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THE AM BULLETIN BOARD => Technical Forum => Topic started by: aa5wg on June 09, 2010, 10:37:45 PM

Title: Tube/Valve HF Reciver Design Software
Post by: aa5wg on June 09, 2010, 10:37:45 PM
Hi to all:

I have a dead Drake R-4C that I am going to bring back to life.  After reading I understand there have been RF amp changes, 1st, 2nd and 3rd mixer changes, product dector changes, IF changes and more to this receiver.

Are there any good tube/valve HF design software programs available to help me with above goal of changing tubes and layout in this radio?

Thank you.
Chuck - AA5WG

Title: Re: Tube/Valve HF Reciver Design Software
Post by: Pete, WA2CWA on June 09, 2010, 11:40:13 PM
A quick Google for "Drake r-4c mods" shows the first page with mostly mods for the R-4C. Since obviously the mods are already documented, a software design program is not necessary unless you plan on redesigning the rig from scratch. If you need to check the particular specs of a tube, you can go here:

Title: Re: Tube/Valve HF Reciver Design Software
Post by: aa5wg on June 10, 2010, 08:39:43 AM
Hi Pete:
I am going to retube the Drake R-4c from scratch.  Mixer and RF amp stages are of interest to me.
I have not found any documentation regarding mixer and rf amp mods with tubes/valves for this rig.  Have you?
Thank you for your consideration.


Title: Re: Tube/Valve HF Reciver Design Software
Post by: Rob K2CU on June 10, 2010, 09:11:30 AM

A lot will depend upon which variation of the R4-C you have, and how many of the filters you have installed or available. When I acquired my R4-C several years ago, I also read up on all the various mods that had been published over the years. I made several changes in the receiver, some of which were fundamental to its design. One thing to keep in mind is that the R4-C evolved over its production life cycle and several fixes that were essentially band aids were implemented. To help figure a starting point, you need to identify what you've got. You can do this by examining the rig and determine which tubes are used for the mixers. another point is how many filter positions are present on the mode switch. In other words, does it have all three CW bandwidths? as I performed my modifications, I also helped a friend on the west coast perform the same by making the individual changes small. It was also important to have a working radio in the first place. I  also documented the changes with lots of labeled pictures of the radio. Oh yeah, you will also have to determine if any previous owner had done any mods as well.

The mods that I generated were as follows:

Added second first IF filter in cascade with original for eight poles of first IF filtering.

Redesign power supply with better filtering and +/- 12 VDC regulators.

Redesign audio output amp to a bridge type amp.

Redesigned Detector circuitry to include 1496 type product detector and precision AM detector

Corrected filter loss imbalance that was caused by second IF filter output mismatch, and third mixer noise issues.

I would strongly recommend that you first get the radio working as is. Each change was done and verified before moving on the next. My friend fabricated blank PC Boards for our mods, but they were all built first on prototyping perf board.

The first three mods were the most important. The need for the others came as a result of discovering issues that became apparent after doing the first fixes.

If you, or anyone else is interested in the details, or help in general, please feel free to email me.



Title: Re: Tube/Valve HF Reciver Design Software
Post by: WA1GFZ on June 10, 2010, 04:46:41 PM
How about an H mode mixer with 4, 4-1000As

Title: Re: Tube/Valve HF Reciver Design Software
Post by: aa5wg on June 10, 2010, 08:45:51 PM
Hi Pete Rob and all:

I agree with everything you said Rob.  This R-4C is a late serial number rig, about 28,000 plus.  It has the 6BA6 RF amp, 6EJ7 1st mixer, I think 6BE6 2nd mixer, 6EJ7 3rd mixer and others.  This radio has the three 2nd IF filters. 

I would like to keep this rig a tube rig as much as possible.  I was thinking about nuvistors for the RF amp and other tubes for the mixers.  I don't know which tubes wuold be best for the RF amp and mixers.  Cascode or Pullman circuits should be considered.  Doubly balanced mixers should be considered too.  There are tons of other considerations to be studied.  Big push for lowest noise and great IMD are two goals among others.

Yes, get the radio running and then take one step at a time.

I have read that the mixer frequencies should be changed. 

I am getting long winded, sorry.  I would like to stay in touch.
Thank you for yoiur consideration.

Chuck - AA5WG

Title: Re: Tube/Valve HF Reciver Design Software
Post by: Rob K2CU on June 11, 2010, 08:57:22 AM

Good news, you have a late model unit, so your power transformer will have the right winding for the 12 VDC supply.  I have all the same tube line up and have changed none of them. My next planned study was the limit of dynamic range and IMD. I had considered changing out the 6BE6 for a lower noise figure mixer, but at present, I see the maximum sensivity that you can ever need for an HF radio. IF anything, a proper RF gain control or attenuator, is desired for the front end, instead of one that merely manually adjusts the AGC voltage. The only reason I might consider changing any tubes would be if it resulted in a significant change in dynamic range. otherwise, you can really screw up a well performing agc circuit by changing tubes that have agc control voltage applied. Keep us posted on your progress to get a working radio first.
AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands