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 Post subject: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Thu 10, 2021 6:06 pm 
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Joined: Jun Wed 09, 2021 11:32 pm
Posts: 12
I hope someone can help me determine if my output IF coil is bad and needs replaced.
Background
I am attempting to restore a 1939ish Montgomery Ward 93BR-714 Series B Airline Radio.
I started as an electronics neophyte, but now know barely enough to be dangerous.
I recapped the radio, replaced the resistors, replaced the power transformer (insulation fried but still worked, voltages high) and output transformer (primary bad).
Had all tubes tested and replaced bad tubes.
Replaced the speaker (bad coil) and put resistors in to take up the electromagnetic coil ohms (schematic listed the coil as 1175 ohms, had to put in 1.6k resistor to get proper voltage).
I got a cheap Chinese signal generator (Feeltech fy3200s). I can put a audio signal (1k) through both the output stage (6AC5G) and the driver stage (6P5G replaced with a 6P5GT) and get a tone through the speaker.
Problem
When I put either an audio signal (1k) or an amplitude modified signal (465kc give or take) through the second detection stage (6SQ7) or the grid of the IF amp stag (6SK7), I get no sound at the speaker, nor do I get an increase in voltage at the primary of the output transformer as I do when I get a speaker tone and as indicated in the alignment instructions.
The IF coils should be tuned to 465 KC per the schematic. I have tried modulated frequencies from 420 kc through 480 kc (with a .1 mfd antenna capacitor on the generator per the alignment instructions).
I took the output IF coil off and it tested 28 ohms resistance on both coils. Neither coil was shorting to ground.
I took the coils out and inspected them under magnification. All connections appeared good, the windings and insulation appeared good. The IF coil looks just like a picture of a Miller 012-c-2 I found on the net.
Questions
Is the secondary IF coil bad?
What additional tests should I do?
Is the fy3200s putting out the correct signal? The online manual says preset 09 is amplitude modulated. Of course I cannot hear it, and I do not have an oscilloscope. I can connect the generator to a computer and generate custom signals, but I have not attempted that yet.
Where do I go from here?
Any help would be greatly appreciated.
Thanks


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Thu 10, 2021 7:55 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Lafayette, CO
I would verify the signal generator is working first. Location? Somebody local may be able to share wisdom. Craig


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Thu 10, 2021 11:00 pm 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 4496
Location: Lexington, KY USA
What other test equipment can you use to work on this? We can try to suggest things you can do with what you have.

If you have a working AM radio, it can be used to verify the signal generator is working to make an RF signal, and to verify the modulation feature works.

An ideal AM radio for this might have a digital frequency readout. Even better if it covers the LW and "police" bands. A battery portable is handy, a car radio can be good, if there is room in your shop.

When you set the generator at 455kHz, the radio should be able to hear the second harmonic at 910kHz.

Ted


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Fri 11, 2021 12:45 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 5151
Location: Rochester NY USA
Well, sounds like 1st audio isn't working - check voltage at plate. Is that tube lit (warm if metal)?

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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Fri 11, 2021 1:16 am 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 4496
Location: Lexington, KY USA
Can you provide a link to a schematic that's correct for your radio? Nostalgiaair doesn't seem to have anything for a Series B.

The Series A sets do have three audio stages. All triodes. The 6SQ7 includes a triode for the first audio stage, as well as diodes for the detector.

So yes, does audio applied at the volume control get to the speaker?

Have you checked voltages? What's on the plate of the 6SQ7 triode, and how was this measurement made?

Ted


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Fri 11, 2021 10:52 pm 
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Joined: Jun Wed 09, 2021 11:32 pm
Posts: 12
First, thank you every one for your replies and pointers.
Second, I will not be offended if you tell me I am wrong on anything I say. I literally did not know what a capacitor or a resistor was when I started this project.
I will try to respond to your questions in the order of the posts.
I live in Alpine Ut.
I will try to pick up a signal from the signal generator on another AM radio. The schematic has the IF frequency at 465 KC. I do not have an AM radio with a digital read out, but I'll play around with that suggestion and post how that goes.
I have the Feeltech FY3200s 24Mhz signal generator mentioned. Preset09 is amplitude modulated per the documentation.
I have an FG100 500Khz signal generator. I got it before I knew the signal needed to be modulated.
I have a Southwire 13070T multi-meter.
I have an old analog multi-meter I inherited from my dad. It sometimes gives bad readings, i.e., doubles the DC voltage if set to AC. Cause enough concern I upgraded to the Southwire.
I have attached a PDF of the 93BR-714B Series B schematic. I found the schematic and the alignment procedures in Riders vol 11.
The 1st audio (6sQ7) was replaced. I had Standard Electric in SLC test the original (bad) and the replacement on their tube tester. They said the replacement tested good.
The schematic shows 6SQ7 pin 6 at 70 volts and pin 7 at 6.4 AC, with all other pins at 0. The actual voltages match exactly except pin 7 reads 6.3 v AC. I tested the voltage with the Southwire Multi-meter.
I get a tone to the speaker when an audible signal is applied to the volume control.
Thanks again,
Kerry


