 6K6.

Robert Downs

From: mrca-bounces at mailman.qth.net<mailto:mrca-bounces at mailman.qth.net> [mailto:mrca-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<mailto:MMRCG at groups.io>; Military Surplus Mail List
Subject: [MRCA] 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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