[R-390] A bit more on my IF deck
eldim at att.net
eldim at att.net
Wed Mar 8 00:40:41 EST 2006
Hello Barry & Crew,
Your statement about swapping 5814's brings to mind a problem that we faced with a DC Test Point Readings on the SMO (Stabilized Master Oscillator) of the AN.KWT-6/5 Collins Radio HF Transceiver circa mid 60's. (Navy version AN/URC-32). The test point was supposed to read typically no less than -3.5 Volt DC at each frequency tracked across the Frequency Band. On one unit we just couldn't achieve that tracking level regardless of how many tubes we substituted in that ckt. We finally replaced the entire SMO with a New or Depot Overhauled Unit which did track across the band with voltages slightly above the minimum -3.5 VDC.
I decided to take a closer look betweeen the two units and discovered that the replacement SMO had a Premium GE 5 Star tube. So we reinstalled the suspect SMO and stuck the 5 Star Tube in the circuit and "BINGO", the levels were in the Pass region. I think the tube was a 5670 or 5670WA. I have also noted that Oscillator Circuits in our older UHF Multi-Channel Collins Transmitters T-217 (AN/GRC-27) were particular which tubes it enjoyed.
Lastly, I recall a TV that we serviced in the early sixties that had a Front End Tuner problem that would not work when one of the Tuner Tubes was replaced. PROBLEM: Tube replacement resulted in overdrive and picture tearing. We found out that the original tubes were all burnt-in to provide an acceptible drive level to the Mixer stage. I think the manufacturer issued a Service Bulletin later on to address this problem. We ended up changing some resistors to lower the gain when tube replacement was necessary. My thought and bottom line is "DON'T CHANGE OUT TUBES AS A CURE or FIX-ALL. I always mark the tube with the V # or where it came out of the circui, and put it in a small zip-lock with the Test Results what radio it came from, and symptoms. Just in the event that something new and unusual occurs to the sets performance, I can look back on what I did. If the Tube is Below Test Specs, Shorted, Gassy or Intermittant, then I discard the tube and press on. I always say,
measure and compare readings specified in the manual, TM, TO, or NAVSHIPS.
73,
Glen Galati, KA7BOJ
Tacoma, Wa.
COLLECTOR of FINE BOATANCHORS
REPOSITORY of OLDER ELECTRONICS
MY MOTTO, "SAVE OUR LANDFILLS"
-------------- Original message from "Barry" <n4buq at knology.net>: --------------
> Paydirt. I think I have some weak/gassy/whatever, tubes. I swapped V506
> with another 5814 in the RF deck and I got about -0.1V at pin 2. I then
> swapped it with one of the other 5814's in the IF deck. This tube yields
> about -0.5V on pin 2. I seem to recall that gassy tubes can cause low grid
> voltages, but not sure about that. Also, it seems that the radio is a bit
> "hotter" with this tube arrangement.
>
> I know Roger created a writeup on swapping tubes for maximum performance.
> Maybe I'll give that a look-see. I didn't put these tubes on the tester
> before firing this thing up. Maybe that will reveal something about them
> too (yes, I know the *best* tube tester is the circuit itself, but I want to
> see if the Hickock will tell me anything obvious).
>
> Oh well, this has been a fun exercise.
>
> Barry - N4BUQ
>
> ----- Original Message -----
> From:
> To: ;
> Sent: Tuesday, March 07, 2006 10:44 AM
> Subject: Re: [R-390] A bit more on my IF deck
>
>
> > Oops!!! In my post below, I wrote Pin 6 of V506. I meant Pin 2 of V506A
> > (the grid of the AGC Time Constant Tube). Sorry.
> >
> > Barry - N4BUQ
> >
> > > Isn't V-506B the AM detector? If I am reading the schematic right, V-
> > > 506B doesn't connect to the RF deck,... I htink it connects to the AF
> > > deck (it provides audio to the AF deck).
> > >
> > > ----- Original Message -----
> > > From: "n4buq at knology.net"
> > > Date: Tuesday, March 7, 2006 9:12 am
> > > Subject: Re: [R-390] A bit more on my IF deck
> > > To: R-390 at mailman.qth.net
> > >
> > > > Okay, I think I'm carrying on a conversation with myself here, but
> > > > I'll
> > > > continue...
> > > >
> > > > When I pull the main connector from the IF deck, the resistance at
> > > > Pin 6 of
> > > > V506 goes very close to 500K (what the book says it should be).
> > > > If I
> > > > reconnect the IF connector and unplug the RF deck connector, the
> > > > same
> > > > thing: 500K. So, I checked the resistance at pin "E" of the RF
> > > > deck (the
> > > > point where Pin 6 of V506 connects to the RF deck). I get about
> > > > 1.8M
> > > > here. Those two resistances in parallel yeild what I'm seeing at
> > > > Pin 6 of
> > > > V506 when everything is connected.
> > > >
> > > > I haven't traced it out, but I assume if I'm supposed to be seeing
> > > > 500K at
> > > > Pin 6 of V506, then the resistance at Pin "E" on the RF deck
> > > > should be
> > > > nearly infinite. Any comments on this?
> > > >
> > > > Barry - N4BUQ
> > > >
> > > > > I got the resistors replaced and all seems fine. I need to do a
> > > > full IF
> > > > > alignment, but it seems to be behaving just a slight bit better.
> > > > I'm not
> > > > > sure, but I think it doesn't take quite as long for the system
> > > > to dump the
> > > > > charge from SLOW AGC as it did. Is that perhaps a function of
> > > > that 2.7M
> > > > > resistor?
> > > > >
> > > > > I wanted to check the resistances and voltages around where I
> > > > had worked.
> > > > > Everything looks pretty good except for pin 2 of V506.
> > > > According to the
> > > > > manual, I should have about -0.4V, but I'm getting nothing
> > > > (HP410B used
> > > > > here). Checking the resistance, the manual states I should be
> > > > seeing 500K
> > > > > in AGC mode and I'm only seeing 400K here. There are three
> > > > resistors to
> > > > GND
> > > > > from V506, pin 2 and they add up to 500K. Apparently I have
> > > > something
> > > > else
> > > > > parallel to this that's pulling the resistance down a bit. It's
> > > > always> something. Any guesses why I don't see -0.4V here?
> > > > >
> > > > > Thanks,
> > > > >
> > > > > Barry - N4BUQ
> > > > >
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