Attachments:
93br-714b schematic riders vol 11-19.pdf [64.78 KiB]
Downloaded 10 times
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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Sat 12, 2021 6:07 pm 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 4496
Location: Lexington, KY USA
Thanks for the info.

I notice that the linked schematic says it's for "Series A". So there may be some difference, but it may be very minor. We will count on you to verify the schematic matches your chassis.

Any AM radio should be able to verify there's a signal from the generator.

No need to connect the generator to the radio. A foot or so of wire on the generator output will radiate enough signal, if they are near each other.

You might start by setting the generator to some frequency inside the AM band to see if the radio will pick it up OK.

Then try this with the generator at the radio's IF, 465kHz. The second harmonic is 930kHz. The generator output level may have to be set much higher for the harmonic to be high enough. If the short wire "antenna" is not getting it, you might try a loop of a few turns across the generator output.

The DDS signal will have less second harmonic content than an old service grade generator would have, so there may be some difficulty hearing the generator set on 465kHz. If you can hear the generator when it is in-band, but not at the IF, there are things to try. Let us know.

Ted


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Sun 13, 2021 1:34 am 
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Joined: Jun Wed 09, 2021 11:32 pm
Posts: 12
Thanks again for your input.
Riders had two schematics for the 93BR-714B. The second is for serial numbers 936600 and up. My serial number is 938492, so a assumed the second schematic was for my series B, maybe incorrectly. The wiring schematic was the same. However, some of the resistor and capacitor values were different. Am I way off base in that assumption?
The 6SQ7 can does get warm.
The signal generator works. I placed it next to an emergency AM portable radio. The radio did not have a digital readout, but I could set the generator at 445 KHZ and get a tone at approximately 890 on the dial. I upped the signal to 455 KHZ and 465 KHZ and could tune in a tone at approximately 910 and 930 respectively. The 930 setting started getting interference from a station, but I could hear the tone.
I have tried the signal generator on the 93BR-714B at 430 KHZ through 480 KHZ on pins 4, 5, 8, 3, 1, and 4 of the6SQ7 with no sound to the speaker or voltage increase to the primary coil of the output transformer. should the generator should be hooked to pin 4 or 5 to simulate the IF coil input. Pin three is also connected to the IF coil on the schematic, but by my limited understanding, pin 3 is latter in the process.
I'll search for a schematic labeled "Series B".
Thanks again for your help,
Kerry


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Sun 13, 2021 3:41 am 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 4496
Location: Lexington, KY USA
Your best bet on the schematic may be to take what you have, and match it up with your chassis. If you decide that it is usable, let us know which one to be looking at.

Gregg (Egg) may be able to help here. There may be more schematics out there. Did you look in Beitman? There may be a correct print listed under Belmont Radio for 1939. ("93BR" has a meaning for Airline sets. At this time MW used mostly Belmont or Wells-Gardner for there radios. Later these firms both became part of Admiral, then Raytheon.)

I just noticed that the Rider schematic I'm looking at shows a RADIO / PHONO-TV switch. If the switch is in the PHONO position, or has a bad contact, you won't hear the radio.
Double check for screen grid voltage on the 6SK7.

When using a modern generator with an old radio, be sure to use a small capacitor in series with the output for any direct connections.

Try putting a modulated 465kHz signal into the plate of the 6SK7 IF tube through about 100pF.

Even if the IF transformer is pretty out of whack, you should get something out if you put enough in. Also try tuning the generator up and down to see if the transformer frequency is where it should be.

