[Milsurplus] [MRCA] Russian US-P Receiver

[Ian Wilson]

Hi Ray,

I just stumbled across my small stash of 6H6G/GT. One can be yours for
postage if you are still looking.

73, ian K3IMW

On Wed, Sep 9, 2015 at 8:34 AM, Ian Wilson <ianmwilson73 at gmail.com> wrote:

> There is a 6H6G - shows up in various places on a search, so should
> be able to find one (I have one here somewhere, but no chance of
> finding it in finite time at the moment).
>
> 73, ian K3IMW
>
>
> On Wed, Sep 9, 2015 at 8:04 AM, Ray Fantini <RAFANTINI at salisbury.edu>
> wrote:
>
>> Wow, did not notice that being the detector and audio stages were just
>> about the only part that was not hacked up. Whoever did the conversion from
>> 24 volt filament to 6 volt did possibly the worst soldering and wiring job
>> I have seen yet with assorted lengths of wire run all over the place and
>> poorly soldered to the tube sockets. I did keep the receiver wired for 6
>> volt filament but cleaned up all the pervious mess and use all yellow wire
>> to make everything match.  All the mechanical tuning assembly had to be
>> removed, cleaned and lubricated and do have it working correctly but have
>> to wonder how anyone was supposed to tune that radio accurately when the
>> tuning mechanism is so course? The fine tuning works but still getting the
>> radio in the right neighborhood is a chore.  Had issues with the three gang
>> tuning capacitor with the brass bearing retainer and brass end screw
>> assembly not being held tightly in the pot meatal of the capacitor body and
>> ended up removing the entire assembly, cleaning and having to use a small
>> amount of epoxy to secure the brass assemblies to the capacitor being the
>> original press fittings were no longer snug. Have to wonder if this is an
>> effect of the ageing of the pot meatal?
>> Will try change to the detector tonight and see how that works out but
>> wonder if will also affect AVC action ? Also I did notice that the 6H6 is
>> not quite up to what it should be on the tube tester when I checked it and
>> hate to replace it with an American 6H6 being the Russian 6H6 is a full
>> size glass tube, way better looking than the squat little American 6H6.
>> I have to wonder what the possibility of getting a Russian 6X6 is?
>>
>> RF
>>
>> From: Meir WF2U [mailto:wf2u at ws19ops.com]
>> Sent: Tuesday, September 08, 2015 5:37 PM
>> To: Ray Fantini; Military Surplus Mail List; MRCA at mailman.qth.net
>> Subject: Re: [MRCA] Russian US-P Receiver
>>
>> Ray,
>>
>> The US-P receiver sensitivity is an issue in the original configuration.
>> The sensitivity is limited as a way to implement a crude noise limiter
>> which is operating all the time in both AM and CW. This is done by biasing
>> the cathodes of the dual-diode detector/noise limiter tube 6H6 (6X6 in
>> Cyrillic) to 3 volts by tying the cathodes to the cathode of the audio
>> output 6K7 tube which is at 3 volts due to the cathode resistor. This means
>> that the signal going into the detector has to be above the 3 volt
>> threshold in order to be detected. Modify the circuit by removing both
>> cathodes of the 6X6 from the cathode of the 6K7, tie them together to the
>> ground. This increases the sensitivity to normal for this kind of tube
>> line-up.
>>
>> 73, Meir WF2U
>> Landrum, SC
>> On September 8, 2015 2:19:36 PM EDT, Ray Fantini <RAFANTINI at salisbury.edu
>> <mailto:RAFANTINI at salisbury.edu>> wrote:
>> I have a Russian US-P receiver that I received from the Ukraine the other
>> day. The US-P is a small eight tube superhet that was used as both a field
>> radio in the RSB luggable radio set or in various aircraft, manufactured
>> during the war till the mid-fifties. The receiver uses all 6K7 tubes with
>> one for the first RF, Oscillator, first and second IF and audio amplifier
>> with the only other two tubes being a 6A7 as a mixer and 6H6 as a detector
>> and AVC. There is also a 6K7 for the BFO.
>> If anything this radio is something like the tube lineup and design of an
>> ARC-5 style receiver except unlike the ARC-5 this radio has five bands and
>> covers 150 KC to 12 MC.
>> The radio had been the victim of much eastern bloc hacking and after
>> restoring much of the circuit to its original condition now it’s working
>> but have been having issues with low sensitivity. It requires around two to
>> three hundred microvolts before you start to get solid static free copy and
>> two to four mill volts before there is any AVC action. Although this works
>> fairly well on the AM broadcast band and on high powered shortwave
>> broadcast stations it still leaves a lot to be desired. I have checked all
>> the bypass capacitors and screen and plate voltages, cathode bias resistors
>> and the AVC bus for any leakage but everything checks good. Did pull all
>> the tubes and test them in my TV-10 and replaced two of the 6K7 tubes with
>> US versions of that tube but going to assume a Russian 6K7 is the same as a
>> US 6K7. All the alignment looks just about right but still stumped by the
>> lack of sensitivity. The IF has two stages and operates at 110 KC and I
>> think that’s where I am not seeing enough gain. The radio works ok on the
>> local AM broadcast stations and sound surprisingly good for its age. I
>> built  an external power supply for the receiver that has an additional
>> audio stage built around a 6AQ5 so it can drive a speaker as opposed to the
>> original sets audio output that was designed around a high impedance
>> headphone system. Do plan to have this at Gilbert if anyone wants to see it
>> in person and if anyone has any speculation of where the additional gain is
>> let me know.
>>
>>
>> Ray F/KA3EKH
>>
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>> --
>> Sent from my Android device with K-9 Mail. Please excuse my brevity.
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