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http://www.elexp.com/t_induct.htm

73's de Edd

In the referencing of the new crop of photos, I see that you invested in some illumination this time , and it seems that my guesstimation was right
on. . .as per that units utilization of a turret tuner and its tube complement of a 6BQ7 Cascode RF amp and a 6J6 mixer.
However I was some what surprised at the use of some Loktal / Octal ? ? ? power rectifier tube, as I was expecting the use of a companion 6X4 to go along with the miniature tube design lineup. Possibly, common surplus stock from an earlier companion instrument of that manufacturer, I guess.

It must be a 6 V rectifier unit, as I look at the power transformer and certainly can see the clipped off wires at my orange square markups [Grid Sectors F26,E27] that must be the 5V fil winding of the power transformer.(Just crying for 2 micro protective blobs of silicone rubber to be placed upon them for insulation !


That would then leave the filament of the rectifier tube with 6.3 VAC and that fil power is then additionally passed down thru my [4 blue squares] wire referencing, to then be feeding the sequentially daisy chained 6AU6[ DC Amplifier tube ] for the meter movement, the pilot lamp, the 6AU6 [ RF AMP-2], the 6AU6 [RF AMP-1],and then the [tuner tubes].


Now, can you confirm for us , that all of the three aforementioned tubes are 6AU6’s ? ? ?

Another thing needing to be clarified is your mentioned “ two floating wires” of the tuner, as I didn’t readily see any from the photos, so if they are on the biggest photo that I marked up, point them out as their sector(s)to us on the supplied second grid layout just below.


For Tuner associative wiring / connections, I can see the need for :

1. ..A dedicated ground wire

2. ..1 filament wire

3. ..B+ supply line

4. ..Possible AGC input feed

5. ..Tuner output

Now I can account for all of those at the top and the left side of the tuner, with the IF output being the terminal lug mounted at the top [ DD-18 ] sector and is utilizing an additional two sandwiched fiber washer insulators.

There is no chance that those two wires are the ones at my red arrow marking. . . as the picture definition prohibits my seeing their termination axes.

In the interim, if you want to start up troubleshooting again before giving me my required feed back info, and we are initially considering that a supply voltage evaluation has confirmed B + plusseseses being present at all plate and screen grids of the tubes and them having hotsy totsy filaments.

Look at the tuner output and you will see it feeding into pin 1 first grid of the RF Amp-1 [Magenta reference A] and then being amplified and then passing its signal on into pin 1 first grid of the RF Amp-2 [Magenta reference B] and the signal finally being detected by the IN34 diode and being RF stripped with the resultant DC level then being applied to DC Meter Amplifier that is
located just behind the meter movement.



Somehow, I was expecting a dual triode akin to a 12AU7 being used in a Dual Differential DC Amplifier configuration for this function. . .BUT… I do seem to see that the existing tube 6AU6 (???) is screen to plate joined / configured for serving in a single triode utilization.

Soooooo, t..t…t..t…t take that seeeegnal genee-wator..a la Elmer Fudd . . .and come down on the band selector a couple of decades from your presently selected CHANNEL 2, and now think about either the 44 MHZ, 21 MHZ or 4.5 Mhz spectrum and with the best that I can see of those coils, but not
their resonating capacitors . . . .I tend to lean towards the 4.5 MHZ frequency, since one does not see any of the typical 6CB6 tube family being utilized for those two RF amp stages..



Initially, inject a tone modulated RF signal into the 1st grid of the second RF amp [magenta reference marked up box B]and sweeeeep across the aforementioned freqs to see if any meter deflection comes up on your unit and then, progressively increasing the RF input until you hopefully get a
reading and then sweeping the frequency will also let you zero in on the actual operating frequency of those stages.



Then you move RF signal injection on back to the 1st grid of the 1st RF amp stage and confirm the same, but with a requirement of but a fracion of that previously injected test signal level if there is gain in that stage.

Standing by. . . .

TECHNICAL REFERENCING DATA:

73's de Edd

‘Bear’ with me, as yours will need a bit more perusing of your reverse engineered schematic that you have in progress. And BELIEVE me that is a repetitive process, with one initially getting all of the parts on the paper and then conforming all of the connections and then the transposing around of parts to look good on the schema layout and then the same thing again… until PERFECTION and more importantly ZER0 errors.

Now I can’t peruse the schemas fine points since it has EITHER been initially composed into too compressed of a pixel format or in the process of transferring between graphics processing mediums, it has ended up getting compressed excessively, but I really suspect the former.

To wit, in the checking of the envelope of a vacuum tube I see that it is composed with a mere 35 pixel width, I use that as a minimum when I am drawing up a even a small transistor case. Preferably, a tube envelope should be I the order of 4-5 times that size shown.
(140-175 pix width /diameter) Since your resistors are also scaled proportionately, the resistor only shows up as 11 pix wide and I commonly use 50 pix.

We don’t even want to talk about the readability of any printing or labeling. And no, not even with all of my graphics enhancing and processing capabilities, can I pull out any greater resolution of what low density info that I am having to initially use.

Now the good news. . . . . lets work with what I can make out from info supplied so far.

Didn’t realize that unit had a dedicated ear phone driver also, supplementing the FS metering .

I think now that after reviewing what you described having done on the injected RF and its signal flow thru the system, it would now be in order to just initially concentrate on the R.F. amp stage that is feeding the next meter driver amp and then the frontal FS meter.
I can’t inspect those coils used in two stages to confirm their winding wires and sizes, but I still want to believe that they are using 4.5mhz, TV sound carrier frequency, with neither 44, or the ‘olde’ 22 MHZ TV IF frequencies even being involved in the system.
I will admit that 1N34 in your unit, was one of a pair that was stashed away by Noah from olden times, but initially lets lift one lead by heat sinking that lead close to the envelope by a firmly gripped pair of needle nose pliers or forceps then quickly unsoldering that lead and then, preferably use an old generation analog VOM to confirm that we still have in the order of a 10 to 1 front to back resistance ratio .

If your diode is still of usable F/B ratio and not having developed “germanium junctionitis” with time, put the unit back in place using the same heat sinking of the lead precaution.

Confirm that the cathode of that stage that we are working with has its cathode grounded, a hot filament and finally that it has somewhat of a norm of plate and screen voltage.

Now in consulting the mark up working schema, check out the area of interest boxed in as magenta and firstly, I hope that ? mark up ceramic capacitor shunting the 1N34 is of a low value.

And since we now know that we are working with a least a decent detector diode, to enhance our readings lets lift the circuitry. . . . to the left of the yellow X mark in. . . so that none of that meter loading circuitry to the left will be loading our detector any, as the other tied in loops are of adequately High Z.

Hook your signal generator into the red X input point and start out down below 4 MHZ and have a DVM in DC mode connected with ground to its neg lead and its positive lead connected into the negative junction of the 1N34, where you will then be expecting a negative swinging voltage being read upon signal detection.

Then you tune the generator across that generators decade seeking for a detected signal, if no signal, then up the RF drive level until you finally max out. . . .at some level you should start reading multi millivolts DC of detected signal, then you do a sweep to find the rough resonating point of that tuned RF L-C combo in the plate circuitry. You may find it on a higher or lower decade.


Lets do a pause at this point for the testing and then the feedback. . . . .


BTW. . .Unanswered ?'s from the past:

Do I understand that one of the plates of the 6BQ7 is without its plate voltage ?

Where were the two "loose " tuner wires mentioned, as per being located on the red grid layout ?