Ted


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Mon 14, 2021 12:12 am 
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Joined: Jun Wed 09, 2021 11:32 pm
Posts: 12
Thank you.
I will look for schematics as you suggest.
Being new, I literally traced all the wiring through to try and make sure I was replacing the resistors and capacitors with the correct parts. I also cross-referenced each resistor and capacitor to the schematic. The parts and wiring all matched the schematic. Sometimes the resistor colors were pretty corroded, but everything seemed to line up. I'll check the resources you listed.
I will also double check the radio / phonograph switch. The phonograph plug had been removed, and the switch would not move. I took the switch apart, cleaned it, and put it back together. I then checked for continuity through the switch and THOUGHT I got it together correctly.
I'll try the plate of 6SK7 again after I check the phonograph switch. Where I get nothing, no static, etc., the switch you mention seems suspect to me. I might try temporarily bypassing it to be sure.
By way of background, I inherited the radio when my grandfather died. I listened to it through junior high and high school. From college through now, it sat in storage. I don't remember plugging it in before the restore, but me or someone else probably did since I needed to replace so much. I just mention this since the radio worked with the phonograph plug removed. If I ever get it working, I'll try to reinstall a phonograph plug.
Thanks so much for you input,
Kerry


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Tue 15, 2021 12:23 am 
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Thanks again for the help and suggestions.
I struck out on relevant schematics at the suggested resources. Based on tracing the wires and matching capacitance and resistor values, I'm pretty sure the schematic attached previously is valid for this radio.

I spent a lot of time testing continuity of the radio / phonograph switch. I'm pretty sure it is working correctly. I didn't bypass it because it goes to the volume switch.

I can put an AF signal through pin 6 and 2 of 6SQ7 and get a speaker tone. I have to turn down the generator amplitude on pin 2 because it is so loud.
I can put an AF signal to the volume control and get a speaker tone.

I cannot get any tone at any of the modulated frequency points. I made sure the radio / phonograph switch was set to radio and used a capacitor between the generator and the radio.
I applied a modulated frequency of 465KHZ as specified in the schematics at a 20 Volt amplitude wave to wave (max of my generator) to pins 4, 5 (input grids) and both 4 and 5 simultaneously of 6SQ7 (2nd Det & 1st Aud). The voltages on all pins of the 6SQ7 match the schematic.

I applied modulated frequencies from 430 KHZ through 490 KHZ in one KHZ steps at a 20 Volt amplitude wave to wave (max of my generator) to pin 4 (grid) and pin 8 (plate) of 6SK7 (IF AMP). The voltages of 6SK7 do not match the schematic. Pin 3 schematic is 1.4, actual is .66; pin 5 schematic is 1.4, actual is .7; pin 6 schematic is 100, actual is 73; pin 8 schematic is 115, actual is 171.

6AD6G (tuning eye) is the only other tube with pin voltages different from the schematic. Pins 3 & 4 are 32 on the schematic and actual is 171. These pins connect to pin 8 of 6SK7 (171). pin 6 schematic is 115, actual is 174; pin 8 schematic is 100, actual is 71. I was thinking these might change if I could ever get a signal through the radio.

I'm open to suggestions. I'm thinking maybe a new 6SQ7. Its been replaced, tests good, but shouldn't I get a tone when applying a 465 KHZ modulated signal to the grid, pin 4? Maybe that stage of the tube is bad?
Thanks for your help,
Kerry


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Tue 15, 2021 5:36 pm 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 4496
Location: Lexington, KY USA
Attachment:
Screenshot from 2021-06-15 12-26-48.png
Screenshot from 2021-06-15 12-26-48.png [ 116.84 KiB | Viewed 281 times ]
I can put an AF signal through pin 6 and 2 of 6SQ7 and get a speaker tone. I have to turn down the generator amplitude on pin 2 because it is so loud.
I can put an AF signal to the volume control and get a speaker tone.


This shows that the audio amplifier stages are working. The CW end of the volume control is the input point for the audio amplifier, so hearing an audio signal injected there is really enough to know.

I cannot get any tone at any of the modulated frequency points. I made sure the radio / phonograph switch was set to radio and used a capacitor between the generator and the radio.
I applied a modulated frequency of 465KHZ as specified in the schematics at a 20 Volt amplitude wave to wave (max of my generator) to pins 4, 5 (input grids) and both 4 and 5 simultaneously of 6SQ7 (2nd Det & 1st Aud). The voltages on all pins of the 6SQ7 match the schematic.


The only grid of the 6SQ7 is on pin 2. Pins 4 and 5 connect to the plates of the two 6SQ7 diodes. The grid of the triode section is where the audio signal goes in to get amplified. The diode with plate on pin 4 is the detector. The diode with plate on pin 5 is connected to the AVC line and is part of that circuit, but since the AVC line has a big capacitor to ground (C9), this plate sees DC only, no IF.

I presume that the signal generator output common is connected to the radio's chassis ground, when injecting either audio or IF frequencies. Another presumption is that the linked schematic matches what's actually in your chassis.

When the radio is in working order, modulated IF injected at pin 4 of the 6SK7 will produce a tone in the speaker. The volume control on the radio must be turned up a bit to hear the tone. If this is not happening, yet the audio amplifier is working, the problem is narrowed down to a small area of the circuit.

Try injecting an audio frequency, through a capacitor (0.001 to 0.047uF) at pin 4 of the 6SQ7. Set the generator for a nice tone when you inject the signal at the CW end of the volume control.

If you don't hear the tone injected at pin 4, the problem can probably be resolved using an ohmmeter. Pin 4 should read under 30 ohms to the CW end of the volume control, and about 1 Meg to ground.

An alternative to the ohmmeter, would be to try injecting the audio where R8 hits C13, and at the associated terminals on switch S3.

Ted


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Tue 15, 2021 9:16 pm 
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I can't thank you enough for your help.
I have been using a .001uf capacitor on the generator output.
I do connect the generator ground to the chassis.
I believe the linked schematic matches the radio. I have traced every wire, resistor, and capacitor. To my limited understanding, they all match.
When I inject a modulated signal into pin 4 of 6SK7, I get NO tone to the speaker. This time I tried 450 KHZ thru 475 KHZ.
When I inject a AF signal into pin 4 of 6SK7, I get Strong tone to the speaker.
When I inject a AF signal into the volume control, I get Strong tone to the speaker.
I didn't try the ohm meter because I got the speaker tone. I can if it helps.
What does this mean?
Thanks again for your help,
Kerry


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Tue 15, 2021 9:59 pm 
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Joined: Jan Tue 16, 2007 7:02 am
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Location: Lexington, KY USA
This is turning into a real head-scratcher.

It would not hurt to use the ohmmeter to measure the resistance from pin 4 of the 6SQ7 to the CW end of the volume control and to the chassis.

Another thing to try with the meter, is to monitor the DC voltage across the volume control while the IF signal is injected at pin 4 of the tube. The voltage here should go negative, with the amplitude being a bit greater than the RMS value of the IF signal being applied to pin 4.

The problem is probably something that cannot be seen at a distance, such as the signal generator output, some connection that does not match the schematic, or a bad component.

Ted


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Wed 16, 2021 8:00 pm 
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From pin 4 of 6SQ7 to the volume control I get 32.3 M ohm resistance.
From pin 4 of 6SQ7 to the chassis I get 28.4 M ohm resistance.

DC voltage across the volume control to the chassis is -28 MV with no signal injected on pin 4 of 6SQ7.
DC voltage across the volume control to the chassis is -67 MV with a 600 HZ 10 V peak to peak signal injected on pin 4 of 6SQ7. Voltage goes to 0 as the volume control is turned down.
DC voltage across the volume control to the chassis is -32 MV with a 465 KHZ 10 V peak to peak signal injected on pin 4 of 6SQ7. Voltage goes to 0 as the volume control is turned down.

I really appreciate you going above and beyond to help me out. Hopefully this points to something. If not, I'll try to find someone local take the radio to.

Thank you,
Kerry


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Wed 16, 2021 11:54 pm 
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Joined: Jan Tue 16, 2007 7:02 am
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Location: Lexington, KY USA
Thanks for getting the measurements.

From pin 4 of 6SQ7 to the volume control I get 32.3 M ohm resistance.

This measurement should narrow down the trouble area quite a bit. If the "M" means Megohms, it is about a million times too high.

The high DC resistance here can account for the minimal response to an AC signal being injected.

There are only two items between pin 4 of the tube and the volume control terminal.
A 26 or 28 ohm IF transformer winding, and the radio / phono switch.
A mis-wire or a bad connection could also account for the high resistance reading.

First, verify what reading you get with the two ohmmeter test probes connected together.
Then, leave one test lead from the meter connected to pin 4 of the tube socket, and march the other along the circuit toward the volume control.
If the circuit were OK, you would see under 30 ohms all along the way. As soon as you don't see the low reading, the last part of the circuit you just went past has to contain the break.

DC voltage across the volume control to the chassis is -67 MV with a 600 HZ 10 V peak to peak signal injected on pin 4 of 6SQ7.

-67MV is going to arc across to the next county. We don't have MV levels in old radios, or even old TVs. Surely this is off by a factor of about a billion. I might believe -67mV.
The 600Hz frequency injected is a bit low, we want 456kHz for this test, although 600Hz might sort of work.

Voltage goes to 0 as the volume control is turned down

This seems a bit strange Turning the control should not make much difference. Are you sure the meter is connected to the end, and not the arm of the control? (I see I said "across the volume control" where I might better have said across the ends of the control.)

Ted


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Thu 17, 2021 10:05 pm 
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Sorry. Please excuse my poor understanding of electrical nomenclature. My Southwire multi-meter is auto-ranging. The MV should have been mV or millivolts. That puts the voltage in the range you suggest.

I tested both an AF and MF frequency across the volume control. Here are those reading from the prior post:

DC voltage across the volume control to the chassis is -67 MV (sb mV or millivolts) with a 600 HZ 10 V peak to peak signal injected on pin 4 of 6SQ7. Voltage goes to 0 as the volume control is turned down.

DC voltage across the volume control to the chassis is -32 MV (sb mV or millivolts) with a 465 KHZ 10 V peak to peak signal injected on pin 4 of 6SQ7. Voltage goes to 0 as the volume control is turned down.

The volume control has a "catch" in the middle of it. I took the reading from full volume to the "catch". It will go further down. I'll read the voltage further down. I was going to work on fixing/replacing the volume control once/if I got the radio working.

I'll trace from 6SQ7 to the volume control with the ohm meter.

Thanks again for your help,
Kerry
PS I think I owe you a Star Bucks card.


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Thu 17, 2021 11:06 pm 
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Joined: Jan Tue 16, 2007 7:02 am
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Location: Lexington, KY USA
It takes some time to get on to the lingo. This is made more difficult by changes over the years.

These days, "m" means 1/1000 and "M" means 1,000,000. However, over the years, m and M have been used to mean different things, particularly regarding the markings on capacitors.

In the present context, the setting of the volume control should not matter. As long as you are only connecting the meter to the ends of the control and not the arm.

What's of interest is where is the DC circuit broken. We hope that this is obvious as soon as you check with the ohmmeter.

Ted


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Fri 18, 2021 3:07 am 
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The multi-meter leads touched together read .6 Ohms.

Pin 4 of 6SQ7 to the other side of the IF coil reads 27.7 Ohms. Earlier, when I took the IF coil off, the IF coil read just over 28 ohms by itself.

Pin 4 of 6SQ7 to the radio/phonograph switch reads 27.5 ohms on both the in and out pins of the switch.

Pin 4 of 6SQ7 to the volume control input wire reads 27.6 ohms, 390 ohms on the out put wire with the volume all the way up, 1.5 K ohms on the output wire with the volume all the way down. The schematic says the volume control is a 1 m ohm resistor. Should I be getting 1.5 k Ohms? I am reading on the wires in and out of the volume control where they are soldered to the volume control, not an arm.

I took the volume control apart and cleaned it thoroughly. It was dirty but looked good on the inside. I go rid of the "click" or sticking midway, but I don't think either it or the automatic volume control is right.

If I put a 465 KHZ AM 10 V amplitude wave to wave signal into pin four of 6SQ7, I get -.66 mV on the volume control input wire with the volume on high. As I turn the volume down, the voltage slowly drops to -.42 mV at about a 3rd of the way down. Then, as I continue moving the volume down, the voltage suddenly jumps to -359.0 mV (not -.359 mV but -359.0 mV), and the voltage continues slowly going down from there in whole mV to 0 mV when the sound is all the way down.

Is something wrong with the AVC or the volume control? Why would the voltage jump like that?

Again, Thank you,
Kerry


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 Post subject: Re: Help with IF stages of Montgomery Ward Airline 93BR-714B
PostPosted: Jun Fri 18, 2021 7:54 am 
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Joined: Jan Tue 16, 2007 7:02 am
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Location: Lexington, KY USA
Before we had:
From pin 4 of 6SQ7 to the volume control I get 32.3 M ohm resistance.
Now, we have:
Pin 4 of 6SQ7 to the volume control input wire reads 27.6 ohms,

This is less than 1/1,000,000 the prior value. It's like having a million bucks in the bank one day and 85 cents the next, without any transactions taking place..

There has to be something crazy going on. Circuit doesn't match the schematic, we suppose we understand what you are doing, but in fact do not at all, the generator or meter is not working. Things that can't be spotted from a distance. I'm not sure what to suggest, other than to look at it again later.

It wouldn't hurt to measure the resistance from pin 4 of the 6SQ7 to the chassis. This should be pretty much the volume control resistance.

Verify that pin 4 on the tube indeed connects to the IF transformer. If the two diodes are swapped, the radio works the same but our diagnostics will not.

One more thing to try would be to measure the DC voltage at pin 4 with the IF signal injected there. If you don't have a VTVM, add a 100k resistor at the tube socket in series with the meter lead to isolate the higher frequencies from being loaded by the meter.

Does the audio amplifier part of the raido work while you are doing the inject a signal and look for the DC voltage? Do you get a healthy buzz from the speaker when you touch the 6SQ7 grid? The results sound almost as if the tube is dead.

Sorry if this is sort of shotgunning. I'm trying to find even a small clue.

Ted


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